Got a Free Peavey Windsor

[JustMike]

And it works fine. The sound...meh. Looking at the schematic I see it has a cathodyne PI. Do these circuits sound different than a LT PI? Would changing it help the sound (make it more Marshally perhaps?).

[PRR]

Did you Google?

There seem to be hundreds of opinions and mods for the Windsor.

[JustMike]

Yes, I'm aware. I guess I should have clarified that there dont seem to be any good explanations of the differences between the sound of a cathodyne vs a ltpi in a marshall type circuit. I read Merlin's article on how a cathodyne can sound nasty when it distorts and the easy fix for it. And in Fender ckts, the ltpi retains some of the "glassiness".
 Anyway, i guess I'll try it and see. But I think i'll Marshallize the front end first to establish a base.

 

[sluckey]

Converting a cathodyne to LTP is not a trivial task when the tubes are mounted on a pcb.

[John G]

Hi,
I think I remember Doug Hammond converting his when he first got it. Its been a few years now though.
John

[JustMike]

Snooping around the schematic I've noticed some similarities and some differences from/to a JCM-800.


1. PV has high gain cathode R values


2. PV has no cathode follower tone stack driver. I thought the point of the cathode follower was to lower the Z of the tube output so the tone stack wouldn't suck the life out of the signal. Also, it serves as the driver for the LTPI in a Marshall. This leads me to point #3.


3. PV has Cathodyne PI which only uses the 2nd triode. Is the first triode in V3 a gain stage to somehow compensate for the lack of a cathode follower?


4. Bias voltage on the Peavey comes in on the supressor grids (pin 1). I guess I don't understand bias circuits well enough to wrap my head around this. My desire is to Marshalize the P.A. and Marshall has pin 1 tied to gnd. I don't think I want the bias voltage going to ground.

[sluckey]

3. PV has Cathodyne PI which only uses the 2nd triode. Is the first triode in V3 a gain stage to somehow compensate for the lack of a cathode follower?

The cathodyne has a gain slightly less than 1. Most people consider the gain stage just prior to the cathodyne to be part of the PI.

4. Bias voltage on the Peavey comes in on the supressor grids (pin 1). I guess I don't understand bias circuits well enough to wrap my head around this. My desire is to Marshalize the P.A. and Marshall has pin 1 tied to gnd. I don't think I want the bias voltage going to ground.

It's fine to connect the suppressor grid to a negative voltage source rather than ground. I'd leave it as is. Not gonna make it more Marshally to connect to ground. And if you use 6L6s it is irrelevant since pin 1 connects to nothing inside a 6L6. You did notice that the bias voltage is also connected to pin 5 in the usual manner?
 

[JustMike]

You did notice that the bias voltage is also connected to pin 5 in the usual manner?
 

Ah! I did just now..so what is the point of the bias on pin 1 as well as the 10k resistors?

[sluckey]

Don't think of it as bias on G3. Just think of it as G3 is referenced to a negative voltage (which just happens to be the negative bias voltage for G1) rather than ground. As I said, either is fine. Why did Peavey do it like this?     Give them a call. They are friendly people. Meanwhile, read some of this...

https://www.google.com/search?q=why+connect+suppressor+grid+to+negative+voltage&oq=why+connect+suppressor+grid+to+negative+voltage&aqs=edge..69i57.37039j0j4&sourceid=chrome&ie=UTF-8

[thetragichero]

I've done this on a marshall-style build just because (really it helped out the wiring since it was done on terminal strips throughout), although it currently has kt77s in it so it's not like pin 1 is connected to anything in the tube

[PRR]

....I thought the point of the cathode follower was to lower the Z of the tube output so the tone stack wouldn't suck the life out of the signal.....

What does 'suck the life' even mean??

The treble is rolled-off if the source impedance is high. But Peavey (unlike Fender 5F6a) has stacked *five* treble-boost stages in front of the tonestack.

Distortion hurts the ears. It hurts less if treble is rolled off afterward. Then to sound OK un-distorted you must boost treble before distortion. V2b and C41 against the tonestack is the top-cut, all before that is top-boost or distortion (in layers).

With all that going on I can't point a finger at the cathodyne. Gobs of "color" before we get to the driver. "My" Ampeg V-40 had the cathodyne and it didn't hinder power or tone.

[JustMike]

What does 'suck the life' even mean??

In my mind it means to take out the high end sparkle, maybe some dynamics. Or fresh, pert and vivacious like a young 20 year old cheerleader with pearly white teeth, silky hair and tight skin as opposed to Walmart Grandma perhaps with lunch lady arms.

[thetragichero]

try decreasing c41? 470pf is a start, maybe 220pf although i probably wouldn't go that low

[JustMike]

Good info PRR. This should keep me occupied for a while. Thanks mucho!