Burnt resister help with 70's Ampeg ???

[G771.4.SALE]

I acquired a late 70's Ampeg B 115 bass amp, upon plugging it in I was only getting a buzz from both of the 2 channels. Opened it up and saw obvious signs of burnt resister(s). See pic.

So I replaced R221 (blue) since I had one and it was totally fried. I powered it up again and channel 1 now works, both hi and lo inputs no buzz, it's good. I get no sound from channel 2 just a constant low hum. I plan on replacing R214, R219 and maybe D210 because they look as some heat issues were present. I'm not really experienced with this kind of thing, however I'm not blind. Question : If I replace the above mentioned items would that fix channel 2 or can you see other things that are problems ??

Any info is much appreciated. Thank you in advance !!

 

[valvenator]

A think the bigger question is what caused the resistor burnout in the first place.
Maybe if you're lucky it's just one of the resistors went bad and took a few more with it,
but also more likely it could be somewhere further down in the circuit.
Sorry, wish I could of some help. Best of luck

 

[G771.4.SALE]

A think the bigger question is what caused the resistor burnout in the first place.
Maybe if you're lucky it's just one of the resistors went bad and took a few more with it,
but also more likely it could be somewhere further down in the circuit.
Sorry, wish I could of some help. Best of luck

I understand what your saying. Without knowing the history of the amp or having the tech expertise on the cause of such things or possessing more than a fundamental understanding of electrical cicuits for the moment all I can do is replace parts, research and ask for assistance. Thanks for taking a look and offering your thoughts.

 

[arts]

Unfortunately,this was one of the very few Ampeg designs that was plagued with problems,and is a very difficult machine to troubleshoot.

The preamp,which uses two types of IC's that have not been available for a very long time,and for which no direct substitutes are available,had a very nasty habit of bursting into ultrasonic oscillation whenever they felt like it.This often very quickly destroyed the output module in the process.

The power modules were also very much less than robust,despite using many weird and wonderful (and also long unavailable) high quality transistors that were more often seen in commercial and military equipment than musical instrument amps.And yet they still failed regularly.....

You may get lucky and repair this yourself,but what you really need to do is find a tech that TRULY understands the solid state designs of this era,and is very savvy with finding transistor substitutes.The cost may well be more than the amp is worth.

I have been servicing (and playing through) Ampegs for more than 30 years,and this is one model that I will no longer deal with.

Good luck!

Art