Hi everyone... seeing that my Matchless clone worked out so well, I thought I might roll the dice again on another tube amp build.
This time I'm thinking even lower power (5W? Matchless is LOUD for 15W), single-ended, cathode-biased, single 6L6 or 6V6... basically a Champ/Princeton type thing.
I love Milkman Sounds Half Pint - which claims to be a modified Princeton circuit.
Anyone any thoughts on the "best" schematic for this?
Or what modifications Milkman has done to the typical Princeton?
Cheers,
Paul
This time I'm thinking even lower power (5W? Matchless is LOUD for 15W), single-ended, cathode-biased, single 6L6 or 6V6... basically a Champ/Princeton type thing.
I love Milkman Sounds Half Pint - which claims to be a modified Princeton circuit.
Anyone any thoughts on the "best" schematic for this?
Or what modifications Milkman has done to the typical Princeton?
Cheers,
Paul
Reason why i got rid of my Blues Jr as well...little to loud for my current living accommodations. Why not just build a basic champ and then modify to how YOU want it to sound? *hint I'm starting this myself 😛 *
Something like...idk...adding a brightness pot and adjustable NGF, maybe a bit different tone stack (like a brownface or james type), play around with the bypass caps, maybe add adjustable bias for some tube rolling?
just a few ideas 😉
Try a Princeton 5C2 circuit. I have 10 amps including blackface Fenders, old Ampegs, etc. and this is the one I use as a practice amp, plugged into a 10" Jensen.
The original Champion circuit with a grid-leak biased pentode input stage is real interesting also.
The original Champion circuit with a grid-leak biased pentode input stage is real interesting also.
Thanks jlangholzj, yea I've been mulling over this mashup list today:
- 5F2 Princeton schematic as a starting point (with choke)
- VVR
- Solid state rectifier (or maybe switchable)
- Adjustable bias
- Adjustable / switchable NF
- TMB tone stack (modified fender style) or TB + brightness
Anything else I really should throw in there?
I'm attempting (failing) to draw the schematic now.
@Joe: do you have a schematic for that Champion? Sounds interesting.
- 5F2 Princeton schematic as a starting point (with choke)
- VVR
- Solid state rectifier (or maybe switchable)
- Adjustable bias
- Adjustable / switchable NF
- TMB tone stack (modified fender style) or TB + brightness
Anything else I really should throw in there?
I'm attempting (failing) to draw the schematic now.
@Joe: do you have a schematic for that Champion? Sounds interesting.
Look at the 5e8a schematic for a "brightness" pot in the NF loop as well. Real simple in implement. Add that to an adjustable "dirty" pot and you'd have a pretty slick deal.
EDIT:
excuse the scribble-scratch but this is what I've been playing with in my head. Doesn't include the PSU or the adjustable bias but it captures the two main mods I wanted to do 😛 :
http://i.imgur.com/poeaEZ6.jpg?1
EDIT:
excuse the scribble-scratch but this is what I've been playing with in my head. Doesn't include the PSU or the adjustable bias but it captures the two main mods I wanted to do 😛 :
http://i.imgur.com/poeaEZ6.jpg?1
Last edited:
5w can still be v. Loud. All other things being equal eg spkrs, you need to drop 15w to 1.5w to halve the volume (correct me if I am off-base). So VVR (just on power tube).
If you are after different or flexible try;
- a triode/pentode tube instead of 12ax7 preamp
- single knob tones after each preamp stage eg tweed, bmp, etc
If you are after different or flexible try;
- a triode/pentode tube instead of 12ax7 preamp
- single knob tones after each preamp stage eg tweed, bmp, etc
This is one thing that's been really intriguing me lately as well. With a "centralized" tone control you're only really affecting the input stages tone...after that its out of your hands. I know somewhere I've come across more literature on local feedback tone control and some other stuff that was pretty interesting.
I took a first stab at a schematic (attached). I'm not sure about any of it really, especially the adjustable bias.
All comments and suggestions very much welcome, it's still a work in progress.
