Hoffman Amplifiers Tube Amplifier Forum
Amp Stuff => Tube Amp Building - Tweaks - Repairs => Topic started by: 1blueheron on September 14, 2018, 07:41:09 am
-
I am starting this as a new thread as it appears the thread we had going on it became corrupted and it had moved past discussion of separate preamp/power amp PT's anyway.
So so for any one new to this discussion, a little background first. I am a newbie in tube amps. A couple weeks ago I found a 1956 Allen s-12s organ at a local thrift store in semi-working condition. The amp worked great but a few keys did not work and the pedal board was MIA. Since my son is becoming a guitar nut, I thought hey, the thing is cheap enough let's buy it and use the amp as the base for a guitar amp.
And so this project was born.
It is a Webster Electric Co. Model 88-24 amplifier. To this point I have been working with some great folks on this forum to get a working schematic of the amp and then figure out where to go from there.
We pretty much have the schematic complete but when I tried to post it in the thread last night something went haywire so we will start fresh and hopefully this will work better.
-
Here are a few photos for those who were not following in the other thread.
Current tube layout is:
V1=6J5
V2= 6SL7
V3, V4 = 6L6
V5= 5U4
-
And a couple more
-
Special thanks to those who have been so helpful to this point, some really nice and helpful folks here. I am learning a lot and appreciate their patience and mentoring.
BTW, It has been brought to my attention by Bccowan that the amp apparently was made under several model numbers as he has one identical to it labelled as a "Type 212-23648"
-
Take some voltage readings. I really need the voltages for points A, B, and C on the attached pic. Voltage readings for all tube pins would be helpful too. Be careful with your probe and be sure the meter switch is in the proper position.
-
Will do. Hoping to borrow a better meter from work today.
-
Here's what I've got for now. The schematic should agree with your wiring diagram at this point. If you have any questions or see anything that doesn't look right just ask.
-
Hi,
This is great of Sluckey to put in this level of effort helping with the project! Bravo - it's in excellent hands. And, does this qualify as yet another Sluckey "one last amp?"
I am the one with the identical Webster with a different model #. When I get a chance I will carefully compare mine with the schematic, but so far I am seeing no differences. I may also take some voltage readings to compare.
I plan to jump this amp in front of others as I think it'll be fun to work on it at the same time. I am likely to use a Valco, or Gibson type preamp, tweaking values trial and error, and may go pentode 6SJ7.
BlueHeron, you asked me about the transformer mfg. I don't know, and the code stamped on the PT does not coincide with any EIA mfg code that I know of. But, they sure look robust, and I have no concerns, as the Allen organs had a good reputation.
-
In the process of creating the schematic, I noticed that one of the black and yellow striped caps had a split in the side. Should this be replaced? What about the other caps? There aren't that many so I could recap but I don't want to ruin any of the old mojo either so I am open to suggestions. As I said in my first post on this, the amp sounded pretty good clean with very little hum or hiss detectable in the organ and was much the same when we hooked it up to a guitar, although it needed more pre-amp gain.
Bmccowan, It will be interesting to see the two of these develop in the same general period of time and see what they sound like. What are you thinking in terms of a speaker for it? Will you build it as a head or combo? I have the speaker from the organ I could use or I have some other speakers in my stash I might try. If nothing suits our taste from the stockpile, I might spring for a new one but I'm getting ahead of myself...
I am going to make a second attempt at pulling the voltage reading tonite. Will post back when I have them.
-
Don't replace anything until we see some voltage readings.
-
You will get way more gain with either preamp Sluckey offered up.
My amp - since I am always experimenting I will keep it as a head, and likely will just mount it on a board, until I decide to give it away to someone. I rarely (well never) sell these projects as I have an unrelated business to protect and do not want to risk a lawsuit if somebody decides to explore the guts and gets zapped! I've been know to trade an amp for a rhubarb pie.
I have vintage 12" and 15" Jensens I typically plug into. I would not hesitate to use any of the vintage series 12" Webers with this amp. But there are many other speakers that people rave about. I want to try the 12" Eminence Legend 1258 at some point.
-
Take some voltage readings. I really need the voltages for points A, B, and C on the attached pic. Voltage readings for all tube pins would be helpful too. Be careful with your probe and be sure the meter switch is in the proper position.
I have some readings for you:
Wall voltage at time of testing was 124.0V AC
Voltage at Point"A" 341VDC
Voltage at point "B" 284VDC
Voltage at point "C" 260VDC
I will be adding them to the drawing. Will take filament and tube pin readings as well and post.
-
OK. Now I want you to disconnect that orange wire from the top side of that big ole brown Ohmite 10K resistor. Tape the end of the wire. Now measure the voltages at A, B, and C again. They should be greater. Post those voltages. Then resolder the orange wire to the 10K resistor.
-
OK, will do shortly. I just unplugged it a minute ago. Detected a slight sizzling sound coming from the 30MFD 500 can capacitor. It was very hot to the touch. Does this mean it is bad, or just "reforming"?
-
Disconnected orange wire from r16
Voltage at Point"A" 326VDC
Voltage at point "B" 310VDC
Voltage at point "C" 283VDC
-
OK, will do shortly. I just unplugged it a minute ago. Detected a slight sizzling sound coming from the 30MFD 500 can capacitor. It was very hot to the touch. Does this mean it is bad, or just "reforming"?
Filter caps should never be warm and definitely not hot. It's bad. Put the voltage checks on hold and replace that cap. It will cause the voltage readings to be invalid.
I suggest you get that 40x20x20x20/500v JJ can cap (and clamp) that Hoffman sells. It will replace that 30, the 16, and the 2x8s. All those filter caps are 60 years old and need to be replaced. That JJ can will save you some space and prevent some headaches later on.
-
The voltage at point A is decreasing because that 30µF can is burning up. Don't turn the amp back on until you replace those caps.
-
Got it. Amp is unplugged and will stay that way until I can get the caps replaced I resoldered the orange wire.
-
> Detected a slight sizzling sound coming from the 30MFD 500 can capacitor. It was very hot to the touch.
You are not a Real Tech until you have blown-up a large cap and cleaned the wadding off the ceiling.
-
When you order that JJ 40/20/20/20 cap can (with clamp) get two Mallory 150 series .1µF @ 630V to replace those two bumble bee caps. And get one 47µF @ 100V Nichion cap to replace the 50µF/100V can. Hoffman has all of these. Don't let the small size of that Nichion cap fool you. Electrolytic caps have come a long way since the '50s. Put the Nichion cap in parallel with R15 (big brown 225Ω resistor). The positive end must connect to V3 pin 8.
-
Ok, I plan to get those ordered today. All the resistors should be good to go right other than possibly needing some differrent values depending on which preamp option we go with?
-
Resistors are probably fine. You should be able to get a good reading on all those resistors except R7 and R17. Those are basically in parallel and the resistance reading for either will be about 1.8K. If you want to know the value of each individual resistor just disconnect one end of R17 and measure across each resistor. In fact, this may be a good exercise while you're waiting on parts. You don't have much time though if you order from Doug. :icon_biggrin:
I wouldn't worry about the preamp mod until the basic amp is up and running again.
