[AMRadio] HQ 180 problem

[Larry Szendrei]

On 1/20/13 6:16 PM, Robert Sauvan wrote:
> Hi all,
> I just acquired a Hammarlund HQ180 C from a buddy of mine. He indicated
> that he didnt know whether it worked or not and had never plugged it in.
> Well it doesnt work of course. I am hoping for a little help to guide me as
> to where I might start to look for a fix by explaining the symptoms.

Hi Bob,

You might start by measuring the voltages at the tube sockets with a 
high-impedance voltmeter and compare to the values given in the manual, 
under the exact conditions specified. If you find anything awry, it will 
lead you to the problem.

But, hearing your symptoms, it might save time to just measure the 
voltages at the control-grid pins of all IF amplifier tubes. The IF 
transformers in the HQ-180 are of the dreaded "K-tran" type, which often 
fail at the silver-mica capacitors integral with the plastic base, 
leaking high-voltage from the primary to the secondary. I have repaired 
an HQ-180 where this was the problem, and the radio had the same 
symptoms you described. If you find a positive voltage on any control 
grid, the associated IF transformer is highly suspect.

Another worthwhile test, to make sure the local oscillators are 
functioning, is to use a 2nd communications receiver to listen for the 
local oscillators in the HQ-180, using a short antenna placed near the 
oscillator circuits as a "sniffer."

Also, if you have a signal tracer and RF signal generator you can use 
signal tracing techniques to isolate the faulty stage.

You will no doubt get other helpful responses from the group, as this is 
just a start.

73/GL,
-Larry/NE1S