Hoffman Amplifiers Tube Amplifier Forum
Amp Stuff => Tube Amp Building - Tweaks - Repairs => Topic started by: Ed_Chambley on May 27, 2012, 04:31:03 pm
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I have been promising to show some of my builds. Here the the cab. Tweed, laquor, Honey pine, 8 coats cut 4 to 1 with alcohol.
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Back of cab showing speakers. One built to vox style, the other is a smooth paper cone, Marshall style. 1.151 paper. The complete turret board. Another photo of the board showing the extra area for an additional bias. It will be a dual bias vary tremolo.
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Very impressive! Thanks for sharing it.
with respect, Tubenit
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Very, very nice Ed! :bravo1:
(You posted Curl bias board for the bias board pic)
Brad :icon_biggrin:
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Looking good Ed. Man I love pumkin tweed and oxblood grill cloth.
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Cab looks fabulous! That's gonna be one loud Princeton with two 10" speakers.
Is the circuit stock AA1164?
Cheers,
Chip
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I am using AA1164 with bias vary tremolo. I have some very nice Teflon wire in solid core and stranded I plan to use. I don't know if it makes a difference as I have never built a fender style amp and not used pushback wire. I used some of it in a high gain area of my last build and it cured some noise.
I made the chassis and just got it back from the chrome shop. It is just like a blackface, but with a few more holes in the back. I am using a Classictone Deluxe PT with a bias tap and plan dual bias as Slucky said for Ah effect. I just want to do it. Dual intensity pot. I got a Mercury OT for a Deluxe as well except it has taps for 4-8-16. It will allow me to add extra cabs. I have a 2 12's I love. It is a JD design cab with Weber Alnico Silver Bell and a Blue dog. It may be loud for a princeton, but what I am wanting is a quieter Fender Twin. I play lead country mostly when gigging.
I'll have some more photos coming soon so you will get the chance to see me do the stupid stuff. I ordered a brown faceplate in metal and they made a mistake and made it plastic. I am sending it back.
When complete it will be pumpkin tweed, oxblood, brownface, brown chickenhead knobs with blackface circuit. I don't know about the cabinet. I used Pine and just sort of enlarged the sides. Fingerjointed. The baffle is birch which I am not sure about yet. All 3/4" #1 ply and solid pine I got from a friend who collects old wood. He ran it through a belt sander and almost kept me from putting the tweed on it.
More to come. Thanks for your interest and please knock me in the head if you see me going astray. I am building what I hope to be my main gigging amp.
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I am using AA1164 with bias vary tremolo. I have some very nice Teflon wire in solid core and stranded I plan to use. I don't know if it makes a difference as I have never built a fender style amp and not used pushback wire. I used some of it in a high gain area of my last build and it cured some noise.
The main difference is it will be a bit more of a pain to install than the pushback wire you've used before, but you don't have to worry about singeing the cloth when you solder.
But I like the stuff too every now and then. Just used it in my last build.
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The 2 problems with Teflon insulated wire are COST and stripping the darned stuff. You need really sharp strippers, adjusted just right. When I'm done with the Teflon coated wire I stocked up on based on mania on 18-Watt.com and AX84, I'm buying old-fashioned PVC coated solid wire.
If nothing else, that'll make me more careful with the soldering iron...
Cheers,
Chip
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The 2 problems with Teflon insulated wire are COST and stripping the darned stuff. You need really sharp strippers, adjusted just right. When I'm done with the Teflon coated wire I stocked up on based on mania on 18-Watt.com and AX84, I'm buying old-fashioned PVC coated solid wire.
If nothing else, that'll make me more careful with the soldering iron...
Cheers,
Chip
[/quote
Chip, I got one of those heat strippers. You just close them and make a quarter turn and it comes right off and not a single nick in the wire. The things cost about $150, but I got one at a garage sale for $2.
Check it out
http://www.teledyneinterconnect.com/products/wire_strippers/wirestrip.asp (http://www.teledyneinterconnect.com/products/wire_strippers/wirestrip.asp)
Most people don't know what they are. I didn't and have passed by them for years until I saw someone using one one day. Get a good look and you will begin seeing them in junk shops.
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i use solid conductor PTFE jacketed wire and i use these (http://www.arcade-electronics.com/detail.aspx?ID=21622) to strip it. absolutely no problems stripping it, and things go together quickly. loathe the push back wire - the stripped ends fur-ball too easily. PVC? - forget it! one mod and that insulation looks like a melted mess. for larger power tube filaments i use stranded PTFE jacketed.
PTFE jacked wire all the way 4 me, just my preference. i wish doug would stock solid PTFE (http://www.awcwire.com/FAQ-NEMA-HP3.aspx) jacketed, E type would suffice, EE type would be better but not essential in either nickel or silver plated copper.
respectfully,
nice looking build ed... keep it rolling. :-)
--DL
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I'll put my vote in for Doug to stock the solid core Teflon. I liked the stranded I got from him just fine except that it's, well, stranded. :laugh:
I use Klein strippers from Home Depot, no problems.
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i use solid conductor PTFE jacketed wire and i use these (http://www.arcade-electronics.com/detail.aspx?ID=21622) to strip it. absolutely no problems stripping it, and things go together quickly. loathe the push back wire - the stripped ends fur-ball too easily. PVC? - forget it! one mod and that insulation looks like a melted mess. for larger power tube filaments i use stranded PTFE jacketed.
PTFE jacked wire all the way 4 me, just my preference. i wish doug would stock solid PTFE (http://www.awcwire.com/FAQ-NEMA-HP3.aspx) jacketed, E type would suffice, EE type would be better but not essential in either nickel or silver plated copper.
respectfully,
nice looking build ed... keep it rolling. :-)
--DL
Thanks
Isn't PTFE just the legal way of advertising the same material as Teflon? That is what the rack I got says on it, PTFE, but the retired Aircraft mechanic I got it from called it Teflon. Anyway, when you strip it it is silver. I just got it. He gave it to me. It is a huge rack with spools in it and most are full. It has solid core in 16,18 and 20. Stranded in 18-24 which is also silver when stripped. It is 8 rolls wide and 8 rolls tall and made from wood with dowels holding the rolls in place. I have never seen anything like it, the rack I mean. Each roll has a tensioned on it so it won't rats nest on you. He said he was cleaning out, but I think he was just being nice to me. He is one of the retire guys in my neighborhood and hangs out in my shop.
He has an Oscilloscope, I think he called a techtronic, that he said I could use since he doesn't use it anymore. I have never use one myself but I hear some of you speak of them often. Off track, this needs to be a new thread.
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Isn't PTFE just the legal way of advertising the same material as Teflon?
PTFE can be Teflon and not all PTFE is Teflon. DuPont owns the trade name Teflon but are no longer the only makers of PTFE.
He has an Oscilloscope, I think he called a techtronic
that is a generous offer. most tektronix gear is well engineered and reliable.
any more progress with the PR? i've been kicking around the idea of a 2pair 6V6 (30W) variant for quite some time... i should get off my lazy duff and at least bread-board it.
--DL
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More progress. Lots. Pix coming soon. Populated the board, but did not solder. Did not like it, so I reordred a couple of things. I decided to use the blue sozo up to the power section and Orange Drops as the .1's. As fate would have it, I should have not drilled the holes in the bottom. Since I am using a Deluxe PT and OT the holes are going to be in a different place. So I am going to have a couple of extra holes. I know it sounds like no big deal, but all the planning and I still missed it. I am thinking about changing the mounting bracket on the OT and use the stock holes. The PT does not matter as I am having to cut that anyway.
It will have a Master Volume, I just have not decided what type. It is really going well. It is the best one so far I have ever done.
I promise to get you guys some more photos soon.
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Getting down to the nitty gritty. On the schematic I did not connect the second hald of the intensity pot. I am aware of this.
My question is more in the layout. The master used in the layout is setup for control of combined 220 resistors. Since it will be necessary for me to split those for dual bias and use a dual intensity pot, will them master volume work as it. I am thinking not, but could be wrong. I thinking I can use the LarMar master but not sure of that either.
I would prefer to use the one in the layout as it is switchable on/off. I do not see it working as is with the split.
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The MV in the layout is a crossline MV. I don't like 'em. I bet you won't either. But I think it will probably work as drawn. Try and see. Change to the larmar if you don't like it. Layout shouldn't be affected.
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Nice job on the schemo drawing Ed.
Took me a lot longer to learn the program to be able to do the same.
Brad :icon_biggrin:
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I believe bnwitt drew that schematic and Ed just added his improvements with a graphics editor.
Here's a PR with MV that tubenit drew a while back. It's gives good performance. I probably would lose the 33KΩ resistors and put grid stoppers on the output tubes. You can find the editable sch version in the schematics section.
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Thanks for the credit Brad. I did not draw it, However I am a graphic artist by trade. I can draw layouts, but have big problems with schematics. That is why I got Merlins 2 books. I can read schematics, but I do not know tube structure. I have printed out tube datasheets, about 400 of them.
