开云体育Ian,
My experience of repairing a 931, with failed PA’s was to try a pair of PA devices from a working PRC-320 back panel. ?They just about produced 20W, as the drive was slightly down from the 2N3866’s compared to that used in the 320, and the bias
current was slightly higher with the 931 bias circuit.
I had the same experience as you with AM, that it produced full carrier, and in my case downward mod, which was clean, and sounded good on air, and via a remote SDR.?
As it was a repair for a friend, and they were happy with it, that was then end of the experiment, and it soldiered on for many years after that until sold.
I don’t know how closely the respective PA’s were tested and matched by Racal and Plessey, but I changed them as a pair, so was probably lucky!
73
Al
G8LIT
From: [email protected] <[email protected]> on behalf of gm0uhc <Ian@...>
Sent: Sunday, March 23, 2025 3:26:48 PM To: [email protected] <[email protected]> Subject: [RacalRadio] TRA-931 ?
Hi,
I currently have on my bench a Racal Syncal 30 aka TRA931. I'm currently involved in looking into alternative PA transistors since good 2N5070s are nearly impossible to source these days.
I currently have a pair of 'experimental' transistors in place and the set is happily generating 20W on all frequencies with a very slight drop (about 2W below 2MHz). What is a bit alarming is that the set will happily deliver 20W (in the High position)
even when AM is selected. Oddly, although the manual specifically states that the o/p is nominally 5W on AM (and understandably too), there is no mention in the circuit description of how this reduction in output power is achieved.
?
Looking at the wiring associated with the Mode Switch, it looks like the Mute pin (66) on the synthesiser might have something to do with it, but poking around in that area has proven inconclusive.
?
Can anyone shed some light on this?
?
Regards,
?
Ian, GM0UHC
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