Hoffman Amplifiers Tube Amplifier Forum
Amp Stuff => Tube Amp Building - Tweaks - Repairs => Topic started by: purpletele on May 20, 2017, 02:58:59 pm
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I didn't know I had a need for a new amp, but I guess I do, so I am going to plan out an amp as precisely as I can prior to building the amp. Visio will play a part in that.
I think the TDR is the perfect style of amp to fill this Lush Fenderish tone. I have a few questions that will help me get started.
Info:
Princeton Reverb Chassis and 1 x 12 Combo Cabinet. That's what I am going to work with.
Questions:
1. The schematic shows a Master, Volume, Treble, Bass, Unmarked, and then Reverb. The Layout doesn't indicate the MV and the unmarked 110K Pot is RAW.
Q: What did you end up doing with the MV?
Q: Dr. Z is implementing a Level Control on his New Amp the Cure. I have not seen any info on a level control on any of the amps that are discussed on this forum. How does a level control work and how is it different to a La Mar MV. I understand the Master on this schematic to drive the Pre-Amp section.
2. I read that you modified the trannies to MM for this amp.
Q: Do you feel that it is worth the extra cost to install MM?
3. Do you have info on the MM xfrmrs that you used for this project?
4. I would utilize 6L6's for this project.
Thanks in advance, this one will take a while to procure a set of transformers and parts. I am going to start laying out the Chassis in Visio. The Princeton Chassis looks like there is a lot of Real Estate to allow for a super clean job.
BV
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Princeton Reverb Chassis and 1 x 12 Combo Cabinet. That's what I am going to work with.
That sounds good when you say it fast. But the Deluxe PT will not fit and if you use 6L6s the PT will be even bigger. Better spend a lot of time researching this!
unmarked 110K Pot
Huh??? All my pots are marked and I've never heard of a 110K pot.
I tried the amp with the raw pot as shown on the layout. Then later changed back to the Master as shown on the schematic. The raw pot gives more tone possibilities than the Master, but I wasn't really looking for any dirty sound back then. If I had to do it over again I'd probably use both pots.
Q: Do you feel that it is worth the extra cost to install MM?
No way!
3. Do you have info on the MM xfrmrs that you used for this project?
The PT is a drop-in replacement for the odd sized DRRI PT. The OT is a little larger than the stock DR OT and required drilling one extra mounting hole. Choke and RT were drop-in replacements. Part numbers and pricing are on the MM site.
4. I would utilize 6L6's for this project.
Then you will also need to carefully choose proper iron.
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Oh, one other point... My project was all about squeezing that circuit into a tweed deluxe cab. The cab dictated a narrow tweed style chassis. And the chassis I chose dictated that I use a narrow board. My point is if I had used a wider chassis, my board layout would look much different.
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Oh, one other point... My project was all about squeezing that circuit into a tweed deluxe cab. The cab dictated a narrow tweed style chassis. And the chassis I chose dictated that I use a narrow board. My point is if I had used a wider chassis, my board layout would look much different.
Thanks Steve,
I will start researching transformers. I also have a Blues Junior Chassis that I had built and it fits into a Mojotone 1 x 12. that might work as well.
This will be a good project to implement Visio!
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Best way to learn Visio is with a project that you are juiced about. Just jump in and start making all the mistakes I made. You'll get better every time you drag something around.
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The Weber Princeton Reverb chassis is cutout for a Deluxe PT. I think they call the Princeton "6A14" Evidently because they don't promise that every detail is an exact copy of the original Princeton Reverb. I don't know for sure if the Weber chassis will fit another makers cab exactly... They do have fairly accurate drawings of the chassis on their website, so one could always get out the tape measure.
However, their Princeton Reverb cab is guaranteed to work with their chassis. What interests me is that they offer a 1x15" Princeton 6A14 cabinet that is about 5" taller than the standard version (the baffle is roughly square.) Someday I'm going to get one of those taller cabs and chassis with the baffle cutout for 12" speaker. I want to think that the slightly larger size cab will sound better. A little narrower and taller than a Deluxe Reverb with more than enough space in the chassis for a single channel 20W 2x6V6 amp.
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The Weber Princeton Reverb chassis is cutout for a Deluxe PT. I think they call the Princeton "6E14" Evidently because they don't promise that every detail is an exact copy of the original Princeton Reverb. I don't know for sure if the Weber chassis will fit another makers cab exactly... They do have fairly accurate drawings of the chassis on their website, so one could always get out the tape measure.
However, their Princeton Reverb cab is guaranteed to work with their chassis. What interests me is that they offer a 1x15" Princeton 6E14 cabinet that is about 5" taller than the standard version (the baffle is roughly square.) Someday I'm going to get one of those taller cabs and chassis with the baffle cutout for 12" speaker. I want to think that the slightly larger size cab will sound better. A little narrower and taller than a Deluxe Reverb with more than enough space in the chassis for a single channel 20W 2x6V6 amp.
Thanks TB,
Now I am going to start looking at what I have and what I need. The Princeton Tall Boy cabinet that I have will take a 12" speaker. I told to use the Mojotone chassis due to the original collaboration. Time to start measuring and drafting.
I bought the cab from Jim at Lil'Dog Amps in Lincoln, CA. He has an incredible on-line business of building really nice Fender Clones.
But for now its all about the chassis and the transformer size.
Thanks,
BV
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I've done two similar amps running push pull 6L6 is in a Princeton chassis and both times used Hammond 290cx power transformer. I had to enlarge the PT hole and from what I remember I was able to use the inside corners of the mounting holes for the original size transformer as a template to fit the 290 CX.
I also built my own cabinet and wound up with a perfect square that was about 20"x20", open back.
So, it's a tall Princeton and you dont have to worry about the transformer or power tubes hitting the speaker frame. Player comments were "its a perfect size 1x12 combo"
I thought so too.
IMHO, sluckey's TDR with 6L6 is a perfect amp, and following his design makes for a sure win.
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OK, so I lied a little...
When I went to find you a pic of the cab I built I noticed that it was taller than it is wide, and I now remember that the baffle board was square at approx. 18.25" x 18.25". (more like what Tony Bones was talking about)
So when you add the height of the chassis to that, it was more like 21.75" high x 19.75" wide approx., overall
EDIT - Had to fix dimensions - kept thinking the Princeton Reverb chassis was 17" wide
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One thing I've noticed about the 60's style Weber cabinets is that they're not tapered top to bottom like the original Fender cabs.
I have a tall 1x15 Deluxe Reverb style cab on order - it should be here tomorrow. I'll let you know if it looks weird with the baffle being perfectly vertical.
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Here are some photos of the Mather Princeton Tall Boy that I am considering.
I ordered the Princeton Chassis from Mojotone but I am going to wait until I get the chassis before I determine what transformer.
I want to get as close to the secondary voltage of 330 V similar to what Steve used.
David Allen suggests his TP25 as a perfect fit in the chassis and that has 310V on the secondary. I would like to use the TP40D, but that will require chassis modification(Hacking)
I looked at the Hammond 290CX and that will work with hacking.
BV
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This will be a good project to implement Visio!
I checked back at some notes from the first time I used Visio to plan an amp build. I realized I spent 4-5 months on the planning/drawing, but only about 1 month on the actual build. And that build-time included getting 2 custom chassis, a custom-engraved faceplate, a custom cabinet (Thanks again Tubenit!!), and painting the chassis & transformer endbells.
Most of the planning time was learning Visio and creating shapes, to be sure the diagram-parts were scaled/dimensioned as the physical parts would be to answer, "Will it fit?"
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This will be a good project to implement Visio!
I checked back at some notes from the first time I used Visio to plan an amp build. I realized I spent 4-5 months on the planning/drawing, but only about 1 month on the actual build. And that build-time included getting 2 custom chassis, a custom-engraved faceplate, a custom cabinet (Thanks again Tubenit!!), and painting the chassis & transformer endbells.
Most of the planning time was learning Visio and creating shapes, to be sure the diagram-parts were scaled/dimensioned as the physical parts would be to answer, "Will it fit?"
I know I am in for a learning curve, which is good. Visio is a great tool and is helping me with my Commercial Real Estate Construction with details and such.
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Looking at transformers and clearances.
With the clearances that I have I don't know why I couldn't mount an upright transformer.
If the clearances work I am going to consider using the Edcor 178. 330-0-330
I am using an Edcor PT and OT with my mini Bassman soon to be HoSo. I don't know what would make them special, good or bad, but they seem to be real quiet and they are very attractive with price point first and looks 2nd.
Any feed back on Edcor or using a standup Transformer for the Deluxe?
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I like standup PTs. Less chassis work. Edcor is a popular name. I haven't heard any bad mouth.
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I like standup PTs. Less chassis work. Edcor is a popular name. I haven't heard any bad mouth.
Sluckey,
I have settled on a transformer for the LDR, I have attached the specs on it
Questions:
1. What wattage of OT did you utilize? 25? 30 Watts?
2. Did you have an input impedance value that you utilized on the Output transformer. I have options for 2.5K, 5K, 6.5K and 10K for input impedance on the OT's.