Something else that will be a worthwhile learning experience... Study your wiring diagram and my schematic. Learn how they relate to each other. Especially the grounds. Schematics use a ground symbol rather than running confusing wires all over the place. Much easier to understand once you realize that all the ground symbols are electrically connected together, either by a wire or the metal chassis. Also, be able to locate a part on either drawing. Those reference designators for the components make that easy. This is all gonna be important when you begin building your new preamp because there aint no wiring diagram for that.
-
Parts are ordered. I will check all resistor values in the meantime and replace if necessary. I will also spend some time familiarizing myself with the schematics you have drawn and how they match up with the one I drew.
I found an additional piece of the puzzle today. I figured I would go ahead and pull the speaker out of the organ. It is connected to some type of transformer. In the process of tracing the wires back it led me to the treble and bass controls and the tremolo/vibrato control. I am not sure what produced the tremolo effect and how it all worked other than the gyro speaker. I intend to draw a schematic of the wiring. Perhaps the tone control portion will prove useful. I will post some pictures of the affair tomorrow. There are two wires that were cut off at the speaker and black taped. Perhaps someone removed something?
-
Took resistor reading last night.
Here is what I came up with first number is the specified, second number in parenthesis is actual measured:
R1 =2.4k (2.74k)
R2 =100k (110k)
R3 =5.6k (5.7k)
R4 =1k (1.18k)
R5 =22k (20.3k)
R6 =300k (310k)
R7 =2k (1.9k) Did not un-solder so parallel reading with R7 will un-solder and check again.
R8 =2k (2k)
R9 =6.2k (6.6k)
R10 = 240k (246k)
R11 =100k (110k)
R12 =240k (244k)
R13 = 1000Ω (1028Ω)
R14 = 100k (108k)
R15 = 225k (236k)
R16 = 10,000Ω Could not get a good reading on this one.
R17 = 16k (1.91K) Did not un-solder so parallel reading with R7 will un-solder and check again.
A quick google says values tend to drift upward with time and it looks like that is what mine have done. Any reason to not just go ahead and replace with 1% metal film resistors? Other than the ohmites, these are 1/2W resistors correct?
-
R15 = 225k (236k)
That should be R15 = 225Ω (236Ω). Probably just an operator error but recheck.
R16 = 10,000Ω Could not get a good reading on this one.
Look at the schematic (not your wiring diagram) and see if you can figure out why.
Any reason to not just go ahead and replace with 1% metal film resistors? Other than the ohmites, these are 1/2W resistors correct?
Yes. DON'T FIX IT IF IT AIN'T BROKE! Nothing wrong with those resistors. There's a chance that something may go wrong during the process and then you'll have to figure out what. Leave 'em be.
-
Responses in Red
R15 = 225k (236k)
That should be R15 = 225Ω (236Ω). Probably just an operator error but recheck. Correct. Typo when I entered this AM. Have it correct in my notebook and drawing. I will edit table.
R16 = 10,000Ω Could not get a good reading on this one.
Look at the schematic (not your wiring diagram) and see if you can figure out why. I have a pretty good hunch based on your hint. I will try again tonite and report back :think1:
Any reason to not just go ahead and replace with 1% metal film resistors? Other than the ohmites, these are 1/2W resistors correct?
Yes. DON'T FIX IT IF IT AIN'T BROKE! Nothing wrong with those resistors. There's a chance that something may go wrong during the process and then you'll have to figure out what. Leave 'em be. OK. Will do.
-
Here is some documentation of the speaker and the bass and treble controls. Not sure if it is of any value in figuring this all out or re-use.
As you can see, someone hacked off the red and black wires here. I assume this took the inductor offline as only one wire is connected to anything. Not sure what its function was.
-
[quote R16 = 10,000Ω Could not get a good reading on this one.
Look at the schematic (not your wiring diagram) and see if you can figure out why.
R16 is good. Lifted wire from one end to get the reading. So before I was trying to read a loop correct? Broke the loop by lifting one end?
-
There's a big ole filter cap parallel to R16. That's messing up the meter reading.
-
Arrived home this eve to find my new parts in the Mailbox. WooHoo!. That was quick, 2 days turnaround on a USOS delivery, Thanks Doug!
OK, so I have the old Caps removed. They did not have removable leads. They had threaded bases and wires extend up inside them. So I will need to find some wire to install the new 40/20/20/20 Cap. Is there a minimum gauge wire I need to use? Wire on the old ones was pretty heavy.
Second question. Can I delete the remote volume control at this point? It is in the way of installing the caps and since I won't need it at least in that position, I thought it might be best to go ahead and delete it now.
I hope to get the new caps in tonite.
-
I've been waiting for you. I have a plan that will remove the remote stuff and also free up some lugs on that terminal strip for the upcoming mod. Take some time to study this partial pic and be sure you understand what's happening. Please let me know if these instructions are too simplistic. Be careful when removing wires and components from the tube sockets and terminal strips. Don't want to break anything.
1. Remove the three cans and their wire leads. Remove C3 (16µF) from the terminal strip. Discard caps.
2. Remove R3 and R4 and the remote connector. Discard resistors.
3. Disconnect the end of R2 (100K) from the small terminal strip. Just clip the lead very close to the small terminal strip. Leave the end dangling for now. The resistor will still be connected to V1-3.
4. Remove the small terminal strip and ground lug. Put the nut back on the choke.
5.Carefully remove R5 (22K) from the big terminal strip. Save it for use later.
6. Now carefully enlarge the hole where C6 (30µF) can was mounted and neatly install the new multi can and clamp. Orient the can as shown in the attached pic. You will probably need to temporarily move the shielded cable (and any other wires) out of the way while enlarging the hole. A hole punch makes this job very easy. You need one that's slightly smaller than the diameter of the new cap can. Hope you have one! Otherwise, roll your sleeves up and get sweaty.
7. Refer to the pic and wire the cap can EXACTLY as shown. Use fresh wires. AWG 20 is fine. Don't reuse any old wires you remove from this amp. Install the 22K resistor directly on the can as shown. If resistor leads are buggered then use a new 22K 1/2W.
8. Trim and connect the dangling end of R2 (100K) to the big terminal strip as shown.
9. Install the 47µF cap as shown. Positive end to the tube.
10. Install the two .1µF exactly as shown. Notice that I repositioned C4 away from the side of the chassis. This is to provide room for the tone pots later on.
Post a hi-rez pic when you are done. Be thinking about which preamp you want to use.
-
BTW, I used that same cap can on my last project. Take a look at the pics. May give you ideas. Try to install your can as neatly as my can.
http://sluckeyamps.com/smoky/smoky.htm
If you have any questions just ask. When you finish the above steps, your amp should be back operational just as before, but without the remote clutter. Don't turn on power until I see your next hi rez pic.
-
Instructions are perfect. Working on it now.