Here is what is weird, I can open up a chassis and using Adobe Illustrator, draw one where it almost looks like a photo, but it took me about an hour to figure out to change a value of a resistor in Visio, you click on it and it opens an editable text box.
I ordered a windows Laptop yesterday just to be able to use the programs that people in electronics use. I am all Macintosh, I know Jschem Blah Blah Blah. If you are gonna do it, do it right. I have found some software which interfaces the PC to use as Scope and MM along with some other cool features.
Slucky, thanks for the info. I think I will pass on the Crossline and go straight to the LarMar, I know it and like it. The main problem with the LarMar is loss of presence, but I have a solution for that. A cut, also I am adding to the bottom of the chassis 2, 10k liner pots. One will be for a middle. I will measure 6.8k and mark that whereas I will always know where stock value is. Also, I am changing the NFB to a 10, but might add a 4k series resistor to give me the ability of having 4- 14k. I did a NFB mod on a princeton for a guy a while back and made a mistake and put in a 14k resistor. It made it have a very voxy chime. I am using small pots with knobs smack dab between the tubes. Easy access and out of sight. I am a tweaking fool. If there is a knob in site, I will turn it. That's why I am putting them on the bottom. Out of site, out of mind.
Like Slucky said, it's just a princeton. I am having a ball with this build. I dry fit everything yesterday and I could not believe how well the chassis and cabinet fit. I am great with metal, but awful at wood. Soon as I decide and wire the MV I will post more photos.
I gonna have a close look at the MV Steve posted.
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I believe bnwitt drew that schematic and Ed just added his improvements with a graphics editor.
Here's a PR with MV that tubenit drew a while back. It's gives good performance. I probably would lose the 33KΩ resistors and put grid stoppers on the output tubes. You can find the editable sch version in the schematics section.
The MV looks interesting and simple to wire in, but how would you ever be able to have stock values? I did not take the time to calculate, but it would always be like having 253k grid resistors. Also what is the need for the added .1uf caps prior to the MV. To keep the possibility of DC off the pot and if that is the case, how could it get DC on the pot anyway?
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Also what is the need for the added .1uf caps prior to the MV. To keep the possibility of DC off the pot and if that is the case, how could it get DC on the pot anyway?
1'st pair to block the PI's plate and cathode dc voltage.
2'nd pair to block the -bias voltage.
Brad :icon_biggrin:
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+1 on not using the cross line mv in a Princeton Reverb. I put one in my first PR build and didn't like it. The owner doesn't use it.
Cheers,
Chip
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Also what is the need for the added .1uf caps prior to the MV. To keep the possibility of DC off the pot and if that is the case, how could it get DC on the pot anyway?
1'st pair to block the PI's plate and cathode dc voltage.
2'nd pair to block the -bias voltage.
Brad :icon_biggrin:
Thanks Brad, makes perfect sense. My mind drifts to blocking DC from the pot, didn't consider signal path. Have you used this master? How do you like it?
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No, I haven't but plan to some day.
From what I've read posted here the guys love this MV, very highly rated.
Brad :icon_biggrin:
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Here's a useful discussion of master volumes:
http://www.el34world.com/Forum/index.php?topic=3496.0 (http://www.el34world.com/Forum/index.php?topic=3496.0)
Cheers,
Chip
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Here's a useful discussion of master volumes:
http://www.el34world.com/Forum/index.php?topic=3496.0 (http://www.el34world.com/Forum/index.php?topic=3496.0)
Cheers,
Chip
Chip, thanks for the link. I have tried most and even a few not listed. I spent one whole Saturday with the Trainwreck pages MV. I normally end up with the LarMar and ground the shields like Slucky said. The main problem with the LarMar is the dual pot. I have 6 linear dual 250k Alpha's and not a single one is even close to the same ohm at a specific rotation. I have one that at half turn that is 23k and 120k. Everyone of them is over 250 at full turn. I had so much trouble with a 5f4 that I finally spent $38 plus shipping to Digikey and got a PEC. Problem solved. The one Bruce Collins came up with is ok, but you still have to get it up in volume.
I have used power scaling in both ways, whole b+ and just the power tubes. I find it muddy in either case. I have been searching high and low for a dual 250k pot which is accurate. I put PEC's in my 5f4 and jtm 45 with the LarMar setup and it is simply the best for me. Everyone likes a different tone. The Gain and Volume setup in the Fargen 800 is the single wire and it works great. I've got a super clean build going. I have a bunch of alpha pot I am going to test. If I get lucky (I did with a bassman) I will use the alpha, if not I guess it will be another PEC. Wiring the LarMar correctly takes time and takes lots of space. This time if I do it to my current build, it will run under the board where I can keep the lead dress looking professional.
My big question is could you ground the shield wires to the main cap ground. I don't know if there would be any problems with doing this, but since I have dual bias the the 220k resistors are only about 1 inch from the ground on the large cap. It would be very neat and I would not have the shield wires out of sight and only shrink wrapped connections at the dual pot with the 2m8 resistors.
I really like the master on the Egnater amps, but I cannot get my hands on a schematic. I called them and they ain't tellin. I have a tweaker combo I practice with. I am getting ready to take it apart.
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Ed - Thanks for that info on the dual-ganged pots.
Cheers,
Chip
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I have 6 linear dual 250k Alpha's and not a single one is even close to the same ohm at a specific rotation.
I am familiar with that problem. What I have done is used is different resistors in parallel from wiper to side on the PPIMV setting that I use the most.
For example, if I am using a 500k dual gang pot ...................... I might parallel with a 470k & a 510k to get very similar values from "5-7".
That seems to work out well for me.
(Don't lock on to the particulars of the example. I just used them to illustrate the point.)
With respect, Tubenit
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I have 6 linear dual 250k Alpha's and not a single one is even close to the same ohm at a specific rotation.
I am familiar with that problem. What I have done is used is different resistors in parallel from wiper to side on the PPIMV setting that I use the most.
For example, if I am using a 500k dual gang pot ...................... I might parallel with a 470k & a 510k to get very similar values from "5-7".
That seems to work out well for me.
(Don't lock on to the particulars of the example. I just used them to illustrate the point.)
With respect, Tubenit
I understand. What you are saying is you get your master set where you like it and balance the pot as most of the time you keep your master close to the same rotation.
My deal is I do not use a MV to get lots of distortion, it is mainly the added sustain which can be achieved. In other words, I never max the gain and turn up the MV. This just loses everything IMO. I like the interaction between controlling the power section separate from the preamp. I am the same as you I guess in regard to setting the master. I find I am either at a little over half turn or completely off.
If you remember I asked you about using 2 separate pots and you said some people try to get a SE in this way. I was asking because I was thinking about finding 2/250k alpha pots that were a good match. It adds another hole, but I put the master on the back or the underside. I tried it and made a round sticker with lines where the pots are very close to the same ohm reading. It is a lot of trouble, but it works and doesn't cost $38.00. I will say this tho, the imbalance of the dual pot will make some weird tones but you can turn it a little more and weird turns to cool.
The reason I am spending soooo much time on this is because of the bias vary tremolo. I think if I get an imbalance to large it will show up vividly in the tremolo. Who knows tho, it may sound like a leslie.
Do you see any problem with grounding the shield to the main cap ground, or would it be better to chassis ground. It would be the same wouldn't it?
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Do you see any problem with grounding the shield to the main cap ground, or would it be better to chassis ground. It would be the same wouldn't it?
Maybe. :think1:
It has the most B+ ripple still left, so it's also the noisiest B+ ground node in the amp and it has the most current flowing to ground.
If this ripple/noise/modulated ground current couples to the center wire from the shield it could be a problem.
I'd try to ground the shields at the screen grid nodes ground.
You might be able to just twist (tightly) the 2 wires that go from the bias pots to the 220K grid return R's together.
Brad :icon_biggrin:
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Here's how I'm going to wire and ground my output tube bias vary tremolo with dual bias, bias balance and bias range.
It's a 5G9.
This way it's 2 pots instead of 3, including the dual pot that might not track right. Less space, less $$, no tracking problem. Just my $0.02.
(The schemo for Ed's build is in reply #15.)
Brad :icon_biggrin:
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So you plan a range resistor instead of a pot and use a bias balance. 1 pot. The other pot is a dual 1meg. I like the idea of a bias balance. Good food for thought. Did detect a little sarcasm tho?
Thanks for the shemo.
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So you plan a range resistor instead of a pot and use a bias balance. 1 pot.
No, 2 pots.
25KL bias balance pot and 25KL bias range pot. Look at the schemo agine, there both there. (There marked as 22KL, they should work also.)
The other pot is a dual 1meg.
There are no dual pots in the schemo drawing.
Did detect a little sarcasm tho?
No, I ment none.
Brad :icon_biggrin:
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Here's the dual bias version, I got both from KOC TUT books.
Brad :icon_biggrin:
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Good Stuff. I am reviewing. How do you plan to do the layout?
