iheartgun

so i bought one of these last year on a whim and its sat around and collected dust due to its crappy tone. are there any mods out there that are easier to do that help with the following:
a. muddy tone
b. unusable gain
c. very limited eq curve

ive tried different tubes and all that with minimal success and i clearly understand what the amp is meant for but is there any way to make this thing usable?
im decent with a solder gun and i can read long line diagrams.

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R45VT

Do you have a wiring diagram for it?

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iheartgun

all that i can seem to find is the univalve print.
http://music-electronics-forum.com/...78-univalve.gif

__________________
Main Rig
Peavey 5150ii
B52 AT412B or carvin 2x12 depends on my mood

Guitars
Epiphone 58' explorer
ltd ex-260
ltd M-100FM
78 Hondo 2 les paul
80's Peavey Horizion 2

Board
i has pedulz

end_citizen

Here's a schematic. I've got all kinds of stuff I need to do in the next couple days. So, I won't have time to draw up any mods (most likely). https://www.box.com/s/027ce4ae42977380ef43

Anyone else competent in tube amp design, help this guy out.

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Back in action, now with brain and spine cyst.

Learn the gist of tube amps

R45VT

Simple amp. What type of components are in this thing to begin with?

Do you have photo of the internals?

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Culler Amps

This should get you close to a JCM800 preamp.

C1, C7, C17, DEV1, DEV8, and R18 have been removed.

Additions or value changes are drawn in.



The above would be my plan of action if I was as unhappy with the amp as you sound to be....

But if you only want to make a few changes you can try just adding the 1uF at R5, and changing the tonestack to the values listed.
That should get you a bit more gain and hopefully some more response from the tonestack.

iheartgun

just so im reading this right i would wire in a capacator starting and ending over the resistor at r5? where can i get these parts? this is also my first true amp mod.

thank god for learning to read long line schematics years ago! ill have to open up

__________________
Main Rig
Peavey 5150ii
B52 AT412B or carvin 2x12 depends on my mood

Guitars
Epiphone 58' explorer
ltd ex-260
ltd M-100FM
78 Hondo 2 les paul
80's Peavey Horizion 2

Board
i has pedulz

Culler Amps

Yep. You got it.

Its what is known as bypassing. Essentially what you are doing is bypassing the resistor with a capacitor.

In this particular application it is called a cathode bypass capacitor.

I'd recommend a 1uF electrolytic capacitor.
http://www.mouser.com/Passive-Compo...pm&Ns=Pricing|0


Mouser the site linked above, is great. You can Google "electrical components" for some more parts options as well.

iheartgun

ok so for the value changes such as r9's 10k resistor id have to buy the 10k resistor and just replace it outright?

also about discharging the caps in this amp which ones would i have to discharge? im assuming c20 and c21. i feel like im missing one though..

__________________
Main Rig
Peavey 5150ii
B52 AT412B or carvin 2x12 depends on my mood

Guitars
Epiphone 58' explorer
ltd ex-260
ltd M-100FM
78 Hondo 2 les paul
80's Peavey Horizion 2

Board
i has pedulz

Culler Amps

Yes. I'd only recommend the R9 change though if you go ahead with the rest of the modifications shown, or you'll probably just get quite a bit less gain.

If your only going to add the 1uf and the change the tonestack then I would leave R9's value alone. You can also bypass it with a 1uf as well. Just like R5, if you're happy with the changes there.

If you plan on doing all the modifications, by all means go ahead and change R9 to 10K. Thats stock for a JCM, but some people like going with a smaller value for more gain. I'd start out with 10K though.



Normally C4, C18, C23 and DEV16.

However this amp actually has 220K bleeding resistors on all the filter caps. So you won't need to do any discharging. Just give it a minute or so after turning it off and you can carefully check with a meter to be certain they are discharged.

iheartgun

oh i was thinking that all amps regardless needed to have caps discharged.

__________________
Main Rig
Peavey 5150ii
B52 AT412B or carvin 2x12 depends on my mood

Guitars
Epiphone 58' explorer
ltd ex-260
ltd M-100FM
78 Hondo 2 les paul
80's Peavey Horizion 2

Board
i has pedulz

Culler Amps

Normally yes. You'd use a resistor and length of wire to discharge the caps. Thats a very important step.

But looking at the schematic we see this amp has a bleeding resistor on each filter cap that will drain it when the amp is turned off.

The 220k resistors at each filter cap are the bleeding resistors.

You should STILL check with a meter just to be safe though.