[GreenKeys] ST-6 Up & Limping On The Work Bench

[Pete Lancashire]

Ralph got there before me. anything > 15 yrs old, first check all
electrolytic/tantalum caps, then carbon comp/film resistors, then caps in
timing/filtering. If transistors/analog parts are in sockets, maybe move
around.

The comment on 709's being unique is an understatement. With that make sure
you mark each one, so you can put back the original part after you have
done swapping or replacing with new ones. You may find out that the passive
compensation values have to be tweeked.

Quoting a 709 data sheet  " ... Provisions are incorporated within the
circuit whereby external components may be used to compensate the amplifier
for stable operation under various feedback or load conditions. .. "

-pete



On Mon, Mar 14, 2016 at 8:08 PM, Ralph Mowery <rmowery28146 at earthlink.net>
wrote:

> It may be that some of the resistor values have changed or maybe the wrong
> values were installed when it was built.
>
>
> ----- Original Message ----- From: "tony.podrasky" <
> tony.podrasky at gmail.com>
> To: "Green Keys" <greenkeys at mailman.qth.net>
> Sent: Monday, March 14, 2016 8:36 PM
> Subject: [GreenKeys] ST-6 Up & Limping On The Work Bench
>
>
> GE OMs;
>>
>> I finally got motivated enough to go into the garage
>> cabinet and get out some of the stuff to tune-up the ST-6.
>>
>> Used rubbing alcohol on the loop current rheostat and she's
>> working nice and smoothly.
>>
>> Tried to do the NULL adjustment on the 2 discriminators,
>> but couldn't do it. I swapped the LM709 Op-Amps, and one
>> of the boards could balance, but the other still can not.
>> I swapped a couple more ICs and didn't have much success.
>> Went on "everyone's favorite auction site", and although
>> some of these "1970's ICs" are selling for $7.00, I
>> found a NOS bag of 15 for $12.00.
>>
>> They should be here some time next week.
>>
>> More updates as they happen...
>>
>> UE,
>> K2EAA- TONY
>> NNNN
>> ZCZC
>>
>>
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