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I have to fix a few things in the layout drawing, when done I'll post it in my 5G9 Tremolator new build thread.
http://www.el34world.com/Forum/index.php?topic=13912.0 (http://www.el34world.com/Forum/index.php?topic=13912.0)
Brad :icon_biggrin:
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More Progress. Chassis is nice. Didn't plan in advance for the large cap so I had to make it larger. Got a couple holes to drill for 10k pots for NFB and a Middle control. Other than that, I a waiting on time and a couple of parts. Very close to start the lead dress.
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Little more photo.
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Looks real good Ed.
Brad :thumbsup:
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Looks real good Ed.
Brad :thumbsup:
Thanks man. I it is haven't decided on bias/balance or dual bias yet. So I am changing a dual setup to bias/balance in my frankenamp first. I have a Plexi build I test stuff with. It is nothing more than a 20 x 12 x 4 inch chassis with modular pieces. Room for days.
I will tell you this, I made a mistake in making the cabinet baffle. I should have placed the top speaker on the left looking at it from the front. It would have given me much clearance for my transformers. I would just flip it over, but it is not a traditional install. The baffle is fitted and the grill cloth is a separate so I can change it. I used velcro to attach the grill cloth frame. I am having some embroidered material of 2 different designs so I can change it. Grill cloth frame, great idea. Baffle stupid. It is going to work out fine, but would be better if I had reversed the baffle.
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I believe bnwitt drew that schematic and Ed just added his improvements with a graphics editor.
Here's a PR with MV that tubenit drew a while back. It's gives good performance. I probably would lose the 33KΩ resistors and put grid stoppers on the output tubes. You can find the editable sch version in the schematics section.
In using this master volume, are the .1 caps pit inline with the dual pot?
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Just wire it like the schematic.
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Just wire it like the schematic.
I hear you Steve. You are direct at times. Just wiring it like the schematic is why I got a great deal on a 66 Blackface bandmaster head. Someone drilled a hole right through the word Bandmaster and installed a master volume. It took me a while, but I found an original faceplate, welded the hole in the chassis. I know this is not what you are suggesting as I would think you give folks more credit than that.
It is how to lay it out is what I am considering. Where I am going to put the MV and add the caps which were not preplanned on my board layout. I prefer to keep the face as is with the controls the same as a stock princeton. Master will go in the back, but the back already has lots of things going on there. I do have a good place for it.
Here is what I see when looking at the schematic. Maybe you can help. I see a Dual 1m pot with terminal 2 (cancel the resistor) hooked to a .1uf cap and then connected to the 220k, x2 because it is a dual pot. On the upper portion I see a .1uf cap connected to terminal 1 of one of the pots, lets say the inside pot, and the lower portion connected to terminal 3 of the outer pot. I don't think it would be that way. So I assume both .1uf caps prior attach to terminal 1 front and back of the dual pot and terminal 2 controls attach front and back and terminal 3 are both grounded.
Also, A lot of times I see mods where people just hang a cap from a wiper, but if I add a couple of turrets above the 220k I should be able to put the caps on the board which in my opinion will make for a better layout.
I have a question though. What kind of effect is the MV going to have on the tremolo considering it connects to the the intensity of the tremolo. Will it just increase and decrease the volume only or will it have some interaction on the intensity strength? I am thinking not since the tremolo is bias vary and the MV would not affect the bias.
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Does this drawing help? I modified Tubenit's drawing. I labeled the pot lugs, removed the 33Ks, and put in the 1.5K grid stoppers. I can't advise you on the layout. I know you have the board done and probably have a spot chosen for the pots. The extra .1µF caps are the only other things you have to figure out where to physically locate. I'd probably mount them on the pot and avoid modifying the board layout.
I can't say how it may affect the trem. I've never seen this circuit on paper, let alone heard it. You tell us.
OTOH, I kinda like Willabe's ideas for the dual bias, or the bias range/balance.
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Does this drawing help? I modified Tubenit's drawing. I labeled the pot lugs, removed the 33Ks, and put in the 1.5K grid stoppers. I can't advise you on the layout. I know you have the board done and probably have a spot chosen for the pots. The extra .1µF caps are the only other things you have to figure out where to physically locate. I'd probably mount them on the pot and avoid modifying the board layout.
I can't say how it may affect the trem. I've never seen this circuit on paper, let alone heard it. You tell us.
OTOH, I kinda like Willabe's ideas for the dual bias, or the bias range/balance.
I did exactly this a while ago except I did add 1 turret above each of the 220k resistors. I assumed the ground would be common to both pots or the dual pot would work opposite. Plenty of room there and will be within about 1.5 inches of the MV pot. It will not hurt the layout as I intend to use the extra turrets even if I end up with a different MV. Even with the LarMar MV, I do not wire it like the layout floating around. Putting all that shielded wire and resistors on the pot makes a mess. And a 2m2 resistor is not correct. It may be technically the closest to 220K, but that is the most the circuit will ever see. If I change to the LarMar, I use the extra turrets to experiment with resistors which are usually on the pot. I first put one on a JTM-45 and the pot ran into a wall at about 1/2 turn and choked the overall volume. I forget what I ended up with now, but the resistors are not 2m2. They are smaller values and the one on the 5f4 I do remember. It has 1m. It will give you a full turn and remove the blanket. The amp will really open up but it seems there no "set" value for any amp.
That is why I put the turrets on the board. Couple gater clips, turn the master wide open and stub in resistors. When you get in the ballpark the amp will get louder, cleaner and have that punch a Non-MV amp has. That was the intention of that style of MV.
With the MV simply controlling a volume control for the power tubes I wouldn't think the intensity will be affected any more than turning down the volume. I do not know for sure, that is why I asked all those questions on how bias vary tremolo works. By the nature of the design, it has to be affected by the volume to some extent. The harder you run the power tubes the more potential of intensity you have.
I am not locked into dual bias and.or bias balance. I am going to do the dual first because Willaby is doing the other. It should give us some feedback of which is best. I am thinking the bias/balance will be the winner. I am using 25lk pots for bias so I can convert to bias/balance easily. I like the idea as well, but I do have a dual pot for the intensity which is exact in rotation.
I built a SS rectifier. 470K-.01cap-Diode, 3 down and 2 across. I am sure you have seen this before. I don't remember where I learned it. I think I did one like it for a guy I converted a Showman to Fender twin. DPST switch for the reds to switch back and fourth. So it will be a dual rectifier. SS rectifiers seem to do the Country twaang real better.
I don't know exactly what I am eventually going to end up with, but I know I can always have a Princeton Reverb. I have never had one, but always wanted one. I just cannot bring myself to buy a Blackface Princeton for $2000 when I know in a few years the price on them will drop like Beenie Babys.
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New stages complete. Heaters in with amphenol sockets for power tubes. I checked 10 7c5 and everyone match at 375 volts. Hulled out the chassis to fit in a dual pec pot for intensity. I have a hole for the old ground switch where the MV will be.
Question, if I have dual rectifier, can I attach a separate bias range resistor for the SS and another for the tube, but have both of them on the board. Then when I flip the switch it will use a smaller resistor for the tube. If so, will I need a diode prior to the resistors?
Also, if I connect a diode from pin 5 to 6 and 3 to 4 and hook p to 3 and 5 to protect the rectifier tube? I have some mullard rectifiers, 34's or should I simply use a 5u4. I want the SS rectifier to eliminate sag as I want the quick punch for tele.
I hate it Brad's bias/balance did not work, so it is back to my original plan. Couple more wires and I will post some more photos. All my parts are here. Not a single resistor, pot or cap which doesn't measure correctly so we know it will not sound like an old blackface.
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I hate it Brad's bias/balance did not work, so it is back to my original plan.
That's only for a bias-vary trem. amp.
With a BF it should be fine. BF trem is injected in a different part of the circuit, so bias/balance wont be alterd by the trem.
Brad :icon_biggrin:
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I hate it Brad's bias/balance did not work, so it is back to my original plan.
That's only for a bias-vary trem. amp.
With a BF it should be fine. BF trem is injected in a different part of the circuit, so bias/balance wont be alterd by the trem.
Brad :icon_biggrin:
I am adding a bias vary tremolo. I do not understand. Could you please elaborate. I do not have the schematic to post as it is on another computer which is currently undergoing a rebuild. Above, I believe there is an incomplete schematic where I have not connected both of the intensity (dual intensity pot) back to the 1 meg resistor. Going from memory here, but I think you get the idea.
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I am adding a bias vary tremolo.
Sorry,my fault Ed, that's the trem the bias/balance wont work with.
I forgot you were going with a bias-very trem.
(But sluckey's working on something that I'd bet will work.)
Brad :w2:
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I am adding a bias vary tremolo.
Sorry,my fault Ed, that's the trem the bias/balance wont work with.
I forgot you were going with a bias-very trem.
(But sluckey's working on something that I'd bet will work.)
