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]

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]

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]

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]

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]

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]

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]

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]

Originally Posted by 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.

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.

[baddog]

ENZO

Thanks again. I ordered new diodes,zener diodes and metal oxide power resistors for the peavey. I was told by the amp tech that worked on my amp prior to my latest problems that this amp is a self biasing amp. is that true? Can i run thiis amp on 4 tubes instead of the normal 6 tubes and if i run it with 4 tubes can i put the other tubes back in later if i sell the amp. Im curently running GT6L6R's (6L6GB) but the schematic calls for 6L6GC's is this a bad idea ?

Thanks
Keith
Mykey Is the bad IC causing the capacitors to buzz ? because i used a piece of tubing and the noise is coming from the filter caps.

[mykey]

Originally Posted by baddog

ENZO

Thanks again. I ordered new diodes,zener diodes and metal oxide power resistors for the peavey. I was told by the amp tech that worked on my amp prior to my latest problems that this amp is a self biasing amp. is that true? Can i run thiis amp on 4 tubes instead of the normal 6 tubes and if i run it with 4 tubes can i put the other tubes back in later if i sell the amp. Im curently running GT6L6R's (6L6GB) but the schematic calls for 6L6GC's is this a bad idea ?

Thanks
Keith
Mykey Is the bad IC causing the capacitors to buzz ? because i used a piece of tubing and the noise is coming from the filter caps.

any short will cause a buzz, but I'm not sure what you mean by buzz. are you talking about a buzz 60 cycle noise from the speakers? or a mechanical vibration buzz? No, the amp is not self biasing. It does not have a bias adjustment because PV wants you to buy special PV tubes. you can bias it by changing the resistor or installing a bias control, which is recommended.
then you can install any tubes you want.
It's not the zeener diodes usually, or the power resistors. you need to be more specific about describing what's going on.
you made it sound like a preamp problem which is usually what goes wrong with those amps.
yes you can run it with four tubes, 2 tubes in sockets 1 and 2 and two tubes
in sockets five and six. (leave out the two middle tubes) then trade the tubes around till you make sure it's not a bad tube causing a hum kind of buzz.
but then again were not sure what you mean by "buzz"?

[Enzo]

Peavey designed the amp so it would not need to be adjusted. That is all they mean by self-biasing. They aren't selling special tubes, they design it cool so the power amp section will run long term on a set of tubes. The powr amp is loud and clean, the tone is developed in the preamp. They don't want kids messing with bias and burning up tubes and circuit patrs by mis-adjusting. The kid would instantly blame PV. Just about any set of tubes you plug in there will fall into a reasonable bias situation.

ANy current production 6L6 will work there. I think the Ruby 6L6GCSTR tubes work well here, but it is not critical. SOvtek, JJ, whatever. I personally don't buy Groove Tube products, I feel their pricing is predatory and won't support it.

[mykey]

Originally Posted by Enzo

Peavey designed the amp so it would not need to be adjusted. That is all they mean by self-biasing. They aren't selling special tubes, they design it cool so the power amp section will run long term on a set of tubes. The powr amp is loud and clean, the tone is developed in the preamp. They don't want kids messing with bias and burning up tubes and circuit patrs by mis-adjusting. The kid would instantly blame PV. Just about any set of tubes you plug in there will fall into a reasonable bias situation.

ANy current production 6L6 will work there. I think the Ruby 6L6GCSTR tubes work well here, but it is not critical. SOvtek, JJ, whatever. I personally don't buy Groove Tube products, I feel their pricing is predatory and won't support it.

the bias in any class AB amp SHOULD be adjusted for the tubes installed. Just because there is no adjustment does not mean it can't be installed.
The purpose of leaving out the adjustment was to force people to buy PV power tube sets rated for that amp. The amp will ALWAYS sound better if the bias is adjusted correctly.
Ruby tubes, sovtek, No thanks. JJ's are much better. Groove tubes are very good, but the price is too high for most people. anytime tubes are lab matched, the price goes way up. Groove tubes does a really good matching job, and it costs lots of money. Best matching? Amprex Bugle Boy at $425 dollars a set, and worth every penny. most people don't need matching that good, but some appreciate it. We will keep those for our $12,000 Marshall clones.

