The Triumph is all tube, the Mace is solid state but for the power tubes.

The diodes in the Triumph are not clipping diodes, they are noise reduction diodes. They never did any clipping.  Totally different function from those in the Mace.

They are the colored wires coming from the transformer.   Fuses must be pulled from their holders and checked with a meter.

First, isolate the problem.

Since all 8 channels act the same, we can assume they are not the cause, at least not directly.

Plug a signal into the Line In jack on the back.  Music from a CD player, a guitar, whatever.   Does it still distort?  That tests the power amp by itself.

Now plug the signal into the EFX return or AUX return jack out front.  Distorted?

Now plug the test signal into one of the eight channel inputs and set the controls as you would normally.  Run a cord from Line Out on the rear panel to the input of some other amp and speaker.  How does the signal sound coming out over there?  Distorted or clear?

And no circuit works right without good power supply.   So are the ICs all getting a solid clean +/-15VDC?

No, impedance at the speaker will not make the tube heaters go dark.   And no, all your tubes did not burn out at the same time.

Does the power light come on, or is that dead too?

Fuses are inside and could be at issue.

If your Bugera is somewhat older, your power connector inside could be bad.  There is a 6-wire connector (or 5, I forget) from the power transformer to the circuit board.  The pins in it for tube heaters fail.  The factory bulletin tells us to solder the wires directly to the connector  male pins.


And the 4x12 speaker?  It is normal to get soun d from all 4 when plugged into the mono jack.  If you plug into the stereo jack, then only half will sound unless you connect two speaker cords.

I guess a good question is what do you want the techs to know.  The fact it is hybrid doesn;t really matter.  The amp is a solid state amp with a very basic tube power amp on the back.  That same preamp could just as easily have fed a solid state powr amp, and in fact PV made a few that way.  SO your techs should know how a PV SS preamp works, because it works like any other PV SS preamp.  HAving specific part number knowledge would be ther only if they had occasion to study the particular amp circuit.

I am not sure about that R100 reference,  in the VT version R100 is the feed resistor to the reverb drive.

The diode trick would be simple to try, and easy to remove if not pleased.  R42 is in the Normal channel.  The same position resistor in the effects channel is R11.

If the amp is so hot it is thermalling, then the chassis will be very hot to the touch.  They all get warm, but this will be noticably hot.


In my humble opinion, enlarging the heat sink in one of these to cure overheating, is like fixing a broken arm by taking pain killers.  The problem that needs to be addressed is why the amp is overheating, not how to dump the excess heat it should not be making.

If amp bias is adjstable, start there.  But a lot of these are not, so we need to explore the bias string in the amp, or if it is a chip amp, we need to make sure the zobel network is keeping oscillation at bay.  I find sometimes I need to shunt across one of the series diodes in some power amps when they run too hot.


I don't spot any thermal protection in the FM65r, other than possibly a thermal fuse in the power transformer.   And in my experience, most things that thermal off don;t cool down enough to come back on in only 10 seconds.

There is a pair of jacks - preamp out and power amp in.  Take a spare guitar cord and plug it from one to the other.  Does that help?  If so, the power amp jack needs service.


When this happens next, plug the guitar into the powr amp jack.  Does it still fall down and get back up, or is that fairly steady - yes, all the preamp controls will have no eeffect then.  You can also run a cord from preamp out to the input of some other amp.  So when your amp falls quiet, is that preamp signal coming out the other amp also falling off, or does it remain striong?

The power amp in is the one causing trouble.   Just plugging something in and out of that jack a few times might clear it.  Can;t hurt to find out.  And if you squirt some contact cleaner into that jack and immediately poke a plug in and out a few times, you might be able to clean the little contacts.  At worst, replace the power amp jack.

It will absolutely not harm the amp in any way to operate it with the cord connected to those two jacks.  SO you can just call it fixed if you are lazy.

There are pops and there are thumps.  Pops are often from the power switch arcing as it opens.  The fully charged amp circuits have enough energy stored to amplify that noise for the brief moment before they go silent.  That has nothing to do with filter cap discharge rates.

