Peavey Mace Problem

[baddog]

Im having a weard problem with my Peavey Mace head. When im playing my guitar through one channel and turn the pre & post gain,treb,mid or bass up on the other channel i get an amplified noise through the speakers , the phazer has some affect on the noise also. This amp has a SS preamp and 6 - 6L6's on the power side. Help!!!!!!!!!!!!!!!!!!!!!!!!!!1

keith

ps Im also getting a buzzing noise from the 4 large filter capacitors.

[Enzo]

Tired filter caps will make hum specifically, rather than noise. Unless the noise you have IS hum.

Call PV parts and get the schematic. Make sure which one you have, there were MAce Mace VT and Mace VTX as I recall. The schematics are diferent.

First thing I suspect is a bad TL604 switching IC in there somewhere. But certainly lots of things could be at fault. We just need to get in there and systematically isolate the problem.

[baddog]

peavey mace problem

I have the schematic already . There are 4 TL604's on the board ' I have tried swaping them around with no diferance in sound. I guess i would discribe the sound as a hum . Would the filter caps cause the problem I described. Is their a way to test the TL604 chips?

thanks
keith

[Twist]

If you have the foot switch then I would check all switching functions to rule out the TLO64's. The TLO64 IC's handle the switching of channels and effects. Check the voltages on the supply pins of the op amps (pins 4 and 8 of 4558 IC's). You should see about +/-15 volts.

[baddog]

Peavey mace problem

TWIST

I tested the amp with the foot switch while i was plugged into the automix jack and found somthing diferant. The switching works fine, the only problem i can find is that when in using 1 channel i can get a distortion signal bleading through if i adjust the the pre gain to 12 and post gain to 12 but only when i play a note or cord on my guitar . I tested the 4558 ic's and read +16 v on the 8 pin and - 19.3 on the 4 pin. Im not sure of the test conditions you wanted me to check the 4558 ic's or does it matter?

Thanks
Keith

Without the footswitch andhaving my guitar plugged into the nornal jack the problem is different.

[Enzo]

Well, there it is, you've lost regulation on the -16v rail. Fix that and tell us what
happens.


That -19 should be -16. Those extra volts are the headroom for the regulation, and they are full of hum and crap. ALso, the op amps will not average out to zero with the power rails skewed.

[baddog]

peavey mace problem

ENZO

Im not sure how to fix the regulation problem. Where should i start looking first? I can send you a copy of the schematic if you would like. can you tell me step by step because I'm new to the electronics area. Im soory to be a pain in the butt.

thanks
keith

[baddog]

peavey mace problem

I noticed 2- 22k 1Watt Allen Bradley resistors are getting hot enough to cause the inside to melt out . These resistors are right after the 4 - 100uf 350v filter capacitors . Would it be a good idea to replace them with metal film or should i use carbon composit replacements. would it be ok to use 2watt resistors or should i stay with the 1 watt type.

thanks
keith

[Enzo]

It is always OK to use higher wattage resistors, unless they just don't physically fit.


The +/-16v supplies are set by a pair of zener diodes - CR10, CR11 in the power supply. Schematic says 30050, but the part is just a 1N4745 16v zener. If your supplier has no 16v zeners, then replace both with 15v 1N4744, a very common type. A pair of 100 ohm 5 watt resustors drop the 25v supplies down to the zeners. While it is possible one of those resistors is way high in value, it is unlikley. I'd replace the 16v zener that now has 19v across itself.

Those 22k resistors are dissipating not quite a half a watt, so 1 watt ought to be OK, but yes, I'd be happier with 2 watters myself. Film resistors would be fine.

[baddog]

peavey mace problem

ENZO

Thanks for the info . I will se what i can do to find some parts. I might as well change them both while im at it. I will keep you in the loop

Thanks
KEITH

[baddog]

Peavey mace problem

ENZO

I was looking at the schematic and ordering parts and was wondering if their is a replacement diode for the CR16 2873 & CR17 2873 in the power amp tube section ?

thanks
keith

[Enzo]

They are transient suppressors. SR2873 is like an MR2502 supposedly, but the specs don't match up. The 2873 is a 2000 volt 250ma diode.

This oart is not under any stress unless you crank the amp without a speaker. Then it will give its life protecting the OT. Franklt, if the ones you have are not shorted, and test like a diode, I would just keep them.

Or, as with any Peavey product, you can order the exact part from PV.

[baddog]

peavey mace problem

ENZO

What is the best way to test a diode?

Thanks
keith

[Enzo]

With an ohm meter, you can see if it is shorted or not. A meter may or may not tirn on the junction, so you may get a lower reading one way than the other. That is why most meters include a diode test function. Read the owners manual for your meter. The diode test reads the voltage drop across the diode. Forwards the diode should read some low voltage like .5. Now I am not sure on these 2kv types, they may be dual junctions and so measure a whole volt. In either case, we then reverse the leads and expect to get an open reading.

Keep in mind that these are wired into a circuit, so the rest of the circuit might confuse your meter.

If the amp is not blowing fuses, these are OK. If one of these transient suppressors shorts, it becomes a dead short across B+, and that blows fuses.

[mykey]

Im having a weard problem with my Peavey Mace head. When im playing my guitar through one channel and turn the pre & post gain,treb,mid or bass up on the other channel i get an amplified noise through the speakers , the phazer has some affect on the noise also. This amp has a SS preamp and 6 - 6L6's on the power side. Help!!!!!!!!!!!!!!!!!!!!!!!!!!1

keith

ps Im also getting a buzzing noise from the 4 large filter capacitors.

in the mace you should check and replace any IC's that are getting hot after the power has been on for a couple minutes. you can feel them with your finger, but don't burn yourself. the mace also has an issue with arcing tube sockets. once the arcing occurs the sockets should be replaced, cleaning off the black carbon won't fix it. The buzz does not come from the capacitors-it comes from something shorted (like an IC) or a bad output tube.