Brad :w2:
No problem man. I've got an amp build going and I know it is going to be cool as hell. It is taking some time, but I have everything and have tested the dual pot on the intensity. It works very well. I hope when i finish wiring it up it works as well. I am trying to build one where I do not say I wish I would have done this as well. It will probably take me another month to finish, but when I am done I will have a Princeton with a mid and NFB, 2 10 in tweed and 2 single 12's in blond extension. The 4 ohm will be the only Ceramic Vintage 30. A Princeton with a vintage 30 and mid up around 14k sounds very vox like.
I have been gigging with a blackface fender twin for years when doing the country thing. Blues is Super Reverb. I am not a big fan of blues, but a gig is a gig.
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Put power to her the first time tonight. Since I am using a 50v bias tap, my resistor is too large 22k. I am reading -16vdc past the diode. What voltage should I be trying to get? Rectifier tube only one in. I get 417 on the plates.
I am using mini pots, 27kl and not getting any adjustment on no the screens which is pin 3 on a 7c5. I am not familiar with these pots and I believe this where the problem is. Should the Diode hook to the wiper the resistor hook to 3 and the cap hook to one. This is not the way I currently have it.
Right now I have the diode to 1, the cap to 2 and the resistor to 3. I assume you cannot swing the bias unless the wiper is receiving the bias voltage.
Everything else is checking out. I have gotten tired so it is time for questions. Experiment do not go well when I am tired. This is by far the best looking build I have ever done and I do not want to muck it up.
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The Princeton Reverb schematic (http://www.el34world.com/charts/Schematics/files/fender/PRINCETON_REVERB_AA1164.pdf) shows -34v with 400v on a 6V6 screen. If I were you, I'd shoot for -35v at the mid-point of your bias pot's travel.
I am using mini pots, 27kl and not getting any adjustment on no the screens which is pin 3 on a 7c5. I am not familiar with these pots and I believe this where the problem is. Should the Diode hook to the wiper the resistor hook to 3 and the cap hook to one. This is not the way I currently have it.
Right now I have the diode to 1, the cap to 2 and the resistor to 3. I assume you cannot swing the bias unless the wiper is receiving the bias voltage.
If I read you right, your bias pot is set up like Hoffman's AB763 (http://www.el34world.com/Hoffman/images/AB763Old.gif), which is perfectly fine. At least, that's how your schematic from earlier in this thread is drawn; cap/bias output at the wiper.
I dunno why your bias voltage isn't changing when you adjust the pot. The trem circuit from your schematic drawing seems suspect: only one of the pair of 250k pots is connected to the output of the trem circuit, so only one side of your output stage would get the trem. But you might not have actually wired it that way in your amp, since you're using a dual-pot. Either way, sorting out the bias is issue #1.
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Looks as if I need to drop down to around 10K resistor for bias range. That should get me much closer. The dual intensity pot is connected to the .1 cap via 1 wire, but through both solder lugs at the pot. There are 2 bias caps. Each is connected to lug 1 front and back. The 220k bias resistors are separate and connect to the wiper (lug2) of the intensity pot front and back.
Both sections of the bias are connected just past the diode using an underboard jumper. I'll check to see if I am getting a voltage swing tonight by disconnecting the wire leading to the cap. That should eliminate any question about the proper wiring of the pots.
What is weird is I am getting -41vdc on the screens, but cannot adjust it. Something is amiss. This is not possible with -16 reading at the diode. I'll have a new look tonight. Probably just got something tangled up as I worked on the amp about 2 or 3 hours past time to give it a break.
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What is weird is I am getting -41vdc on the screens, but cannot adjust it. Something is amiss.
Screen grid should be a + voltage, close to the plates voltage and not adjustable.
The control grid, grid #1 gets the -bias.
You either have the names mixed up or it's wired up wrong at the 7C5 tubes socket.
My GE book says, pin #6 is control grid (grid #1) and pin #3 is screen grid (grid #2).
Brad :dontknow:
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What is weird is I am getting -41vdc on the screens, but cannot adjust it. Something is amiss.
Screen grid should be a + voltage, close to the plates voltage and not adjustable.
The control grid, grid #1 gets the -bias.
You either have the names mixed up or it's wired up wrong at the 7C5 tubes socket.
My GE book says, pin #6 is control grid (grid #1) and pin #3 is screen grid (grid #2).
Brad :dontknow:
Yep, that is one of the problems. Nothing should be hooked to screen, Correct? Also, I have the master volume wired to the wrong side of the caps and resistors. Tonight I am going to remove the master and change to pin6.
Another question, I have the choke connected in the B+ rail from 470 Ohm 3 watt to the next one. Basically in-between the 2 control grid resistors. Thinking there is some resistance in the choke should I move it up so it is connected to 1k 3w resistor then to the 470 3 watt?
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The screen is pin 4 of your normal 6V6.
Yes, you'll need a B+ node attached to it, or you output tube will pass very, very little current.
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Guys, getting confusing.
7C5
1-Heater
2-P, Plate
3-G2 or Screen Grid
4-NC
5-NC
6-G or Control Grid
7-K, Cathode
8- Heater
6V6
1-NC/Glass
2-Heater
3-Plate
4-G2 or Screen Grid
5-G1 or Control Grid
6-????????
7-Heater
8-K, Cathode
Now I have what is pin 4 on a 6V6 connected to Pin 3 of the 7C5, so this is correct. I have a 1k5 resistor inline from the OT wire and shrink wrapped and connected to Pin 2 of the 7c5, the plate.
I do not see where this is wrong as the schematic shows a connection to pin 4 of the 6V6.
Should I connect the 1k5 resistor from pin 6 to pin 2 to pickup the Control grid and then connect my lead from the OT to pin 2, the plate.
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What is weird is I am getting -41vdc on the screens, but cannot adjust it. Something is amiss.
Screen grid should be a + voltage, close to the plates voltage and not adjustable.
The control grid, grid #1 gets the -bias.
You either have the names mixed up or it's wired up wrong at the 7C5 tubes socket.
My GE book says, pin #6 is control grid (grid #1) and pin #3 is screen grid (grid #2).
Brad :dontknow:
The Schematic shows the 470 ohm resistors connected to pin 4 of the 6V6 which is the Screen Grid (G2) not the Control Grid. The only connection of Pin 5, the control grid (G1) is when people install grid resistors. Maybe I am reading it wrong, but pin 4 of a 6V6 is pin 3 of a 7c5.
Let me know if you agree.
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I have a 1k5 resistor inline from the OT wire and shrink wrapped and connected to Pin 2 of the 7c5, the plate.
Why??? The plate should only have a wire from the OT connected.
Should I connect the 1k5 resistor from pin 6 to pin 2 to pickup the Control grid and then connect my lead from the OT to pin 2, the plate.
That will destroy your tubes.
You really, really, really need to draw out what you are building, especially since you have changed to 7C5s. Maybe this simple drawing will help you unravel some of this.
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I have a 1k5 resistor inline from the OT wire and shrink wrapped and connected to Pin 2 of the 7c5, the plate.
Why??? The plate should only have a wire from the OT connected.
Should I connect the 1k5 resistor from pin 6 to pin 2 to pickup the Control grid and then connect my lead from the OT to pin 2, the plate.
That will destroy your tubes.
You really, really, really need to draw out what you are building, especially since you have changed to 7C5s. Maybe this simple drawing will help you unravel some of this.
I do have it drawn out. I made some mistakes. In your drawing you have the cathode going to ground. I have them going back to the board to the 1 ohm resistor which is grounded. Same thing?
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I do have it drawn out.
Please share with us. It's so much easier to troubleshoot when we have an accurate schematic to follow. You have deviated too much from stock PR for us to keep your changes in our heads.
In your drawing you have the cathode going to ground. I have them going back to the board to the 1 ohm resistor which is grounded. Same thing?
Yes
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Here is the layout. I am using those bias tips on the back. I have never used them when connecting to a board, only when I connect them to ground. Should the wire from the ground one simply attach to the ground side and the red one connect at the cathode.
I am still learning to draw schematics, but I can do layouts. I do not have the master on here or the nfb pot or the middle control.
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Schematics are confusing to me. Like this one. I have always seen a pot like this. I do not have a great background in electronics, but I am reading and attempting to draw schematics, but when I see them I do not know what goes where.
I have downloaded many schematics and have actually begun understanding them some. In time I will.
See, you guys seem to know when the zig zag is a resistor and when it is a pot. To me they both look like resistors unless someone actually wrote out 1Ma or B1M or even 1kl or 1M pot. I am beginning to figure it out tho.
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There is an error in the first upload. I have G2 connected to pin 4 and should be pin 3. Here it is corrected. Have not had a chance, but I found the wiring error.
I still would like to know the best way to hook up the bias tips. I have 3 on the back of the amp. One black and 2 red. Should the black go to the ground side of the 1 ohm resistors and the red hook to each cathode?
Also, I have never used a small reverb tank, but I have one that requires a dwell (3 spring). Are the larger ones better to use?