-
I've been waiting for you. I have a plan that will remove the remote stuff and also free up some lugs on that terminal strip for the upcoming mod. Take some time to study this partial pic and be sure you understand what's happening. Please let me know if these instructions are too simplistic. Be careful when removing wires and components from the tube sockets and terminal strips. Don't want to break anything.
1. Remove the three cans and their wire leads. Remove C3 (16µF) from the terminal strip. Discard caps. Done.
2. Remove R3 and R4 and the remote connector. Discard resistors. Done
3. Disconnect the end of R2 (100K) from the small terminal strip. Just clip the lead very close to the small terminal strip. Leave the end dangling for now. The resistor will still be connected to V1-3. Done
4. Remove the small terminal strip and ground lug. Put the nut back on the choke. Done
5.Carefully remove R5 (22K) from the big terminal strip. Save it for use later. Done
6. Now carefully enlarge the hole where C6 (30µF) can was mounted and neatly install the new multi can and clamp. Orient the can as shown in the attached pic. You will probably need to temporarily move the shielded cable (and any other wires) out of the way while enlarging the hole. A hole punch makes this job very easy. You need one that's slightly smaller than the diameter of the new cap can. Hope you have one! Otherwise, roll your sleeves up and get sweaty. I have a Greenlee slug buster at work. I will bring it home tomorrow to neatly enlarge the hole.
7. Refer to the pic and wire the cap can EXACTLY as shown. Use fresh wires. AWG 20 is fine. Don't reuse any old wires you remove from this amp. Install the 22K resistor directly on the can as shown. If resistor leads are buggered then use a new 22K 1/2W. Tomorrow
8. Trim and connect the dangling end of R2 (100K) to the big terminal strip as shown. Done
9. Install the 47µF cap as shown. Positive end to the tube. Done
10. Install the two .1µF exactly as shown. Notice that I repositioned C4 away from the side of the chassis. This is to provide room for the tone pots later on. Done
/quote ]
Will post a couple pics in the AM.
-
I have a Greenlee slug buster at work. I will bring it home tomorrow to neatly enlarge the hole.
My JJ can is 1-19/32" diameter. I used a radio chassis punch that cuts a 1-1/2" hole. This was perfect. The 1" conduit punch (1-3/16" actual size) is too small but may work. The 1-1/4" conduit punch (1-11/16" actual size) is too big but may also work if you have enough chassis left to drill the mounting screw holes for the clamp. Might be a good idea to punch a 1" and a 1-1/4" hole in a scrap piece of sheet metal and see which works best. Or you could just use the 1" punch and a little round file or Dremel work.
Also, a 1-3/8" step bit is an option.
EDIT... Here's another option that avoids making the big hole. If doing this, put the can in the same general location as my plan.
https://el34world.com/projects/images/Img_9085.jpg
-
Ok, First, thank you for your kind help and clear instructions. I was very tired last night and signed of without thanking you. I apologize.
So here we go with some photos and questions.
1. After installing the (2 ) .1uf Caps, and looking at the work, particularly C4, it occurred to me it might be best to put some insulating sleeves on the leads. Are they fine as is or is shorting or is arcing an issue. If so I can go back and install sleeves. Please advise.
2. The old input leads and volume switch with grounding lug etc. Should it be deleted at this time and (b) do I need to order a 1/4" shorting input jack? If so, does input need to be insulated (isolated from chassis like marshal style input jack)
3. What about Caps C1&C2? Should I replace them?
As to the mounting location of the can cap. I have space under the chassis ( tired it last night and it just fits) if we are not going to re-use the holes where the remote volume connector and the input jack were at. This would be cleaner and leave the chassis in more original condition than making a bigger hole in the top and also require less work. It may also be easier for accessing and soldering the cap. I can also do a little more work and mount it topside as I have it layed out in the pictures and as you originally advised, which would give more working space underneath. Is there a preferred method? I see pros and cons to both so I will seek your wisdom.
There was insufficient space in the hole of V4 pin 4 to make all the connections so I wrapped the orange wire that will run from V4 pin 4 to X on the can, around the leg of R13 and soldered it. Is there an issue with this?
I still need to run the red wire for the cap can. I was unclear on this. I assume this is going to connect to the junction point of the red wire from V5 pin 5, the red wire from the output transformer and the red wire from the choke? In the drawing it does not show the red OT wire and the other two lines morph together without a clear junction point. I am assuming the solder point on terminal strip is just left out?
-
And the Cap positioning
-
Obviously the can is upside down and just there to simulate size and location.
With any of the new connection points I tried as much as possible to remove old solder, clean, install a mechanical connection of the wire and then re-solder. It is tight space to work in. But I believe I have good joints on everything I touched.
Please feel free to criticize so that I can correct bad habits, learn, and improve my craft.
-
1. After installing the (2 ) .1uf Caps, and looking at the work, particularly C4, it occurred to me it might be best to put some insulating sleeves on the leads. Are they fine as is or is shorting or is arcing an issue. If so I can go back and install sleeves. Please advise.
Yes. Put sleeves on the leads of both caps.
2. The old input leads and volume switch with grounding lug etc. Should it be deleted at this time and (b) do I need to order a 1/4" shorting input jack? If so, does input need to be insulated (isolated from chassis like marshal style input jack)
No. Don't delete those yet. They will be eliminated eventually, but not now.
3. What about Caps C1&C2? Should I replace them?
Leave them. They will eventually be eliminated, but not now.
As to the mounting location of the can cap.
My preferred method is to enlarge the hole so the body of the can will sit on the outside of the chassis and only the solder lugs will be inside the chassis. This will be the neatest and easiest to wire/work on solution. Next choice would be to mount the cap inside the chassis with the clamp attached to the end wall of the chassis.
There was insufficient space in the hole of V4 pin 4 to make all the connections so I wrapped the orange wire that will run from V4 pin 4 to X on the can, around the leg of R13 and soldered it. Is there an issue with this?
That's fine for now, as long as there is a good connection and no possibility of shorting to anything. Keep in mind that we will probably be removing R16 (10K/10W) and the orange wire that connects it to V4-4. If so, you can redo the soldering on V4-4 at that time.
I still need to run the red wire for the cap can. I was unclear on this. I assume this is going to connect to the junction point of the red wire from V5 pin 5, the red wire from the output transformer and the red wire from the choke?
That's correct. Let's call that lug 2. In future drawings I will label the lugs 1, 2, 3, etc., from left to right. There will be a wire from V5-5, another from the OT, another from the choke, and another from the cap can. There is another red wire that jumps to lug 6 on the terminal strip. Remove that wire. That will leave lugs 6 and 7 empty. We'll use them later.
Our goal at this point is to get the amp back up and running but without the remote control. I still want a good set of voltage readings. And we need to verify that the amp still works as it did before, although the volume will be low.
-
OK, I think I can handle that. My time tonight will be limited and I will be off the grid over the weekend helping with cleanup effort in North Carolina. I will try to post up any progress I make tonite.
As to the thoughts of which preamp...
