Kingston Amp

[birdSG]

Hey guys,

So a few months ago I bought a rough looking amp for $25. After doing some digging it turns out it is a 1960s Kingston Solid State Amp. I basically bought it as a fun project to clean up and give to my kid someday.Well intitially it didnt make a sound because the output transformer was dead. So I bought a new one and replaced it. After it started putting out sounds I kept updating it.  I replaced all of the pots, jacks, Capacitors, and gave it a 3 prong power cord. The only pieces I did not replace were the 5 transistors throughout the board. I bought replacements, but while they were "equivalents" in what they did, when I put them in there was no output. Turns out the pinout was wrong. After putting the originals back in the amp fired back up. All of the controls functions as they should, and even the included tremolo and reverb sound great. The only problem with each note you play there is a low pitched hum that happens behind your note. This occurs at any volume. Any ideas? Really the only other things to replace are those transistors and the speaker itself which is 60 years old by now.

Thanks!

[Enzo]

So disconnect your speaker, and connect the amp chassis to some other working speaker.  Do you still hear that undertone?  I am 70 years old, and have some undertones myself.

Transistors are remarkably flexible, and MANY types would work.  Equivalent means electrically.  But a Asian type like 2SC1815 versus American type like 2N3904 could be electrically similar, but Asian parts have different leg order than American types.  Experienced techs know this and know you can use one for the other as long as you turn the part sideways and bend the legs to go to the appropriate holes.

[J M Fahey]

Post the amp schematic.

Ok, ok, it´s older than Santa Claus, I get it 

Plan B : post some sharp well illuminated gut and board closeups (which in general means no cellphone pictures but any old crummy real camera you have lying around) so we have an idea of what you have.

Gaving only 5 transistors I guess it´s s real old job, with a driver transformer, and in that case you most certainly have some crossover distortion.

If so, you´ll have to get used to it, no practical way to solve that.