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I still would like to know the best way to hook up the bias tips. I have 3 on the back of the amp. One black and 2 red. Should the black go to the ground side of the 1 ohm resistors and the red hook to each cathode?
yes
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I still would like to know the best way to hook up the bias tips. I have 3 on the back of the amp. One black and 2 red. Should the black go to the ground side of the 1 ohm resistors and the red hook to each cathode?
yes
Thanks Huckleberry.
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Here's how I did mine - the ground is now at the PT main ground lug (thanks, Steve).
(http://i443.photobucket.com/albums/qq151/frank_desalvo/17b5cbb7.jpg)
I still would like to know the best way to hook up the bias tips. I have 3 on the back of the amp. One black and 2 red. Should the black go to the ground side of the 1 ohm resistors and the red hook to each cathode?
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Here's how I did mine - the ground is now at the PT main ground lug (thanks, Steve).
(http://i443.photobucket.com/albums/qq151/frank_desalvo/17b5cbb7.jpg)
I still would like to know the best way to hook up the bias tips. I have 3 on the back of the amp. One black and 2 red. Should the black go to the ground side of the 1 ohm resistors and the red hook to each cathode?
Very neat looking. I like it. Thanks.
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Thanks - I looked at a few implementations of the idea and I believe this style was from an SLO clone. I like the orientation of the tube sockets, as well. Made it really easy to run the heaters and the tube alignment keys point straight out back, so it's easy to change tubes by feel if you have to do it on a dark stage.
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I have gotten the dual bias working. It is sort of interactive, but I expected that. Still no problem separate voltages on the control grid. In the Screens I have 389v and 417 on the plates.
I have a problem. I have not spent much time with it yet, but v4b has no voltage. All the voltages look good until this area. Could just be a bad tube, but it get its voltage from the B+ as far as I can tell. I have 223 on the plate of 4va. Nothing on pin 6-7-8.
I can hear pops as I check voltages so I getting close. I will get all the voltages later today and post them.
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I have gotten the dual bias working. It is sort of interactive, but I expected that.
It's interactive with what? Each other? ie, if you adjust one pot it affects the voltage on the other pot?That should not be. If it's interactive with something else, like cathode current thru the output tube, please explain.
Could just be a bad tube, but it get its voltage from the B+ as far as I can tell. I have 223 on the plate of 4va. Nothing on pin 6-7-8.
Not likely a bad tube. More likely a wiring error or bad solder joint, or bad resistor. V4 pin 6 (plate) gets its B+ thru a 56K to the B+ rail at the junction of a 18K 3W and a filter cap in the can. Should be pretty easy to locate this problem.
BTW, you have your choke in the wrong place. The choke is meant to replace that 1K 3W resistor. Just move the left choke lead over to the right side of the 1K 3W. Then remove the 1K 3W. Be sure you have a jumper between the 1K 3W and the 18K 3W.
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Ed, it's looking great. I wish my stuff looked half as nice. I only get by because I can play reasonably well and it fools a lot of people into thinking the amp is good. :laugh:
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What I meant by interactive is they are on the same connection after the diode. I did not split the bias tap to individual diodes. For instance, if I turn one pot a great deal with my MM connected to the Control Grid v5 I will get a swing from about -22 to -50, bump to bump in the other pot is centered. If I leave one pot wide open the other control grid will read about -17 fully closed. Both fully closed are -22 and both fully open are -50. Centered they are both around -35.
The pots are 25kl and each one will pass more current than provided by the bias tap.
I assumed this is caused by one of the pots when fully open is using enough current to cause the other to drop. This only happens at full turn. If you put both pots in the center and turn them oh say 20volts, the other one will not change.
With no resistor prior to the diode I get -46 vdc. I was thinking if I use too much of that current on one pot, the other one would have to drop as there is nothing left for it. These are only readings at the Control Grid with no load. I put the tubes in for a very short time to darken the room and check to make sure all the tubes were heating up. The tubes I use, like I mentioned, are very old and I only use them for checking new builds. If I kill one, no big deal.
Would it be better to split the bias tap and individualize each bias section? Right now I just have an underboard jumper. It is shown on the drawing as on top.
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Ed, it's looking great. I wish my stuff looked half as nice. I only get by because I can play reasonably well and it fools a lot of people into thinking the amp is good. :laugh:
Funny thing, you don't even need an amp to play well.
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Not likely a bad tube. More likely a wiring error or bad solder joint, or bad resistor. V4 pin 6 (plate) gets its B+ thru a 56K to the B+ rail at the junction of a 18K 3W and a filter cap in the can. Should be pretty easy to locate this problem.
[/quote]
No voltage at the end of the B+, that is the problem. I remember now that you mentioned this. When I was taking readings of the B+ Rail I did not get a reading there and forgot to go back and recheck it. It may be a bad resistor, but I always use steel wool on the leads and measure each before installing. I guess that does not insure it did not go bad once current was applied. I can always use the one I remove to change the choke position.
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I was thinking if I use too much of that current on one pot, the other one would have to drop as there is nothing left for it.
The amount of current thru the pots is fixed. It does not change as you crank on the pots. The voltage across each pot is the same. The only thing that changes is how much voltage you pick off with the wiper to send to the tube grid.
The only thing I'd change about your bias circuit would be to add an additional filter cap. Connect it from the anode of the diode to ground. This will give you a two pole filter that will greatly decrease the 60hz component on the bias supply, making the dc voltage much smoother.
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I was thinking if I use too much of that current on one pot, the other one would have to drop as there is nothing left for it.
The amount of current thru the pots is fixed. It does not change as you crank on the pots. The voltage across each pot is the same. The only thing that changes is how much voltage you pick off with the wiper to send to the tube grid.
The only thing I'd change about your bias circuit would be to add an additional filter cap. Connect it from the anode of the diode to ground. This will give you a two pole filter that will greatly decrease the 60hz component on the bias supply, making the dc voltage much smoother.
What size cap? I assume polarity consistant, negative to anode and positive to ground. So basically it is just adding another filter stage prior to the bias circuit. I've got some sprague 50uf/100v. That too much? I have many others, just not any 47uf/100's. Never used them until this build so I only bought 2.
Question 2: What is the - voltage should I have after the diode? With no resister at all it is a -46. HBP said to get the Control Grid at -35 with the pots centered and that is what I have with no resistor. Should I put a small value there as protection or will the diode suffice?
#3: I usually do not use a 12AX7 in a tremolo circuit, normally a 12ay7. I know fender tube chart has 7025/12ax7. It being bias vary will will it benefit from the stronger tube? I find with the roach, the clicking is not near as obvious with the 12ay7. When I get it working well I have some true 7025 I will put in. Not being familiar with the Bias Vary I was just wondering if subbing tubes causes problems or if it is the same, just preference.
Oh yea, thank you for the assistance.
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I've got some sprague 50uf/100v
That's fine.
Should I put a small value there as protection or will the diode suffice?
What value resistor do you have between the diode and the PT?
I have some true 7025 I will put in
I wouldn't waste a true 7025 on a trem oscillator or PI.
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I've got some sprague 50uf/100v
That's fine.
Should I put a small value there as protection or will the diode suffice?
What value resistor do you have between the diode and the PT?
I have no resistor. I have clamps to stub different one in. The pt is direct to the diode. I am at -46, but with the bias trim pots centered I have -35 on the Control grid of the tubes. That's what I was asking. should I put something like an 18 ohm, 1 watt. It seems as tho what the bias tap and the combination of the bias circuit is sufficient to get a good bias adjustment swing. I am not certain. I guess I will do the usual and hook up my meter once I get proper voltages and watch the bias. if it climbs too high, turn it off and raise the resistor value or vice-visa.
That is why I asked what the voltage should be just past the diode.
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You're feeding the diode from a low voltage bias tap, right? Put a 470Ω 1W between the PT and diode just like fender did on their AB763s. And put the cap in that I recommended. Now with no tubes in, recheck the bias voltage swing on the output tube grids. What do you have?
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It is jumping around. Turn the speed know all the way up the swing is -17 to -60 which seems pretty good. Something wired wrong with the tremolo.
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It is jumping around. Turn the speed know all the way up the swing is -17 to -60 which seems pretty good. Something wired wrong with the tremolo.
That's what bias vary trem does.
Now, pull the trem tube Vee4 and repeat the bias voltage test. What's the range?
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The tube was not in it. The only tube in it is the rectifier. I took some voltage readings earlier and found some things that seemed strange. I figure I \'ll give them to you.
v1
1-203
2-0
3-1.34
6-202
7-0
8-1.41
v2
1-409
2-.013
3-7.77
6-409
7-.013
8-7.77
v3
1-287
2-0
3-0
6-297
7-0
8-0
v4
Speed knob all the way up 1-240
Speed know on o jumps
2-jumps vary small voltage and the voltage is negative when speed know turned up -1.33
3-.7 stable with speed know all the way up
6-297
7-0
8-0
v5
2-417
3-417
6- Negative 35
V6 Same
At this point I did not have the additional cap. Had an 18 ohm, 3 watt resistor between the pt and diode.
