Can the old Peavey 50 50 Classic be modded to 25 25?

This forum is for talking about all kinds of Peavey power amplifiers.
Post Reply
adam_mizer
New Member
Posts: 6
Joined: Sun Dec 10, 2017 9:43 am

Can the old Peavey 50 50 Classic be modded to 25 25?

Post by adam_mizer » Sun Dec 10, 2017 10:22 am

Hi all my first post here.
A couple questions may help me use the amp better.
1)Is there a way to modify this old Classic Peavey 50 50 power amp to get 25 25?
2)Can the amp safely run 1 channel only at 50watts without causing damage to 2nd channel.

My dilemma is playing small clubs, or practice rooms.
Running in mono 100watts is just too much power, there is a minimal point to get a good gritty punch out of the amp where it starts to give this great live punch from the amp that cuts right through.
At this point it gives a great quality sound for R&B gives me a boost inside and the sound has a life of its own. The tones become much more meaningfull each with a color of their own, my playing gives me a quality of a much more choice expression.
Running at lower volume the quality of this point is not there.
I'm thinking okay what if power was cut in half, would that same point of clipping or is it drive, I suspect be there? (At a lower volume of course.)

The only other way is changing amps, I suspect a Mesa 20 20 dyna watt would work.
Well here's a Peavey 50 50 that may have the ability to be modded to 25 25 I would like to try that provided no internal damage would happen to the components.

Can someone help me out, would this work.

User avatar
Enzo
Member
Posts: 9089
Joined: Fri Sep 12, 2008 10:24 pm
Location: Lansing, Michigan

Re: Can the old Peavey 50 50 Classic be modded to 25 25?

Post by Enzo » Tue Dec 12, 2017 1:19 am

25 watts is only 3db less loud than 50 watts.

The two channels are separate, each has its own standby switch, so if you want to run only one channel, leave the other channel off.

You can pull half the tubes, pull the top two on each side for half power. Step your load down on the output, ie run 16 phms on the 8 ohm tap.

adam_mizer
New Member
Posts: 6
Joined: Sun Dec 10, 2017 9:43 am

Re: Can the old Peavey 50 50 Classic be modded to 25 25?

Post by adam_mizer » Tue Dec 12, 2017 11:08 am

Thank you Enzo,
That answers a lot.
Will try 1/2 the tubes later.
Didn't know I could run just one channel leaving the other in standby. I always thought this could be damaging.
If the tube removal works it might help.
3db might make the difference.

User avatar
Enzo
Member
Posts: 9089
Joined: Fri Sep 12, 2008 10:24 pm
Location: Lansing, Michigan

Re: Can the old Peavey 50 50 Classic be modded to 25 25?

Post by Enzo » Tue Dec 12, 2017 3:23 pm

On a zillion old Fender amps, like a Twin reverb, you have the high and low gain input jacks. Those are 6db apart. Just a frame of reference.

adam_mizer
New Member
Posts: 6
Joined: Sun Dec 10, 2017 9:43 am

Re: Can the old Peavey 50 50 Classic be modded to 25 25?

Post by adam_mizer » Thu Dec 14, 2017 3:33 pm

Hi Enzo,
Have another question for you.
Was wondering if I break the ground plate from the tube and install a switch for each channel.
Would I get the same result as removing the tubes?
I'm looking at the tube circuit board, if I make 2 cuts install a switch for each, also maintain the ground jumper because of a cut.
Will this work?
Peavey5050tube.jpg
Peavey5050tube.jpg (880.76 KiB) Viewed 2929 times
removedtubes.jpg
removedtubes.jpg (854.45 KiB) Viewed 2929 times

User avatar
Enzo
Member
Posts: 9089
Joined: Fri Sep 12, 2008 10:24 pm
Location: Lansing, Michigan

Re: Can the old Peavey 50 50 Classic be modded to 25 25?

Post by Enzo » Sat Dec 16, 2017 1:45 am

I dunno, but you seem to have removed the end tubes rather than the top ones. (Or the bottom ones)

adam_mizer
New Member
Posts: 6
Joined: Sun Dec 10, 2017 9:43 am

Re: Can the old Peavey 50 50 Classic be modded to 25 25?

Post by adam_mizer » Sat Dec 16, 2017 1:26 pm

Hi Enzo,
Checking the prints it doesn't matter which 2 you remove.
There's a channel A or B on the print.
UP/Down 2 on the left are A next is B then A then B.
A B A B
A B A B
Same as you said also Top left A second top left is B works either way.
Also found out from old texts, I could remove 1 or 2 or 3 each side.
However an amount of drive tone (less tubes) is lost a person now has the ability to drive the remaining tube(s) at low live volume.
Have not tested this in a live scenario, just at home. Works great!

My next experiment is to try the cheap attenuator on the output.
I'll check the tones to see if I can get what I want.
After that I'll decide whether to cut traces and install switches for the tubes or just use an attenuator on the output.

I believe I can make these mods and not suffer any damages.

User avatar
Enzo
Member
Posts: 9089
Joined: Fri Sep 12, 2008 10:24 pm
Location: Lansing, Michigan

Re: Can the old Peavey 50 50 Classic be modded to 25 25?

