[Hallicrafters] SX-100 troubleshooting

[rbethman]

The P/N for the power transformer in the sx-88 is not the same as the 
sx-100(xx), nor the same as the one in the SX-99.

Bob - N0DGN

On 1/8/2013 11:44 AM, hallicrafterssr2000 at k9axn.com wrote:
> Good morning Roy et Joe:
>
> Thanks for the reminder about the internal capacitor in the 
> transformer. Did you record the value of the capacitor in your notes?  
> Don't have a good one to test but would like the value for the 
> record.  BTW, if one has failed, the other sideband should oscillate.
>
> Roy, is the transformer in the 88 the same PN as the 100 and were 
> there any paper caps under the sub-chassis in the SX-88?  I believe 
> the SX-88 was built four or five years before the SX-100. The SX-100 
> series did not use any paper under the sub-chassis.
>
> Kindest regards Jim K9AXN
>
> -----Original Message----- From: Roy Morgan
> Sent: Tuesday, January 08, 2013 10:05 AM
> To: Joe Balestrini
> Cc: Hallicrafters at mailman.qth.net
> Subject: Re: [Hallicrafters] SX-100 troubleshooting
>
>
> On Jan 8, 2013, at 10:00 AM, Joe Balestrini wrote:
>
>> Hi All,  I'm trying to get some life out of my SX-100.
>
> A noble endeavor.  Keep at it!
>
>>  I found that the voltage on the plates of V12 (12AT7 - 2nd 
>> converter/oscillator in the sub-chassis) is at 25v rather than 90v.
>
> (I did not look up the details of the circuit):
> Two possible causes come to  mind:
> - plate dropping/isolation resistor seriously drifted high in value
> - trouble in the grid circuit causing excessive plate current.
>
> Some more probing with an ohmmeter may be in order.
>
> I have taken the 2nd converter sub-chassis out of an SX-88 in the
> past.  Its not all that difficult but you must:
> - note and label each wire  you remove (there are some 6 or 8 or so)
> - be careful in threading the wires out through the chassis to get
> them free
> - best to replace most or all components under there to avoid future
> removal
> - remember to put the bottom plate back on the sub-chassis before
> remounting it and soldering all the leads back in place (you may not
> need to ask me how I know this.)
>
>> ... I did find that adjusting the primary or secondary of T9 seems  
>> to have no effect on tuning.  I dread the thought of tearing into  
>> that sub-chassis.
>
> Patience may be needed.
>
> These radios have a known malady in the IF cans:  There is a mica
> capacitor across the primary and/or secondary of the thing that gets
> very leaky or shorted.    It is moulded into the base of the IF can
> plastic structure.   The cure is to remove the IF can from the radio,
> remove the mica cap and replace it/them with new dipped mica caps on
> the transformer terminals.   A dremel tool may be helpful in getting
> it out of there.  Think like a dentist.
>
> Get good caps from justradios.com a Canadian couple who have good
> stuff at good prices and send things fast.
>
> I will send to Joe my notes file on the radio ... collected
> discoveries and tips posted to the mailing list over time.  It likely
> has the IF can Mica Cap problem detailed.  Trouble is the values of
> the caps are not on the schematic if I remember right.
>
> To locate plate and screen resistors that have drifted high:
> - measure operating B+ voltages at the tube (with a high impedance
> meter)
> - power off, put one lead of the ohm meter on the B+ line, and measure
> resistances at the screens and plates.
> - take notes to help identify values of new resistors needed and which
> ones to change out  (Bits of blue painters tape and a fine sharpie pen
> help here.d)
>
> Roy
>
> Roy Morgan
> k1lky at earthlink.net
> K1LKY Since 1958 - Keep 'em Glowing!
>
>
>
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