https://theultimatetone.com/ Tue, 21 Apr 2026 11:14:31 +0000 MyBB https://theultimatetone.com/Thread-Hood-Amp-Bridge Fri, 27 Mar 2026 10:16:24 +0000 Strelok]]> https://theultimatetone.com/Thread-Hood-Amp-Bridge

I am plannng to build the Hood Amp, it is in Tonnes of Tone.

Is it necessary to use the hefty diode bridge or can discrete diodes be used?



Warm regards,

Strelok]]>

I am plannng to build the Hood Amp, it is in Tonnes of Tone.

Is it necessary to use the hefty diode bridge or can discrete diodes be used?



Warm regards,

Strelok]]> https://theultimatetone.com/Thread-Cutting-a-Circuit-Card Fri, 17 Oct 2025 10:43:44 +0000 Strelok]]> https://theultimatetone.com/Thread-Cutting-a-Circuit-Card
I used to have circuit cards that were rather easy to cut. Just score it a little and it would break failry clean.
But that was a long time ago.

The cards I have now will break rather ugly.
It will follow not the cut but the structure inside.

Does anyone have tips?

Warm regards,

Strlok]]>
I used to have circuit cards that were rather easy to cut. Just score it a little and it would break failry clean.
But that was a long time ago.

The cards I have now will break rather ugly.
It will follow not the cut but the structure inside.

Does anyone have tips?

Warm regards,

Strlok]]> https://theultimatetone.com/Thread-Is-this-power-transformer-up-to-the-task Tue, 05 Aug 2025 16:49:49 +0000 makinrose]]> https://theultimatetone.com/Thread-Is-this-power-transformer-up-to-the-task
The power transformer has rating of 300 ma for the 325-0-325 secondary.  In a Super Reverb with a 5U4GB about 248 ma would be drawn leaving a healthy safely margin.  My best calculation is that this circuit would draw about 270 ma.  Is that enough of a safety margin? The 6k6 is drawing about 30 ma.  Should I be concerned?]]>
The power transformer has rating of 300 ma for the 325-0-325 secondary.  In a Super Reverb with a 5U4GB about 248 ma would be drawn leaving a healthy safely margin.  My best calculation is that this circuit would draw about 270 ma.  Is that enough of a safety margin? The 6k6 is drawing about 30 ma.  Should I be concerned?]]> https://theultimatetone.com/Thread-Desireable-interactive-guitar-player-feedback-generation Thu, 17 Jul 2025 11:51:41 +0000 MelodianChew]]> https://theultimatetone.com/Thread-Desireable-interactive-guitar-player-feedback-generation
I wasn't exactly sure which category I should post this question, but anyway, this is a question about a phenomenon that I have rarely seen addressed in guitar amplifier forums. And that is:

Which components or stages of a guitar amplifier should I direct my attention to, for modification or parameter tweaking, that would have the most success in enhancing the phenomenon of having that entirely desirable sort of spontaneous, sustaining feedback, that can happen while you are playing, that seems to be a natural by product of SOME certain rare amplifiers? What is it that I can change or modify about a circuit in a tube amplifier to build this kind of interactivity with the guitar into an amplifier? Is such a thing even known?

I KNOW that this kind of playability in an amplifier is possible, within reach, and NOT built with some special kind of "un-obtanium," because I had the opportunity to play through such an amplifier, ONE time. This was when I was in a studio during some recording sessions, in which I was tasked with dubbing in a little solo part into a section of a song. I only had my guitar with me that day so, the engineer just grabbed one of his friend's heads that happened to be at the studio that day. When I plugged into that amp, the tone completely floored me. I wasn't even ready for it! 

No. seriously. When I plugged my guitar into that amplifier, hit a chord to check for tune and then played a couple of notes, just merely bending into vibrato, the thing CAME ALIVE!  How easily it would just sing... and sustain perfectly into these notes that were some portion of the harmonic series, that seemed to work with every note I played. I was so astonished at the incredibility of the tone from that amplifier, that I actually DID NOT get to play on the solo in that song that day. 

I know this sounds silly, but every time I tried to do a take, I got completely distracted by this amazing electric tone that I had never heard coming from my guitar before. So much so, that those emotions totally devolved my playing into nothing but fits of laughter and Tourette's Syndrome like cursing, just stuck in postures of complete exasperation, high-fiving nothing but air; like some over-excited Patriots fan watching some epic touchdown. Embarrassing. I simply couldn't keep it together. And because time is money in a studio, after about 3 or 4 tries, I got quickly switched out to give someone else a try on the solo. (Which he nailed, by the way.) 