Thanks,
BV
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This is the OT I used. MM is usually pretty skimpy with details...
http://www.mercurymagnetics.com/images/transformers/schematics/OT/FBFDR-O.pdf (http://www.mercurymagnetics.com/images/transformers/schematics/OT/FBFDR-O.pdf)
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That last PT you listed is under rated for your application:
(http://el34world.com/Forum/Themes/default/images/icons/clip.gif) Edcor XPWR047 330-0-330.pdf (http://el34world.com/Forum/index.php?action=dlattach;topic=21976.0;attach=65344)
With it, you're already .5 amp over rated current for the filaments (running 6L6GC)...it would possibly be ok, but with Edcor, I'm sure there is a better choice. 120mA secondary for running 2-6L6s is also low That PT would be an OK choice if you were building a stock DR with 6V6
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That last PT you listed is under rated for your application:
I agree.
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That last PT you listed is under rated for your application:
(http://el34world.com/Forum/Themes/default/images/icons/clip.gif) Edcor XPWR047 330-0-330.pdf (http://el34world.com/Forum/index.php?action=dlattach;topic=21976.0;attach=65344)
With it, you're already .5 amp over rated current for the filaments (running 6L6GC)...it would possibly be ok, but with Edcor, I'm sure there is a better choice. 120mA secondary for running 2-6L6s is also low That PT would be an OK choice if you were building a stock DR with 6V6
Silvergun,
Can you take a look at the specs from these two transformers. Let me know if either of these will cover all of my bases.
BV
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I actually thought that the first one you posted earlier in the thread was a better choice (than either of these two)
Edcor 178...for what you are trying to accomplish.
Both of these two new choices 'will work', it's just a matter of how high you're willing to go with your B+
I think the 380-0-380 unit is too high.
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I actually thought that the first one you posted earlier in the thread was a better choice (than either of these two)
Edcor 178...for what you are trying to accomplish.
Both of these two new choices 'will work', it's just a matter of how high you're willing to go with your B+
I think the 380-0-380 unit is too high.
Oh! Thanks, I appreciate the feedback.
The 178 has 3.15V on each of the HT taps instead of 6.3 Volts.
I'll find one yet.
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I actually thought that the first one you posted earlier in the thread was a better choice (than either of these two)
Edcor 178...for what you are trying to accomplish.
Both of these two new choices 'will work', it's just a matter of how high you're willing to go with your B+
I think the 380-0-380 unit is too high.
Oh! Thanks, I appreciate the feedback.
The 178 has 3.15V on each of the HT taps instead of 6.3 Volts.
I'll find one yet.
3.15-0-3.15 gives you 6.3VAC for your heaters, and that's what you want :thumbsup:
The term HT is usually reserved for the high voltage secondary winding...in this case 330-0-330
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This is my choice from Edcor...
http://www.edcorusa.com/xpwr124 (http://www.edcorusa.com/xpwr124)
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This is my choice from Edcor...
http://www.edcorusa.com/xpwr124 (http://www.edcorusa.com/xpwr124)
All,
I really appreciate the assistance. Steve, I like the selection of the XPWR124.
I found that the Tone Clone OT that you used from MM had a 6.6K Input Impedance.
I selected an Edcor 30 Watt 6.6K to go with the PT
Please let me know if the OT is within range of what I am trying to procure[/b].
Thank you, unfortunately Edcor is closed on Friday.
I have the HoSo to work on this weekend.!
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LDR Update:
I haven't started laying out the chassis, board and components for this Bad Boy on Visio to date,
however, I received my custom Princeton Blanks and I an very pleased. We verified the angle of the faceplate and ended up at 72 degrees.
I decided to load the speaker and turn over the cabinet to view the clearances of the transformer's
Clear sailing unless I am missing something.
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That cab looks really nice. Looking forward to watching this build progress!
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Most of the planning time was learning Visio and creating shapes, to be sure the diagram-parts were scaled/dimensioned as the physical parts would be to answer, "Will it fit?"
[/quote]
We'll, most of you guys probably know this, but I had just figured out that JJ 20uF 500 V caps are too big compared to the F & T 22uF 500V, so I have avoided that pitfall by being able to simulate the board with the Visio design.
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I am moving forward with the layout for the Luckey Deluxe Reverb.
I figure it is best to get as much computer work done while the familiarity of each program is fresh.
I have decided that I am going to utilize a Head Cabinet for this project, I have also set up the chassis so that I can turn it over a slip it into a Combo Cabinet. I am going to have a set of faceplates reversed and printed for the Combo Configuration
Here is a pdf of the faceplates.
PS., I put a spot on the back of the chassis for a Mojotone FX Loop. I am testing a unit out on my Gies Audio Dual Watt this week.
I'll be constructing this amp and the HoSo FX on paper very soon.
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Wish I had seen this thread earlier. Next time go the easy route and order transformers from Allen Amps that drop right into the PR chassis holes and allow you to run EL34 or 6L6.
Mark
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Wish I had seen this thread earlier. Next time go the easy route and order transformers from Allen Amps that drop right into the PR chassis holes and allow you to run EL34 or 6L6.
Mark
Mark,
Thanks, I will most likely build more than one, I would like to try that transformer.
I'll hit you up soon.
BV
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Visio Progress; time to study layers in Visio, otherwise coming along.
A couple more sessions and I'll be ready to build, but I am going to get the layout complete on the HoSo 56 as well while I am into layout design mode.
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A little progress on the Deluxe, things are coming together quite well.
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Lookin' good! Tell me again, what are you building? A schematic would be even better.
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On of the things some beginning Visio users aren't familiar with is the Size and Position Window. This is a little pop up window that gives you X,Y coordinates as well as width, height and angle of an object you have highlighted. For line elements you will get the X beginning and end and the Y beginning and end points too. You can use this window to type in exact coordinates and dimensions of objects which is very important when drilling chassis holes and face/rear plate holes.
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Lookin' good! Tell me again, what are you building? A schematic would be even better.
This is the single channel Deluxe in a head configuration.
I have a second Deluxe developing that will be in a combo that utilizes a super light frame. That amp will most likely have traditional transformers as opposed to the stand up Edcor's.
I have a little work to do to complete my layout drawings on Visio. I also need to determine exactly where I am going to place the Cap Board.
I am thinking I am going to place it above the transformer wires next to the main board.
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On of the things some beginning Visio users aren't familiar with is the Size and Position Window. This is a little pop up window that gives you X,Y coordinates as well as width, height and angle of an object you have highlighted. For line elements you will get the X beginning and end and the Y beginning and end points too. You can use this window to type in exact coordinates and dimensions of objects which is very important when drilling chassis holes and face/rear plate holes.
I may need a phone call consultation Barry. My accuracy in Visio is less than perfect.
Thanks for the Tip.
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Which version of Visio are you using PT?
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Which version of Visio are you using PT?
The latest version which I believe is 2016.
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The latest version which I believe is 2016.
Ackk! A ribbon version.
Well let's set up a drawing. With Visio open and in a blank drawing, choose the "Design tab on the ribbon menu and then in the page setup area chose orientation and set it to landscape, then choose size and set it to tabloid 11" x 17" and finally make sure "Auto Size" is not highlighted or is turned off by clicking on it until the shading goes away.
Ok now go to your "View" tab on the ribbon menu and in the "Show" section of the "View" ribbon click on "Task Panes" and then click on size and position in the drop down menu. That will open up and dock at the bottom left corner of your drawing area a small menu (Size and Position) where you will see X,Y coordinates and other info as I mentioned before whenever you have an object highlighted. If you don't have an object highlighted you'll see nothing in the bars.
So now draw a rectangle and with it highlighted/selected type into the size and position window's width bar 15.375" and in the height bar type 1.75" hitting enter after each input and you will then see your rectangle conform to those dimensions or what you have typed. You can also type in the X or Y bars where you want the center location of an object horizontally on the page and vertically on the page. So after you create your rectangle you can position it's left side on an even ruler point like 2" and it's bottom edge on let's say 5" on the page You have to have your dynamic grid and ruler turned on to see these. So now we have a rectangle representing a chassis face and it has a left starting point at 2" on the page and a bottom starting point at 5" on the page.
Now, draw a random circle (ellipse) anywhere on the page and afterwards in the size and position window set it's width and height both to 0.375" It doesn't matter where you draw it on the page for now. After size is set then we type in where we want it in the X and Y bars. So since your chassis left edge is on 2" of the page grid type in 2.875" for the X position of the circle and to put it in the middle of the vertical face of the chassis which would be 1.75"/2 or 0.875" above the 5" page location of the bottom edge of the chassis face you type in 5.875" for the Y location in the size and position window. Now you have an input jack hole 7/8" from the left edge of the chassis and in the middle of the vertical face of the chassis. First hole done
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Now that the first hole in the chassis face is in position, each subsequent hole to the right will be placed in relation to the previous hole. If we have a typical Fender 1-2 input dual jack assembly then the next hole for jack 2 will be 7/8" to the right from hole one. Here is where we use the Visio Array function:
With the pointer tool, select your first hole and then up on the ribbon there is a search bar (Tell me what you want to do..) where you can type in the word array. "Array Shapes" will show up and click on that. The you get the Array window pop up. Your first hole circle should still be selected but if not use the pointer tool to select it again. Now we will use the array window to make the next hole. For Rows in the spacing bar type 0 and in the number bar type 1. Why, because we only have one row in this array we're making. Rows are up and down columns are left and right. Now in the columns spacing bar type 0.875" because that is how far you want the next hole to be centered from the hole you have selected and in the number bar type 2 because that is the number of hole columns you will have counting the original when the array is complete. Make sure "between shape centers" is selected and not between shape edges and then click OK. Boom! your second input jack hole is in place.