Had the bias on both power tubes at 25ma bias with the plates at 417.
I know there is something going on, so I pulled the tubes and began reviewing the wiring.
Where it sits now is where you last said. Additional cap. no tubes except rectifier. It seems the speed pot is working backwards. I would think the higher your turn it the more the bias jumps.
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In that case, you have some major wiring issues.
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Just finished retracing. Nothing. I was hoping to find a wire or 3 wrong. No such luck. I have the 3meg pot. It should be reverse which means it should read 3 meg off and go to zero as you increase. It does.. The resistor changes it some, but that is the general idea. Correct?
The only things I have done different is I added a wire from the bass lug repacing the 6k8 resistor with a pot. Wire to left lug and 3k3 resistor to ground. I bypassed the NFB resistor and connected it to a wiper of a pot 10kl then to the high tap on the ot. That is the only things which are not wired the same.
When I removed the crossline MV should I have separated the bias resistors from the .1 cap? Sort of at a loss here. I have made many wiring errors, but thoroughly checking them I always find them. One at a time, mark the sheet and wire. I have 6 different color sharpies on this amps wiring and 6 marked up sheets.
I made one bad mistake right at the beginning. I connected the end of the B+ to the ground leading to the inputs and through the pot bus. That is why I had no voltage on v4b. but I have checked all the parts and they seem fine. I guess I am going to have to disassemble and begin again checking each part, but the only parts that got the B+ were input jacks and pots and they check out.
What else could have happened?
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I made one bad mistake right at the beginning. I connected the end of the B+ to the ground leading to the inputs and through the pot bus. That is why I had no voltage on v4b. but I have checked all the parts and they seem fine. I guess I am going to have to disassemble and begin again checking each part, but the only parts that got the B+ were input jacks and pots and they check out.
No e-caps anywhere in that path?
Also on your voltage readings (I'm not looking at the schem so forgive me if this sounds stupid) your V2 voltages are much higher than V3. Doesn't seem right?
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your V2 voltages are much higher than V3. Doesn't seem right?
V2 is the reverb driver. It's voltages should be much higher than V3 voltages. However, V3 pins 3 and 8 should have similar voltages to V1 pins 3 and 8. Zero on those pins indicates a problem.
I connected the end of the B+ to the ground leading to the inputs and through the pot bus. That is why I had no voltage on v4b.
OK, so what are V4 voltages now? Are the bias pots still working OK and giving a good range of bias voltage to the output tube grids?
EDIT... added the below comment...
When I removed the crossline MV should I have separated the bias resistors from the .1 cap? Sort of at a loss here.
No. That's how the negative bias voltage gets to the output tubes' grids. The crossline mv had to be removed. You went to a lot of effort to separate the grids for dual bias. That crossline would have just tied them back together.
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V2 is the reverb driver. It's voltages should be much higher than V3 voltages.
''
So am I forgiven? :laugh:
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V2 is the reverb driver. It's voltages should be much higher than V3 voltages.
''
So am I forgiven? :laugh:
Man, I forgive you. I appreciate you being involved. I am going crazy with this.
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None needed. Now go to the board and write 100 times, "I will look at the schematic." :wink:
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your V2 voltages are much higher than V3. Doesn't seem right?
V2 is the reverb driver. It's voltages should be much higher than V3 voltages. However, V3 pins 3 and 8 should have similar voltages to V1 pins 3 and 8. Zero on those pins indicates a problem.
I connected the end of the B+ to the ground leading to the inputs and through the pot bus. That is why I had no voltage on v4b.
OK, so what are V4 voltages now? Are the bias pots still working OK and giving a good range of bias voltage to the output tube grids?
EDIT... added the below comment...
When I removed the crossline MV should I have separated the bias resistors from the .1 cap? Sort of at a loss here.
No. That's how the negative bias voltage gets to the output tubes' grids. The crossline mv had to be removed. You went to a lot of effort to separate the grids for dual bias. That crossline would have just tied them back together.
Ok Steve, those readings were taken after I correct the ground issue. Here is the way it went. I had no voltages on v4b and knew I had a wiring issue. Flipped on the amp to take readings. B+ rail seemed low as I moved from lug to lug. When I reached the last one it was 0 after the 18k resistor, before it it was 190. I touched the resistor and it was fire hot. Bam, here is the problem. Looked and said shit because I saw the ground bus connected. Pulled the plug. Clipped the wire and connected it where it should be.
Pulled the resistor, checked out. Back in rechecked wiring again completely. Found one error on v2. Cross wire not connected, one of them.
Then I put an 18ohm 3 watt resistor between the Bias tap lead and diode. At this point I had not done any of the things you suggested about the bias, I had just moved the choke. Got steady reading at the control grid, but only with the speed know wide open. This is when I took the readings. Since these readings I put in the added filter cap, negative from anode to positive ground. Put in 470ohm.
Now to your current question. I cannot get the bias pots to work independant. Turning one changes the negative value on BOTH Control grids. With the speed knob at 0 it just jumps so much you cannot even see a reading. If you turn it up all the way the Control grid will stabilize. Either pot you turn will change the negative reading of the control grid. I have checked the continuity of the under-board wiring and it checks out.
Also, those voltage reading are with tube out. Even preamp tubes.
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Since the pots were in the path, I checked them. They seem ok, but I think I need to remove the wires from them. Since they interact with each other I do not know for sure if they are ok, but they all sweep. I have a 1 meg resistor at the inputs and shielded wire grounded and the input jacks with 68k resistor and a 33k on a switch for input 2. That was in the path and I have not checked these as the bias issue seems priority.
The 250 Dual Intensity pot only reads half that at full turn, but it is grounded differently and not in direct line with the ground bus. Grounding the B+ has to effect everything. It seems as tho the speed pot is not reverse, but all the way off I get a reading of 3M3.
I am frustrated and very close to pulling the board and taking it to my table saw and cutting off the second bias. Put octal sockets in and 6v6's, but it should work. I was very meticulous with everything. All vishay 1 watt metal resistors. Teflon wire. Sozo blue caps. Took my time and double checking along the way. I could understand it if I had never done this before.
All I know is at one point the bias section was stable. Now it is not and I cannot see how grounding the B+ can affect the bias caps.
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If your bias did work before you grounded the B+, something in there must have gotten messed up. I have yet to mess with the fixed bias, but what I would try is clipping in a fresh e-cap at the bias pots. Also, Tubenit just said something about he had a brand new resistor with the lead broken just inside the ceramic part, took him weeks to find it. I'm thinking that the juice to the ground buss may have broken a lead somewhere and is making it funky? I dunno, trouble shooting isn't my strong suit, but I have found plenty of errors (cause I've made plenty) with a chopstick and meter. I keep whacking on things till something goes zzzt. :laugh:
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I am frustrated and very close to pulling the board and taking it to my table saw and cutting off the second bias. Put octal sockets in and 6v6's
NO, don't you do that. :laugh:
Come on Ed, slow down a little, you'll find it.
Divide and conqure as the guys say.
Brad :icon_biggrin:
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If your bias did work before you grounded the B+, something in there must have gotten messed up. I have yet to mess with the fixed bias, but what I would try is clipping in a fresh e-cap at the bias pots. Also, Tubenit just said something about he had a brand new resistor with the lead broken just inside the ceramic part, took him weeks to find it. I'm thinking that the juice to the ground buss may have broken a lead somewhere and is making it funky? I dunno, trouble shooting isn't my strong suit, but I have found plenty of errors (cause I've made plenty) with a chopstick and meter. I keep whacking on things till something goes zzzt. :laugh:
The B+ was grounded from the beginning. At one time the bias worked, but the amp never has. I haven't gotten there yet. I never install a part before checking it. Mainly because with resistors I cannot see the stripes.
The problem here is I am building something I have never seen and I have never had a bias vary tremolo build. You are correct in the part department tho. Steve is great at zeroing in on a particular section and he has helped me many times to locate the problem area.
The most frustrating part of this is I have really put my heart and soul in this build. I cut no corners and used the best parts. Made the chassis and had it chromed, cabinet, 2 smaller cabinets for extensions. It is really a work of art as I have never put so much effort into a build. Then to make such a stupid mistake. As soon as I put my meter on 4vb plate and had noting I turned everything off and walked away to calm down. Waited a day and looked into the chassis and saw what I had done. I still cannot believe I did it. All the main parts, the expensive ones are fine. I am just deciding now if it is worth finishing it as planned or pull the board and make it like Binwitt did.
Just feeling a little beat up right now. I have no doubt I will get it going, but if not for such a stupid mistake I would be plaing it instead of writing about it.
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I am frustrated and very close to pulling the board and taking it to my table saw and cutting off the second bias. Put octal sockets in and 6v6's
NO, don't you do that. :laugh:
Come on Ed, slow down a little, you'll find it.
Divide and conqure as the guys say.
