Peavey Classic 30 Problems

[gfxbss]

hey guys,

working on a peavey classic 30.

the issue is when turned on, none of the tubes glow, no pre nor power. the main light turns on, but the tubes arent getting power.....

i have changed all of the tubes(pre and power).
i have checked the fuses, and all is fine there.

wanted to see if you guys may have any ideas...

im thinking an open resistor in the power supply?

thanks,

Tyler

[ChrisK]

I'm not sure that there is a resistor in the power supply that is common to all tube filaments.

It could be a number of things. You'll need a digital voltmeter, amp schematics, and working knowledge related to working on a tube amp.

THIS INVOLVES POTENTIALLY LETHAL HIGH VOLTAGES.

IT CAN KILL YOU.

NEVER WORK ON A TUBE AMP UNDER POWER, OR WITHOUT PROPERLY DISCHARGING ALL POWER SUPPLY STORAGE CAPACITORS, OR WAITING A SPECIFIED PERIOD OF TIME FOR INTERNAL DISCHARGING TO HAVE COMPLETED.

DO NOT WORK ON A TUBE AMP UNLESS YOU UNDERSTAND HOW THEY WORK AND THE NECESSARY SAFETY ASPECTS OF DOING SO.

IF THERE ARE ANY QUESTIONS REGARDING SAFETY OR THEORY OF REPAIR, TAKE IT TO A PROFESSIONAL REPAIR PERSON.


With that being said;

www.blueguitar.org/new/schem/peavey/modnotes/c30schmd.pdf

www.schematicheaven.com/newamps/peavey_classic30.pdf

The power tube filaments are in series across 24 VAC. the preamp tube filaments are in series across -36 VDC.

A bad power tube would cause all four of them to not be heated and a bad preamp tube would cause all three of them to not be heated. A problem with this secondary/circuit would cause all tubes to be unlit.

[gfxbss]

chris,

thanks for the quick reply.

i am quite familiar w/ the dangers in working on a tube amp. i have been reading books and articles on it, and have now decided it is time to get my hands dirty.

in regards to the resistor i was guessing at it because of one part in tom mitchells "how to service your own tube amp."

on page 202(not sure if you have or are familiar w/ the book) one of the bullets under service tips is "no voltage on tubes means open resistor in power supply."

am i missing something here?

thanks for the links to the schems, i already had one, but i am interested in the mods once i get this thing back up and working.

thanks,

Tyler

[sumgai]

Ty,

Tom is likely referring to the B+ (high voltage, to be sure) being dependent on the resistor(s) he mentioned. In most cases, there's no need for a resistor in series with the filament line(s). However, in your amp, Peavey made it a different story.

As shown in the schematic, it'd be highly unusual (like, Mr. Murphy would have to really shower his love on you!) for at least two of the three resistors to blow at the same time - R66 (DC preamp filaments) and R71 or R72 (AC power amp filaments). Yes, it's possible, and you should check it just to ease your mind, if nothing else, but if they don't look like pieces of burnt toast, then they're not the most likely culprit(s).

In fact, from your symptoms, the first thing I'd check is to see if there's approximately 24vAC present across the two Orange leads that feed into this rectifier circuit. Methinks you've got an issue with the incoming power here.

HTH



sumgai