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From here you can place the rest of your control holes and their center to center distances will vary with the amp model. The positioning of bolt holes, tube sockets, transformers and other items can be done in a similar fashion. The size and position window is critical to positioning components exactly on your drawing. Bare in mind that on many chassis the horizontal positioning of control holes is not always exactly in the vertical center of the chassis face.
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Attached is a screen grab of Visio 2003. This is a non ribbon based version which I prefer. You can see that I have all of my most used tools right where I can get at them. No poking around looking for them like with the ribbon versions. I'm pretty sure the ribbon versions can be customized but who has the time.
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Barry, thank you! I'll work through that later this evening.
I have a new amp to layout, the Princeton in a Champ chassis. The chassis came in today, so I can start verifying layout issues.
BV
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Which Princeton? Which Champ?
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Which Princeton? Which Champ?
I'll start a new thread called Princeton in a Champ
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I am moving along with the final field layout of components within the chassis.
I had two spots possible for the Cap board. The best place is on 1" stand offs above the transformer wires.
I do not see any issue with the location, does any have any thoughts that would make that location a poor choice?
Thanks,
BV
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OT Screen Windings.
My Edcor OT came with a Screen winding, I think that is the correct description. I have not seen this configuration before.
I connected the OT screen wire to pin 4 of each power tube in line with the 470 Ohm 3 watt screen resistor.
Is that the correct logic and position to enter into the circuit at pin 4?
What is the function and why would Edcor add that feature?
Things are coming together quite well so far.
Thanks BV
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Those screen taps are for ultra-linear (UL) operation and are not used for this amp. Just tape the ends and tuck away. Pretend they don't exist. Wire the tube pins 4 according to your schematic/layout.
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Those screen taps are for ultra-linear (UL) operation and are not used for this amp. Just tape the ends and tuck away. Pretend they don't exist. Wire the tube pins 4 according to your schematic/layout.
There I go thinking again. Thank you!
BV
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> I connected the OT screen wire to pin 4
You can do that. It won't be Classic Fender/Luckey DeLuxe. At this scale, it will probably be "too polite" for rock and roll. It's for Hi-Fi amps. A similar thing has been done on HIGH power guitar amps, which can't be "polite" even when too-clean. But this build, stick with the plan, insulate the excess wires and forget them.
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> I connected the OT screen wire to pin 4
You can do that. It won't be Classic Fender/Luckey DeLuxe. At this scale, it will probably be "too polite" for rock and roll. It's for Hi-Fi amps. A similar thing has been done on HIGH power guitar amps, which can't be "polite" even when too-clean. But this build, stick with the plan, insulate the excess wires and forget them.
Thank you for the insight, you learn something everyday if you let yourself.
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I was looking at my layout and more specifically the routing of my OT speaker wires. I have it tucked away on the left side in the red shrink tubing.
Do you think I am going to have too much noise from having the OT wires too close to the volume and input wires?
I could keep the Input and Volume wires below the board and then raise the output wires and run them along the side of the chassis above the board.
Any input would be appreciated.
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Maybe you will get lucky, but having those speaker jacks and high current OT wires right next to the most sensitive tube in the amp is inviting heartache. I would have put the OT near the PT and put those speaker jacks next to the fuse.
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I've done the same on JCM800 builds but not that close to 1st tube or input jack. Better to lay the wires on the opposite side away from 1st tube/input jack or outside the chassis on top.
Also, you could make a shield around the input jack.
I would try the amp first before changing anything.
Mark
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Thanks Steve and Mark,
That is my first significant layout error. it all comes back to the faceplate and thinking the whole thing through.
I am going to make a move now so I don't have to perform desperate tests after its all tied down.
At this point it would seem to me that it would be very simple an effective if I go over across the top of the chassis and then drop down right on top of the speaker jacks.
It fouls my aesthetics but everything is a prototype until it is not a prototype.
Are there any detrimental issues of running the OT wires across the top?
As always, thank you all for the guidance.
BV
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Update on OT Placement:
I moved the PT toward the PT an inch and re-routed the speaker Output wires. I feel much better about the route.
Please let me know if my move impacted anything that I don't see at this point.
Thank you
BV
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Much better!
Is there some reason you don't want to move the speaker jacks over to the fuse? Maybe a rear faceplate or something cosmetic?
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Much better!
Is there some reason you don't want to move the speaker jacks over to the fuse? Maybe a rear faceplate or something cosmetic?
UPDATE
I couldn't take having a faux paus on layout, I moved the speaker jacks to the middle and put the reverb jack near V2.
Costly, but much better.
Steve,
I am reluctantly trying to make it work due to my cool rear plate that I made. I spent a lot of time on the faceplates and hastily designed the backplate backward.
I can move things areound and easily get another faceplate for $45 but I would like to avoid that unless I am still vulnerable for noise.
Overall this amp is coming together well, hopefully I can get through this layout issue without collateral damage.
I had also prepped the back for a hybrid Mojotone type FX loop for the future.
Thanks for the eyes and advice.
BV
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RCA Jacks
This is my first amp with reverb as well as the first use of RCA jacks.
I have the the independant ring physically grounded as I would any other jack.
When I look at others it appears that the chassis is used as a ground and the jacks are not connected to a specific ground point.
Do I need to wire a ground to each jack or just let the chassis be the ground?
Thank for the guidance.
BV
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Don't connect the ground lugs of any of those RCA jacks to your speaker ground! Just let the chassis be the ground connection. Make sure the nuts are tight. Use star washers if you got'em.
Your jacks are also wired wrong. Look at this pic of Hoffman's Princeton Reverb (same circuit) and wire your jacks like that.
http://el34world.com/Hoffman/images/Img_8415.jpg
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Don't connect the ground lugs of any of those RCA jacks to your speaker ground! Just let the chassis be the ground connection. Make sure the nuts are tight. Use star washers if you got'em.
Your jacks are also wired wrong. Look at this pic of Hoffman's Princeton Reverb (same circuit) and wire your jacks like that.
http://el34world.com/Hoffman/images/Img_8415.jpg
I thought I had responded to this.
Thank you for the advice. I reworked the reverb jacks and I am confident that I have it correct, but any fresh eyeballs would be appreciated.
I finished the installing the components early this morning but I haven't started it up yet.
I did check the motor before I installed the components and I had great voltage reading at all of the sockets, I got to use my cool Light Bulb Limiter.
I'll spend a while double checking the wiring this evening and then hopefully start it up tonight.
I have a spot for a Master Volume. but I am going to get this amp up a running before I cut that MV in.
Here are some progress photos of the Orange Bomb.
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Reverb jacks are still wrong. Wire it like this...
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Reverb jacks are still wrong. Wire it like this...
I'll take you up on that. Thank you
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PROGRESS UPDATE
I corrected the Reverb wiring, thank you Steve for the detail.
I have one last question before I start up.
I have the Bias Tap connected to Pin 6 on the Rectifier. That is the way I interpreted the detail, however, I have had wrong interpretations before.
Is that the correct interpretation for the Bias Tap?
Thanks for the input
BV
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I have the Bias Tap connected to Pin 6 on the Rectifier... Is that the correct interpretation for the Bias Tap?
Yes. You must make a simple change on the board though. Hoffman shows a 470Ω bias range resistor. That is fine if your AC voltage source comes from a dedicated bias tap on the PT. But your PT does not have a dedicated bias tap, so instead, you are using a much higher AC voltage source. Therefore you must use a much larger bias range resistor. 100K @ 3W is a good starting point. That's what a Princeton Reverb uses. You may have to adjust that value up or down a bit to get a good negative voltage adjustment range. And you may just be lucky. The 100K may be just what you need.
DO NOT POWER THIS AMP UP USING THAT 470Ω! You will fry the bias caps.
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I have the Bias Tap connected to Pin 6 on the Rectifier... Is that the correct interpretation for the Bias Tap?
Yes. You must make a simple change on the board though. Hoffman shows a 470Ω bias range resistor. That is fine if your AC voltage source comes from a dedicated bias tap on the PT. But your PT does not have a dedicated bias tap, so instead, you are using a much higher AC voltage source. Therefore you must use a much larger bias range resistor. 100K @ 3W is a good starting point. That's what a Princeton Reverb uses. You may have to adjust that value up or down a bit to get a good negative voltage adjustment range. And you may just be lucky. The 100K may be just what you need.
DO NOT POWER THIS AMP UP USING THAT 470Ω! You will fry the bias caps.
Thank you! That didn't make sense to me, but now it does.
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Start Up Notes and Questions
1. I changed the Bias resistor from 470 Ohm 3W to 100K 2W.
2. Prior to this start up I had tested and recorded the voltages at each point prior to the board and tubes being installed.
3. Those volatges were 6.46 V across all Points without tubes or any connections.
4. I made a parallel heater connection from V5 to the Heater connection on the board. Very similar to the Doug's Deluxe project.
4.5 I started it up and it is idling fine, it's real quiet, the whole pre amp section is powered but not enought to operate correctly.
4.8 No sound
5. My voltages across the heaters are as follows:
V1 5.84
V2 5.85
V3 5.86
V4 5.88
V5 5.93
V6 5.94
V7 5.94
Light 5.99
Heater Connection on Board 5.91
There are two things going on that I see.
