Anyone heard of Hudson Electronics?

[armstrom]

I've been asked to see if I can repair an amp for someone. It's a Hudson Electronics "All Solid State Amplifier Model 592". I can't seem to find any information online about this brand of amplifier.

I'm hoping the problem is just in the power supply wiring so a schematic is probably not necessary... But I am curious if anyone knows anything about these amps. Here's what I have been able to observe so far:
-Has three numbered inputs (presumably different gain levels?)
-Controls: Tone, Volume, Reverb, Intensity, Speed
-Reverb tank is mounted to the chassis in the top of the cabinet
-Has an ~8" 10W 8Ohm speaker
-Has two un-labeled 1/4" jacks on the front panel, presumably some sort of preamp output/input like an effects loop(?)

If anyone is curious I can post some pictures.

If anyone knows anything about this amp please share
-Matt

[J M Fahey]

Hi Armstrom.  Please post some pictures, front panel but even better: chassis insides, as detailed as possible, showing the output and driver transistors. Also: what´s the proble m? Thanks.

[armstrom]

well, I've gotten the amp to power on (some broken wires in the mains circuit and a blown fuse) but now the amp has a bad hum. Uggh...

I'll try to post some pictures tonight.

[armstrom]

I finally got the chance to snap some pictures of the amp. To show maximum detail I kept the images fairly large (~350k each)

rather than list out everything, here's a directory containing the pictures. The file names should describe the contents fairly well. I was unable to show the power transistors directly as they're held down to the chassis with a little clip (you can see it in the pictures) The decades have nearly welded that screw in so I didn't want to strip it trying to remove the clip.

http://www.mr2-power.com/photos/hudson/

Now back to diagnosing the annoying hum I've discovered.

At first I was thinking the humming was just AC ripple making its way into the DC rails (bad power supply cap maybe?). But after attaching a mic. to the amp I noticed some odd behavior. When I hum into the mic I notice that in addition to the background hum (Which is quite loud) the amplified signal seems to "pulse". Even more odd is that the higher the signal level (humming louder into the mic) the more rapid the pulsing became. I had the reverb level turned down completely at the time.

I'm not really sure where to begin. I could trace out the circuit schematic to get a better understanding of what's going on.. but I'm not sure it's worth it. I'm doing this as a favor and I don't even know the last time this amp worked (might have been 20 years, who knows).

Any thoughts or suggestions?
-Matt

[tonyharker]

Definitely sounds to me like bad PS caps.  You'd get the pulsing effect with hum on the supply as the ripple beats with the input "hummmmm"

Tony :0)