RME 4350 weak BFO?
 

I recently aquired a nice RME 4350 receiver. I cleaned a lot of dust & dirt
out of it. Cleaned & relubed the vernier tuning knob(some of the balls are
missing), tightened some slipping shaft couplings, put a drop of oil on just
about everything that moves, powered it up very slowly with a variac. It
seems to work fine except the BFO seems weak. The RG gain has to be reduced
a lot and the AF gain has to be high to tune any SSB or CW with the INJ knob
on max. I swapped the tube and no differance. It doesn't seem right to me
but I just don't have enough experiance SSB/CW receivers to know. You can
get a good strong audio from a AM signal but the SSB/CW is wimpy. Is this
normal for this radio?
John

"John D" wrote in message
...
I recently aquired a nice RME 4350 receiver. I cleaned a lot of dust &
dirt
out of it. Cleaned & relubed the vernier tuning knob(some of the balls are
missing), tightened some slipping shaft couplings, put a drop of oil on
just
about everything that moves, powered it up very slowly with a variac. It
seems to work fine except the BFO seems weak. The RG gain has to be
reduced
a lot and the AF gain has to be high to tune any SSB or CW with the INJ
knob
on max. I swapped the tube and no differance. It doesn't seem right to me
but I just don't have enough experiance SSB/CW receivers to know. You can
get a good strong audio from a AM signal but the SSB/CW is wimpy. Is this
normal for this radio?
John

Hi John,
The SX-88 I worked on was similar, at least as far as having to reduce the
RF gain in order to make CW sound right. I checked everything and then read
the manual- which said to reduce the RF gain for CW! However, in SSB
position, CW sounded great w/o the need to reduce the RF gain.

Dale W4OP

"John D" ) writes:
I recently aquired a nice RME 4350 receiver. I cleaned a lot of dust & dirt
out of it. Cleaned & relubed the vernier tuning knob(some of the balls are
missing), tightened some slipping shaft couplings, put a drop of oil on just
about everything that moves, powered it up very slowly with a variac. It
seems to work fine except the BFO seems weak. The RG gain has to be reduced
a lot and the AF gain has to be high to tune any SSB or CW with the INJ knob
on max. I swapped the tube and no differance. It doesn't seem right to me
but I just don't have enough experiance SSB/CW receivers to know. You can
get a good strong audio from a AM signal but the SSB/CW is wimpy. Is this
normal for this radio?
John


Is it an SSB receiver? I can't place it at the moment.

Remember, that until the mid to late fifties, there were no SSB receivers.
There were receivers with BFOs, that of course allowed for CW reception.

But when SSB came along, those receivers were less than perfect. The
ratio of the BFO to the incoming signal was not correct, and so it still
sounded like an overmodulated AM signal.

So all the books told you to reduce the RF gain, turn up the audio gain (to
compensate) and this way the BFO is much stronger relative to the incoming
signal. If the receiver didn't have a product detector, you had to do this.

It was only as receivers designed for SSB that this need went away. They
added product detectors, and the BFO was in proper ratio to the incoming
signal, so you did not need to attenuate the incoming signal to get useful
operation.

Michael VE2BVW

The 4350 does not have a product detector. The variable injection allows a
small variation, but I recall that reducing the rf gain is still necessary.

RME sold a separate product detector that plugs into the back.

73, Colin K7FM


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Thanks for the replies.
Maybe I can find a simple product detector circuit to build into it.
John