1. Voltage drop starting at .36 V
2. Graduated Voltage drop of .01 at each tube
Questions
1. Should I make the board the first parallel node on the heater string and then go to the tubes?
2. Should I try a smaller Bias resistor like 470K?
3. I am not sure why I would have a .01 graduated voltage with V1 having 5.84 volts.
Any ideas or input is very much appreciated.
BV
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1. Should I make the board the first parallel node on the heater string and then go to the tubes?
You have the heater center tap (white/brown) wire connected to chassis? If so, don't connect the filament string to the resistors on the board.
2. Should I try a smaller Bias resistor like 470K?
Don't change it until you check the voltage at pin 5 of each power tube. Power tubes should not be plugged in until you have proper bias voltage at pin 5. Turn the bias pot end to end. What voltage go you have at each end of the pot?
You only have .1v drop from the beginning of the filament string to the end of the string. Ain't no big thang!
However, looks like you may be using 22 gauge wire for the filaments? I would use stranded 20 gauge . Bigger wire equals less voltage drop.
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1. Should I make the board the first parallel node on the heater string and then go to the tubes?
You have the heater center tap (white/brown) wire connected to chassis? If so, don't connect the filament string to the resistors on the board.
2. Should I try a smaller Bias resistor like 470K?
Don't change it until you check the voltage at pin 5 of each power tube. Power tubes should not be plugged in until you have proper bias voltage at pin 5. Turn the bias pot end to end. What voltage go you have at each end of the pot?
You only have .1v drop from the beginning of the filament string to the end of the string. Ain't no big thang!
However, looks like you may be using 22 gauge wire for the filaments? I would use stranded 20 gauge . Bigger wire equals less voltage drop.
Thanks for the input,
The wire size and voltage drop seem significnt in this configuration, I am now using 18 Ga for the power tubes and then going to 20 Ga for the pre amp. That was a painful surprise, that I had not anticipated. So far I am getting 6.3 at the Power Tubes and I am moving on.
The two 100 ohm resistors on the board confused me, but it makes sense now, thank you.
I have my hands full for a while.
Thanks for the keen observation and assistance!
BV
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1. Should I make the board the first parallel node on the heater string and then go to the tubes?
You have the heater center tap (white/brown) wire connected to chassis? If so, don't connect the filament string to the resistors on the board.
Corrected
2. Should I try a smaller Bias resistor like 470K?Don't change it until you check the voltage at pin 5 of each power tube. Power tubes should not be plugged in until you have proper bias voltage at pin 5. Turn the bias pot end to end. What voltage go you have at each end of the pot?
V7 Pin 5 Without tubes 40.3 V - 27.58 V
V6 Pin 5 Without Tubes 40.4 V - 27.62 V
You only have .1v drop from the beginning of the filament string to the end of the string. Ain't no big thang!
However, looks like you may be using 22 gauge wire for the filaments? I would use stranded 20 gauge . Bigger wire equals less voltage drop.
Corrected
I'll set it for 32 V +/- and put the tubes in and set the bias. Stay tuned
Here is a photo of the rewired filament harness.
The amp Motorboats when I flip the Standby into play.
V7 6.19 V
V6 6.18 V
V5 6.17 V
V4 6.16 V
V3 6.15 V
V2 6.14 V
V1 6.13 V
I don't understand how I could get 6.3 V at the the end of the Power tubes and then when I go on with the Pre-Amp tubes and 20 Ga wire it reduces the voltages of the whole string.
That's a clue that its time to sleep.
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The amp Motorboats when I flip the Standby into play.
Check ground connections, especially filter cap grounds.
V7 6.19 V
V6 6.18 V
V5 6.17 V
V4 6.16 V
V3 6.15 V
V2 6.14 V
V1 6.13 V
Those are very respectable voltage drops. Nothing wrong here.
I don't understand how I could get 6.3 V at the the end of the Power tubes and then when I go on with the Pre-Amp tubes and 20 Ga wire it reduces the voltages of the whole string.
You have 5 little tubes, each pulling .3A filament current. That's 1.5A total. That extra load on the filament winding causes the voltage to drop.
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The amp Motorboats when I flip the Standby into play.
Check ground connections, especially filter cap grounds.
V7 6.19 V
V6 6.18 V
V5 6.17 V
V4 6.16 V
V3 6.15 V
V2 6.14 V
V1 6.13 V
Those are very respectable voltage drops. Nothing wrong here.
I don't understand how I could get 6.3 V at the the end of the Power tubes and then when I go on with the Pre-Amp tubes and 20 Ga wire it reduces the voltages of the whole string.
You have 5 little tubes, each pulling .3A filament current. That's 1.5A total. That extra load on the filament winding causes the voltage to drop.
Thanks for the input.
I abandoned my Weller XL100 a few days ago, I was really having to work to get a clean solder joint. I picked up a Hakko 951 and it is making a big difference, that's a nice tool. I wouldn't be surprised to find a cold joint around my cap board from the failing XL100.
BV
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You have 0.06V drop at 1.5 Amps. 0.04 Ohms.
#20 is 10.4 Ohms per 1,000 feet. So 3.8 feet out and back, 1.9' length, makes the 0.04 Ohms.
While you only have about a foot as the crow flies, the zig and zag to sockets, plus the twist, may well be 2 feet of pair-line.
I don't see 0.06V (1% of 6V!!) as any sort of "problem".
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You have 0.06V drop at 1.5 Amps. 0.04 Ohms.
#20 is 10.4 Ohms per 1,000 feet. So 3.8 feet out and back, 1.9' length, makes the 0.04 Ohms.
While you only have about a foot as the crow flies, the zig and zag to sockets, plus the twist, may well be 2 feet of pair-line.
I don't see 0.06V (1% of 6V!!) as any sort of "problem".
Thanks for the input, I'm looking for clues.
I went through and rewired the Capacitor Reservoir with 18 Gauge ground wire and touched up the whole grounding system.
Still getting a little motor boating, but within 1 minute the 820 Ohm feedback resister smoked.
So I'm trying to think like an electron and determine if this is now directly related to the Bias resistor that I changed from 470 Ohms to 100K.
I can manipulate the motoring with the intensity knob which is directly tied to the bias circuit, so I have to conclude that I have too much resistance in front of the bias circuit.
I'm not quite processing how a starved bias circuit creates too much voltage through the feedback loop, enouugh to smoke a resistor quickly.
Should I proceed with reducing the bias resistor to say 82K 3 Watt?
Thanks for any input, trying to not get obseessed and think logically.
BV
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Leave the 100K bias resistor alone! You have a perfect bias voltage range on pin 5 of the output tubes. This has nothing to do with that smoking 820Ω resistor. That will likely be a missing ground wire.
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Leave the 100K bias resistor alone! You have a perfect bias voltage range on pin 5 of the output tubes. This has nothing to do with that smoking 820Ω resistor. That will likely be a missing ground wire.
Ha! I had just been staring at that section looking for poor ground connections. Obviously I didn't find any bad ground connections in the power section.
That is humorous in a geeky amp dude kind of way!
Thank you, good eyes.
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Update
I hooked up the power section ground and that selttled everything down. I had also replaced the 820 Ohm feedback resistor.
I also reworked the entire grounding system again with a nice clean connection strip and new clean joints.
I get filament voltages starting at 6.10 V and decreasing down the string.
I am getting .421 Volts at Point A and throughout the critical power points.
Obviously the OT is not powered up
The power section is really steady and so I rebiased the tubes to 32 mA.
I have the ground for the OT connected to the speaker ground that goes back to my 4 position ground strip.
I can see I want to rework my control wires for the Trem and Reverb but that's not preventing the OT from being energized.
I'm hoping the smole I had earlier was just the resistor and not the OT.
Thanks for any input and thoughts. I'm getting into amp building shape
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I had also replaced the 820 Ohm feedback resistor.
I would also replace that 100Ω that connects to the 820. I was subjected to the same current that smoked the 820 when that ground wire was missing.
I am getting .421 Volts at Point A and throughout the critical power points.
You really mean 421v???
Obviously the OT is not powered up
Not sure what this means. Please explain. If you have 420v at point A and have adjusted the bias for 32mA then the OT must be "powered up".
so I rebiased the tubes to 32 mA.
That's pretty hot if your plate voltage is 420v. 6V6 max dissipation is 14 watts. Most of us like to set the bias to deliver about 70% of max, or 9.8 watts. I would crank the bias down to around 25mA, remeasure plate voltage, and recalculate by multiplying bias current times plate voltage. Readjust bias slightly until you calculate 9.8 watts.
that's not preventing the OT from being energized.
Again, what does this mean? Does the amp make any sound in the speaker? The OT should not have been damaged when that resistor smoked.
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I am getting .421 Volts at Point A and throughout the critical power points.
You really mean 421v???
My Klein MM1000 reads 123.2 when I check the AC voltage coming in. When I go to measure Volts in DC at the critical points the meter is reading 0421 Volts. I am waiting clarification from Klein. I took it to read .421 Volts but that certainly doesn't make sense.
Obviously the OT is not powered up
Not sure what this means. Please explain. If you have 420v at point A and have adjusted the bias for 32mA then the OT must be "powered up".