I'm sorry for such a long dramatic anecdote of my first time with a really great amp, but up until that day, I had NO IDEA that kind of tone was possible in a guitar amplifier. Of course, you guys will relate, because that kind of feeling is, after all, why we are all here. So, I guess what I am asking is, what do I need to do to get, build, modify or acquire an amplifier like that one? And I'm talking about getting that singing spontaneous feedback, that would just miraculously appear at the end of a run.

The gear I used couldn't have been more straight forward. That is why I KNOW that tone was ALL the amp. I had my own guitar with me that day, which was an all stock 1996 Japanese Fujigen made Fender, '68 reissue Strat in naturally finished swamp ash, and a maple neck. This guy's mythical amp that I plugged into was a non-master volume, non-plexi (i think), '68-72 or so, 100w Marshall Super Lead head, plugged straight into an older, slanted Marshall 4x12 cabinet. The engineer told me that the amp WAS modified in some way, but he didn't know how. And curiously, I WAS NOT playing at any deafening kind of level or even really loud at all.  

He had grabbed that amp for me to use because it was very similar to my OWN, which was a stock '69 100w Marshall Super Bass that I plugged straight into a vintage 30 loaded slanted Marshall 4x12 cab. But it didn't sound like that!

So, can that kind of feedback come from any type of amp? If so, what kinds of things should I focus on in an amp build, or WHICH KIND of amp build should I target in building to get that kind of feedback? Does it have to be a Marshall style circuit? I do love that Marshall kind of tone, by the way. Could I get something like that from a modified or tweaked 18w clone or a JCM800 micro kind of kit, or something else? 
(Am I playing 30 years and still an amp noob?   )

Thanks for ALL of your kind help, 

Scott]]>
I wasn't exactly sure which category I should post this question, but anyway, this is a question about a phenomenon that I have rarely seen addressed in guitar amplifier forums. And that is:

Which components or stages of a guitar amplifier should I direct my attention to, for modification or parameter tweaking, that would have the most success in enhancing the phenomenon of having that entirely desirable sort of spontaneous, sustaining feedback, that can happen while you are playing, that seems to be a natural by product of SOME certain rare amplifiers? What is it that I can change or modify about a circuit in a tube amplifier to build this kind of interactivity with the guitar into an amplifier? Is such a thing even known?

I KNOW that this kind of playability in an amplifier is possible, within reach, and NOT built with some special kind of "un-obtanium," because I had the opportunity to play through such an amplifier, ONE time. This was when I was in a studio during some recording sessions, in which I was tasked with dubbing in a little solo part into a section of a song. I only had my guitar with me that day so, the engineer just grabbed one of his friend's heads that happened to be at the studio that day. When I plugged into that amp, the tone completely floored me. I wasn't even ready for it! 

No. seriously. When I plugged my guitar into that amplifier, hit a chord to check for tune and then played a couple of notes, just merely bending into vibrato, the thing CAME ALIVE!  How easily it would just sing... and sustain perfectly into these notes that were some portion of the harmonic series, that seemed to work with every note I played. I was so astonished at the incredibility of the tone from that amplifier, that I actually DID NOT get to play on the solo in that song that day. 

I know this sounds silly, but every time I tried to do a take, I got completely distracted by this amazing electric tone that I had never heard coming from my guitar before. So much so, that those emotions totally devolved my playing into nothing but fits of laughter and Tourette's Syndrome like cursing, just stuck in postures of complete exasperation, high-fiving nothing but air; like some over-excited Patriots fan watching some epic touchdown. Embarrassing. I simply couldn't keep it together. And because time is money in a studio, after about 3 or 4 tries, I got quickly switched out to give someone else a try on the solo. (Which he nailed, by the way.) 

I'm sorry for such a long dramatic anecdote of my first time with a really great amp, but up until that day, I had NO IDEA that kind of tone was possible in a guitar amplifier. Of course, you guys will relate, because that kind of feeling is, after all, why we are all here. So, I guess what I am asking is, what do I need to do to get, build, modify or acquire an amplifier like that one? And I'm talking about getting that singing spontaneous feedback, that would just miraculously appear at the end of a run.

The gear I used couldn't have been more straight forward. That is why I KNOW that tone was ALL the amp. I had my own guitar with me that day, which was an all stock 1996 Japanese Fujigen made Fender, '68 reissue Strat in naturally finished swamp ash, and a maple neck. This guy's mythical amp that I plugged into was a non-master volume, non-plexi (i think), '68-72 or so, 100w Marshall Super Lead head, plugged straight into an older, slanted Marshall 4x12 cabinet. The engineer told me that the amp WAS modified in some way, but he didn't know how. And curiously, I WAS NOT playing at any deafening kind of level or even really loud at all.  

