Amps Amps in the shop.

[CapnDenny1]

I got this cute little Ampeg for $110 with free shipping from ebay. 350W into 4 ohms, nice small class D amp. the guy said the light went out, and then it quit working.

It tuned out to be a bad solder connection. It sort of worked but was low power out and heavily distorted, like a fuzz box. The Gain know also was jumpy. I opened it up and looked on the back side and found a component lead that didn't appear to be soldered very well? Not sure what it was, but I soldered it down and the power came back. The gain pot was scratchy and jumpy, but I put some Peavey Funk Out spray and it seemed to fix it. I prefer to change the pots, but shipping would be $8 on a $3 pot. The spray worked. Plus, I could not find the right replacement pot.

IMG_4800 by Dennis Kelley, on Flickr

IMG_4802 by Dennis Kelley, on Flickr

IMG_4793 by Dennis Kelley, on Flickr

Glad it was an easy one!

In the background you can see the other amp I am working on for a customer. A Marshall JCM 900, model 4100, 100W Dual Reverb.

 

[CapnDenny1]

Some better pics of the Marshall.

IMG_4778 by Dennis Kelley, on Flickr

IMG_4803 by Dennis Kelley, on Flickr

This thing is Looooooooong! as you can see it is a mix of pcb's, solid state, and tubes. My customer is selling it, but wants it checked out before he sells it. He said it has been sitting for 15 years. It crapped out in the middle of a show, and barely limped along to finish the show, and then just died.

One of the power tubes has a lightning storm inside. The others seem OK, but bot B+ protection fuses were blown. everything else seems OK, so far, so it would appear the fuses did their job and protected the amp. The customer is buying the tubes. Once he gets them I can check out the rest of the amp.

 

[dan5150]

I had read somewhere that the JCM 900 used clipping diodes (like in a distortion pedal) to give its gain channel. Is that true?

 

[CapnDenny1]

There is a diode circuit, that to me looks like it is more of a limiter circuit, not really a distortion creating device. That part of he circuit has a lot of opamps, so limiting the signal is probably a good idea.

It will be interesting to hear it once I get it working. I just had the JCM800 in to set bias, and really like that amp. So I will be able to compare them somewhat.