I get the same reading at the Blue and Brown OT wires which is 0420 V or similar. The OT is cold and there is no sound at all.
so I rebiased the tubes to 32 mA.
That's pretty hot if your plate voltage is 420v. 6V6 max dissipation is 14 watts. Most of us like to set the bias to deliver about 70% of max, or 9.8 watts. I would crank the bias down to around 25mA, remeasure plate voltage, and recalculate by multiplying bias current times plate voltage. Readjust bias slightly until you calculate 9.8 watts.
OK I'll redo that step.
that's not preventing the OT from being energized.
Again, what does this mean? Does the amp make any sound in the speaker? The OT should not have been damaged when that resistor smoked.
[/quote]
The transformer is cold, no hum or vibration, and no sound. I'll replace the 100 ohm resistor in line with the 820 ohm feedback resistor.
Thanks for the eyeballs. I'll see what Klein says shortly on my meter.
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That meter probably displays 4 digits even when the leading digit is zero. A leading zero does not imply a decimal point. If you don't see a decimal point in the display, you cannot just assume there is one.
Try this. Measure the voltage across a flashlight battery, or 9 colt battery, whatever you have handy. I bet the display will light up all four digits even if the voltage is exactly 1.5v or 9v.
I get the same reading at the Blue and Brown OT wires which is 0420 V or similar. The OT is cold and there is no sound at all.
Those voltages don't indicate a problem. And it's perfectly normal for the OT to be cold unless you have been driving it hard. No sound is a problem, but it could be caused by a thousand things that could be wrong anywhere between the input jack and the speaker. On a new build the most likely reason for no sound is a wiring error. Click the link in my signature line of this message for some good tips on locating wiring errors.
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Looking the picture of your amp, few things puzzle me:
Are the unused speaker output jacks grounding the signal?
Where does the black wire go from the two e-caps (100uf350v) that are connected in series?
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That meter probably displays 4 digits even when the leading digit is zero. A leading zero does not imply a decimal point. If you don't see a decimal point in the display, you cannot just assume there is one.
Try this. Measure the voltage across a flashlight battery, or 9 colt battery, whatever you have handy. I bet the display will light up all four digits even if the voltage is exactly 1.5v or 9v.
I get the same reading at the Blue and Brown OT wires which is 0420 V or similar. The OT is cold and there is no sound at all.
Those voltages don't indicate a problem. And it's perfectly normal for the OT to be cold unless you have been driving it hard. No sound is a problem, but it could be caused by a thousand things that could be wrong anywhere between the input jack and the speaker. On a new build the most likely reason for no sound is a wiring error. Click the link in my signature line of this message for some good tips on locating wiring errors.
Thank you,
I reviewed a video on the MM1000 display. It is indeed reading 421 V.
So I have a wiring issue somewhere.
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Are the unused speaker output jacks grounding the signal?
Good catch! Yes, they certainly are! This pic from way back shows the switch lugs of the speaker jacks connected to ground. That will kill any sound the amp tries to make. Remove that bus bar. You should only use two lugs on those speaker jacks. A wire from the OT will go to the tip lug. Nothing connects to the switch lug. And you can run a wire from the sleeve (ground) lug back to power ground point, although it's not really necessary if the speaker jacks are tight. I like to use the ground wire though.
(http://el34world.com/Forum/index.php?action=dlattach;topic=21976.0;attach=70168;image)
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Looking the picture of your amp, few things puzzle me:
Are the unused speaker output jacks grounding the signal?
I certainly have the grounds on the unused speaker jacks connected to my ground grid. If I am grounding the signal with this connection that would be a welcome surprise of a mistake. Please let me know if you see an issue.
It appears that my voltages are correct and I definitely have a wiring issue. My next step is to review the shielded input wires.
Thanks,
BV
Where does the black wire go from the two e-caps (100uf350v) that are connected in series?
That black wire goes a short distance to a main grounding strip right below.
Thanks for the eyeballs.
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Are the unused speaker output jacks grounding the signal?
Good catch! Yes, they certainly are! This pic from way back shows the switch lugs of the speaker jacks connected to ground. That will kill any sound the amp tries to make. Remove that bus bar. You should only use two lugs on those speaker jacks. A wire from the OT will go to the tip lug. Nothing connects to the switch lug. And you can run a wire from the sleeve (ground) lug back to power ground point, although it's not really necessary if the speaker jacks are tight. I like to use the ground wire though.
(http://el34world.com/Forum/index.php?action=dlattach;topic=21976.0;attach=70168;image)
Fantastic!! Great catch guys.! I happen to have the proper jacks that just arrived from Doug's swift shipping.
I'll start there and redo that section.
Thanks for the help
BV
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Where does the black wire go from the two e-caps (100uf350v) that are connected in series?
I looked wrong this part so it's most likely correct. Concentrate on those output jacks now and you can use those that are on place, just remove the wire that is connecting all the switching lugs.
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AB763 Deluxe Reverb Update
I have sound, however I still have a wiring issue somewhere.
The volume is maybe 1/4th of what it should be. The tone is a little muddy. I had a bad left turn with two bad pre-amp tubes. I checked the 6 v 6's by installing another pair without a change.
I did not exchange the rectifier, it seems to be stable and it was a known NOS 5ar4.
Here is what I did today which is really yesterday.
1. Re-Worked the speaker jacks with new two prong type. I went ahead and replaced the buss on the grounds for the speaker jacks. The OT ground ground wire and the speaker jacks are on the same 16 GA wire that goes back to a common grounding strip.
2. Re-Worked the input jack and the shielded input wire with a 33K resistor. I tossed the other one and mounted this one so there was not any stress on the connections points.
3. Re-Worked the control panel, cut lead wires to a taut length
4. Re-biased the 6 v 6's, I could only go as low as 26 mA, so I left it there.
5. Re-flowed all the connections on the control ground buss.
6. Re-flowed all connections.
7. Re-traced the layout with a highlighter twice.
8. The TMB seem to work, they can be altered.
9. The vibrato is working
10. I posted the voltages from this evening.
11. My past experience with this situation would direct me to a ground wiring issue with the controls, or a problem with the control pot itsef. However I taped up these pots during construction and made sure I didn't drop anything into the gap.
It was good day to hide and get lost in an amp. I feel like I made some good progress, I feel like I'm staring at a simple grounding issue and cannot see it. Maybe tomorrow.
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4. Re-biased the 6 v 6's, I could only go as low as 26 mA, so I left it there.
What is your meter connected to when you measure 26mA? You will probably need to change that 100K bias resistor to 82K to be able to reduce the bias current. I would want to get about 25mA with the bias pot set to about mid range.
10. I posted the voltages from this evening.
I don't see any voltages? Voltages for every tube pin would be very helpful. Also voltages for each PS node, ie, filter caps A, B, C, and D.
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is the green wire coming from outputjack your nfb wire and if so, why is the nfb resistor connected to 250pf cap?
Or is my eyes playing tricks again and it just look like it is?
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That 250pF cap should be a 0.1µF cap! :huh:
When using the highlighter to verify wires are in the correct place you should also verify that component values are correct.
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I was wondering the value of that cap too but i have not followed this thread from the beginning so wasn't sure what layout was used.
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Here's the layout and schematic...
http://el34world.com/Hoffman/files/Hoffman_AB763_1.pdf
Easy to see why he used a 250pF.
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That 250pF cap should be a 0.1µF cap! :huh:
When using the highlighter to verify wires are in the correct place you should also verify that component values are correct.
Stuckey/VMs,
You guys are good.
I remember looking at that and thinking I need to review that value. Then I was distracted , came back and installed the 250pf cap.
Clearly a mental error that I didn’t double check.
Great CSI work.
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Look at reply #88 again.
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Look at reply #88 again.
[/quote
Ok
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AB763 Update
1. I changed the 250 pF cap with a .1/400V that I had, ordered a .1/250V for permanent installation. I was locked into that silver mica from my initial component list. :dontknow:
2. Rechecked all of the components again, I may be looking at a forest at this point, but I went through and checked again with a highlighter.
3. I installed the .1/400 V cap in lieu of the 250 pF cap without much volume or tonal change.
4. I was able to go below 25 mA on the bias setting. Full control and very stable, I set the bias at 25 mA
5. Very quiet amp. The sound is still 1/4 of the volume and still muddy.
6. I have posted a voltage pin chart as well as a schematic with As Built voltages in red.
7. It appears I have an issue with the V3 section. I'll be focusing on those components.
Thanks in advance for any ideas.
BV
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Do you have the wire in place that connects V3-b plate resistor R27 and the point D
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Do you have the wire in place that connects V3-b plate resistor R27 and the point D
Do you mean a wire like a rail that should be in between my Plate resistors?
No I don't have that wire, good eyes. I'm going in for a clean up.
That was a major faux paus on my part.
Got it all tied together, plenty of volume!
The tone is getting there, I have a really noisy treble and bass including some whining and oscillation.
The Bias jumped to 48 mV and that is now the bottom of the range. The oscillation came down as I turned the bias down as low as I could get it. I have to wait a few days for the 82K 3 watt bias resistor.
I need work on the Reverb as well, it's noisy and not working correctly, but we will see after I ge the bias cooled down.
I've had to work pretty hard this spring training to get into building shape. It's coming together.
Thanks for the help!
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You might need to reverse your OT primary wires if it's oscillating badly.