All comments and suggestions very much welcome, it's still a work in progress.
If you mean it's "out of your hands" with "centralized" tone control as far as it being adjustable in later stages, I agree. But otherwise, there is tone shaping that can be done with the value of the coupling cap(s) you chose. Also if you chose to only partially bypass the next stage(s) cathode(s), you can add higher frequencies to the signal. Also, you can use a
cap along with the NFB resistor to shape the frequency of the NFB signal. You can make this adjustable with a pot added to the NFB loop.
Lightreel, the FMV stack tends to be very lossy, so if you want to get more signal to the 6V6, you can go to a 470k for your grid leak there instead of the 220k. Getting some power tube grind adds to the complexity of the distortion. Or you could make this a 500k pot instead of messing with the bias. If you adjust the bias pot to zero ohms, it might be biased too hot depending of course on your plate and screen voltages.
Last edited:
Unless you're doing something I don't know about, the NFB needs to be connected ONLY at the cathode of V1b (pin8). Looks like you've also got it tied in after the coupling cap as well, which is not correct per the original 5f2 scheme. Its a bit hard to tell from the original 5F2 schematic but if you look at the "layout" DWG its a bit easier to tell.
Also I'd take all of your voltages post-choke. Remember that's doing a fair bit of work for you in terms of power quality.
And for curiosities sake, what PT are you thinking of using? Does it have a 6-0-6 output? If so, you might want to think of wiring that as a 12V output, and then using an LM350 for a regulated 6.3V DC output to the heaters to help reduce noise!
Also I'd take all of your voltages post-choke. Remember that's doing a fair bit of work for you in terms of power quality.
And for curiosities sake, what PT are you thinking of using? Does it have a 6-0-6 output? If so, you might want to think of wiring that as a 12V output, and then using an LM350 for a regulated 6.3V DC output to the heaters to help reduce noise!
You are 100% correct in that assessment! I was trying to make a statement that by placing your tone stack between the first two stages you're only adjusting the tone after the first stage and after that it's left to the other means you listed (coupling caps, NFB changes, etc). But you did a much more eloquent job of that than I did 😀
Your PSU will allow a lot of ripple thru. A 0.1- 0.47 cap from VVR wiper to ground will dramatically reduce this.
(Have you decided on 6v6 or EL84 power tube? That affects how much gain you can throw away in nfb and tonestack).
(Have you decided on 6v6 or EL84 power tube? That affects how much gain you can throw away in nfb and tonestack).
Yes, I noticed that as well but forgot to mention it. It seems as though there should be no connection of the NFB at the output of the .022 coupling cap. You are correct, jlangholzj, there is no connection there on the original.
Last edited:
I learn so so much from you guys. Thanks for taking the time, it's much appreciated.
Comments:
- NFB joint was a mistake
- 470k grid leak (or pot instead of adj. bias) will be integrated
- 47uf to ground off VVR wiper is a great call too
- I'm planning on running a 6V6
- I haven't decided on a power transformer
Questions:
- Should I beef up the power supply?
- Any suggestions on transformers? (inc. choke)
Comments:
- NFB joint was a mistake
- 470k grid leak (or pot instead of adj. bias) will be integrated
- 47uf to ground off VVR wiper is a great call too
- I'm planning on running a 6V6
- I haven't decided on a power transformer
Questions:
- Should I beef up the power supply?
- Any suggestions on transformers? (inc. choke)
One thing that I did forget to ask is do you have an affinity for a different style tone stack? I will say that I've seen 250k/10k for the bass/mid respectively to help give it a bit flatter response and also cut down on some loss.
Any thoughts on a Baxandall stack? Us guys over in the HiFi world love it. But that's a discussion for a different day 😛 I'm curious if a Bax circuit was used how much we'd have to change the rest of the circuitry to give it the sound we like, or if it wouldn't need any tweaking at all for that matter.