He had grabbed that amp for me to use because it was very similar to my OWN, which was a stock '69 100w Marshall Super Bass that I plugged straight into a vintage 30 loaded slanted Marshall 4x12 cab. But it didn't sound like that!

So, can that kind of feedback come from any type of amp? If so, what kinds of things should I focus on in an amp build, or WHICH KIND of amp build should I target in building to get that kind of feedback? Does it have to be a Marshall style circuit? I do love that Marshall kind of tone, by the way. Could I get something like that from a modified or tweaked 18w clone or a JCM800 micro kind of kit, or something else? 
(Am I playing 30 years and still an amp noob?   )

Thanks for ALL of your kind help, 

Scott]]> https://theultimatetone.com/Thread-CNC-cutting-finger-joints Mon, 16 Jun 2025 06:03:37 +0000 physics]]> https://theultimatetone.com/Thread-CNC-cutting-finger-joints
I have access to a CNC router table at the local makerspace, and realized it can probably cut down on the time for me to fabricate some cabinets. The one thing I'm unsure about is the finger-joints. Assuming I'm only able to work with the bit perpendicular to the sheet stock, I'll have to cut "dogbones" for the internal corners of the finger joints (picture from here https://cutlasercut.com/getting-started/cnc-machining/):

 Now I've seen that there are ways to minimize their visibility (https://fablab.ruc.dk/more-elegant-cnc-dogbones/), but I was wondering if anyone has any strong opinions about dogbones in general for finger joints. Effects on strength, durability, air-tightness of cabinet, extra work to fix these issues, etc.

Thanks!]]>
I have access to a CNC router table at the local makerspace, and realized it can probably cut down on the time for me to fabricate some cabinets. The one thing I'm unsure about is the finger-joints. Assuming I'm only able to work with the bit perpendicular to the sheet stock, I'll have to cut "dogbones" for the internal corners of the finger joints (picture from here https://cutlasercut.com/getting-started/cnc-machining/):

 Now I've seen that there are ways to minimize their visibility (https://fablab.ruc.dk/more-elegant-cnc-dogbones/), but I was wondering if anyone has any strong opinions about dogbones in general for finger joints. Effects on strength, durability, air-tightness of cabinet, extra work to fix these issues, etc.

Thanks!]]> https://theultimatetone.com/Thread-Need-help-with-decisions-for-PA-to-Guitar-amp-convo Sun, 04 May 2025 20:06:52 +0000 MelodianChew]]> https://theultimatetone.com/Thread-Need-help-with-decisions-for-PA-to-Guitar-amp-convo
This is my first post ever here, and thank you for taking the time to peek at my question.

MY QUALIFICATIONS/SKILLS (you can skip this part): I am basically a very enthusiastic and adventurous amateur electronics repair and build enthusiast. I have tinkered with fixing and morphing electronic gear for myself and bandmates throughout my years. I have a small working set of test gear and a solder station. I have mostly been educating myself through reading various books, manuals, websites and forums. I'm getting much better at reading through schematics. I feel like I am ready to up raise the difficulty of my project levels.

I have a little 20w McMartin PA head that is wired point to point that has 2x 6L6, 2x 12ax7, and 1x 6av6 tubes. This is my first attempt at trying to convert a PA into a Guitar amplifier. This attempt is an intention to both sharpen my electronic skills and hopefully end up with a killer little tube amp in the process. The project is a little bit above my pay grade but not drastically so, and besides, there is no greater teacher for an ambitious mind than 450v and an idiot that just feels lucky. (That's a joke)

What I could really use some help with here though is possibly some coaching through this process. (you don't know how difficult it is to find mentors once you reach the age that you start to look like a mentor.)

Some questions I have right at the outset mostly concern with trying to figure out the best direction to steer this carcass into, and which direction makes the most sense as per guitar amplifier designs that I could use for inspiration to try to model:

Here's the schematic:


  McMartin MA-20 Schematic GOOD.pdf (Size: 43.17 KB / Downloads: 5)
and some pictures:


  WIN_20250504_15_52_11_Pro.jpg (Size: 252.19 KB / Downloads: 33)
  WIN_20250504_15_56_09_Pro.jpg (Size: 226.31 KB / Downloads: 32)
  WIN_20250504_15_53_35_Pro.jpg (Size: 255.95 KB / Downloads: 33)

1) what does an expert notice right off the bat that this amplifier's design is telling you when you see the physical layout and read through the schematic?