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You might need to reverse your OT primary wires if it's oscillating badly.
Thanks, I had the OT wires scream at me the other day so I switched them and they are much happier.
The oscillation started going away when I turned down the bias setting, but I limited out on the low side with 48 mV.
The oscillation could be affected through bass, middle and treble controls.
The amp felt like it was ready to take flight on its own, so I checked the bias and noted that it was right at double of what it should be, so I shut down.
I'm pretty certain that I now need to reduce the Bias resistor from 100K 3W to at least 82K 3w, there could be other adjustments as well.
I had originally changed a 470 Ohm Bias resistor to 100 K Ohm due to my transformer not having a specific bias tap for this circuit. I am using an Edcor Stand Up Transformer.
BV
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Pull V5 tube. Does the oscillation disappear when you pull V5? Recheck bias with V5 pulled.
Bias needs to be set with no signal applied. This also includes any oscillation due to a problem. The oscillation looks just like a signal being applied to the output tubes and causes the tube current to increase (bias mA goes up).
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author=sluckey link=topic=21976.msg248881#msg248881 date=1521635143]
Pull V5 tube. Does the oscillation disappear when you pull V5? Recheck bias with V5 pulled.
Yes. The bias is reading 22.5 mV with V5 pulled.
I reset it to 25 mV. The amp is certainly loud, the chords still have a mild distortion and the end and then the notes fade quickly. The tone is getting much better.
When I turn the volume up as well as the treble it goes into a high pitched scream.
I also have a decent hum going on constantly. The reverb gets real buzzy when the turned up.
Definitely getting close but not there yet.
Based upon your recommendations and analysis of the bias, I have reset the bias at 25 mV. I'll assume that the bias has jumped up because of the interfering oscillation or noise that is emulating a signal.
I'm going to retrace and recheck the components and wiring around that side of the circuit.
Chopsticking around the Reverb circuit I have found V3-6 to be a very loud and sensitive plate. Not sure where to take it from here.
Bias needs to be set with no signal applied. This also includes any oscillation due to a problem. The oscillation looks just like a signal being applied to the output tubes and causes the tube current to increase (bias mA goes up).
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Did you chopstick the yellow wires going to tonestack? KOC recommends twisting wires going to tonestack together.
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Did you chopstick the yellow wires going to tonestack? KOC recommends twisting wires going to tonestack together.
d
I did play around with the tone stack wires and I couln’t Get a reaction. I think i’ll Post a video, the actual sound might provide indicators that don’t register with my experience yet.
Thanks
BV
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Here is an updated video of the noise I am getting from the Tone Stack.
Also, I am not getting my reverb to work, I am getting very loud sensitive wires at V3-6 & 7. I am focusing in the reverb circuit to see if I have something wired incorrectly.
I am wondering if I need to create a better ground for the reverb jacks.
Please let me know if anyone has advice on where to look.
Thanks,
BV
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Update to the Video
I grounded the reverb jacks amongst themselves and grounded to the chassis with a bolt. That made a world of difference.
I am down to a constant hum and my reverb.
I am getting 400 V on V2-1 as well as the red side of the transformer, However I do not get any reading more than 0.0 mV on Pin 2 as well as the green secondary coming off of the reverb transformer.
Shouldn't I be getting a low voltage from the reverb driver rather than 0.0 mV
The tube that I have in there is a fresh 12AX7, I don't have an 12Au7 on hand. I may have a 12AY7 I can try.
The tone was really nice tonight with room for improvement.
Thanks for any insights
BV
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I am down to a constant hum and my reverb.
That's progress. So the gremlin sounds are gone? Can you kill the hum by turning any knob to zero? Which knob(s)? Or, is the constant hum associated only with the reverb? IOW does the hum disappear if you turn the reverb pot to zero? Do you get any reverb effect? If you bang on the reverb tank do you hear a crash or thunder sound in the speaker?
I am getting 400 V on V2-1 as well as the red side of the transformer, However I do not get any reading more than 0.0 mV on Pin 2 as well as the green secondary coming off of the reverb transformer.
That's all normal.
Shouldn't I be getting a low voltage from the reverb driver rather than 0.0 mV
no
The tube that I have in there is a fresh 12AX7, I don't have an 12Au7 on hand. I may have a 12AY7 I can try.
The correct tube is 12AT7. I've had to try several different 12AT7s for this reverb driver to find one that did not hum.
Your posted tube voltages are messed up for V2. Would you re-check pins 1, 2, 3, 6, 7, and 8 and post the correct voltages?
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One more thing... Your tremolo is very weak. You should be able to almost get a throbbing tremolo effect with 6V6s.
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All my reverb problems went away when I unplugged the footswitch. I was using a switch that wasn't intended for reverb switching. (Needs to be shielded). It introduced awful noise. I couldn't tell if you had one plugged in. If so, try that in addition to what Sluckey said.
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Thanks guys!
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That's progress. So the gremlin sounds are gone?
Not entirely, when the volume is maxed it sounds like an x ray machine on idle. If I max out the volume and turn the tone stack uniformly up to 12:00 it gets real noisy.
Can you kill the hum by turning any knob to zero?
I can kill the noise but I am left with a constant hum, which certainly could be a pre-amp tube, but it's pretty loud.
Which knob(s)? Or, is the constant hum associated only with the reverb? IOW does the hum disappear if you turn the reverb pot to zero?
When all knobs off and I turn the reverb pot up full it seems to be the same frequency and cycle noise, only louder. I put an Ay7 in V-2 and that is noisy, I am trying to get some AT7's today.
Do you get any reverb effect? If you bang on the reverb tank do you hear a crash or thunder sound in the speaker?
Yes, when I turn the reverb up and drop the tank it sounds like a crash cymbal.
Your posted tube voltages are messed up for V2. Would you re-check pins 1, 2, 3, 6, 7, and 8 and post the correct voltages?
I updated the voltages on V-2 please see attached.
I'll put together a quick video later, Thanks for the ideas.
BV
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Have you tried the amp in its cabinet, circuits can sometimes pickup all kinds of noises from lights and other things on your workbench.
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Have you tried the amp in its cabinet, circuits can sometimes pickup all kinds of noises from lights and other things on your workbench.
I have not, good point.
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Update on Deluxe Progress
1. Had full power yesterday with really nice blooming tone but I had noise in the background, and the reverb was not working.
2. I was probing without any findings when I had a pop, not sure if I caused it with a wire but I couldn't repeat it or make it change. It took the amp into a real flubby tone like a rectifier going bad. The rectifier is red hot .
3. I didn't have a replacement so I decided to clean up the grounding. I changed my scheme to the way I have been building my last three amps, which is to have the CT's and one ground connection from the Capacitor Reservoir. The control wires ground go back the a negative buss on the circuit it came from.
4. I went ahead and grounded the ground tabs on the reverb and tremolo jacks. I took that ground back the a negative buss in the reverb circuit.
5. When I started it up the noise was gone but the volume and tone was flubby as it was before.
6. I picked up a new rectifier, 5AR4 and loaded it in. Prior to energizing I pulled V-5 and reset the bias at 25 mA, it was at 24 mA. I replaced the tube and then started it up.
7. The bias was right at 24.6 mA with the tube in, which I hope means that it is not picking up noise or oscillation in the circuit.
8. I went through and updated a voltage chart including a new column for todays voltages so you can see the delta.
Question
What would cause the rectifier to get really hot? Too much voltage? How do I regulate or affect the rectifier voltage?
[ Invalid YouTube link ]
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Check the AC voltage going into the rectifier. Check the dc voltages at all filter caps.
Tell me about that reverb tank. Who made it? What is the number on it? Where did it come from?
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Check the AC voltage going into the rectifier.
5. 2 VAC on the yellow
678 VAC on the Red Secondary's
Check the dc voltages at all filter caps.
Node A = 434 V two caps wired in series
Node B = 431 V
Node C = 426 V
Node D = 410 V
Tell me about that reverb tank. Who made it? What is the number on it? Where did it come from?
The tank is from Antique Electronics
MOD P-RMOD8AB2A1B
10 Ohm
2575 Ohms Output Impedance
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Voltages look fine. No clues here. Reverb tank is suitable also.
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Voltages look fine. No clues here. Reverb tank is suitable also.
It is curious, and I don't have a full grasp on how DC voltages are flowing to and from the rectifier.
The only thing physical thing that could be affecting the voltage of the rectifier output could be the bias tap, correct?
I don't understand what would cause the rectifier to be so hot other than it is getting energy backed up. I am going to change the bias tap wire to an 18 GA wire just to see if that has any effect.
When I play the amp with its half power tone I still get decent response and pinch harmonics. It feels like I'm a half step from the correct note, real close.
Thanks for reviewing and assisting
BV
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The only thing physical thing that could be affecting the voltage of the rectifier output could be the bias tap, correct?
No.
