Thanks guys. All the caps I'm finding have much smaller packages. Am I searching for the wrong kind of cap? (aluminum electrolytic) or are they just made smaller these days? Do I have to rig up a new mount?

QuoteSo what if I plug a cable into the effects return on my good amp and use the other end to pick up the signal at points between the tone pots and the pre out. That should tell me where the buzz starts. Right?

Okay, That didn't work. I got some very loud (scary) humming, and was afraid to continue. I did notice that one of the big filter caps looks like it's been hot. Where is the best (cheapest) place to buy replacements.

It did occur to me that it might be normal for this amp, but it is pretty loud, and my RG80 is pretty quiet. Yes I do realize they are different amps. If I can't find anything wrong with it I may just learn to accept as it is.

Actually mine is not exactly like the schem that J.M. so generously provided. My pre out comes right off the master vol. through a 1k resistor.
The reverb control has no effect on the buzz. The only control that does is the master vol., though the buzz does pulsate with the tremolo.

Bummer, I was hoping I was almost done. Okay, so the tone controls don't affect the hum, and if I run a line from pre out on this amp to the effects return on my other amp I get buzzing in it too. So what if I plug a cable into the effects return on my good amp and use the other end to pick up the signal at points between the tone pots and the pre out. That should tell me where the buzz starts. Right?
I don't know where to get a scope, and don't know how to use one anyway, though I guess I could learn (if I knew where to get one)

Since there aren't that many components between the eq and the master vol, I thought I might use the shotgun approach and just replace them all. So as I'm tracing the circuit, and comparing it to the schem. I found that Q4 which should be an MPSA 13 is another TIS 58. Could this be the problem?

Thanks again JM! Now I guess I need to check voltages against those given on the schematic. The only control on the amp that has any effect on the buzz is the master volume, so I'm thinking that the problem should be in the area between the eq. and master vol.
I've never done this before, and I don't have an electronics education, but I have done some tinkering(built a chip amp, effect kit, cap job on tube amp, replace pots, etc.) Trouble shooting on a circuit board is new to me. So please don't get too frustrated with my ignorance. And thanks very much for what ever guidance you can give me.

Thanks JM. This one is like a twin. It's a 1976 model. Two non switching channels, tremolo on ch2. It has a good clean sound (except for the buzz) It will distort if I turn the channel vol. up, but it's not a good kind of distortion. (at least to my ears)
I'm hoping someone here has had this exact problem and knows exactly what to do. (I'm hoping to win the lottery too )

I just got a really good deal on a Randall rg120 Commander II, but it has a hum, or a buzz. It sounds like the buzz that some fluorescent lights make. It's volume follows the master volume control, and it pulses with the tremolo. The channel volumes don't affect the buzz. Also the eq controls act funny. When they are turned to 0 they turn their portion of the signal off. In other words, if they are all turned fully counter clockwise there is no sound. If I turn the bass control up I get volume, but very bassy. If I turn up the mid I get volume in the midrange. Same with the treble. with all eqs on (above 0) it sounds great, except for the buzz. Is the eq supposed to work like this, or is this maybe related to the buzz?
I don't have a schem. and don't know where to get one.
Anyone have an idea about how to fix the buzz?
Thanks

I will. Actually, I'll probably be asking for help. I haven't had time to even pull the chassis yet, but when I do I'll give it a good cleaning and see if that helps. There are a couple of big caps sticking down from the chassis. Can those cause hum on a SS amp like they can on a tube amp?
The date codes on the speakers show they were made in 76. Now I'm really impressed with the condition.

I just got this big bro. on craigslist for $20.!!!!! The young lady was moving and wanted it out ASAP. Her uncle had given it to her years ago when she thought she wanted to play guitar. She said it has been in storage for at least ten years. It is pretty good cosmeticaly, sounds great except for the hum. Turn on the reverb and tremolo and it makes a perfect "surf" guitar sound.

http://i858.photobucket.com/albums/ab141/dmartn149/randall120002.jpg?t=1301448019

TopTop, That's really cool! I figured you would have something for this contest.

The plug is a three prong.

I just ran up stairs and snaped those. When i take ebay shots I use a tripod, lots of lights, and the timer.

Here are some shots. As you can see it's pretty beat. I had to re-tension the footswitch jack and clean the pots. One of the pots is still a little funky, but good enough for home use. It sounds great. I had it about a year before I found out about the pull knob for more distortion. The wah on the floor is a Clide McCoy that I got on a local on-line (oxymoron?) police auction for $11.00

http://i858.photobucket.com/albums/ab141/dmartn149/th_DSC00080.jpg?t=1299114419

http://i858.photobucket.com/albums/ab141/dmartn149/th_DSC00082.jpg?t=1299114419

http://i858.photobucket.com/albums/ab141/dmartn149/th_DSC00081.jpg?t=1299114419