Hi Koreth, Note; I'm not a qualified teck,
I just got sick of music shops exploiting my lack of knowledge so I started learning how audio gear works by reading lotsa books (long before computers and the net)
----
Now it sounds like you have a more in depth learning than myself.
Well I went deep trying to learn a lot of tecky stuff which sent me quite mad for a while.
But over time I started to come to understand a lot better by simplification and basic observation.
We all Ask why do Valve Amps have the magic mojo?
I came to understand a Valve power stage for *What it DOES*
rather than *How it Works*.
**It's a COMPRESSOR that distorts badly with big signals**
Most of the favored Valve amps of a bygone era were of very basic design.
My no 1 rule of thumb (Valve or SS);
If you want a great rock guitar amp, just build a crappy basic circuit.
Old OTx,s were cheap and suffered from all the quirks you likely already know about. Leo built to a budget so interleaved OT were out of the question.
(at least in the early days)
As the signal goes big the bandwidth gets truncated as they can't pass low freq well at high volume hence the classic flabby bass when cranked up.
The highs also get rolled off as well. This of course is exactly what you need for
Overdriven guitar Sound/Tone. Leaving plenty of bandwidth to cover the rather limited range of guitar. Some Tx spec sheets actually show this as a chart.
So by design cheap Tx's can't pass all the high freq hash which magically filter off all the nasty top end fizz. A simulation would likely show a lot of hifreq crud on the top edge of the signal at the plates of the power valve but vanishes on the secondary. Bingo a filter altering as signal goes big.
While in a SS power stage this does not happen hence they often got a bad wrap as being harsh. (a lot of those issues can be filtered out with smart design)
You have to spend a lot of money to get an OT to do a clean 20/20 hifi bandwidth.
Don't fool yourself into thinking Valve amps can't do hifi clean, they can be on par with even the best SS hifi rig. But OT will cost big money.
The compression in those classic guitar amps happens simply because of the often
**Overlooked soggy power supplies that were used**. It has a profound effect on the
outcome. plus Add in all of the other limitations and quirks you already know about.
A SS PSU is rigid while the old valve amps used high voltage supplies which were very soggy. So the moment you belted a big cranked power chord the HT drops like a brick and hence the compression effect.
Also don't forget the voltage drop from Screen grid to PI section. Just altering those voltage nodes along the supply paths can result in a very different performance.
I've tweaked a couple of later model Marshall's which use a 4k7 drop from screen to PI. Simply changing back to 18~22k makes them respond/sound much more like the older models. This thickens up and tends to smooth out the crunch effect.
the PI stage then distorts before the power valves.
Unlike most compressor circuits whether they be builtin or in guitar pedal format may well compress but seldom do they distort an if they do it's often crappy.
One way I found to get a simple SS discrete power stage to do this magic trick;
Years back I scored a little 20 watt combo with a 10 inch speaker.
While trying to tweak it and draw out the circuit I had the mains running through a light bulb limiter. It finally sounded really good but the moment I removed the limiter bulb the magic was lost.
So I permanently installed a 40Watt light bulb into the chassis with a switch to bypass it. A 20watt bulb was too low and the sound just cracked up badly.
I have fond memories of playing along with some Clapton songs and impressed that my tone sounded very much like Clapton's tones.
Darn stupid of me to swap it for bigger amp, thinking I could do the same trick and get a bit of extra volume but alas it had a Chip power stage and the idea did not work.
Those power chips are too perfect for that to work, obviously it only seems to work with a discrete power stage.
Now I'm sure far greater minds than mine have come up with even better ways but That's what I have come to understand after years of sending perfectly working transistors to smoke heaven.
I hope that helps, Phil.
I just got sick of music shops exploiting my lack of knowledge so I started learning how audio gear works by reading lotsa books (long before computers and the net)
----
Now it sounds like you have a more in depth learning than myself.
Well I went deep trying to learn a lot of tecky stuff which sent me quite mad for a while.
But over time I started to come to understand a lot better by simplification and basic observation.
We all Ask why do Valve Amps have the magic mojo?
I came to understand a Valve power stage for *What it DOES*
rather than *How it Works*.
**It's a COMPRESSOR that distorts badly with big signals**
Most of the favored Valve amps of a bygone era were of very basic design.
My no 1 rule of thumb (Valve or SS);
If you want a great rock guitar amp, just build a crappy basic circuit.
Old OTx,s were cheap and suffered from all the quirks you likely already know about. Leo built to a budget so interleaved OT were out of the question.
(at least in the early days)
As the signal goes big the bandwidth gets truncated as they can't pass low freq well at high volume hence the classic flabby bass when cranked up.
The highs also get rolled off as well. This of course is exactly what you need for
Overdriven guitar Sound/Tone. Leaving plenty of bandwidth to cover the rather limited range of guitar. Some Tx spec sheets actually show this as a chart.
So by design cheap Tx's can't pass all the high freq hash which magically filter off all the nasty top end fizz. A simulation would likely show a lot of hifreq crud on the top edge of the signal at the plates of the power valve but vanishes on the secondary. Bingo a filter altering as signal goes big.
While in a SS power stage this does not happen hence they often got a bad wrap as being harsh. (a lot of those issues can be filtered out with smart design)
You have to spend a lot of money to get an OT to do a clean 20/20 hifi bandwidth.
Don't fool yourself into thinking Valve amps can't do hifi clean, they can be on par with even the best SS hifi rig. But OT will cost big money.
The compression in those classic guitar amps happens simply because of the often
**Overlooked soggy power supplies that were used**. It has a profound effect on the
outcome. plus Add in all of the other limitations and quirks you already know about.
A SS PSU is rigid while the old valve amps used high voltage supplies which were very soggy. So the moment you belted a big cranked power chord the HT drops like a brick and hence the compression effect.
Also don't forget the voltage drop from Screen grid to PI section. Just altering those voltage nodes along the supply paths can result in a very different performance.
I've tweaked a couple of later model Marshall's which use a 4k7 drop from screen to PI. Simply changing back to 18~22k makes them respond/sound much more like the older models. This thickens up and tends to smooth out the crunch effect.
the PI stage then distorts before the power valves.
Unlike most compressor circuits whether they be builtin or in guitar pedal format may well compress but seldom do they distort an if they do it's often crappy.
One way I found to get a simple SS discrete power stage to do this magic trick;
Years back I scored a little 20 watt combo with a 10 inch speaker.
While trying to tweak it and draw out the circuit I had the mains running through a light bulb limiter. It finally sounded really good but the moment I removed the limiter bulb the magic was lost.
So I permanently installed a 40Watt light bulb into the chassis with a switch to bypass it. A 20watt bulb was too low and the sound just cracked up badly.
I have fond memories of playing along with some Clapton songs and impressed that my tone sounded very much like Clapton's tones.
Darn stupid of me to swap it for bigger amp, thinking I could do the same trick and get a bit of extra volume but alas it had a Chip power stage and the idea did not work.
Those power chips are too perfect for that to work, obviously it only seems to work with a discrete power stage.
Now I'm sure far greater minds than mine have come up with even better ways but That's what I have come to understand after years of sending perfectly working transistors to smoke heaven.
I hope that helps, Phil.