Peavey Mace doesn't power up anymore

[noilifcram]

Hi everyone, first post here so I'd like to salute all of you!

I've had this Peavey Mace head (used to be combo) for 15 years but didn't play it in the last 6. Last weekend I took it out and played it for about 15 minutes. I found some of the pots very scratchy so I decided to clean them up with Deoxit.

I took the amp out of its case thinking I could feed the contact cleaner from some opening on the back of the pots. In order to do so I carefully removed the tubes just in case.

Once that was done I took the amp back in its case, plugged it to the wall outled, plugged the cab in and my guitar. Powered it up and took it off standby after 30 seconds or so. After a minute of figuring out why it didn't put out any sound I realized I forgot to put the tubes back in...

So I turn it off, replace the tubes in and turn it back on. There was no sound coming out. I noticed that only the mid pair of tubes got warm, the outermost four stayed cold. Then I realized the red lamp at the front wouldn't turn on and the two middle tubes were getting cold. Something was blown for sure.

I tried to turn the amp back on using only four tubes and swapped them to test each pair to no avail.

Took the amp to Steeve's in Montreal for repairs and got it back today. The work order says the amp is too old to bother with... I disagree.

I'm sure there's something to be done with this beast. I checked inside and saw two tube sockets that had their resistor burnt out. I know these were ok when I first opened it up. Could this be it? I also checked the fuse; it is fine. This spurs a few questions I'd love to get some input on:

- Can the amp be saved or did I toast it when turned it on w/o tubes?
- Assuming the amp can be saved can the two resistors simply be the cause?
- Can an old/corroded tube have blown up the resistors?

I'll post pictures later when I'm home.

Thanks all!

[52 Bill]

Welcome to the board.

Of course the amp is worth repairing if you want to keep it.

The resistors could be burned out by the power tubes. One or more could be shorted, and they may have also caused a fuse to blow.

Is it possible that when you reinstalled the power tubes, one of the center locator pins was broken off allowing the tube to be inserted into the socket incorrectly?

I'd suggest first checking the fuses. Then pull out the power tubes and see if the amp will power up without them.

[noilifcram]

The fuse is fine. I tried to power it up w/o any tubes: the light does not turn on and I cannot hear any buzzing sounds of any kind.

How can I tell if the power transformers are out?

[52 Bill]

Are there any internal fuses on the pc board?

Are there any loose push on connectors? Peavey uses push on connectors for the transformers and for board interconnects.

Do you have a basic multimeter? You'll need one to test the transformer.

[noilifcram]

I get a 120V reading on the fuse so I know it is not out. Other than that I don't know exactly where to poke so I guess it is trial and error here.

Here are some pics. As you can see the resistors are now completely off. They probable broke down during transportation to the repair shop. I couldn't get a voltage reading (AC nor DC) between the poles where the resistors (4700 ohm?) once were.

The amp


Burnt resistors


Good resistor


Left side of amp


Right side


I'll poke around and report my findings, thanks fior your help!

[Enzo]

What do you mean you get 120v on the fuse it is OK? 120v to ground on both ends? That might be OK. 120v from one end to the other? That means it is blown open. Remember, a good fuse is a piece of wire. A piece of wire would not have 120v from end to end.

Find a different shop to take it to. You don;t need some arrogant tech to tell you your amp is too old to bother with. he probably didn't want to embarass himself that he didn't know what he was looking at. You think he would tell you your 1959 Fender amp was too old? or an old AMpeg? Maybe an original Marshall is too old.

Clearly you have had a power tube failure. Had nothing to do with firing up the amp without tubes. The resistors are not the cause, they are the result. And did you answer the earlier question posed to you, is the center post snapped off of any of the power tubes?

[noilifcram]

Indeed after a few minutes of poking around I realized something was wrong with the fuse... turns out it's blown indeed. (insert " I'm with stupid" sign here)

I took it to a local shop in Verdun and the owner told me his tech enjoyed working on older amps such as this one.

The tubes' posts are all find and I've always been careful when inserting them. Do you think the tube failure might have damaged the power transformer?

On a side note while at the shop the owner showed me a 1980's Hiwatt they're restoring.. What a monster!


Thanks for the input! I'll let you guys know how it turns out.

[bluesfreak]

Hi,
i do not like the 22µF/400V Cap in pic 4, to me it looks like the cap has vomit his guts already onto the PCB (hard to see but at least it seems to me) so ensure that the Tech checks the electrolytics as well....

just my 2c
bluesfreak

[noilifcram]

Hi,
i do not like the 22µF/400V Cap in pic 4, to me it looks like the cap has vomit his guts already onto the PCB (hard to see but at least it seems to me) so ensure that the Tech checks the electrolytics as well....

just my 2c
bluesfreak

The white stuff underneath it is glue. This cap was replaced in a prior repair in 1995 so the glue is a different color that that used on the original caps. It's a 450V btw.

That reminds me; in case the amp is repairable how can one tell if a cap needs to be replaced? Last I looked there weren't any leaks but that might not be enough.

[bluesfreak]

For the Illinois Caps I usually replace them if >20yrs, LRCs might hold up longer depending on the environment. Depending on the amount of repair required it would be advisable to get a cap job on this amp together with the repair already required....

just my 2c
bluesfreak

[noilifcram]

I'll follow your advice then. Should all caps be replaced or only the larger ones?

[bluesfreak]

I would swap at least the HV Caps (mainly the large one's) and replace them with JJ or F+T