[baddog]

The buzz isn't coming through the speaker & it isnt a physical buzz it's coming from the + side of the 100uf 350V filter capacitors. specificly capacitors C9 & C7. None of the IC's got hot . Everything i have read about removing tubes to reduce wattage says to remove the outer tubes only.

thanks
keith

[mykey]

Originally Posted by baddog

The buzz isn't coming through the speaker & it isnt a physical buzz it's coming from the + side of the 100uf 350V filter capacitors. specificly capacitors C9 & C7. None of the IC's got hot . Everything i have read about removing tubes to reduce wattage says to remove the outer tubes only.

thanks
keith

well I have seen similar things in PV amps
you most likely need to replace the caps.
call PV 601 483 5365 unless it's been changed
ask them where to get new ones and swap them out
they don't cost much.
changing the zeeners etc. to get rid of a cap noise?
i don't think so.
There have actually been issues with caps in the past
and changing them solved it.
talk to the techs at the factory and get their opinion.
they keep track of those things, it's in Meridian Mississippi.
my only idea is to change them out.
Oh OK you can take out the end tubes or the middle ones.
either way works the same.
but it won't reduce the volume much, just a little.

[baddog]

Enzo

What do you think?

thanks
keith

film at 11

[Enzo]

The purpose of leaving out the adjustment was to force people to buy PV power tube sets rated for that amp.

Mykey, that is an utter fabrication. ANother pointless conspiracy theory. The tubes Peavey sells are not selected in any way. They use several brands of tube in prodiction, and in fact are not even installing matched sets into the amps. You may feel that bias is some supercritical adjustment, but in reality there is a wide range of perfectly acceptable bias current. The amp may sound better to your ear at some higher current, but thousands of Peavey amp owners are perfectly happy listening to their amps at lower current levels.

Matching tubes adds anywhere from nothing to at most $2 per tube, depending on where you buy it. Unless you buy from Groove. Then you pay an extra 50%.

Since Groove doesn't make the tubes, most of your Groove tubes will be from Sovtek, China, or JJ anyway.

And a mechanically buzzing cap? If it makes you unhappy, replace it. Peavey will sell you any part you need, but caps are available all over the place.

[baddog]

Enzo

I have GT for my amp already but truth to be told i would have bought a different brand if i had known better. Its great they are reproducing the old style tubes but i dont think the average joe needs to get assraped by their prices. I might just order capacitors for my amp after i try changing the other stuff out . I am planing on selling it and want it to be working great when i sell it. Dammit i hate having a contious

Thanks
Keith

PS parts should be arriving soon

[baddog]

ENZO
I changed the zener diodes and it didn't take care of the problem but it did even out the rail voltage somewhat. Both are 16.? volts. I guess im just trying to figure out why when im using the foot switch i can get a dirty signal bleading into the channel im using. Is there naything else i can check?

thanks
keith

Would changing the 4558 ic chips with say new JRC 4558D's change the sound of the amp or could one of them be causing a problem.

[Enzo]

If you have a bad 4558, chenge it, but the brand of 4558 you use doesn't matter. And I wouldn't hesitate to use a 4560 or 4580 if 4558s were not handy.

You needed to fix the coltages even if it wasn't part of the problem.

Let's try it this way, which input jacks are you using? If you plug into the Automix, then both channels are live. Plug into either the Normal or the Effects inputs and ONLY that channel is live. DO the individual channels sound OK by themselves, leaving the other channel down? Is the amp OK without the footswitch?

I am trying to follow if you are plugging into one channel and having the other channel still live and adding unwanted sound. Or are you in the automix jack and one of the channels is OK, but the other distorting? Or does one channel just sound bad period?

Look at your schematic. The automix jack simply feeds BOTH circuit inputs. Plugging directly into a channel opens the link to the other channel. If the jacks are working right anyway.