2) We have to start somewhere, right? And there is no better first step than arriving at establishing a goal or endgame for our project. So, looking at the schematic and considering the transformer voltages and tube compliments, etc. what type of known good guitar amplifier design could be most easily cloned or used as a model for this build? 

3) There are three (extra) tube sockets on the chassis for mic and line transformers. Does having those sockets already built in and ready for use change or expand the range of tube amp models we might like to try to emulate with this build?

4) I understand that this amp, being intended for PA use, will have been designed with the intention of avoiding the kind of distortion characteristics that are most pleasing for guitar amplifiers, so what types of changes would need to be addressed in order to make the conversion?

5) What logical steps should we take in assessing the schematic, and then planning our approach to hashing out the methods for accomplishing this mod?

6) Is it a best practice here to piece through this mod by breaking up the schematic, referentially, into separate systems that we should work on solving, one at a time, in order to keep our goals and tasks focused and with clear endpoints for each of those?

7) Should I break this down into DC Signal path, Input section, Gain stage 1, stage 2, power tube amplification, output section. AC Power section, etc.?
 
Well, I was going to ask a ton more questions, but I think I should probably take my time and try to get the full benefit of having expert advice at my disposal, and would be best served by letting more knowledgeable eyes guide me that can lead me through a project like this so that I can somehow through osmosis or some other such wizardry, absorb some of your wisdom and logical methodologies in trying to adopt them for my own.

Well, OK, but there are just a couple of questions right off the bat that I know would be further down the road but that I find irresistible in inquiring about right now:

1) the sections of the amp that were intended for plugging in transformers for the microphones in the input sections: what will most likely become of those extra tube sockets? If I were planning on just eliminating those sockets from the whole build, would I just remove most of those connections to those sockets and then run through the schematic one section at a time trying to figure out where each connection should go to in following my new plan?

2) could those now empty and not needed mic trans tube sockets be used as potential opportunities to build in other new gain stages, like for reverb or tremolo?

Thank you to any that could offer any help to me for this kind of thing, I really appreciate it.

Scott]]>
This is my first post ever here, and thank you for taking the time to peek at my question.

MY QUALIFICATIONS/SKILLS (you can skip this part): I am basically a very enthusiastic and adventurous amateur electronics repair and build enthusiast. I have tinkered with fixing and morphing electronic gear for myself and bandmates throughout my years. I have a small working set of test gear and a solder station. I have mostly been educating myself through reading various books, manuals, websites and forums. I'm getting much better at reading through schematics. I feel like I am ready to up raise the difficulty of my project levels.

I have a little 20w McMartin PA head that is wired point to point that has 2x 6L6, 2x 12ax7, and 1x 6av6 tubes. This is my first attempt at trying to convert a PA into a Guitar amplifier. This attempt is an intention to both sharpen my electronic skills and hopefully end up with a killer little tube amp in the process. The project is a little bit above my pay grade but not drastically so, and besides, there is no greater teacher for an ambitious mind than 450v and an idiot that just feels lucky. (That's a joke)

What I could really use some help with here though is possibly some coaching through this process. (you don't know how difficult it is to find mentors once you reach the age that you start to look like a mentor.)

Some questions I have right at the outset mostly concern with trying to figure out the best direction to steer this carcass into, and which direction makes the most sense as per guitar amplifier designs that I could use for inspiration to try to model:

Here's the schematic:


  McMartin MA-20 Schematic GOOD.pdf (Size: 43.17 KB / Downloads: 5)
and some pictures:


  WIN_20250504_15_52_11_Pro.jpg (Size: 252.19 KB / Downloads: 33)
  WIN_20250504_15_56_09_Pro.jpg (Size: 226.31 KB / Downloads: 32)
  WIN_20250504_15_53_35_Pro.jpg (Size: 255.95 KB / Downloads: 33)

1) what does an expert notice right off the bat that this amplifier's design is telling you when you see the physical layout and read through the schematic?

2) We have to start somewhere, right? And there is no better first step than arriving at establishing a goal or endgame for our project. So, looking at the schematic and considering the transformer voltages and tube compliments, etc. what type of known good guitar amplifier design could be most easily cloned or used as a model for this build? 

3) There are three (extra) tube sockets on the chassis for mic and line transformers. Does having those sockets already built in and ready for use change or expand the range of tube amp models we might like to try to emulate with this build?

4) I understand that this amp, being intended for PA use, will have been designed with the intention of avoiding the kind of distortion characteristics that are most pleasing for guitar amplifiers, so what types of changes would need to be addressed in order to make the conversion?