I have some questions here in choosing. My son primarily plays strats. He and I prefer a full, thick tone and he tends to play more classic/hard southern rock, Van Halen, Pink Floyd, 38special, Dire straits,Mark Knopfler, David Gilmore, type tones. This may change over time but that's where he is at right now. He is not into jazz, blues, or metal.
So I guess we fall somewhere between a Fender and a Marshall as far as overall sound charachter. The Ampegs we have heard seem to generally fit in this category but I know very little about the tonestack configurations from a sonic perspective and use. A little book work says I would probably lean towards a baxandall stack for functionality? However, I like the sound and flexibility of the tone controls on Greis 5 which I understand is a Champ with modified AA764 tone stack?
I have not heard the ampeg b12n played on anything but a bass guitar. How does it break up? Any sound clips?
As for use, this amp will primarily be for home or school assembly use. He is not playing in a band over drums or clubs. It doesn't need to be loud. More concerned with quality and flexibility, than qty of sound.
I don't fully understand tube gain stages and how overdrive/distortion works in a tube setup. Is all of the gain developed in the first stage carried through by a multiplication factor with the second stage, or does a lower mu tube in the second stage damper gain or become overdriven by the first stage?
On the Rockola project you used (2)6SN7, (2) 6L6 setup. Fender AB763 preamp which is interesting to me based ono the sounds you describe.
do you have any sound clips of it?
" I wanted to stay with the 6SN7, even though it's a medium mu tube, just to see if I could get away with it. I figured that if this amp could provide loud jukebox music from a ceramic phono pickup thru a meduim mu gain stage and cathode follower, it should be able to make a loud guitar noise through two medium mu gain stages. Sounds logical, right?
So, I simply duplicated the first gain stage and sandwiched the Fender tone stack between them. I was pleasantly surprised! It all worked very well together. I did add a raw control to the tone stack. And I put a switch on that 5KΩ field coil simulator. With that switch open, the B+ at nodes B and C increased about 80 volts, getting a little closer to the blackface sound. Just close the switch for a browner sound."
What is the difference between this and the (2)6SL7, (2) 6L6 setup? Is it just more gain with the 6SL7's? From what I understand the first stage should be low noise high gain correct? Could the 6SL7 we have be moved to V1 for and then use a 6SN7 I have as V2 rather than another 6SL7 for V2?
I am trying to do a lot of reading on theory to understand this and wrap my head around it... If you have some recommended primers to help me understand how the gain stages work please send a link.
-
New can cap is mounted and connections soldered up. Volume pot and input back in place and I put sleeves on the legs of the caps that could touch anything else. Will post a picture of it all tomorrow. Thanks for your continued patience and support. I feel like I'm making headway!
-
He and I prefer a full, thick tone and he tends to play more classic/hard southern rock, Van Halen, Pink Floyd, 38special, Dire straits, Mark Knopfler, David Gilmore, type tones.
Hey, I like those too, except for Van Halen.
The Ampeg has a warm, clean sound, a little creamy when pushed hard (Think "Long Cool Woman in a Black Dress"). The Rockola with the Fender preamp with the added raw control into cathode biased 6L6s will give you a good clean sound or a gritty slightly overdriven sound with some added compression. This is probably closer to the stuff you like. BTW, my Rockola runs two 6SL7s and two 6L6s. I switched out the 6SN7s shortly after building it and just never updated the web page. I would expect your amp to sound a lot like my Rockola if you choose the Fender preamp.
The reason I've suggested these two preamps is because I know the circuits I used will work well. And either would be pretty easy to stuff into your chassis. I don't have any sound clips.
-
OK, I guess we will go with the Rockola setup then.
I will save the 6SN7 tubes and maybe later use them for a Moonlight build or something like that.
Here are pictures of last nights work. I noticed some solder splatter shows up in the photos, I will make sure I get that all out before powering up and testing. I think it all came out pretty nicely and the cap looks good sitting there. Looks kinda like a black rook sitting there in its corner square with pawn in front , and the bishop king and queen... Not sure why I thought of that, random thoughts...
I removed the red lug 6 jumper.
Can is in place and wired up.
Question on AC power cord. I replaced the old cracked 2 wire cord with a 3 wire. It it OK to ground the green wire on the chassis? Should it run to the central chassis ground point or just the nearest convenient location?
Provided this all passes inspection, I guess I can take new readings when I return Sun. eve or Monday.
-
And here is the underside.
-
That looks great! The green wire in the power cord needs to connect to chassis. Put a ring lug on the green wire and fasten to chassis with a nearby power transformer bolt/nut. Look at the attached pic. This is what I envision the mains wiring to look like.
The resistor on the cap can... Is it red/red/orange (22K)? On my monitor it looks like the orange band could be a yellow band.
Tell me about the wire you used for the cap can. That's not low voltage wire such as you would use for a HVAC thermostat, or sprinkler system, or door bell, is it?
1. The next step will be to power the amp on and measure the voltages on the cap can at points A, B, and C.
2. Then temporarily disconnect the orange wire from R16 and remeasure the voltages on the cap can at points A, B, and C. Reconnect the orange wire when done.
3. Finally, measure the voltages for all tube socket pins.
After voltage measurements, connect a guitar to the input jack and see if the amp sounds similar to what you heard before.
-
OK, I will get the green wire soldered to a lug and put it on the PT transformer bolt/nut. That will be very convenient.
The resistor on the cap can was taken out of a new package that said 22k on it but in honesty I did not check it with ohm meter or check the color bands closely. I will confirm its value and make sure is correct and replace if need be.
The wire I used for the cap is definitely not thermostat doorbell type wire. It is a 18AWG stranded/tinned wire. Looks very similar to MTW type wire. I will strip a piece back and take a picture of it so you can see it. I do not know the specs on the insulation. It is heavier than any of the other wire presently in the amp. Is the concern current/voltage carrying capacity or insulation temp/breakdown? I can replace with known spec wire if needed.
-
Here's a parts list for everything you need for the mod. I highly recommend Hoffman's parts. You can get the 6SL7 from AES...
https://www.tubesandmore.com/search/node/6sl7
-
Sluckey,
Thanks! That list is great. I will try to get it ordered ASAP. Just got back in town late last night and was pretty wiped out. We had a flash flood Sat. eve while I was out of town that took out part of our driveway so I have to play a bit of catch up and get that fixed and the grass mowed, but hope to get back on this very soon. Might be able to get the voltage readings tonite or tomorrow night.
-
I was able to get the ground wire from the mains bonded to the chassis and the 22K resistor put in last night. Then I powered it up and took some voltage readings.
Here is what I came up with:
A= 415V
B= 346V
C= 260V
V1
Pin 3= 97V
Pin 8=3V
V2
Pin 2= 132V
Pin 3= 2V
Pin 5= 101V
V3
Pin 3= 407V
Pin 4= 346V
Pin 5= 1V
Pin 8= 26V
V4
Pin 3=409V
Pin 4=346V
Pin 5=0V
Pin 6= 389V
Pin 8= 26V
V5
Pin 2=415V
Pin 5= 415V
Pin 6=26V
-
I plotted voltages on drawing.