ALSO AS AN EDIT:
The original reason I had thought of/suggested a VVT and the Bias adjust was to allow for some tube rolling. Possibly sneaking in a 6550 or KT88 in. In comparison to OP's scheme, I was thinking of omiting the "A" HV tap, and pulling the OPT source from "B" as well (adjusting the PSU ckt for desired voltages, etc) and then in addition adding a second VVR for the "C" HV tap. So that you could both adjust the plate voltage of your power tube and the preamp tubes. I'm a bit worried about the noise this may induce but it was a thought....
Last edited:
for OP, Duncan's PSUD2 is a pretty slick resource for sizing your power supply. I was planning on making mine a bit more stout than required and using the VVT to adjust down to where I need it for the tune I'm running. This also then can account for the ~20% loss once the whole circuit is connected and will allow for a bit better plate voltage setting and so-forth!
First off Paul, congrats on a very successful Matchless clone build.
You were wondering about the milkman Half Pint. He only has a tone control on one version and treble and bass on the other, so he has much less insertion loss from the tone circuit, especially on the one with just the tone control. The TMB typically loses about 80% of it's input signal depending on component values, so using a full TMB stack might take you out of the Milkman territory almost all by itself. One sim I ran a while ago lost 87% of its input signal. The amps I build/mod very rarely get more than a simple tone control so as to reduce signal loss. This is one of the "secrets" of many newer boutique amps. More controls usually lead to more insertion loss. You then need more gain make up stages to recover those losses. The key is to get a good sound out of the design, not make up for poor design with adding a bunch of controls. Just some food for thought.
Also, maybe go to 16uF for both the second and third nodes of the power supply.
Last edited:
Note I said 0.1 to 0.47 for the VVR wiper cap. In this position the VVR is also working as a cap multiplier. 47u is way over big.
Last cap in PSU (supply to preamp) could be bigger to keep ripple out of 1st stage.
I personally would go for a bigger trafo. And save the money on the choke. Personal preference. DIY is for fun and learning.
@jlangholzj: no particular affinity for any tonestack, still very open on this one. Baxandall looks interesting, but also looks like similar losses to TMB.
I think one VVR is enough for me, but I really like the idea of attempting to run a big tube. So I'm leaning towards leaving the bias adjust in.
I played around with PSUD, but I'm not sure exactly how I can tell if what I'm doing is better or worse!
@boobtube: In no small way the success of my Matchless was down to you! You were exceptionally patient and helpful with me. So thank you!
The only reason I considered a TMB tonestack was because I don't particularly need or want this to be a "loud" amp (hence the VVR), and I felt the losses were acceptable. But I take the point that a well designed simple stack might be best for TONE! 🙂
@djgibson51: sorry, that was a typo! Missed the decimal point.
Hammond are easily obtainable over here. Anything specific you would suggest?
I think one VVR is enough for me, but I really like the idea of attempting to run a big tube. So I'm leaning towards leaving the bias adjust in.
I played around with PSUD, but I'm not sure exactly how I can tell if what I'm doing is better or worse!
@boobtube: In no small way the success of my Matchless was down to you! You were exceptionally patient and helpful with me. So thank you!
The only reason I considered a TMB tonestack was because I don't particularly need or want this to be a "loud" amp (hence the VVR), and I felt the losses were acceptable. But I take the point that a well designed simple stack might be best for TONE! 🙂
@djgibson51: sorry, that was a typo! Missed the decimal point.
Hammond are easily obtainable over here. Anything specific you would suggest?
Also here's a pretty rad resource on a bunch of the tone stack controls:
Adam's Amplifiers: Tone Stacks
The "garnet" style control is the one I mentioned to boobtube earlier about using local feedback loops. As stated in the article you could use a rotary switch for different capacitors and make an interesting result 🙂 Could place it on the input stage, and then use the NFB to the 2nd stage for further control.
Adam's Amplifiers: Tone Stacks
The "garnet" style control is the one I mentioned to boobtube earlier about using local feedback loops. As stated in the article you could use a rotary switch for different capacitors and make an interesting result 🙂 Could place it on the input stage, and then use the NFB to the 2nd stage for further control.
- Status
- Not open for further replies.