5) What logical steps should we take in assessing the schematic, and then planning our approach to hashing out the methods for accomplishing this mod?

6) Is it a best practice here to piece through this mod by breaking up the schematic, referentially, into separate systems that we should work on solving, one at a time, in order to keep our goals and tasks focused and with clear endpoints for each of those?

7) Should I break this down into DC Signal path, Input section, Gain stage 1, stage 2, power tube amplification, output section. AC Power section, etc.?
 
Well, I was going to ask a ton more questions, but I think I should probably take my time and try to get the full benefit of having expert advice at my disposal, and would be best served by letting more knowledgeable eyes guide me that can lead me through a project like this so that I can somehow through osmosis or some other such wizardry, absorb some of your wisdom and logical methodologies in trying to adopt them for my own.

Well, OK, but there are just a couple of questions right off the bat that I know would be further down the road but that I find irresistible in inquiring about right now:

1) the sections of the amp that were intended for plugging in transformers for the microphones in the input sections: what will most likely become of those extra tube sockets? If I were planning on just eliminating those sockets from the whole build, would I just remove most of those connections to those sockets and then run through the schematic one section at a time trying to figure out where each connection should go to in following my new plan?

2) could those now empty and not needed mic trans tube sockets be used as potential opportunities to build in other new gain stages, like for reverb or tremolo?

Thank you to any that could offer any help to me for this kind of thing, I really appreciate it.

Scott]]> https://theultimatetone.com/Thread-Compressor Thu, 23 Jan 2025 14:00:09 +0000 Strelok]]> https://theultimatetone.com/Thread-Compressor
Have any of you built a tube compressor?

Over at analogvibes I see an interesting project.
You can buy a chassis there for the LA-2A compressor.
It is always nice to have a professional chassis to build your work around.

A tough question: would it be worth it to build one?
It will be pretty expensive.

Are there better, newer designs out there?
I mean it was designed befor the '60s, that's old.
Maybe some better designs came along?

I am not a professional and with bass I hear a lot of variaton in the envelope as I play.
So a limiter or compressor would be nice.



Strelok]]>
Have any of you built a tube compressor?

Over at analogvibes I see an interesting project.
You can buy a chassis there for the LA-2A compressor.
It is always nice to have a professional chassis to build your work around.

A tough question: would it be worth it to build one?
It will be pretty expensive.

Are there better, newer designs out there?
I mean it was designed befor the '60s, that's old.
Maybe some better designs came along?

I am not a professional and with bass I hear a lot of variaton in the envelope as I play.
So a limiter or compressor would be nice.



Strelok]]> https://theultimatetone.com/Thread-6v6-stereo-amp-using-a-bi-amp-preamp Thu, 14 Nov 2024 06:07:17 +0000 mooreamps]]> https://theultimatetone.com/Thread-6v6-stereo-amp-using-a-bi-amp-preamp
https://www.youtube.com/watch?v=3hIFsjAmqyg]]>
https://www.youtube.com/watch?v=3hIFsjAmqyg]]> https://theultimatetone.com/Thread-82-JCM-800-4104-Service-and-Mods Fri, 18 Oct 2024 06:18:07 +0000 physics]]> https://theultimatetone.com/Thread-82-JCM-800-4104-Service-and-Mods https://theultimatetone.com/Thread-Water-Slide-Decals Sun, 02 Jun 2024 10:02:18 +0000 ZeusMC]]> https://theultimatetone.com/Thread-Water-Slide-Decals Anyone got any advice of preventing the edge of the decals showing?
Thanks.]]> Anyone got any advice of preventing the edge of the decals showing?
Thanks.]]> https://theultimatetone.com/Thread-Bogen-CHB-50-Rebuild Sun, 10 Mar 2024 21:12:35 +0000 physics]]> https://theultimatetone.com/Thread-Bogen-CHB-50-Rebuild
As mentioned in the CHB-20 rebuild thread, my friend decided that 50W was a better fit for his needs so I am working on making a Bogen CHB-50 usable as a clean pedal platform. Schematic for the curious:

  bogen-chb50-6.jpg (Size: 1.52 MB / Downloads: 95)

My primary mission right now is rebuilding the power supply with some new electrolytics and also a film cap to replace the paper-in-oil one from the bias supply. However, there are a few other caps (coupling caps) which I'm unsure on whether to replace or not. I think they are film types since they don't look like paper-in-oil caps that I have seen before, but I was hoping some of you would recognize them. I've heard chatter on other forums that old coupling caps between stages should be replaced too even if film types, but given the same forums also worship at the altar of all sorts of audiophoolery that doesn't seem like a reliable source of advice. Are there any guidelines for determining whether coupling caps are bad, assuming one doesn't have a fancy high voltage capacitor checker?

