[Hammarlund] SP-600 AVC line levels at spec'd inputs.

[James A. (Andy) Moorer]

The reason you don't find a spec is because there isn't any - and there 
can't be.

Every different receiver will have a somewhat different AVC voltage for the 
same input and output. This is what takes care of the natural variation of 
gain among the tubes. Replace the tubes and the AVC will be different by 
several volts. The best you can do is make sure it hits the rails. If there 
is no input, it should float up pretty close to -1 volts or so. If you 
saturate the input, the AVC voltage could dive down as far as -40. If there 
is something besides a 6BA6 as the first RF tube, then all bets are off - it 
will never hit the -40 volt rail.

The way to check the AVC is to set the RF gain to fairly high (7-8 maybe), 
set the AF gain to get some voltage that is reasonable (maybe 25 volts or so 
across 600 ohms) then click the gain of your RF signal generator from as low 
as it will go to as high as it will go. If the AVC is working, the output 
will stay within a few percent of the same RMS voltage and will not saturate 
or look ugly until the input gets above 100 mv or so. It may fall off a bit 
when you get down to the microvolt ranges.

James A. (Andy) Moorer
www.jamminpower.com

----- Original Message ----- 

> Hi Gang!!
>
>    Making my way through an SP-600/JX-28.  It's been PHUN!!  I've gotten 
> it working, but was looking for a piece of info not found in the service 
> manuals that I've been looking at.  Does anyone know (or can you/they 
> measure) the AVC line levels (voltage is what we're looking for) that 
> should be found when the receiver is running at spec.  The manuals call 
> for 2 to 3 uV in at the antenna and should produce .667 mW across a 600 
> ohm load (20 volts I believe is what the manual calls out). I'm asking 
> because I'm chasing several issues in this receiver and I had to wind 
> replacements for the AM detector and AVC line coupling transformers.
> If you don't have a JX-28 you won't know what the transformers are, but 
> you may have the rest of the info.  I'd like to be able to verify the AVC 
> line levels to be sure that I have enough drive for the AVC line.  I can 
> rewind the transformers if I need to.
>
> TIA!!!
>