-
Here are some parts I have on hand.
The SPST switch looks identical to the one on the parts list.
I have these jewels and lamp assembly in my stash. I realize I would need to buy a 110V bulb rather than the 6.3V bulb that is in it but is it possible to use one of these vs. the plastic neon light? I like the vintage look more.
I have some pots as well but assume it is best to use new rather than re-use?
-
That switch and the 6.3V lamp assembly are fine to use. But buy new pots.
Now I need three more voltage readings. Disconnect the orange wire from R16 (big ole brown power resistor). Tape the end of the wire. Now remeasure the voltages on the cap can (points A, B, and C).
Does the amp still work the same as it did when you last plugged a guitar in it?
We're just about ready for the fun part. Have you ordered parts?
-
I need you to take an old pot and see if it will fit over the tube sockets without touching. Use this pic as a guide. We really need to install the pots like this if possible.
-
I will check it out tonite and see if the pots fit. I am pretty sure they will but soldering in the space left will be challenging. I like a challenge :l2:
It was 12:30 last night when I finished up so I didn't try to plug up a guitar. :icon_biggrin: I will try to take the voltage readings with r16 lead lifted and plug it up tonight.
I have the parts list made up, was just waiting to know if I should order the pots before I sent it out.
Our internet service is out at home due to the storm so you may not hear back from me until tomorrow AM.
-
Don't worry about the challenge. I'm gonna break this down so it will be easy. Don't drill any holes yet.
-
Plugged a guitar in and it works great. Even better than previously.
Here are the new readings:
With orange wire connected at R16:
A=415V
B=346V
C=296V (The previous reading was off for some reason, probably I transposed some numbers wrong)
With orange wire lifted at R16:
A=420V
B=405V
C=345V
Is this what you were expecting to see?
I am not seeing any issues with mounting the pots as shown. It looks like they will clear the tube bases. Getting the standoff/ lug mounted between V1 and V2 will be very tight but doable as well.
I sent the parts order out. Only thing left not ordered is the 6SL7.
Thanks again for tutoring me on this. Looking forward to the next phase. Haven't drilled any holes yet.
Is it OK that the 2 -6L6 tubes do not match? At least from the envelope shape standpoint.
-
Voltages acted as I expected with the orange wire removed. You can reconnect it now.
Mounting the terminal strip will be easy when you remove the old components connected to V1 socket.
You can temporarily use a 6SN7 until you can get a 6SL7.
Don't drill any holes until you have the parts in hand.
The 6L6s don't have to look the same unless it bothers you. You may want to buy a matched set later on.
-
You may want to go ahead and install your switch and pilot lamp. I suggest over near the power transformer as shown in this pic. Lamp connects to V3 pins 2 and 7. Be sure they will fit before drilling.
-
Here's a plan. Take a look. Ask questions if you have any.
-
Wow! You went to a lot of detail and effort to put that together for me. I really appreciate it.
The parts have shipped out. In the meanwhile I will do tasks 1&2.
Questions:
1. I was just reading the thread on the 1 tube reverb. If I added a tube socket could I do a the 1 tube reverb addition to this amp in the future? I believe there is plenty of room to get 1 more tube socket in, I just don't know if the order/placement would work and if I would have room for the components. Of course a spring tank would need to be added.
2. The dimensions for pot placement are very clear for horizontal placement. Does vertical placement matter?
-
Don't do task 2 until you have the parts on hand and can verify that the pots will fit according to the plan.
The one tube reverb will work with this preamp. But hold off on that for now. Let's get the amp up and running first.
Yes, vertical placement matters. The body of the pots must not touch the sockets or any other components. Ideally, you would strike a centerline on the front of the chassis running from left to right. Your centerline would be 1" from the bottom of the chassis. Then just drill all holes along that centerline. But, since your sockets are so close to the front of the chassis, you may have to shift that centerline toward the bottom (open side) of the chassis in order to provide clearance between the pot bodies and the tube sockets. This is why you should not drill any holes until you have the parts on hand. It's critical that the pots do not touch the sockets. I would even hold off installing your switch and pilot lamp until you know where that centerline will be. Put a piece of masking tape across the front of the chassis to make marking easier. And use a center punch and a pilot drill bit rather than just drilling the big holes first.
Even the small terminal strip needs the pots to be mounted first before drilling it's mounting hole. So, you're just holding on until you get the parts. If you ordered from Hoffman you'll probably have them tomorrow.
Oh yeah, I find that a step bit is easier to control and less likely to damage sockets and components than a standard twist drill bit when modifying an existing chassis.
-
I cleaned off V1 last night. (just noticed I still have 1 wire that needs to come out. :BangHead:)
Also cleaned up some of the lug standoffs.
Not drilling any holes until the parts come.
Just waiting on the postal service now.
I went scrounging to see what I could come up with for knobs. Found some nice machined aluminum ones. Will need a few mods to make em work but like the style.
Here is what I had in mind on the extra octal tube socket. I could also fit two noval type tube sockets in the old cap can holes as shown in the pics below
-
Better stick to the plan!
You removed a 330K resistor that was between V2-4 and terminal 5, and a jumper between terminals 4 and 5. Gotta put those back. Maybe use a new 330K. If you prefer, connect the 330K between V2-4 and terminal 4. That way you don't need the jumper between terminals 4 and 5.
Remove the black wire from V1-1 and save it.
Move the brown wire from V1-2 to V1-8
-
I am a bit confused, please straighten me out. I removed R6 (300k). I understood it was to be replaced with a new 330k as in the drawing. Do I need to put the 300k back?
The lead wire from C2 passed through lug 5 and bridged to lug 4. Do we still want lug 4 bridged to lug 5?
-
You removed a 330K 300K resistor that was between V2-4 and terminal 5, and a jumper between terminals 4 and 5. Gotta put those back. Maybe use a new 330K 300K. If you prefer, connect the 330K 300K between V2-4 and terminal 4. That way you don't need the jumper between terminals 4 and 5.
OK, the confusion is my fault. I have been erroneously calling the 300K a 330K because I did not have a 300K in my resistor templates. The value is not critical, but you may have difficulty finding a 300K carbon comp resistor today. Bottom line, you must have a 300K (or 330K) connected between V2-4 and ground for the amp to work properly. I offered two options for doing this above.
-
OK, I think we are on the same page. Thanks for clarifying and checking behind me.
Part are being delivered today according to tracking info. :icon_biggrin:
-
Got the parts yesterday. Was able to get it all put in. Had a minor accident in that i dropped th bulb for my pilot light and it shattered. :sad2: will have to buy a new one. I think everything is in and checks out with fig 5. I have the 3 large blue resistors left over. They were for twerking the cap correct?
Will try to take pictures tonight and post for critique and review before taking voltage readongs and firing it up.
-
What'cha waiting for?
You can use a 6SN7 in the V1 socket until you get a 6SL7. Who knows, you may even prefer the 6SN7.