Brad :icon_biggrin:
Thanks Brad, you don't know how much help you guys are. Maybe I will get out the tele and play some through my Bassman. That always helps when I feeling down. I just can't believe I grounded the B+ :BangHead: :BangHead: :BangHead: :BangHead: :BangHead: :BangHead: :BangHead: :BangHead:
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Sounds like a good idea.
Brad :icon_biggrin:
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I turned everything off and walked away to calm down. Waited a day and looked into the chassis and saw what I had done. I still cannot believe I did it. All the main parts, the expensive ones are fine. I am just deciding now if it is worth finishing it as planned or pull the board and make it like Binwitt did.
Like you said, no expensive parts burned up. It was a mistake and we all make mistakes. :dontknow:
Main thing is you didn't get hurt. :w2:
When my trem wouldn't wiggle, I gave my self a little time to think about and then went back in and got it working.
Brad :icon_biggrin:
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I would keep track of the stupid things I do, but it's embarrassing. :laugh:
What helps me a lot when I've got a problem like this is to let it be for a couple days, sometimes most of a week. Work usually makes that easy to do anyway. And at some point, the way becomes clear. I almost guarantee you if you take a break from staring at it for a while, something will occur to you to check and that'll be it. And for sure, if you've done the layout etc, no reason to tear it down. There's simply a faulty part somewhere or a wire that's not going where you're absolutely positively sure it is (ask me how I know) and you'll find it without destroying all your hard work.
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GOT IT! I have independent swing on the control grid of both from -21 to -47. Speed control on 0000000000000000000000. Now I am not sure, but I think 7c5 tubes should bias around 25 with a plate of 417. I have a resistor 2k2, 3 watt between the bias tap and diode. Not sure of the change once a load is on it.
Anyone know what would be the best center position swing? Right now it is about -35 with no load. I am not going to put any tubes back in yet. I will wait for one of the masters guidance.
Anyone want to guess what the problem was?
The answer. The thing between the stool and the amp. :l2:
Rectifier tube. I have never seen this before. It's an old JJ and it was putting out varying voltages. I do not know how. Put it in my tube tester and the needle would swing up and hold and then drop into the bad zone. Wait a few minutes and back to really good. Visually, you cannot see anything. I have never seen this in my life and I have tested easily 10,000 tubes in my life.
That still doesn't remove the stupidity, but it helps.
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Any more progress? What's the state of the amp today?
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Some promising news and some not. I checked the resistors which were in the path of the and all checked out. I found one, the 470 ohm that the reverb pot connects to, when I touched it with my meter it would make an on and off distorted noise and continue when I removed the probe for 4 or 5 times. I pulled it and it had drifted to 1k4. I replaced it and this stopped. I have the tubes biased 22ma ant they are both independent. To get to this range I had to install a bias range resistor of 7 ohms. I am not sure of what the bias should be on the tubes, but going by weber's bias calculator and using a plate of 417 it shows 25.
So I need to know if 25ma is the number and then I can change the range resistor where this is close to center travel.
I checked out all the voltages and I am a little higher everywhere than the Fender schematic. This is understandable. Plug in guitar and hear a pop, but no sound. Since the B+ voltage did get send to ground bus, the first thins in line would be the 1m resistor on the inputs. Today, I plan on removing these as they are soldered as 1 piece and the shielded cable with the 68K resistors I cannot get to to check as they are under the board. I usually make these by putting them on the outside of the amp and just flipping them over and connecting to the tubes. Lot easier.
Other than that, I do not know. I don't know what else would have been in the path. I am not sure if it could have destroyed any of the bypass caps, especially the first one which connects to pin 3.
I am open to suggestion.
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Some promising news and some not. I checked the resistors which were in the path of the and all checked out. I found one, the 470 ohm that the reverb pot connects to, when I touched it with my meter it would make an on and off distorted noise and continue when I removed the probe for 4 or 5 times. I pulled it and it had drifted to 1k4. I replaced it and this stopped. I have the tubes biased 22ma ant they are both independent. To get to this range I had to install a bias range resistor of 7 ohms. I am not sure of what the bias should be on the tubes, but going by weber's bias calculator and using a plate of 417 it shows 25.
So I need to know if 25ma is the number and then I can change the range resistor where this is close to center travel.
Whatever resistor gets you where you wanna go is good. You can bias the 6V6s down to 60% and it should still sound good.
I checked out all the voltages and I am a little higher everywhere than the Fender schematic. This is understandable. Plug in guitar and hear a pop, but no sound. Since the B+ voltage did get send to ground bus, the first thins in line would be the 1m resistor on the inputs. Today, I plan on removing these as they are soldered as 1 piece and the shielded cable with the 68K resistors I cannot get to to check as they are under the board. I usually make these by putting them on the outside of the amp and just flipping them over and connecting to the tubes. Lot easier.
Other than that, I do not know. I don't know what else would have been in the path. I am not sure if it could have destroyed any of the bypass caps, especially the first one which connects to pin 3.
I am open to suggestion.
When you (carefully) do the pop test on each stage, which ones pop and which one's don't?
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should bias around 25 with a plate of 417V
....should be similar to princeton reverb; around -35V, no?
--DL
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Some promising news and some not. I checked the resistors which were in the path of the and all checked out. I found one, the 470 ohm that the reverb pot connects to, when I touched it with my meter it would make an on and off distorted noise and continue when I removed the probe for 4 or 5 times. I pulled it and it had drifted to 1k4. I replaced it and this stopped. I have the tubes biased 22ma ant they are both independent. To get to this range I had to install a bias range resistor of 7 ohms. I am not sure of what the bias should be on the tubes, but going by weber's bias calculator and using a plate of 417 it shows 25.
So I need to know if 25ma is the number and then I can change the range resistor where this is close to center travel.
Whatever resistor gets you where you wanna go is good. You can bias the 6V6s down to 60% and it should still sound good.
I checked out all the voltages and I am a little higher everywhere than the Fender schematic. This is understandable. Plug in guitar and hear a pop, but no sound. Since the B+ voltage did get send to ground bus, the first thins in line would be the 1m resistor on the inputs. Today, I plan on removing these as they are soldered as 1 piece and the shielded cable with the 68K resistors I cannot get to to check as they are under the board. I usually make these by putting them on the outside of the amp and just flipping them over and connecting to the tubes. Lot easier.
Other than that, I do not know. I don't know what else would have been in the path. I am not sure if it could have destroyed any of the bypass caps, especially the first one which connects to pin 3.
I am open to suggestion.
When you (carefully) do the pop test on each stage, which ones pop and which one's don't?
I will check and post.
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should bias around 25 with a plate of 417V
....should be similar to princeton reverb; around -35V, no?
--DL
Not sure, that is why I am asking. I want to know so I can get the proper resistor so the "optimum" bias will be in mid travel of the pot.
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Ed - getting that resistor value is a bit of science and a bit of suck it and see. You just have to take the plunge
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Treat the 7C5s just like 6V6s. Set the bias to -35v and forget about it until you fix the amp.
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Treat the 7C5s just like 6V6s. Set the bias to -35v and forget about it until you fix the amp.
That was my plan. I just needed the number, I can get all the little tweaks done later.
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Its playing. It sounds great and I don't even have it in a cab, just my test cab. I have a problem which is not a big deal to me, but my wife will hate it. The volume knob does not work. It is at full volume all the time. I will check it and insure it is working. It is fairly straight forward tho. Wiper direct to pin 7 ov v1b, lug 1 to treble and 3 to ground.
The nfb pot will squeal if above 8k ohm with the tremolo running. the tremolo is great. I have not hooked up the reverb yet. Gotta work out this volume pot. Is it possible the volume pot is acting this way if I added a mid control incorrectly?
Anyway, thanks for the help guys. Still got some bugs, but I've got sound.
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I found one, the 470 ohm that the reverb pot connects to, when I touched it with my meter it would make an on and off distorted noise and continue when I removed the probe for 4 or 5 times. I pulled it and it had drifted to 1k4. I replaced it and this stopped.
I have found an issue. V3b, pin 7. Touch it with the meter and I get a fairly large negative reading and it sets a helicopter in motion.
I'm quoting from two different posts because they're probably related. First, there is no 470Ω resistor connected to the reverb pot. That resistor should be 470 thousand ohms. Check to be sure you have a 470K connected to the pot now. If not, make it so.
Now notice that that resistor also connects to V3 pin7? Helicopter when you touch pin 7 could mean the grid does not have a good ground path. Turn the amp off and check the grid resistance. Put one meter lead on the chassis (not your pot ground buss). Put the other meter lead on V3 pin 7 (directly at the socket). With the reverb pot set to zero you should measure 470KΩ. With the reverb pot turned all the way up you should measure 570KΩ. What two numbers do you get?
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Mistake, reverb pot not grounded 3rd lug. Now high pitched squeal.
Seems I write too slowly! :wink:
The squeal could simply be NFB is wrong phase. Disconnect the NFB loop (lift one leg of the 2700Ω) from the speaker jack. If this fixes the squeal, reverse the OT primary plate leads. If not, keep lookin'.