The two channel mix into one at U5A. U17 is the output for the effects channel. Remove that IC and it should eliminate that channel from the mix. U18 is the normal channel output, and pulling it should remove the normal channel from the mix. Both channels were sent to the revern, and the reverb return also mixes in here from U16. Pull it and the reverb disappears.

The footswitch works by turning off any of those chips to kill their function. Also U13 for the phaser.

Let's make it work without the footswitch first. This is really not a difficult amp to troubleshoot sitting in front of me, so once I am clear what your problem is, I know we can fix it.

[baddog]

ENZO

I had a extra 4558 and tryed it in the amp but it didn't seem to change the sound at all. Im not sure what affect the 4558 has on the sound of the amp if any. I know they are all the hype in the vintage tube screamer pedals.

The rail voltage is now -16.25 & +16.90 at the zener diodes i replaced

Her is whats happening without the foot switch and my guitar plugged into the normal channel with a clean signal . If i turn the volume off on my guitar and turn the pre gain and post gain to 12 on the channel im using you get that amplified noise that tells you if i turn my guitar volume up my amp is going to be very loud. Now if i turn the pre and post gain to zero on the channel that im plugged into and turn the post and pre gain on the effects channel up to 12 i get that same amplified noise without being plugged into that channel and if i engage the fazer it affect that noise also. I think if im plugged into the normal channel i shouldn't get any noise from the channel im not using . Am i wright ?
Im not getting a guitar signal through the effects channel just the amplified noise.

I think the distortion could sound better ( kind of grainy & thin) but everything i read about this amp says the distortion sucks but the clean sounds good in my opinion very Lynyrd Skynyrd when overdriven.

Now if i plug into the automix channel and have the footswitch pluged in ,I can get a faint distortion signal in the channel that im using from the channel that im not using if i set the pre gain on that channel to anything above 8 and the post gain to 0 . The distortion saignal doesnt get louder if i turn the post gain to 12 it still stays a faint signal. Both channels do this and i can even do it in the combined channel mode . The footswitch is a peavey and it does say Automix on it but i dont think it is the original one for this head. It has a channel switch, combine switch and a reverb switch but no fazer switch option . Im not sure if could be part of the problem but i thought i should let you know.

thanks
keith

[Enzo]

Phasor or not, if the other switches select one, the other, or both channels, it is working.

When you plug into automix, the FS selects the channel(s) you play through by silencing one or the other or neither. Without a FS, both channels are live, so you can turn either channel up to max and listen to its noise at any time. The guitar will of course only come through the one you plug into, or both with the automix jack. The circuit noise through the effects channel goes through the phasir, so I don't doubt the noise sounds phased. Plugging into one channel does not mute the other.

Aside fromthe noise at 12, do both channels work if plugged into? And in automix, can you play through either set of controls and even blend them together? THEN with the footswitch can you kill either channel. Try this. Set the effects on 12 so it is noisy. Plug the guitar into the automix but turn the guitar volume down, all we want to hear is channel noise. Now, by flipping the channel select back and forth, does it switch the noise on and off? You can also turn the efects channel down and the normal channel up and see if it is controllable by FS.

Whuere would you normally set the post controls for playing this amp?

[baddog]

The switching is working fine . I can mix the two channels together and it does switch between them fine. Apearantly that amplified noise is normal when im not using the foot switch because Peavey confermed that today.

The only problem i have then is if im useing the foot switch and playing clean on the one channel but have the other channel set to full distortion i can get that faint distortion siganal throughy my clean channel . Peavey also said that the buzzing from the filter capacitors could be normal because of the hi voltage running through them , what do you think ?

thanks
Keith

[Enzo]

I'd agree with them on the preamp, but I'd expect to be able to clean up any hum from filter caps.

[baddog]

Enzo


Im not to concerned about the hum just the distortion signal that is bleeding through. Im not sure the filter capacitors should be buzzing either. I dont think they are the original capacitors . they are Sprague Atom Capacitors.


keith