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Every time I've had a pop and then a change in signal or output but some partial output is still there, it has been a bad connection or solder joint at a component lead or wire. I'd aggressively chopstick every board component and every tube pin wire. Do you have under board wires? If so did you bring the leads up inside the turrets and fold them over ala Sluckey. In cases like this it helps to have an audio signal generator, a dummy load and a signal tracer (listening amp) to trace the signal through the different stages of the amp. If you don't have those below are ebay links to the ones I use.
https://www.ebay.com/itm/Heathkit-IT-12-Signal-Tracer-Working/273133747401?epid=1300239703&hash=item3f980a3cc9:g:AOgAAOSw93ZavUVC
https://www.ebay.com/itm/Heathkit-audio-generator-model-IG-5218/132549445825?hash=item1edc9008c1:g:zFsAAOSw5i5atX0E
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Barry,
Thanks for the thoughts and insight;
Every time I've had a pop and then a change in signal or output but some partial output is still there, it has been a bad connection or solder joint at a component lead or wire. I'd aggressively chopstick every board component and every tube pin wire.
I have fondled every connection and wire a few times. I know there is a bad connection but I can't find it yet.
Do you have under board wires? If so did you bring the leads up inside the turrets and fold them over ala Sluckey.
I learned that lesson a while back. I have solid wire jumpers with a hook lead over the turrets. Doesn't mean I didn't suspect them and then proceed to tear it apart to verify.
In cases like this it helps to have an audio signal generator, a dummy load and a signal tracer (listening amp) to trace the signal through the different stages of the amp. If you don't have those below are ebay links to the ones I use.
I have a tone generator on my Ipad and I made a test probe that hooks into another amp. I have ggod signal coming into V1-2 and I loose it coming out of V1-1.
I have an ESR coming today to check Capacitors, but I suspect it is a bad ground joint.
I invested in a new Hakko iron about half of the way through the construction of this amp. My Weller was giving up the ghost.
I'm going to keep searching, it was there and I lost it.
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I have a tone generator on my Ipad and I made a test probe that hooks into another amp. I have ggod signal coming into V1-2 and I loose it coming out of V1-1.
Does that mean there is no signal at V1-1? If so, that should be really easy to find. Start by measuring the voltage on V1 pins 1, 2, and 3. What have you?
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Does that mean there is no signal at V1-1? If so, that should be really easy to find. Start by measuring the voltage on V1 pins 1, 2, and 3. What are your voltages?
V1-1 = 271 V
V1-2 = 3 mV
V1-3 = 1.9 V
V1-4 =
V1-5 =
V1-6 = 273 V
V1-7 = 0 mV
V1-8 = 1.88 V
V1-9 =
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With those voltages you should hear a signal on pin 2 and you should hear a louder signal on pin 1.
Your home made probe has a dc blocking cap in it, right?
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With those voltages you should hear a signal on pin 2 and you should hear a louder signal on pin 1. Your home made probe has a dc blocking cap in it, right?
I rebuilt a probe the other day with the same results. The probe has a .1 uF 400V Cap with a resistor in series and another resistor going to ground. It works well at V-2 as I mentioned. I'm going to make a video of that testing as well as the muddy tone.
I pulled all of the Orange caps and tested them, I also tested the by pass caps in circuit with an ESR, that was cool.
I took photos of the wiring and cross checked it.
I replaced the caps but utilized some Jupiter caps to utilize the space more efficiently so I can see the connections.
Plugged it in and not a thing changed and I couldn't get any probing reactions. Muddy tone with pinch harmonics, weird.
I re-measure the transformer voltages again, 678 V. The Edcor is rated for 640 V, it sure feels like an overheated or dying rectifier.
Here is a video of the probing etc.
http://www.youtube.com/watch?v=lkUIHE1xvYQ (http://www.youtube.com/watch?v=lkUIHE1xvYQ)
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That's very odd!. I wonder if your probe is a factor. All you need inside that probe is a series .1µF cap. I suggest removing those resistors and try probing V1-1 again.
Also, I'd like you to temporarily install a 1/4" phone jack for testing purposes. See attached drawing. This will allow you to connect your guitar directly into the PI of your amp. Sound will not be as loud as playing through a properly working amp. But it should be bedroom loud and it should be clean. Make a recording and post for us to hear and evaluate.
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That's very odd!. I wonder if your probe is a factor. All you need inside that probe is a series .1µF cap. I suggest removing those resistors and try probing V1-1 again.
My probe was originally a simple BillM nail to a .1/400V Cap, it worked well and picked up the signal, but when I lost it immediately I looked on line and tried another version. I'm curious and will rule out every thing.
Also, I'd like you to temporarily install a 1/4" phone jack for testing purposes. See attached drawing. This will allow you to connect your guitar directly into the PI of your amp. Sound will not be as loud as playing through a properly working amp. But it should be bedroom loud and it should be clean. Make a recording and post for us to hear and evaluate.
I'll put that together soon.
.
Thanks for the ideas.
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That's very odd!. I wonder if your probe is a factor. All you need inside that probe is a series .1µF cap. I suggest removing those resistors and try probing V1-1 again.
My probe was originally a simple BillM nail to a .1/400V Cap, it worked well and picked up the signal, but when I lost it immediately I looked on line and tried another version. I'm curious and will rule out every thing.
Also, I'd like you to temporarily install a 1/4" phone jack for testing purposes. See attached drawing. This will allow you to connect your guitar directly into the PI of your amp. Sound will not be as loud as playing through a properly working amp. But it should be bedroom loud and it should be clean. Make a recording and post for us to hear and evaluate.
I connected the jumper jack and hooked up the wire as directed, but when I connect my guitar to that jack the amp goes silent, no mild hum, no signal, nothing. When I plug into the front end then I get muddy tone.
No need for a video on that one. I'm not sure what the field result means, I hope that gives you an idea.
.
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Really! Show me a close up pic. I want to clearly see the jack and the wires attached to it. I want to clearly see the wire connected to the cap on the board. And I want to clearly see V5 pin 2. Take more than one pic if necessary to show me all three of those things.
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Really! Show me a close up pic. I want to clearly see the jack and the wires attached to it. I want to clearly see the wire connected to the cap on the board. And I want to clearly see V5 pin 2. Take more than one pic if necessary to show me all three of those things.
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I'm beginning to think you are cursed. Take that same guitar and cable and plug into a known working amp. Does it work properly?
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I'm beginning to think you are cursed. Take that same guitar and cable and plug into a known working amp. Does it work properly?
I have a very nice amp right behind me that I play, I just finished 45 minutes of staring at a circuit and playing guitar. I have the same muddy tone on the amp as it has been for 3-4 days now.
I could not find information on the maximum secondary voltage hitting the GZ34, but there is a tremedous amount of AC voltage going to that rectifier. Am I hunting in the wrong forest with the rectifier and the 678 V?
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the 678 V?
warning, I did not read the other pages;
rail voltage is easy to check and monitor, even during play;
is it close to "spec" DC?
what does it fluctuate when being hammered?
Is there gobs of unfiltered ripple?
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t
he 678 V? warning, I did not read the other pages;
rail voltage is easy to check and monitor, even during play;
is it close to "spec" DC?
I posted the As Built Voltages below. Looking for a posted Voltage Chart for that amp?
what does it fluctuate when being hammered?
Is there gobs of unfiltered ripple?
The voltage is at 394 Vdc on the B+ rail.
When I hammer a chord it drops to 350 Vdc.
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Ha. I wrote you were cursed but I meant the amp is cursed. Sorry about that.
Am I hunting in the wrong forest with the rectifier and the 678 V?
Absolutely. We covered this earlier. That 678VAC is measured from one plate to the other plate. Perfectly normal. If you measure from chassis(center tap) to either plate you will see 339VAC. You could say your PT puts out 339-0-339. Or you could say your PT puts out 678VAC center tapped. Both descriptions mean exactly the same thing. Your GZ34 is FINE. My Sunn Sceptre puts 430-0-430 (or 860) on a GZ34. Data sheets list 550-0-550 (1100) as max.
You have gremlins in that amp or you have gremlins in your test equipment, or you have gremlins in your procedures. Maybe all three. There is no logical explanation to not be able to plug your guitar into the PI and hear some music. Given the normal voltages you gave for V1, there is no logical explanation for having a test signal on V1-2 but having nothing on V1-1.
We have already found multiple errors. I'm sure even more are hiding. I think you need another set of eyes and hands on your amp.
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I'm going to keep looking but at a less intense pace.
I agree it could be a number of things, I sure don't understand the Audio Signal testing results. I ended up with the same result's with two different probes, which was a loud signal at V1-1 and then gone.
I'll find the issue but it's a bit humbling, especially after I have esentially rebuilt it and corrected it along the way.
There not that many places to hide.
I have to keep working forward on the solution, but I also have some other projects lined up that I have started.
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sometimes it helps to walk away from an amp and come back later with fresh eyes
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sometimes it helps to walk away from an amp and come back later with fresh eyes
I am setting it aside for know, I am hoping I'll come across something on another amp that will inspire a resolution. 've probably rebuilt that amp three or four times already, but it will not rule me. Although it has knocked down some confidence.
It's will be resolved!
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When you do figure it out it will be a lesson that lasts.
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The Luckey Deluxe Lives!
I'm sure I punished the OT with an early Flame Job :blob8: . The OT was just barley passing current.
I was able to remove and replace without destroying anything.
I have a little issue with the reverb, but that can be cured I'm sure.
Felt like a monkey on my back
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This Deluxe Reverb is up and running strong with exception to the reverb part.
I went through and cleaned up the wiring, I cannot find any blatant errors.
I am getting the following voltages:
Node B = 382 V
V2 1 & 6 = 378 V
0.0 mV @ Reverb Secondary
V3-1 = 170 V
V3-2 = 0.0 mV
V3-3 = 2.64 V
V3-6 = 168 V
V3-7 = 0.0 mV
I'm not getting anything at all from the reverb.