Post by Enzo » Sat Dec 16, 2017 9:32 pm

OK fair enough, I saw that removing the top row was a solution, and I looked no further.

adam_mizer
New Member
Posts: 6
Joined: Sun Dec 10, 2017 9:43 am

Re: Can the old Peavey 50 50 Classic be modded to 25 25?

Post by adam_mizer » Sun Dec 17, 2017 4:39 pm

Okay looked at the prints more and although it works well enough with outer tubes pulled,
This changes the output transformer turns and changes the speaker matching ohms, because it does not use the full winding.
4 center tubes and still get lots of volume and punch but when standby switch turned off puts out a tiny pop sound.

Installed tubes on bottom row only, this matches output transformer windings for ohms setting I believe.
That sounds like a better way.
When I turn the standby switch off it doesn't pop as loud, its very quiet now.

Even though pulling tubes works in any order there is an output ohms match, so if you pull these outer tubes in pairs, the output to speaker won't match.
I think the little pop is the other half of the transformer releasing stored energy in the transformer metal and winding.

So my final thought is, yes it's better to pull the top row of tubes.

User avatar
Enzo
Member
Posts: 9089
Joined: Fri Sep 12, 2008 10:24 pm
Location: Lansing, Michigan

Re: Can the old Peavey 50 50 Classic be modded to 25 25?

Post by Enzo » Sun Dec 17, 2017 9:54 pm

As long as each channel has one tube from each side, it doesn;t matter which ones you remove.

I trusted your earlier response, but...

Look at the schematic. All tube numbers are in the 200 series.

The top side is #2,3, the bottom #4,5 - other channel top #8,9 and bottom #10,11.

You need to pull one from top and one from bottom in each channel.

Now look at the layout. The top row is #3,5,8,11, which is exactly one from each side of each channel I suggested removing them. yes, you could pull the bottom row instead if you wanted. #2,4,8,10.

Actually my drawing is upside down from your photo, but it doesn;t matter.

You removed the outside tubes, leaving the center four - #2,3,11,10.

Back to the schematic, you removed the top two of one channel and the bottom two of the other. In other words your first arrangement turned a push-pull amp into, well, a push amp.

SO I buy your ABAB thing, but if you remove the ends of both rows, your result is BB on one channel and AA on the other.

What you need is an A and a B for each channel.

Pulling two tubes does change the impedance, you need to run a 16 ohm speaker on the 8 ohm tap, and so on.

When you went with a whole row across, you still have push/pull for both channels, pops are reduced becaus e PP amp naturally cancels out power supply noise. When you had the ends removed you unbalanced the PP circuit so the pop is amplified.

The speaker impedance will not match regardless, that is why you need to step down a notch. The whole row sounds better than the ends off, because you have the whole circuit, not just one side of it.

adam_mizer
New Member
Posts: 6
Joined: Sun Dec 10, 2017 9:43 am

Re: Can the old Peavey 50 50 Classic be modded to 25 25?

Post by adam_mizer » Mon Dec 18, 2017 7:17 am

Right on!
Have a merry Christmas.

Thanks for your input Enzo, its very appreciated.

LoveRock
Member
Posts: 10
Joined: Mon Mar 22, 2010 6:45 pm
Location: Louisville, KY

Re: Can the old Peavey 50 50 Classic be modded to 25 25?

Post by LoveRock » Sun Apr 11, 2021 6:10 pm

Hi there. I'm glad I found this forum!

Not to flog a dead horse, metaphorically speaking, but I wanted to ask for a bit of clarification on this old thread. I have this amp (Classic Series 50/50 stereo rack amp), just acquired from it's original owner along with some other mint condition Peavey rack gear he bought new as a package (Ultraverb II, Rock Master Tube Preamp and two 412MS slant front stereo speaker cabinets). It all functions fine (replacing the U'verb's battery right now, tho.) The 50/50 even has Peavey-branded Sovtek tubes which the owner had replaced at some point in it's past by the dealer and they seem to have a good amount of life in them left. He'd placed all of the original manuals and factory inspection tags in individual zip-lock baggies for safe keeping. Love this guy!

The matter at hand: If I understand correctly: I can pull two tubes from each side, i.e. one horizontal row from each side, doesn't matter which row, either top or bottom is okay, to run it at 25W per channel, stereo for "bedroom" use.

If I run the amp in stereo I set impedance like this:

for a 16 ohm load I put the amp switches on 8 ohm. If it's an 8 ohm load I set to 4 ohms on the amp.
The speaker cabinets (no manual) have a switch for stereo or mono operation.
When used in stereo the load is 8 ohms PER SIDE. I.E each cab has left and right inputs. I'd use one input per cabinet for nice
    stereo separation.
    Which amp setting should I use if I do choose to run it at 25/25? I think it's 4 ohms per channel into the 8 ohm speaker load. Am I right?
    Thank you for your help.
    Peavey: Classic 50/50, 412MS 4x12 stereo cabs (two), Rock Master Tube Preamp, Ultraverb II, and lots of other makers various rack and traditional gear.

    Post Reply