I got a set of clamp adapters for the analog multimeter I already had. Want to see if this works first before I get a digital one.

It has three ranges for DCV: 10, 250 and 500. Which range should I use?

I also got a can of that spray-cold stuff to check transistors if it comes to that. I've never used it but it might come in handy.

Now I just have to wait for the little woman to leave the house so I can CRANK it! 

Thanks DrGonz!

Waiting on a new multimeter. Will perform suggested test as soon as it arrives!

Just to make doubly extra-sure, I played it a good while at bedroom levels to see if it would fart out using it's on-board power amp. Nothing. Then I turned it up a little over "1" and after playing for about 10 more minutes it started to crap out intermittently (sounded fuzzy/buzzy/muddy with a drop in volume but not much). It came in and out for several minutes then after about 5 minutes, it stayed farted-out. I switched it off then back on and it was OK for about 20 seconds then it did it again. Switch it off and back on and it stayed farty.

Also, there was a low-level hum that was present at the same intensity no matter where the volume settings were placed. This happened before but I thought it was because of the disconnected reverb (which is now connected) but the hum was back along with the farty sound. Swiched off the amp and back on quickly and the hum was still there. Switched it off and left it off for a several seconds then turned it back on and the hum was gone.

Thanks Roly!

This one doesn't have effects send and return. Just the high/low inputs for each channel and the footswitch, speaker out (only one jack) and preamp out.

Yeah, the Randall/Peavey combination sounds fantastic! Might try running a couple of other amps through the Peavey and see how they sound. It is my only amp with tube power section that has power amp in option. Would never have tried it if I wasn't having problems with the Randall. From lemons come lemonade! 

My Peavey is a '79 with phaser. Randall is a '79 also.

Ok, back to business...

I think the Commander and Commander II are pretty much the same. I believe the numbers following the name indicate the number of speakers in the combo (I, II, IV or no number at all for the head). Not sure if there are any real meaningful differences in circuitry among them.

If I start with volume cranked up loud enough to where it cuts out (never cuts out a bedroom-ish levels), it only takes maybe 10 minutes or so before it poops out. It isn't highly predictable though but that has been mostly the pattern so far. Sometimes it cuts and stays cut. Sometimes it cuts for a second the comes back. But always seems to be preceded by a crackling/static sound just before it goes.

I do not have a digital multimeter. I do have one with a needle though it is pretty cheap. I got it to check the resistances of unmarked speakers. I'll get a digital one though. Be a few days before it arrives. Any recommendations on brand/model? Probably need one with little clamps on the end of the wires?

LOL- I saw that thread with the schematics! What a coincidence. I love this site. 

I did as you suggested and it did NOT fart out! Played it loud and long and it sounded GREAT running through the power section of my Peavey Classic VT 212 (two 6L6s in the power section). It sounds BETTER to me running through the Peavey (stronger). I was just using the Peavey as a cab for the Commander so speakers haven't changed. But wow. No crackling or even a hint of misbehaving. Sounds really punchy and clear/clean and heavy attack single notes or chords really power through. The two together sound better than either does separately. Anyway... I digress.

So, yeah. Doesn't seem to be any problems with the preamp on the Commander.  :dbtu:

Ok-

I cleaned all the jacks again, worked plug in and out, hooked the reverb back up and jammed on it at higher volumes and it still cut out. A slight crackling sound precedes a drop in volume with a tone that sounds farty and flubby (not unlike a blown speaker to my ears). It only lasted a second or so the few times it happened this morning.

No footswitch is attached. Happens if reverb is on or off.

Appears to only happen at louder volumes and on heavy attacks. Playing lightly or at lower volumes doesn't seem to make it happen.

Cab is detached. Head is on a table cab is on the floor so excessive vibration doesn't seem to be contributing.

Hey DrGonz-

That's actually the footswitch jack but I plugged into the preamp out (next to speaker out) with 8 ohm load cab plugged into the speaker out jack and the speakers did not cut out.

Owner's manual says they can take an 8 ohm load for 75 watts or 4 ohm (min) load for 121 watts.

Thanks.

After more poking, seems like this static is associated with the reverb.

The leads are disconnected and one makes a static noise when jostled. But also when the board is or case is tapped without necessarily moving the lead.

No noise when reverb dial is all the way off.

Ok- Had just tried Enzo test again and there is clearly a static-y sound.

No iPod or guitar plugged in- speakers in but no input. Volume up and if I give the casing a whack, I can hear it. Probably didn't hear it before because I was playing my iPod through it at the time.

If I tap the PCB board it happens. Really, if I tap it anywhere, I hear a crackling sound coming through the speakers. Not really loud but it is there.

Welp, just traded this to my guitar tech for a Vox wah, AnalogMan DS-1 and a setup on one of my Telecasters. He really seems to like it. He plays a lot of country sounding stuff with twang and it really delivers that. He's going to keep it in his shop for testing guitars.

Bye, Bye little buddy... I know you will be well-loved.

Hey DrGonz! Thanks for the ideas...

Ok-

1. Performed said Enzo test while amp was on and no pops or crackles when tested.

2. Poked and prodded all accessible joins and connections with kabob skewer. Again, nothing.

3. Remembered that the issue only seemed to occur at higher volumes (above bedroom levels- which is anything above 1.5 lol). Ran it for about 20 minutes at higher volume connected to iPod loaded with favorite tunes.

4. Went back and poked and prodded again. Still nothing.

5. Noticed excessive amounts of contact cleaner solution on wires from when I hosed the pots about a week ago. Used Q-tips to swab off best I could. This would correspond with the cutting out sound (never happened before this). However, it also never happened while volumes were relatively low which is the way I mostly played it until recently (when the cutting out appeared).

6. Just went back a poked and prodded some more... nothing.

7. Observed dog does NOT like "What I Like About You" by the Romantics. He ran around trying to find a place to hide from the sound. Skipped ahead to "Roadhouse Blues" and he is fine now.

8. Cranked volume up to 8 which I could only handle for a few minutes and still nothing abnormal sounding. Poked and prodded too. Whacked it too.

9. Took some pics while I had it open.

10. Disconnected iPod and plugged in guitar and played fairly aggressively at higher than bedroom levels and nothing unusual.

11. Noticed a low-level hum (not buzz) that I had heard before but not always. Switched off the amp, turned it back on and the hum was gone.

Nothing looks loose. The low-level hum is now a concern. At least one of the big grey transistors (?) looks like there is some reddish-brown corrosion around the edges of one end. Doesn't look like anything has been replaced ever on the board but I wouldn't know for sure.

So that's where I am now.

Hey- just got this head about a month ago and has sounded great up until yesterday and today- a few times the volume dropped and made a fuzzy/farty sound but came back to normal within a few seconds. Sometimes it did this but did not return to normal and I switched it off and back on and it was fine. Sometimes it sounds a little crackly or static-y too often just before it drops in volume. 

Checked all connections to the amp and effects, guitar, etc and I'm pretty sure it is the amp.

Any ideas what to check first? I'm no certified amp tech but I can open it up and clean, solder and probably replace something if necessary.

Thanks.

Well, picked up a momentary SPST switch at the electronics store for $3 and that fixed it. So it was definitely the switch.  :dbtu:

For $3 it was worth a try for a possible fix and a definite for at least ruling the switch out as the problem.

Thanks for the help guys! 

Hey- no I haven't verified it is the switch- I just made the assumption it was the switch.

I think I need to try a momentary switch then?