Pictures of the caps in question:


  20240310_135727.jpg (Size: 487.69 KB / Downloads: 91)

  20240310_135841.jpg (Size: 480.41 KB / Downloads: 91)

  20240310_135812.jpg (Size: 436.02 KB / Downloads: 91)

Thanks for any input!]]>
As mentioned in the CHB-20 rebuild thread, my friend decided that 50W was a better fit for his needs so I am working on making a Bogen CHB-50 usable as a clean pedal platform. Schematic for the curious:

  bogen-chb50-6.jpg (Size: 1.52 MB / Downloads: 95)

My primary mission right now is rebuilding the power supply with some new electrolytics and also a film cap to replace the paper-in-oil one from the bias supply. However, there are a few other caps (coupling caps) which I'm unsure on whether to replace or not. I think they are film types since they don't look like paper-in-oil caps that I have seen before, but I was hoping some of you would recognize them. I've heard chatter on other forums that old coupling caps between stages should be replaced too even if film types, but given the same forums also worship at the altar of all sorts of audiophoolery that doesn't seem like a reliable source of advice. Are there any guidelines for determining whether coupling caps are bad, assuming one doesn't have a fancy high voltage capacitor checker?

Pictures of the caps in question:


  20240310_135727.jpg (Size: 487.69 KB / Downloads: 91)

  20240310_135841.jpg (Size: 480.41 KB / Downloads: 91)

  20240310_135812.jpg (Size: 436.02 KB / Downloads: 91)

Thanks for any input!]]> https://theultimatetone.com/Thread-Bogen-CHB-20A-Rebuild Thu, 18 Jan 2024 08:40:28 +0000 physics]]> https://theultimatetone.com/Thread-Bogen-CHB-20A-Rebuild https://theultimatetone.com/Thread-Peavey-ValveKing-100-Overhaul Fri, 22 Dec 2023 04:18:22 +0000 physics]]> https://theultimatetone.com/Thread-Peavey-ValveKing-100-Overhaul huge pain to get out. It is single-sided though. Maybe I'll install some eyelets in the through-holes to remedy that. Some spots on the board may be a bit tight for that though. Anyhow...

First issue: no sound. Tried different inputs, tried different channels, tried a patch cable in the fx loop, tried going direct into the effects loop return, nothing. Next I tried checking for signal coming out of the FX send, but at that moment my scope which I was hooking up to the other end of the cable decided to go for a smoke break, so I'm going to fix that first then resume troubleshooting the VK100 in between rebuilding a Bogen PA for a friend.

First planned upgrade: 1k 5W screen resistors. Stock it comes with 330R 2W resistors. I wonder if the screen resistors have gone out to lunch, and that's why the amp is silent.

Second planned upgrade: threaded inserts for the front and back panels. A previous owner thought self-drilling screws were a bright idea when they replaced the stock front panel with diamond plate, and my efforts to secure all the screws on it, not just the bottom two, did several of the holes in . Something to deal with after the electrical issues are sorted. Maybe before, depending how annoying it gets it deal with.]]> huge pain to get out. It is single-sided though. Maybe I'll install some eyelets in the through-holes to remedy that. Some spots on the board may be a bit tight for that though. Anyhow...

First issue: no sound. Tried different inputs, tried different channels, tried a patch cable in the fx loop, tried going direct into the effects loop return, nothing. Next I tried checking for signal coming out of the FX send, but at that moment my scope which I was hooking up to the other end of the cable decided to go for a smoke break, so I'm going to fix that first then resume troubleshooting the VK100 in between rebuilding a Bogen PA for a friend.

First planned upgrade: 1k 5W screen resistors. Stock it comes with 330R 2W resistors. I wonder if the screen resistors have gone out to lunch, and that's why the amp is silent.

Second planned upgrade: threaded inserts for the front and back panels. A previous owner thought self-drilling screws were a bright idea when they replaced the stock front panel with diamond plate, and my efforts to secure all the screws on it, not just the bottom two, did several of the holes in . Something to deal with after the electrical issues are sorted. Maybe before, depending how annoying it gets it deal with.]]> https://theultimatetone.com/Thread-0C3-Guitar-Amp-Controlled-Smooth-Sag Fri, 05 May 2023 12:44:04 +0000 enorbet2]]> https://theultimatetone.com/Thread-0C3-Guitar-Amp-Controlled-Smooth-Sag  
One of the non-linear characteristics that SS and especially digital can't do well is to deal with/model/emulate smooth and progressive edge of breakup transition revolves around analog sag that is powerfully affected by extremely slight differences in string gauge, EQ, power amp overdrive and especially pick attack and fingering.  This characteristic of tube power amps is responsible for a very "human voice" type of nuance creating inflection and expressiveness. 

