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Heathkit SA-3 questions

Ziradog

Ziradog

AK Subscriber
Subscriber
Picked this up in a trade from Tubeampking recently, and just started playing with it. It is a neat little SE amp with two EL84 outputs & two 7199's. I found a schematic online, but I have had no luck finding an assembly manual (I want to check the wiring runs). Does any one have such a thing or know where I might find one?

I also need to get a couple shields to replace missing ones - see pictures. I have no idea how these are spec'ed - what do I look for?

The amp has 2 minor problems - a low-level hum that does not change regardless of input or volume level. And the two channels are badly mis-matched (one is much louder than the other). The only trouble shooting I have done is to swap the tubes - first the outputs, then the 7199's. Neither made any difference. Once I figure out how to take the guts out of the chassis, I will start chasing voltages & such but any input is appreciated, including where to source a new volume pot if needed.

I'll probably also rewire the ceramic phono inputs to use as regular line-level inputs (replace the caps with resistors?) once I get the rest done.
 

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Got it this time...Those shields would be the type with the springs in them...They fit over the part that is mounted on the socket, and lock on with a quarter turn...
 
All resistors are suspect - wouldn't surprise me to find some that have gone WAY up in value. I have the Heath spec sheet with schematic and probably the Sams folder too - but no assembly instructions. And I have a few dozen of those shields...
 
Once I get the thing physically apart, I will check voltages & resistors. I will probably replace the tone control caps as well. But I think wiring is going to have to be addressed too.
 
Email me for the Heath spec sheet. Sams folder will take a little longer. tbavis(at)rochester(dot)rr(dot)com
 
Thanks Tom, the docs you sent are helpful. Even if I don't get the assembly manual some where, I should be able to get started.
 
Well there is about 50K difference between the 2 halves of the volume pot, over the center 95% of their range (values at either very end are really weird). I cleaned the control really well, made no difference. Should I just add a resistor to one side (or change the value of the existing fixed resistor) by 47K or 56K?
 
Why don't you just put a new pot in? Some old parts are physically damaged and no amount of cleaning can repair them.
 
Good question. 1. I want to make sure the pot is the main issue, & 2. I will have to tear the whole thing down to get the pot out to take the dimensions & see if I can find a standard replacement. Or to put it another way: sloth.
 
I don't know how far you have gotten on this project but I have finished the one I was working. You are welcome to any of the data I have and I took a ton of pictures taken before and after the restore. This amp sounds wonderful. I replaced all the caps and all the resistors. The 7199's were very microphonic in mine so I replaced them and the EL84's were pretty weak so I put a new set of Mullard NOS in it and it really cleaned up the sound a bunch. Now this amp is a pleasure to listen to. Btw. all the resistors except 2 were way out of spec
 
Honestly haven't worked on this for a while. I will PM you about copies of what you have for info. Thanks again.
 
Ziradog said:
Honestly haven't worked on this for a while. I will PM you about copies of what you have for info. Thanks again.
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I received your message and I will put all the stuff I have together and email it to. I really like this little amp. It sounds great for what I'm using it for. Now I'm restoring a ST-70 Dynaco. All cloth covered wire on the transformers. Fun projects.
 
Had a Heathkit SA-2, still miss that amp... I highly recommend TAD EL84-STR tube for it. It makes a lot of difference.
 
PR Audio said:
Had a Heathkit SA-2, still miss that amp... I highly recommend TAD EL84-STR tube for it. It makes a lot of difference.
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Thanks for the info. I have a set on order and can't wait until they get here. /in the mean time I'm using a NOS set of Mullards that sound pretty amazing.
 
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