Peavey Classic 50 Mods! (Telebert!)

[BoldAsLove]

Hey all,

Here is the setup!

image removed


Super happy with it, but really hating that thin OD channel. I was impressed by a mod schematic posted in another thread, but was wondering if there was a better version of it...

Also, any opinions on what types of tubes would go well in this

Thanks!!

 

[e-merlin]

I think a few of the Classic 30 mods on Blueguitar.org will work on the C50.

It's pretty common for a Peavey Classic owner to love one channel and not the other. Lots of the guys around here just use a stompbox for dirt.

 

[JohnnyCrash]

You could beef up the preamp at the cathode bypass caps. On second thought, I just looked up the schematic at SchematicHeaven.com and it's not the typical Marshall cascade style circuit...

In this case I see two or three immedaite approaches - removing treble peaking caps, increasing a cathode bypass in a later gain stage, or increasing coupling cap values.

1. Clip/tweak a treble cap in the Dirt channel:
The 1st gain stage is typical Fender (1500 ohm resistor with a 22uF cap) and the next gainstages trim the bottom end. The 1st stage feeds either the Clean or Dirty Pre pots/knobs via a 0.047uF cap (C13). At this point at the Dirt pot there is a 470pF cap - you can either clip or tweak the value of (C24). The same idea can be used at C4 (though I'd start with C24). Small caps mean smaller bass/mids. Big caps can mean woofy, tubby, muddy bottom.

2. Increase bottom end at a later cathode:
Increasing the value of C6 will add bottom end beef. I'd try a 1uF instead of the stock 0.47uF. I wouldn't go as high as 10uF and if 4.7uF or 5uF don't cut it, I'd take a different approach (or multiple approaches).

3. Fatter coupling caps:
Most of the couplers are of sufficient size (0.047uF), but one is quite small (C1 is a 0.001uF). With this circuit though, I'd leave the coupling caps alone.

You could also play with the tonestack, but I wouldn't... you'd likely only get different play out of the pots/knobs.

In this case - if it were my amp, I'd simply try to bump up C6 first. If going to 1uF or even 2uF doesn't cut it, I'd go back to the the Dirty Pre pot and clip or increase C24. Too much woof/bass afterwards? Go back and decrease C6 a smidge. You might have to play with them to strike a balance... you could always play with C4 as well.

The problem with modern Clean/Dirty channel amps is in having a fat, warm Clean channel and cascading other tube stages for gain. Once you start cascading you have to trim bass to keep things from getting woofy at higher Pre/Gain settings. To make the circuit simple is the goal and to use as few preamp tubes as possible.

If I build another amp, I'm going to follow my "dual JCM800" build's approach... two entirely seperate preamp tubes, using 12v relays in the footswitching circuit to select which is fed the input and which output is fed to the next stage (the tonestack)... only trouble is I'd be wasting a triode in a 12AX7 in the "clean" channel... I could toy with a tube buffered FX loop...

Good luck!

 

[BoldAsLove]

Hey there, thanks for the advice! Will keep you posted. Perhaps having a pedal would just be a better work around, as I'm not exactly experienced inside an amp...

You could beef up the preamp at the cathode bypass caps. On second thought, I just looked up the schematic at SchematicHeaven.com and it's not the typical Marshall cascade style circuit...

In this case I see two or three immedaite approaches - removing treble peaking caps, increasing a cathode bypass in a later gain stage, or increasing coupling cap values.

1. Clip/tweak a treble cap in the Dirt channel:
The 1st gain stage is typical Fender (1500 ohm resistor with a 22uF cap) and the next gainstages trim the bottom end. The 1st stage feeds either the Clean or Dirty Pre pots/knobs via a 0.047uF cap (C13). At this point at the Dirt pot there is a 470pF cap - you can either clip or tweak the value of (C24). The same idea can be used at C4 (though I'd start with C24). Small caps mean smaller bass/mids. Big caps can mean woofy, tubby, muddy bottom.

2. Increase bottom end at a later cathode:
Increasing the value of C6 will add bottom end beef. I'd try a 1uF instead of the stock 0.47uF. I wouldn't go as high as 10uF and if 4.7uF or 5uF don't cut it, I'd take a different approach (or multiple approaches).

3. Fatter coupling caps:
Most of the couplers are of sufficient size (0.047uF), but one is quite small (C1 is a 0.001uF). With this circuit though, I'd leave the coupling caps alone.

You could also play with the tonestack, but I wouldn't... you'd likely only get different play out of the pots/knobs.

In this case - if it were my amp, I'd simply try to bump up C6 first. If going to 1uF or even 2uF doesn't cut it, I'd go back to the the Dirty Pre pot and clip or increase C24. Too much woof/bass afterwards? Go back and decrease C6 a smidge. You might have to play with them to strike a balance... you could always play with C4 as well.

The problem with modern Clean/Dirty channel amps is in having a fat, warm Clean channel and cascading other tube stages for gain. Once you start cascading you have to trim bass to keep things from getting woofy at higher Pre/Gain settings. To make the circuit simple is the goal and to use as few preamp tubes as possible.

If I build another amp, I'm going to follow my "dual JCM800" build's approach... two entirely seperate preamp tubes, using 12v relays in the footswitching circuit to select which is fed the input and which output is fed to the next stage (the tonestack)... only trouble is I'd be wasting a triode in a 12AX7 in the "clean" channel... I could toy with a tube buffered FX loop...

Good luck!

 

[telbert twang]

hi,

here is the result of my story - i had the same, ´OD channel not liking´ issue. ruger9, Johnny Crash , Foreign Made helped me a lot. Also couple of answers to my questions from Steve Ahola. Mr (link removed) Kasak helped to put it all together. Different animal now.

Actually, i´d still not give "10" to mine (perhaps 9 of 10), because now the OD channel is ´on another side´ - 1 hair more boomy than my ideal imagination (anyway it still is much better than stock circuit can offer). But the tiny (shared)EQ disbalance improves and gets close to "10" right as i have cranked it (PV C50 likes to work on near full throttle, imo).

BEsides the OD, the "green mods" for the inputs make it much more sensible to string attacking nuances - the somewhat tight and stuck response of it has been cured totally.

 

[JohnnyCrash]

Hey there, thanks for the advice! Will keep you posted. Perhaps having a pedal would just be a better work around, as I'm not exactly experienced inside an amp...

I believe the circuit board has every part labelled (white silkscreened lettering).

I would think that swapping only one (or two at most) of the capacitors would help a great deal.

To discharge the filter caps you'll need insulated alligator clips, a small bit of wire, and a large resistor. After this it will be easy to discharge the amp's big filter caps so you could work on the amp safely.

It sounds like a lot, or that its complicated - but its not. Its really a 10 minute mod (inlcuding removing the chassis).

As far as unintrusive stuff... cranking the Master has always helped. C50's sound better LOUD as Telbert mentioned.

 

[BoldAsLove]

I cleaned the pots and had an opportunity to play in my living room with relatively good acoustics (and the amp propped up around chest high). Clean channel set on 12, master 5, and guitar 7-8. Sounded amazing! Thanks for the summary of the mods, I'll have a chat with the old man, and get some help with this..