[Hammarlund] RE SP600-JX-17

[Joe Connor]

Jimmy:

Per what Richard said, I am wondering what kind of caps you have in this set. If memory serves me right (which it does not always do), a JX-17 can have either notoriously bad black beauties or usually reliable ceramic disks. Do you know which kind you have? As Richard also noted, the bathtub caps can be bad, too. Bad caps can certainly cause low gain.

Joe Connor
On Saturday, April 5, 2014 11:04 PM, Richard Knoppow <1oldlens1 at ix.netcom.com> wrote:
 

>----- 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 
>
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