#47 or #1847 are cheap at Amazon or eBay.
https://www.amazon.com/10-PACK-Eiko-Miniature-Light/dp/B00455IHYM/ref=pd_lpo_vtph_60_bs_t_1?_encoding=UTF8&psc=1&refRID=K767Z4AFQW2HB16YK1VN
This time when you check voltages I want to see voltages on nodes A, B, and C for the cap can, as well as voltages for every pin on every tube socket.
-
Was out of town today and just got back. Hope to get back on it tomorrow. Here's some pics to check out. Does this look right?
-
:thumbsup: Good job. Looks like it's always been there.
I see two issues...
1. After all that talk about R6 you used a 2.4K! Gotta fix that.
2. The 6.8K is connected to the wrong lug on the RAW pot.
-
:thumbsup: Good job. Looks like it's always been there. Thanks! That's a huge compliment
I see two issues...
1. After all that talk about R6 you used a 2.4K! Gotta fix that. OK, that's fixed glad you caught it... again :worthy1:
2. The 6.8K is connected to the wrong lug on the RAW pot. Not sure how I messed that up but it's fixed now.
Thanks for once again keeping me on track, I am attaching two pics, one of the corrections and one of the mains with the pilot lamp (bulb still missing :sad2:)
Hope to fire it up after church today.
A couple questions on use of the 6SN7 as substitute for 6SL7.
1. Is the amp wired so that these are interchangeable now?
2. Should V1 be the temp 6SN7 or should I use the 6SL7 in v1 and the 6SN7 in V2?
3. Could both v1 and v2 be 6SN7 for a lower gain version?
Lastly, I have found some Russian made Reflektor brand 6H9C which are supposed to be direct replacement for 6SL7 and have good reviews. Is there a reason not to use them?
-
6SN7 and 6SL7 have identical pin assignments. Put your 6SL7 back in the V2 hole for now and put a temporary 6SN7 in the V1 hole. Why would you want to mess with that Russian oddball?
Give it a sound check. Measure voltages. When the amp is up and running properly you can experiment with different tubes in V1 and V2 sockets.
-
Voltage readings by pin:
V1
1=0
2=82VDC
3=4VDC
4=0
5=84VDC
6=4VDC
7=6.2VAC
8=6.2VAC
V2
1=0
2=132VDC
3=405VDC
4=345VDC
5=0
6=0
7=6.2VAC
8=6.2VAC
V3
1=0
2=6.2VAC
3=406VDC
4=345VDC
5=0
6=387VDC
7=6.2VAC
8=26VDC
V4
1=0
2=6.26.2VAC
3=406VDC
4=345VDC
5=0
6=387VDC
7=6.26.2VAC
8=26VDC
V5
1=0
2=415VDC
3=0
4=3VDC
5=413VDC
6=3VDC
7=0
8=413VDC
A=415VDC
B=346VDC
C=296VDC
Getting ready to do a sound test.
-
WOOHOO. It works. Very clean. Sounds great. Not getting any form of distortion at room playable conditions. Is there a way to dial in a little crunch?
-
WOOHOO. It works. Very clean. Sounds great. Not getting any form of distortion at room playable conditions. Is there a way to dial in a little crunch?
That's characteristic of AB763 amps. You should be able to get some grind by using the RAW control. It functions as a MID control for the first half of rotation, then it starts 'lifting' the tone stack, which will increase the gain and grind. May have to get loud to get the real crunch.
When you have listened to the amp for a while I want you to replace the 22K on the cap can with that 4.7K 3W resistor. Also recheck the A, B, C voltages on the cap can with the 4.7K.
And don't do anything drastic until you have another 6SL7 plugged into V1 hole.
-
A very heartfelt thank you for all your help and guidance on this. You put a smile on our faces today. We had a hard time putting it away to do our work.
Agenda now is as follows:
1.Change the cap resistor you mentioned
2.Order 6SL7 and #47 bulb
3.Find a proper speaker (we were playing through a little practice amp cabinet I made him with two speakers out of a big screen TV. If memory serves they were 3X5's or some such thing. Fine for the little LM386 amp but not near enough for this beast.
4.Build a proper housing for it.
Past that, maybe doing the 1 tube reverb or an EFX loop.
We did play with the raw control and swapping the tubes around a bit. Running with (2) 6SN7's is still plenty loud and it has a great tone. I don't think it is possible for us to get into grind territory until we get a proper speaker, And even then it may be too loud for use in the house.
He has a little Line6 POD he can use for now when he wants something other than clean.
Thanks again. I will continue to post as I work on the housing, speakers, etc.
Is there a way to post sound clips here? Don't see an audio file type.
-
Read the first message in the "Sound Clips" forum.
-
Swapped the can cap and put in the new bulb.
With the new cap in place and a 6SN7 in V1 and 6SL7 in V2 the voltages were:
A=414
B=345
C=334
-
Have the basic drawings/plans for the cabinet finished. This is a rough sketch of what it will look like.
-
Looks like you're about done. I would open up the back panel a lot more to allow the amp to breath better.
Here's my final drawing. Let me know if you want the actual Visio file.
http://sluckeyamps.com/misc/Visio-webster.pdf
-
Thanks sluckey! and thanks again for all your help on this. I should be getting the 6SL7 (ordered a JJ) soon and will try it out with the correct tubes.
I have posted up a sound clip. The sound clip is with the "raw" at 10, and volume at about 2.
Link to the sound clip below...
https://el34world.com/Forum/index.php?topic=23832.0
I will open up the back some more for ventilation. Will likely make the cabinet from spalted maple and poplar with a teak control plate. I will start a thread on the cabinet build in the Speaker and cabinet section.
-
The JJ 6SL7 i ordered finally arrived today. Popped it in and powered it up. Short lived excitement. Sounds like a badly scratched record playing.
Gain is exceptionally high. Can still hear it even with volume turned all of the way down. On 2 its beyond comfortable in the house and thats with the raw turned down.
Any reason this tube should be sounding scratchy? Amp is dead quiet wth the two 6SN7s or with old 6SL7 and one 6SN7
-
I got discouraged on the Webster when the 6SL7 acted up... So Sluckey's comments on the Conn project and VVR etc. got me thinking I should stick with fine tuning the Webster a bit more before moving on.
Last night I had a crazy thought. What if I swapped the matched 6L6 tubes out of the Conn amp into the Webster. So this AM, that's what I did. I don't know why but with the Conn 6L6 tubes in place of the mis-matched ones the thing really came alive and the issues disappeared. I have renewed faith and interest in the project. After I did this, we took it to a local guitar shop and plugged it into a Marshall 4X12 cab. No scratchy sounds!
So now that I have that issue addressed, two issues remain:
1. Getting some distortion or distortion effects at lower volumes
2. Taming the power.
I am thinking in the direction of either an FX loop for distortion pedal, or distortion pedal before the amp to solve #1
Perhaps power scaling or VVR to address dealing with the power when not needed and perhaps help with #1 as well.
Of course I still need to finish the cabinet as well.
I did add a 1/4" output jack to what used to be the hole for input on the back. It's wired to the output screw terminals so impedance can be adjusted.