Granted some players, especially Metal and Shred lovers want the exact opposite, extreme consistency that lends itself to speed articulation but passion players tend to prefer singing lead work and much of that comes from tube analog sag.  This thread is about a severely unrecognized design that improves sag by creating an especially sweet balance between predictable and serendipity that every player that I've known immediately hears and feels.

This design is only a very small step removed from common design since "all it does" is regulate screen grid voltage by tracking plate current and maintaining a constant voltage difference between plates and screen grids so the grids are never positive relative to plates (a distinctly disastrous effect on harmonics) and maintains a constant relationship between the business end of power pentodes in relation to input signal.  While this does tend to improve high end response as well, apparent headroom goes way up especially in high current demand caused by low end frequencies that naturally require more power.  The result is that lop end never "farts" but still generates pleasant and articulate overdrive harmonics.

The design difference that creates such dynamic response is the 0C3 "regulator" valve that is still rather cheaply available as NOS devices (was never very popular among the bean counters that chopped design costs fort instrument amplification back in the day).  AFAIK this tracking regulation has no single element counterpart in solid state electronics and we all know (or should know) that in general simple is better where instruments are involved.  This is because of one long overlooked perspective that

INSTRUMENT AMPS ARE NOT REPRODUCTION DEVICES BUT INSTEAD PART OF THE INSTRUMENT OF ELECTRIC GUITAR!  IOW, one important view is that very few players want an electric guitar to sound the same as a non-amplified strum only louder.  Most want "color".  Especially these days where very few venues allow the volume levels that allow that incredible feedback loop where volume makes a guitar system, including the air in between speaker and strings, makes an electric guitar "come alive".  I'm not going to insult anyone's intelligence by saying this amp design negates that physical attribute that only comes to that degree with sheer SPL, but it does indeed reduce the levels at which the effect begins at more reasonable levels.  You can't possibly know this without experiencing this for yourself and as noted, this design has been all but non-existent in guitar amps so how could you.. with the vaguly possible exception of one playing through an old Leslie rig (that depended  on the 0C3 to get extreme headroom for extreme frequency response, especially in the low end for bass pedals on a B3) ?  Most players who actually played through a Leslie like model 147 simply thought the sound came only from rotating speakers since they generally only switched a Leslie on when they wanted the modulation, never hearing the effect for straight clean.

This is the design schematic of a similar setup modified to be more aligned with guitar needs than organ that can very easily be tried out, even temporarily and in some cases with no newly drilled holes, in existing amps just to get a glimpse of the improved dynamic and tracking response that sounds so sweet and human.  It works with either SS bridge rectifier systems or valves like 5AR4.  Naturally an amp with a 5AR4 or similar rectifier amp can easily be temporarily rewired to employ SS diodes so the 5AR4 socket can be used for the 0C3, and put back if one doesn't like the results before one is faced with the decision of adding an octal socket to make the mod permanent OR just build one from scratch.


Without any further explanation, here it is, but with some coupling cap values left out for personally desired EQ response characteristics....BTW worthy of note one doesn't need to buy a Leslie 125/147 Output Transformer since any OT with a dual output secondary like 16 ohm and 8 ohm, or 8ohm and 4 ohm can do the job.  Also one could simply ignore the local feedback loop to the cathodes and eliminate the need or use another NF geometry.


]]>  
One of the non-linear characteristics that SS and especially digital can't do well is to deal with/model/emulate smooth and progressive edge of breakup transition revolves around analog sag that is powerfully affected by extremely slight differences in string gauge, EQ, power amp overdrive and especially pick attack and fingering.  This characteristic of tube power amps is responsible for a very "human voice" type of nuance creating inflection and expressiveness. 

Granted some players, especially Metal and Shred lovers want the exact opposite, extreme consistency that lends itself to speed articulation but passion players tend to prefer singing lead work and much of that comes from tube analog sag.  This thread is about a severely unrecognized design that improves sag by creating an especially sweet balance between predictable and serendipity that every player that I've known immediately hears and feels.

