[Boatanchors] Hammarlund SSB filter needed
hurstjsj at verizon.net
Fri Jul 29 23:14:27 EDT 2011
Hi Glen. This happened to me on my HX-50 back in 1966 or so. I opened the
filter and found one bad crystal. I bypassed the crystal and it seemed to
work pretty well (for an HX-50).
From: boatanchors-bounces at puck.nether.net
[mailto:boatanchors-bounces at puck.nether.net] On Behalf Of Glen Zook
Sent: Friday, July 29, 2011 3:11 PM
To: Boatanchors at puck.nether.net
Subject: [Boatanchors] Hammarlund SSB filter needed
The filter in my Hammarlund HX-50A bit the dust! The same filter is used in
the HX-50 but I don't know if any other Hammarlund unit uses this same
>From the troubleshooting list in the manual I suspect that this filter has
always been a source of problems. The only "tip" in the manual for loss of
operation on SSB is this filter! The transmitter still works fine on CW.
I also suspect that the actual center frequency of these filters is no where
near as exact as, say, a Collins filter. The frequencies of the LSB and USB
BFO crystals starts with the kHz being printed on the filter but everything
to the right of the decimal point is added by hand.
The center frequency of this particular filter is 3036.2 kHz. Also, the 6
dB points are listed at a 3 kHz bandwith. However, there are trimmer
capacitors for each of the BFO crystals which are used to get them on the
"exact" frequency required and therefore it is possible to compensate for
slight variations in the filter.
Out of the circuit, when the proper frequency is input, there is a little,
but not much, on the output. When in the circuit there is absolutely
nothing showing when measured using an oscilloscope.
Before I resort to building a filter or trying to adapt a filter with a
different frequency (heterodyning up and down) I need to see if someone has
a working filter at a reasonable price or for trade. A last resort will be
to try and open the filter and get inside to try and fix it.
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