BTW, the sound of this amp on the 4X12 Marshall cabinet rivaled any clean amp in the store, some well over $1500.00
-
I think VVR is what you are looking for. Trinity Amps sells a VRM kit (same as VVR)…
http://www.trinityamps.com/product/voltage-regulation-module-vrm/
Great documents too...
http://www.trinityamps.com/docs/VRMBuildersGuide3.pdf
-
Here is something that Kevin O' Connor said about VVR among other things. He has a new forum that has some good information on it for those who are interested. You can find it at http://theultimatetone.com/Thread-London-Power-Power-Scaling-with-SV1-and-RBX-Fixed-Bias (http://theultimatetone.com/Thread-London-Power-Power-Scaling-with-SV1-and-RBX-Fixed-Bias)
Greg
London Power invented Power Scaling, so our method is the correct one to use if you want cranked amp sounds at Human Scale Loudness. It's not just hyperbole - it works!To maintain the sound of the amp you have to do two things: keep the speaker-amp interface intact, and maintain the transfer function of the amp. The first part is easy - just leave the speaker connected to the amp. This means that using a speaker attenuator is problematic as they interfere with how the speaker and amplifier interact. Everyone who has used an attenuator also knows that the tone changes quite a lot when you get down to useful loudness reductions.The second condition sounds complex but it is not. When Power Scaling (PS) is installed correctly the tone of the amp is maintained as you dial the controls down. The only thing you lose is that the aural compression of your own hearing is no longer being invoked to change your perception of the sound. Because the intent is to maintain the transfer function (input versus output), bias and other internal parameters are all addressed and taken care of.VVR is a bastardised copy and wrong implementation of a part of the Classic-PS circuit. Dana Hall was asked by a licensed Power Scale amp builder to design a PCB, at which time Dana could see the entire implementation, yet his version can only be applied to small amps and cannot dial down to truly quiet levels. The crippled application also requires bandaids in the form of extra capacitors being added to the amp to keep controls from becoming scratchy - including the guitar volume pot!Marshall's EPA used in the YJ and Slash models is a form of PS-TT (two-thirds Power Scaling), but a poor implementation. Techs who have bypassed the EPA find the amp sounds like a Marshall again, and if they modify the EPA per our standards the amp remains Marshally-sounding but has useful power reduction.Victor Mason of Mojave Amps did not understand the circuit of the Power Scale kit he bought, and copied the Mesa Limit control depicted in TUT. He used our Power Scale ad copy to describe what his control would do - which it does not - and stated "Kevin O'Connor likes complicated circuits". That is not true. A circuit must be as Einstein describes, "Simple enough to do the job properly and no simpler". Power Scaling does what we say it does and the alternatives simply do not.As our books TUT2, TUT4 and TUT6 show, there are a wide variety of circuits that can be used to implement Power Scaling, each with its own benefits and cost.
-
It seems like this is a subject with numerous opinions and lot of ways to achieve bedroom levels from larger amps. I thank everyone for the links.
In reading through the "authorized licensed installers" list, I noticed Bob Reinhardts name and that he is in Evington, VA which is across the river 5 mi. from me. Unfortunately he is no longer building amps and the links are down. The excitement was short lived... but not without benefit. I spent a good hour looking at posts on Reinhardt amps. It appears they used partial Power Scaling (output power section only)
So, regarding VVR, VRM, Power Scaling etc. Since I am starting out with an amp that does not have a particular signature tone I paid a fortune to get and am trying to maintain at all loudness levels, is there any benefit to doing this the KOC "right way" vs. doing VRM?
I have a cathode biased amp correct? Is it "self-adjusting" or "fixed bias". A few hours of reading lead me to think it is "self-adjusting" using fixed value cathode resistors. Can I interpret this as the cathode bias actively changes based on grid voltage but changing tubes may require cathode bias resistor replacement/adjustment?
-
"self-adjusting"
yup, you have a self biased amp, also referred to a cathode biased
I don't pay attention well to the vvr stuff, but from what I recall, they are usually done with fixed bias, I believe it's pricey when you get into self biased configs
-
here's something I was gonna try;
-
the KOC "right way"
Guess whose opinion that is! :icon_biggrin:
I don't pay attention well to the vvr stuff, but from what I recall, they are usually done with fixed bias, I believe it's pricey when you get into self biased configs
VVR is easier and simpler to implement with cathode biased amps. The circuit gets more involved with fixed bias amps because you have to add circuitry to make the bias supply track with the B+ supply.
-
simpler to implement with cathode biased
:laugh: I knew I didn't know what I was talking about :think1:
-
This has been a fun thread to watch. And the success of it has been great.
Sluckey, your generousity and contribution to the forum is unmatched! Bravo! What a remarkable guidance you have given to the success of this project and many other successes including a handful of mine.
THANKS for being a moderator and sharing your wealth of knowledge! :headbang: :headbang: :thumbsup: :thumbsup: :thumbsup:
With respect, Tubenit
As an aside, there is considerable documentation on VVR and cathode biased amps in ARCHIVES: http://el34world.com/Forum/index.php?topic=6899.0
-
Hey guys. I'm not a vvr, or vrm, or power scaling guru. In fact, I have zero hands-on experience and never will. I do understand the circuits and have picked up on some of the quirks involved with simple vvr (such as scratchy guitar pots when vvr is adjusted to very low voltages, not really a fault of vvr, just a byproduct of operating the first preamp tube at extremely low plate voltage). All I know is just what I've read on this computer screen. I know that KOC has a more sophisticated system. In fact, he has a lengthy chapter devoted to power scaling in TUT-4. He's definitely thought about this a lot more than I ever will. What can I say? I'm just a hobbyist and I like keeping my amps simple. :icon_biggrin:
I do see vvr as a viable option for the common cry, "Help, my B+ is too high!"
-
here's something I was gonna try;
That's kinda cool. A low tech solution! Better buy your incandescent bulbs now before they are gone.
If you had each bulb light a power level indicator jewel it would look awesome and be quite functional as system
The drawback I see is you are still stuck with fixed levels rather than being able to vary the power. In that sense, I guess VVR or PS is a better system?
