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Knight KS-55 Schematic?

Nac458

Nac458

Member
Hey all,

I'm embarking on a new restoration project.
A Knight KA-55 40 Watt amplifier with the matching tuner.

I was wondering if anybody had a copy of the schematic. There are a few caps and resistors I'm unable to read the value off of.

Any help is most appreciated.

Thanks,
Nicholas
 
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Hi, recently re-capped a friends Knight KA-55 he bought at an estate sale that also included the complete assembly manual in great condition! See schematic, parts list, block diagram, performance curves, specifications and page for adjusting the hum balance pots.
 

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I can not thank you enough for posting the schematic for this amp. My amp tech was at his wits end trying to figure out some issues he is having repairing this amp. Now he knows what is wrong and can finish the amp up.
 
I have one of these and have replaced a few capacitors in it. What I did find is that most of the coupling capacitors in my KA-55 were Mylar and still in specification. You also may know that there were two different versions of this amplifier, and used different tubes (and different PC board). It is a very nice amplifier when operating properly, just like most Allied Radio Knight-Kit amplifiers.
 
MD_Spencer said:
I can not thank you enough for posting the schematic for this amp. My amp tech was at his wits end trying to figure out some issues he is having repairing this amp. Now he knows what is wrong and can finish the amp up.
Click to expand...

Hi, glad to be a help. I repair/restore vintage HIFI and amateur radio equipment and I know how frustrating it can be when no info can be found.
 
Maybe you can help with a nasty hum that I am getting in the phono MM input on the amp. All the other inputs have some hum (crapy wiring in my house) but the phono is LOUD. I have hooked up the TT through a preamp to the AUX and it sounds fine. The guy that restored the amp is at a loss for why that channel is humming so loudly. I have done all the usual trouble shooting and nothing has helped. Any ideas if where to look next? Tubes maybe?
 
MD_Spencer said:
Maybe you can help with a nasty hum that I am getting in the phono MM input on the amp. All the other inputs have some hum (crapy wiring in my house) but the phono is LOUD. I have hooked up the TT through a preamp to the AUX and it sounds fine. The guy that restored the amp is at a loss for why that channel is humming so loudly. I have done all the usual trouble shooting and nothing has helped. Any ideas if where to look next? Tubes maybe?
Click to expand...
Hi, not sure what you mean by "the usual troubleshooting". You mention, "the guy that restored the amp", what did that encompass? You did not mention if the hum is in one channel or both channels? Were the phono preamp tubes V1 and V2 (6EU7), tested not just for emission or gm but in particular for shorts or leakage from the filament to cathode? Have the signal coupling caps C1, C3, C4 and C7 (left channel), and C31, C32, C34 and C37 (Right channel) been replaced? Since these are kits, poor soldering connections are very common, have you re-soldered all components and wire connections to the CB for the phono preamp V1 & V2 tubes? Also look for any possible broken wires.
 
I had DJL do the refresh on the amp. All caps were replaced and the tubes were tested. He cleaned up the wiring and checked all the solder joints and re-did them as needed. The hum is in both channels. The hum is worst in the Phono channel but it present (and acceptable) in all the other channels as well. With the volume off there is a hum, but the phone is 60% louder than tape, aux, tuner with volume off. As I turn the volume up on any of the channels the hum goes up with the volume setting but is much worse (unusable) in the Phone channel. Wiring in my house is crap, 1950 house with 60's-70's renovations with florescent lighting and dimmers. I know, but I rent so there is not much I can do.

With his help I have tried the following.

1. Lifted the turntable ground(s) looking for ground loop.
2. lifted the amp plug and flipped the plug over . I know that trick from owning vintage tube guitar amps.
3. Tried a second turntable. Still loud hum.
4.Tried a CD player into Aux, still hum but at the acceptable levels.
5. Used a phone pre-amp that I have and put the turntable into the Aux channel. It now works fine with a low (but audible hum) which I find expectable.
 
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