[Premium-Rx] WTD - Racal RA6790/GM 40.455 filter for A3 second mixer board

[Nick England]

Thanks to a very helpful list member, my 6790 is Back in Business! He had
spare filters and I had an A9 board he needed, so now two receivers are
much happier.
Thanks to others for advice and parts offers. This is a great list full of
knowledgeable and helpful folks.
Cheers,
Nick England K4NYW
www.navy-radio.com

p.s. yes the input and output of that A3 crystal filter are fed through
baluns, so 0 ohms is normal.


On Wed, Jul 10, 2024 at 4:06 PM Nick England <navy.radio at gmail.com> wrote:

> I'm trying to resurrect an RA6790/GM that I got out of the bin of parts
> units at Fair Radio some years ago. I repaired the microprocessor board and
> replaced the LCDs. (and still need to replace a bad membrane switch pad).
> And find a 3kHz plug-in filter.
>
> Actually I think I have everything working except for no gain through the
> A3 board where there ought to be 60dB or so. I've got good input from the
> 1st mixer feeding the 40.455 MHz filter FL1 on the A3 board. But almost no
> output from that filter - and the filter output pin measures 0 ohms to the
> case. The rest of the A3 board looks OK with adequate 40MHz LO and
> 40.455MHz input from the first mixer.
>
> The receiver barely "works" because there must be enough leakage to feed
> the 2nd mixer stage - I can see 455 kHz output and hear signals but only if
> they are -30dBm or so.
> I guess I could use it for my nearby AM broadcast station but that's about
> all...
>
> So, does anyone have a parts unit with a filter or an extra A3 board?
> I have cash or an A6A1 remote control interface board to trade.
>
> Or can someone say - don't worry about 0 ohms because on some versions of
> filter there's a coil across the output pin
>
> I suppose I can torch open this soldered metal case filter and see what I
> find. or haywire in a filter of some sort...
>
> The parts list just says 08576. This Filter case says
> 08576
> 00136-164B75
> Fc40.455Mhz Bw1db-20Khz
>
> The working unit I have says the same except 00136-164Q75
>
> Thanks in advance,
> Nick England K4NYW
> www.navy-radio.com
>