This design is only a very small step removed from common design since "all it does" is regulate screen grid voltage by tracking plate current and maintaining a constant voltage difference between plates and screen grids so the grids are never positive relative to plates (a distinctly disastrous effect on harmonics) and maintains a constant relationship between the business end of power pentodes in relation to input signal.  While this does tend to improve high end response as well, apparent headroom goes way up especially in high current demand caused by low end frequencies that naturally require more power.  The result is that lop end never "farts" but still generates pleasant and articulate overdrive harmonics.

The design difference that creates such dynamic response is the 0C3 "regulator" valve that is still rather cheaply available as NOS devices (was never very popular among the bean counters that chopped design costs fort instrument amplification back in the day).  AFAIK this tracking regulation has no single element counterpart in solid state electronics and we all know (or should know) that in general simple is better where instruments are involved.  This is because of one long overlooked perspective that

INSTRUMENT AMPS ARE NOT REPRODUCTION DEVICES BUT INSTEAD PART OF THE INSTRUMENT OF ELECTRIC GUITAR!  IOW, one important view is that very few players want an electric guitar to sound the same as a non-amplified strum only louder.  Most want "color".  Especially these days where very few venues allow the volume levels that allow that incredible feedback loop where volume makes a guitar system, including the air in between speaker and strings, makes an electric guitar "come alive".  I'm not going to insult anyone's intelligence by saying this amp design negates that physical attribute that only comes to that degree with sheer SPL, but it does indeed reduce the levels at which the effect begins at more reasonable levels.  You can't possibly know this without experiencing this for yourself and as noted, this design has been all but non-existent in guitar amps so how could you.. with the vaguly possible exception of one playing through an old Leslie rig (that depended  on the 0C3 to get extreme headroom for extreme frequency response, especially in the low end for bass pedals on a B3) ?  Most players who actually played through a Leslie like model 147 simply thought the sound came only from rotating speakers since they generally only switched a Leslie on when they wanted the modulation, never hearing the effect for straight clean.

This is the design schematic of a similar setup modified to be more aligned with guitar needs than organ that can very easily be tried out, even temporarily and in some cases with no newly drilled holes, in existing amps just to get a glimpse of the improved dynamic and tracking response that sounds so sweet and human.  It works with either SS bridge rectifier systems or valves like 5AR4.  Naturally an amp with a 5AR4 or similar rectifier amp can easily be temporarily rewired to employ SS diodes so the 5AR4 socket can be used for the 0C3, and put back if one doesn't like the results before one is faced with the decision of adding an octal socket to make the mod permanent OR just build one from scratch.


Without any further explanation, here it is, but with some coupling cap values left out for personally desired EQ response characteristics....BTW worthy of note one doesn't need to buy a Leslie 125/147 Output Transformer since any OT with a dual output secondary like 16 ohm and 8 ohm, or 8ohm and 4 ohm can do the job.  Also one could simply ignore the local feedback loop to the cathodes and eliminate the need or use another NF geometry.


]]> https://theultimatetone.com/Thread-Thoughts-on-variable-NFB-control-in-Fender-Bandmaster57-Style-PA Mon, 02 Jan 2023 21:31:45 +0000 dtbradio]]> https://theultimatetone.com/Thread-Thoughts-on-variable-NFB-control-in-Fender-Bandmaster57-Style-PA
I'm currently working on my third amp project. Its basically a JCM800-type front preamp and tone stack coupled with a Fender Bandmaster57-style power section, with a few minor alterations. The Bandmaster has fixed NFB using a 56K into the cathode of the 1st PI tube, with a 5K-ohm and .1uf presence circuit. I'm using 3.3k on that cathode, and am going to try a variable NFB circuit using a 68K fixed resistor in series with a 50K variable resistor on a switch to allow either adjustment or elimination of the NFB. The presence control I've selected is using a 50K variable instead of the 5k used by Fender, basically for more range of control.

I'd like any and all opinions of those changes to the basic Fender circuit. Thanks in advance for all replies!]]>
I'm currently working on my third amp project. Its basically a JCM800-type front preamp and tone stack coupled with a Fender Bandmaster57-style power section, with a few minor alterations. The Bandmaster has fixed NFB using a 56K into the cathode of the 1st PI tube, with a 5K-ohm and .1uf presence circuit. I'm using 3.3k on that cathode, and am going to try a variable NFB circuit using a 68K fixed resistor in series with a 50K variable resistor on a switch to allow either adjustment or elimination of the NFB. The presence control I've selected is using a 50K variable instead of the 5k used by Fender, basically for more range of control.

I'd like any and all opinions of those changes to the basic Fender circuit. Thanks in advance for all replies!]]>