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I found one, the 470 ohm that the reverb pot connects to, when I touched it with my meter it would make an on and off distorted noise and continue when I removed the probe for 4 or 5 times. I pulled it and it had drifted to 1k4. I replaced it and this stopped.
I have found an issue. V3b, pin 7. Touch it with the meter and I get a fairly large negative reading and it sets a helicopter in motion.
I'm quoting from two different posts because they're probably related. First, there is no 470Ω resistor connected to the reverb pot. That resistor should be 470 thousand ohms. Check to be sure you have a 470K connected to the pot now. If not, make it so.
Now notice that that resistor also connects to V3 pin7? Helicopter when you touch pin 7 could mean the grid does not have a good ground path. Turn the amp off and check the grid resistance. Put one meter lead on the chassis (not your pot ground buss). Put the other meter lead on V3 pin 7 (directly at the socket). With the reverb pot set to zero you should measure 470KΩ. With the reverb pot turned all the way up you should measure 570KΩ. What two numbers do you get?
Rverb pot 470 to 578. the resistor is correct, my typing, not so much.
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Mistake, reverb pot not grounded 3rd lug. Now high pitched squeal.
Seems I write too slowly! :wink:
The squeal could simply be NFB is wrong phase. Disconnect the NFB loop (lift one leg of the 2700Ω) from the speaker jack. If this fixes the squeal, reverse the OT primary plate leads. If not, keep lookin'.
Found the squeal. Fixed. The squeal was very faint, not like an ot reversal. I just limited the pot, no problem. 8K is plenty of nfb. I can go from 0 to 8k.
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Here is where I am. The squeal is coming from increasing the reverb pot. The high, the louder. I am looking for the problem with the volume pot. I don't know if they could be related, but it needs to be working.
The ohms checked out on the reverb. Don't know why it wound cause a squeal. Without the reverb pan connected, I would think it would do nothing.
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DISCONNECT THE NFB LOOP AND POSITIVELY RULE IT OUT. NFB issues do not always have screaming/howling symptoms. It's a new build. You must rule it out.
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DISCONNECT THE NFB LOOP AND POSITIVELY RULE IT OUT. NFB issues do not always have screaming/howling symptoms. It's a new build. You must rule it out.
No squeal with NFB disconnected. Change the PT primarys and squeal loud. I have no resistor at the NFB, just a jumper going to a 10lk pot. Lead to wiper, lug 1 to Secondary 8 ohm and ground lg 3. Should I reverse the pot wiring?
Also the footswitch will not turn off the reverb. Tremolo, yes. I have the the red red yellow 220k resistor from tip to ground.
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Another alpha pot got me. Checked the pot and nothing. I had just gotten rid of all those things right after I put this one under the board. Removed it and put in the 2k7 resistor. The amp squealed. Changed the ot wires. Working fine. All I have left, other than getting a 10kl adjustable resistor mini I can put on the board (the amp sounds better with a smaller value NFB resistor, but I want to be able to clean it up as well) is putting in the MV. Already have it hooked to the cab and it sounds great. I think I need to install a dwell and get a large tank. The tank can be done later. I have it hooked up to a small 3 spring tank and the reverb is a little thin, but the tremolo is great. What a wonderful lower power amp these are. I have never had a princeton.
It is very quiet with all dale 1 watt resistors.
The 7C5 are a good choice as well. The amp is very versatile. I've got some real 7025 for it. Bugle Boys, NEW. The rca 12at7 seems fine in the reverb.
The control grid is sitting at -35 on both and I am reading 25ma from the cathode.
Thanks Steve, with your help and the encouragement from Brad and John, I really have something special. I will post some completed photos in a week or so. I've got some playing to catch up on.
I really don't know how to express my appreciation. Brad, man you are a cool dude. Thanks for the push. Hell everyone, Thank You!
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Glad you got it going. What about the reverb footswitch? That's got to be a simple fix. Remember though, you must use shielded cable for the reverb footswitch. Tremolo does not have to be shielded.
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Glad you got it going. What about the reverb footswitch? That's got to be a simple fix. Remember though, you must use shielded cable for the reverb footswitch. Tremolo does not have to be shielded.
I have a 2 button footswitch, not a fender type. If I remember correctly it grounds on, lift the ground and the reverb is off. With my Supers, I don't even use a footswitch. I have a a rotary switch on the intensity and just turn it on an off from the front with a jumper RCA on the back. I use some reverb all the time, sometimes I turn it up or down, but it is on all the time.
Should be a simple fix, but it wasn't last night. Probably, all I have to do is use Fender type footswitch. The one I had connected is the old Marshall type with RCA. I am quite sure it is not shielded. I've got a box full of the fender style, but I never really liked them. The 2 buttons are too close together and they do not weigh enough. I will get it going, but will probably end up with a single button for the tremolo.
Can you use a 1 meg switchable dwell pot to turn on and off the reverb? I am going to order a large tank 3 springer from Doug today, so I will need to add a dwell. If a switchable dwell will turn off the reverb, I may go that way. Either way, Like I said, I always have some reverb running with Fender type amps. It just seems like it is part of the Fender sound to me.
I still can't get over the difference in the tremolo and how smooth it is compared even to my Bluesbreaker and I never use the roach tremolo. I made a pedal years ago. The click has always driven me crazy.
Next will be the Master Volume. I have the one you posted wired and ready to install, but I have a feeling it is going to be a non-master amp and the hole I have in the back will have a dwell in it. I have room for both, but I have not drilled a hole for a dwell. Reason being is when I had the NFB disconnected the amp has breakup at very low volumes. I may be wrong, usually am, but I don't know if adding a MV will benefit.
Also, I read where the 7C5 is just a 6V6 in a different socket, but I have never heard such a strong and tight bottom end from a 6V6. Maybe that is just what a Princeton does. If it is just the AA1164 I question why my Blackface Deluxe won't do it and why this circuit was not used in anything other than the Princeton Reverb. I don't know the differences in the AB763 and the AA1164 are as I have not compared the schematics of both. I know right off hand they are filtered differently.
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I have a 2 button footswitch, not a fender type. If I remember correctly it grounds on, lift the ground and the reverb is off.
All the footswitches for Fender tube reverb circuits operate the same.
Switch contacts closed = ground = reverb OFF
Switch contacts open = ground lift = reverb ON
Can you use a 1 meg switchable dwell pot to turn on and off the reverb?
sure.
Next will be the Master Volume. I have the one you posted wired and ready to install
I don't recall which circuit you're referring to. I hope it doesn't tie into the bias for the output tubes. That circuit is already busy enough with dual trem intensity and dual bias. That's 4 pots that could fail and kill the bias. I'd be nervous adding two more pots that could possibly fail and kill the bias. I'm not convinced that a MV on a PR has any benefits.
Switching the NFB might be useful. And a raw control in the tonestack could be useful.
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I have a 2 button footswitch, not a fender type. If I remember correctly it grounds on, lift the ground and the reverb is off.
All the footswitches for Fender tube reverb circuits operate the same.
Switch contacts closed = ground = reverb OFF
Switch contacts open = ground lift = reverb ON
Can you use a 1 meg switchable dwell pot to turn on and off the reverb?
sure.
Next will be the Master Volume. I have the one you posted wired and ready to install
I don't recall which circuit you're referring to. I hope it doesn't tie into the bias for the output tubes. That circuit is already busy enough with dual trem intensity and dual bias. That's 4 pots that could fail and kill the bias. I'd be nervous adding two more pots that could possibly fail and kill the bias. I'm not convinced that a MV on a PR has any benefits.
Without a doubt the added mid control and sweepable NFB is good. I put them on the bottom of the chassis under the board. I am going to have to saw the shaft off the alpha pot I had for the nfb to get it out. I am going to replace it with a fender bias adjustment.
The alpha pot only has 1 more chance to bite me in the butt. The only one I have left is the mid control on this amp. I must be snakebit with them. I have lots of trouble from them. I found a guy who has the Allen Bradley NOS. I bought a supply of them. The CTS I have had good service out of as well. PEC's are the best, but I only use them in certain places as they are expensive. I have a dual in this amp for the intensity. Since that location is so important I thought it was worth it.
Switching the NFB might be useful. And a raw control in the tonestack could be useful.
You remember the MV, it was the one that had the 33k resistors you redrew them out. Basically a .1 to a .1 and back, Dual pot, 1 meg. I'm with you, I am not convinced it needs a master. After I wrote that, I reconsidered. It is so nice the way it is. Really!
I will use the hole for a dwell and sew me a reverb bag out of some of the tweed I have left.
Got a schematic for a raw control?
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The proper footswitch took care of the on and off of the reverb. Installed a NFB switch this evening. Next thing is deciding on the reverb tank. I gotta PM Doug for the specs on his large 3 spring tank.
Anyone using one? If so, does it have that deep undertone or is it more sparkley? I prefer the deep, like you are playing over it if you know what I mean.