[Hammarlund] RE SP600-JX-17

[Richard Knoppow]

----- Original Message ----- 
From: "James Green" <honobia061960 at hughes.net>
To: <hammarlund at mailman.qth.net>
Sent: Saturday, April 05, 2014 10:42 AM
Subject: [Hammarlund] RE SP600-JX-17


> First thanks to all who replied.
> The AM station I listen to was a religion station  and it
> was outside of 7.300 I guess 3 Kc.
> This morning I went back to the shop and using the
> T.O.31R2-4-18-2 handbook service instructions, on page 65
> table 6-6. I preceded thru the first 6 steps and all went
> well.
> I am using a Logimetrics 925-S125  signal generator.
> I have built the 2 cables the book suggest and am using
> the one to connect to the antenna feed point.
> Question-the  RF out on the generator shows max. at 3 V
> RMS (+23 dBm at 50 ohms,  Is this enough?
> I can hear SSB QSO,s on 40 meters but have little or no RF
> gain control.
> Jimmy

     Right now I would be more concerned with whether the
radio is working correctly than how to align it. Alignment
is simple when the set is working properly. The lack of gain
adjustment suggests the bias supply is not working. First
thing is to replace the 6AL5 bias rectifier V-20. There are
three 6AL5 tubes in the set; V-20, V-15, the noise limiter
and meter rectifier, and V-14, the detector and AVC
rectifier.  Try swapping V-15 and V-20. If the RF gain
starts to work you know the tube is bad. If you have access
to a tube tester its worth testing all the tubes to catch
any bad ones.
   If changing the tube does not fix the problem you 
probably have a bad by-pass capacitor in the AVC line that 
is pulling it down. Note that some of these receivers still 
have their original paper caps in them. All will be bad even 
though some receivers were made with other caps than the 
notorious Sprague Black Beauty caps (Black Beauty was a 
Sprague trade-mark). There are about 42  paper caps in the 
receiver than need to be changed but there are also a lot of 
bathtub type electrolytics that can and do go bad. Some 
people open the cans and re-stuff them but that is a lot of 
unnecessary work and very messy. Modern electrolytics can be 
mounted on terminal strips and used.
    Another note: The DC voltages in the tube socket charts 
are measured with a 1000 ohm/volt voltmeter.         If you 
use a more modern 20,000 ohm/volt meter or a vtvm some of 
the voltages will read high but are OK. The exception are 
the grid voltages which are measured with a 10 or 11 megohm 
VTVM.  If the AVC/bias line is OK the grid voltages at the 
tubes will be about 51 volts with the RF gain control at 
minimum gain.  It should vary down to about 1 (one) volt at 
maximum gain with the antenna terminals shorted. You can 
also measure this at the AVC terminals at the back of the 
chassis.


--
Richard Knoppow
Los Angeles
WB6KBL
dickburk at ix.netcom.com