-
Here is something that Kevin O' Connor said about VVR among other things. He has a new forum that has some good information on it for those who are interested. You can find it at http://theultimatetone.com/Thread-London-Power-Power-Scaling-with-SV1-and-RBX-Fixed-Bias (http://theultimatetone.com/Thread-London-Power-Power-Scaling-with-SV1-and-RBX-Fixed-Bias)
Greg
London Power invented Power Scaling, so our method is the correct one to use if you want cranked amp sounds at Human Scale Loudness. It's not just hyperbole - it works!To maintain the sound of the amp you have to do two things: keep the speaker-amp interface intact, and maintain the transfer function of the amp. The first part is easy - just leave the speaker connected to the amp. This means that using a speaker attenuator is problematic as they interfere with how the speaker and amplifier interact. Everyone who has used an attenuator also knows that the tone changes quite a lot when you get down to useful loudness reductions.The second condition sounds complex but it is not. When Power Scaling (PS) is installed correctly the tone of the amp is maintained as you dial the controls down. The only thing you lose is that the aural compression of your own hearing is no longer being invoked to change your perception of the sound. Because the intent is to maintain the transfer function (input versus output), bias and other internal parameters are all addressed and taken care of.VVR is a bastardised copy and wrong implementation of a part of the Classic-PS circuit. Dana Hall was asked by a licensed Power Scale amp builder to design a PCB, at which time Dana could see the entire implementation, yet his version can only be applied to small amps and cannot dial down to truly quiet levels. The crippled application also requires bandaids in the form of extra capacitors being added to the amp to keep controls from becoming scratchy - including the guitar volume pot!Marshall's EPA used in the YJ and Slash models is a form of PS-TT (two-thirds Power Scaling), but a poor implementation. Techs who have bypassed the EPA find the amp sounds like a Marshall again, and if they modify the EPA per our standards the amp remains Marshally-sounding but has useful power reduction.Victor Mason of Mojave Amps did not understand the circuit of the Power Scale kit he bought, and copied the Mesa Limit control depicted in TUT. He used our Power Scale ad copy to describe what his control would do - which it does not - and stated "Kevin O'Connor likes complicated circuits". That is not true. A circuit must be as Einstein describes, "Simple enough to do the job properly and no simpler". Power Scaling does what we say it does and the alternatives simply do not.As our books TUT2, TUT4 and TUT6 show, there are a wide variety of circuits that can be used to implement Power Scaling, each with its own benefits and cost.
Greg,
I very much appreciate the feedback and info. I am very limited in my understanding of things and I will trust those of you who know much more than I do as to the good, better, and best ways to achieve what I am trying to do.
Although I understand cheaper is seldom better, I do have to put things in perspective from a $ perspective. I paid $50 for the whole organ. I added another $100 in parts and a new 6SL7 to get a great sounding amp for about $150.00 That's $150.00 too much in the wife's opinion (who would just like her kitchen table back free of parts and soldering operations) and I am handing this amp off to a 16 year old. Do I want to spend $70 for a KOC PS kit, not really, $40 Trinity kit is nearly half, and $20 for mouser parts sounds even better. For me this is all about learning. I suspect there will be many more mods to come with this amp and am glad that with Sluckey's help and guidance I have been able to give it new life.
Whichever direction I go, I have absolute respect for all those who have offered their good time and their opinions. If I had the extra money on hand and was going to put this in a vintage amp that I paid a bundle of cash because I liked a specific tone it had, I would be firmly in the KOC camp. As it sits right now, the cheapest solution that gets the job done will likely be the direction I go and the more I learn on that path the better as my goal here is to learn and have fun.
-
As an FYI, I like VVR and have put that in a few amps that are cathode biased and was pleased with the results.
Having said that, I discovered I like the PPIMV approach better as a way of controlling volume. The VVR is useful for lowering voltage. I think perhaps the PPIMV has done a somewhat better job at preserving the original tone at full volume when you are dialing down from 10 to maybe 5.
The VVR changed the tone slightly when dialing the volume down.
For example, let's say I have some 6AQ5 tubes and I really don't want them to run at 345v and would prefer they are running at 305v. Then the VVR is a reasonable approach to lowering the voltage.
Just a thought and a personal preference. Not saying one way is "better" then another.
With respect, Tubenit
-
Greg,
I very much appreciate the feedback and info. I am very limited in my understanding of things and I will trust those of you who know much more than I do as to the good, better, and best ways to achieve what I am trying to do.
Although I understand cheaper is seldom better, I do have to put things in perspective from a $ perspective. I paid $50 for the whole organ. I added another $100 in parts and a new 6SL7 to get a great sounding amp for about $150.00 That's $150.00 too much in the wife's opinion (who would just like her kitchen table back free of parts and soldering operations) and I am handing this amp off to a 16 year old. Do I want to spend $70 for a KOC PS kit, not really, $40 Trinity kit is nearly half, and $20 for mouser parts sounds even better. For me this is all about learning. I suspect there will be many more mods to come with this amp and am glad that with Sluckey's help and guidance I have been able to give it new life.
Whichever direction I go, I have absolute respect for all those who have offered their good time and their opinions. If I had the extra money on hand and was going to put this in a vintage amp that I paid a bundle of cash because I liked a specific tone it had, I would be firmly in the KOC camp. As it sits right now, the cheapest solution that gets the job done will likely be the direction I go and the more I learn on that path the better as my goal here is to learn and have fun.
Given what your needs are for this amp, I would say install a master volume of some sort and go with that. It will be adequate to get some crunch at low volumes if you design the preamp to have some gain, and it is certainly cheaper. It sounds like you will likely do future projects and if so, you can design an amp to use Power Scaling or VVR or whatever you want at that point. I've used Power Scaling from KOC on a couple amps and I really like it, but I also like my non master volume Vox AC30 a lot too. The Vox can't be used at a gig if you want crunch and you have to be quiet though unless you use a pedal to get the crunch, because it needs to be halfway up to get the crunch and then it is very loud. If I put Power Scaling on an amp, it can get the crunch and still sound very close to how it does when it is full up, yet be very quiet. You don't have the speaker distortion when it is low volume so that is one element that is missing, but it is the closest that I have found to simulate that loud tone and be quiet and still be natural sounding and easy on the amp.
The VVR is based off one of KOC's early Power Scaling designs and it isn't as versatile, but it is cheaper and easier to incorporate, especially with a cathode biased amp. I personally haven't tried VVR myself as I went right to Power Scaling when I considered building an amp that was going to use something like that. A lot of others here have used VVR and can tell you all about it. Some people don't like KOC as his products are somewhat more expensive, and he can come across as arrogant in some ways. Certainly if you ask him a question his answer often appears to be the most obtuse way to explain it, which I think is just his way of thinking and talking and is not intentional. If you buy his products they come with full technical support, which is often very helpful. His books are a bit more difficult to understand than some of the simpler ones like the Dave Funk Tube Amp Workbook, or the very clear ones like Merlin's books, and the drawings are scanned hand drawings rather than computer generated ones but there is a wealth of information in the books which makes them worthwhile in many cases.
In short, I can't make your decision for you, but if I was in your shoes I think I would just use a MV and design the preamp to get some crunch and use the amp that way. If it is for a 16 year old, the amp will likely be played at full volume most of the time anyway so it doesn't matter quite so much...haha.
Greg
-
I would just use a MV and design the preamp to get some crunch and use the amp that way
Good advice
I typically have a gain pot and a drive pot (MV). the gain pot I use to get the pre into unbalanced squarish wave and ~~ 2X what the PA needs to clip hard. I use the drive to just that, provide drive to the PA tube
so you have a guitar controlling signal, gain controlling pre and MV controlling PA vol & OD.
-
I was going to ask what was to be gained by using VVR vs. adding a MV, but it looks like you guys have pretty much answered that for me. :icon_biggrin:
So many options.... :dontknow:
Will think about it and talk it over with the end user....