I am not getting any signal from dropping the tank.
I tested the .0033 cap and it is fine.
Question: Is it possible to have the secondary not function properly but not indicate a short?
Thank you all for any advice.
BV
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Question: Is it possible to have the secondary not function properly but not indicate a short?
The secondary of the RT (green/black wires) should read about zero ohms between them.
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> I am not getting any signal from dropping the tank.
Then tank pickup or recovery stage.
Unplug the recovery cable and put your finger on it. Does it BUZZZ! ? If not, carefully put a finger on the reverb return control pot. (Don't have any other body part touching amp or anything grounded!) Does it Buzz! there?
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Question: Is it possible to have the secondary not function properly but not indicate a short?
The secondary of the RT (green/black wires) should read about zero ohms between them.
I am getting a reading of 2.5 ohms. Not sure if that indicates a failing transformer.
Replacement transformer comes tomorrow.
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> I am not getting any signal from dropping the tank.
Then tank pickup or recovery stage.
Unplug the recovery cable and put your finger on it. Does it BUZZZ! ? If not, carefully put a finger on the reverb return control pot. (Don't have any other body part touching amp or anything grounded!) Does it Buzz! there?
PRR,
I am not getting any buzz from the return cable when I touch it.
However, I get a good buzz when I touch the Pot for the reverb.
Does that give you an indication of something?
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I am not getting any buzz from the return cable when I touch it.
However, I get a good buzz when I touch the Pot for the reverb.
You won't get any buzz from the return cable if you unplugged it from the amp. PRR wants you to unplug the cable from the tank and put your finger on the center pin. You should get a louder buzz than you got by fingering the reverb pot. If not, there's a problem with the reverb recovery triode.
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I am not getting any buzz from the return cable when I touch it.
However, I get a good buzz when I touch the Pot for the reverb.
You won't get any buzz from the return cable if you unplugged it from the amp. PRR wants you to unplug the cable from the tank and put your finger on the center pin. You should get a louder buzz than you got by fingering the reverb pot. If not, there's a problem with the reverb recovery triode.
Got it, thanks for the clarification
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> I am not getting any signal from dropping the tank.
Then tank pickup or recovery stage.
Unplug the recovery cable and put your finger on it. Does it BUZZZ! ? If not, carefully put a finger on the reverb return control pot. (Don't have any other body part touching amp or anything grounded!) Does it Buzz! there?
(Update) PRR,
I have the return cable unplugged from the tank and I am not getting any buzz from the return cable when I touch it.
However, I get a good buzz when I touch the Pot for the reverb.
Does that give you an indication of something?
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If I read your tangled quote correctly: the problem is in the reverb recovery stage.
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If I read your tangled quote correctly: the problem is in the reverb recovery stage.
PRR,
Thanks for the bread crumb trail. The return jack was missing a plastic sleeve and therefore I was grounding out the signal. All fixed and sounding really nice!!
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Ah tenacity. Always pays off. Way to hang in there Brian.
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I had planned on a PPIMV for this upgraded Deluxe Reverb.
The amp sounds so nice right now but as anticipated, it is loud.
Am I going to spoil the sweetness of this amp by adding the MV?
Is it worth trying or do I make this amp a performance amp only?
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Luckey Deluxe Update and New Question
I have been enjoying my Deluxe Reverb very much, it sounds exactly as I hoped.
I decided to not install a Master Volume, however, I would like to try a Mojotone FX's Loop.
Advice Needed: I had anticipated utilizing a Pot for the level on the send and return on the loop but I am limited on space so I jumped the Pot connections and made the circuit a fixed level.
The instructions from Mojotone are weak at best and I would like to verify my logic.
1. I was going to insert the Send signal into the 250 pF cap in the tone stack feeding the Treble Pot
2. I was going to place the Return route into the 1 Meg resistor of the PI.
3. I was going to pick up B+ from node D
I am a bit parnoid about damaging this circuit via a boner move. Do the connections as desribed make sense for entry and exit points? I have attached a schematic and layout for reference.
Thank you,
BV
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Here's the whole schematic...
http://el34world.com/Hoffman/files/Hoffman_AB763_1.pdf
1. I was going to insert the Send signal into the 250 pF cap in the tone stack feeding the Treble Pot NO
2. I was going to place the Return route into the 1 Meg resistor of the PI. NO
3. I was going to pick up B+ from node D Probably. May need to add another RC filter stage.
The loop would normally go between the preamp output (page 3) and the PI input (page 4). Is this the FX Loop?
http://www.mojotone.com/Accessories_x/Attenuators_x/Mojotone-Discrete-Hi-Voltage-Series-Effects-Loop-for-Vacuum-Tube-Amplifiers
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Here's the whole schematic...
http://el34world.com/Hoffman/files/Hoffman_AB763_1.pdf
1. I was going to insert the Send signal into the 250 pF cap in the tone stack feeding the Treble Pot NO
2. I was going to place the Return route into the 1 Meg resistor of the PI. NO
3. I was going to pick up B+ from node D Probably. May need to add another RC filter stage.
The loop would normally go between the preamp output (page 3) and the PI input (page 4). Is this the FX Loop?
http://www.mojotone.com/Accessories_x/Attenuators_x/Mojotone-Discrete-Hi-Voltage-Series-Effects-Loop-for-Vacuum-Tube-Amplifiers
That's the FX loop that I bought and plan on using.
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This is how I would connect that FX board to the Hoffman board...
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This is how I would connect that FX board to the Hoffman board...
Thank you Steve! I'll give it a shot.
Update
Oh dear, remove jumper!! I wonder if it is worth the trouble?
Maybe I design it into my 2nd Deluxe Combo.
Update Again
Steve, thank you for the detail. I think I am going to hold off on that mod for right now. I would be upset at myself if I created a mess.
BV
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You gonna let a little jumper whip you? Here's an alternative. Unsolder the .001 cap bottom lead as seen in the pic. Stand the cap up and attach the FX OUT wire to the dangling end of the cap. Secure the cap lead so it can't move around and short to anything else.
If you do decide to remove the jumper and for some reason don't care for the fx loop, just remove the loop and replace the jumper on the TOP SIDE OF THE BOARD.
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You gonna let a little jumper whip you? Here's an alternative. Unsolder the .001 cap bottom lead as seen in the pic. Stand the cap up and attach the FX OUT wire to the dangling end of the cap. Secure the cap lead so it can't move around and short to anything else.
If you do decide to remove the jumper and for some reason don't care for the fx loop, just remove the loop and replace the jumper on the TOP SIDE OF THE BOARD.
Ok, thanks for the push.
I better get a good video demo of the amp prior to this operation.
Thanks,
BV
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You gonna let a little jumper whip you? Here's an alternative. Unsolder the .001 cap bottom lead as seen in the pic. Stand the cap up and attach the FX OUT wire to the dangling end of the cap. Secure the cap lead so it can't move around and short to anything else.
If you do decide to remove the jumper and for some reason don't care for the fx loop, just remove the loop and replace the jumper on the TOP SIDE OF THE BOARD.
Steve,
I cowboyed up and installed the FX loop as detailed and it seems to work quite well. I will plan for the variable Pots next time.
The FX loop seems a tad noisy. I'm sure there are quite a few reasons for that, I did use the cool Belden RG 188 Shielded wire. It's not noisy enough to warrant any surgery.
I think it is an asset to the amp, I'm glad I did the mod.
Thank you Steve for the nice detail and encouragement.
This amp is just about complete.
BV
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A couple of clips of the Luckey Deluxe Reverb
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Sounds very Fendery. Nice playing too. So, what are your thoughts about the DR as compared to the PR? Do you prefer one over the other?
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Sounds very Fendery. Nice playing too. So, what are your thoughts about the DR as compared to the PR? Do you prefer one over the other?
Good question on the comparison of the two amps.
I like the articulation of the Princeton for comping tunes by myself, the amp has the power to really sing nicel.
The DR is definitely a do it all workhorse of an amp. I can see a long useful life of that amp for personal use. The way that amp is set up with the upgraded transformers and the really nice speakers lends itself to be played with some volume to get it to breath. I like its ability to produce nice loud and pure chords at performance volumes.
I have played reissue model DR and they don’t compare to the power and feel of this circuit.
I have concluded that I like each amp for the purpose they were originally designed for!
I am very impressed and quite pleased with the whole building experience for these two amps, thanks again for the work and assistance that you and the rest of the mad scientists provide.
Note: I sold both of my Princeton’s to some friends and they are getting played quite a bit without issue, so that’s another cool factor.
I have parts for one more DR to complete, then i’m on to a 50 Watt Plexi
BV
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Luckey Deluxe Story
My friend Adam Block has been using the Deluxe with a open back 1 x12 with Cream Alnico, it sounds fantastic, but we hadn't tried it live until last night.
Adam was the guitarist hosting a Blues jam at the Torch in Sacto. I was coming down to film and see how it sounds and I was pleasantly surprised at the tone. The place was jammed with a retirement party.
The singer harmonica player was bent over at about 90 degrees and wailing. Mick Martin joined in with the band and didn't get anything on film, but it was cool.
He is a nice guy but man I feel for him with the scoliosis or whatever ails him.