Thumps, or that whump sound you sometimes get turning off is the result of everything collapsing. As power rails collapse, the amp goes through a moment of instability.

Tube amps don;t pop at turn on, but they sure as hell pop at turn off.  Very common.

One thing about the thump on a solid state amp.  The highest voltage the amp has to deliver is one of its power rails.  At turn off, those start to drop.  Whatever transient noise that results can be no larger than the loudest peak the amp could make during normal operation.  If your speakers can handle the full power of the amp, then the turn off thump will be fine as well.  To your speaker, it might as well be just another kick drum hit.

Plug a cord from PREAMP OUT to POWER AMP IN.   ANy help?

Well, that IS hard to imagine.

In talking about an amp, it is always good to specify the model, so I can look up a schematic.   SHould be on the front panel in small letters.   8080 maybe?

The switchable op amp like the 5201 is convenient for a company like Marshall to use in their design.  But  can use switches and relays with common op amps instead, yes.  For Marshall, who uses 5201 ICs 10,000 at a time, they cost a LOT less than relays.  But for you making one or two amplifiers, the cost difference is not so important.

Relays or switches could possibly result in pops when they switch, but there are simple things to do to prevent that.

Crate is a part of Loud Technologies.  IN general, you can contact them for schematics.   And of course you can often get them through forums like this one.

They all have switchers now, but they all didn't go that way at once.  Remember, a 1990 TV set is 20 years old, and a 2000 set 10.


I recall 50+ years ago, I used to go down the street to the local TV repair shop, and after they closed in the evening, I went out back and looked in their trash for dead TV sets.  I hauled them home in a wagon, and tore them down for parts.  Tube circuits all.   I think if I looked in my parts drawers I might even still have a few of those old parts.  Little resistors with short bent up lead wires.  Their values won;t even be close.

Now I am in my 60s, and I still find it soothing to tear something down.  An older VCR is always a favorite.  LOTS of screws and stuff.  Or a cassette deck.  I think of it as therapy for a half hour. 

Useful parts?  These days I mostly save the power cord and the screws.  I have a pretty darn good collection of metric screws, almost entirely from stripping old consumer electronics.

TVs today wouldn;t be my first choice.  If you have lots of time anad a soldering iron, but no money, then you might find a few useful transistors or diodes.  But since I can buy most small transistors for a few cents, I don;t bother with them.   I will admit I needed some dumb little transistor in whatever that smaller than TO92 package is.  I had just tossed the main board from a cassette deck into the trash.  I fished the board out and sure enough, it had some small signal transistors exactly as I needed.

Cassette deacks and VCRs almost always have some lengths of shielded cable - like from the tape heads back to the board.  I find the occasional hunk of that useful for a project or repair.  Tiny stuff, not big clunky coax.

I have considerable experience in the arcade industry working on video monitors.  And MOST problems with those monitors is due to bad caps..  In fact several companies sell "cap kits" for the video monitors.  If you don;t know much but can solder, when your monitor has an issue, replace all these caps, and 95% of the time, your issue is solved.  For that reason, I would not be saving caps from monitors.  And a monitor is a TV set without a tuner.

I will admit, many time I have looked on a dead board for a little trim pot for some application.


TV set - speakers, pots, they can be useful.

A 7411 could be an old TTL logic IC, a triple three input nand.  Can't imagine it would belong there or function, only common quality being the 14 pin DIP.  So I suspect you are correct that it is a date code.

The uA739 doesn;t lend itself to any drop in replacements, but other than pinout, is there anything special about it?  Any reason we can;t take a modern op amp and mount it with a few jumper wires?  it has those compensation pins we never see anymore, but if we ignored those and wired in a 4558, would we be missing anything?  Or are they more than compensation pins, and they set gain or bandwidth or something?

The RC4739 doesn't have those compensation pins, does it?

other than as historical notes, I have not worked with either of them much, at least not in the last 20 years.

It would if the amp had one.  Like most PV combo amps, at least of that era, the speaker wires come up from the speaker and terminate with a white Molex connector that plugs onto a couple pins on the circuit board.