I have a B&W 51SB-B sideband generator which I use with a 5100-B
transmitter. The generator worked fine until recently, when output from
the grid circuit disappeared. I discovered a faulty resistor and
replaced it, plus I replaced the two 1N34 diodes, which are nearing 50
years old and, I am told, don't age well.

The result: Grid current is up--although it seems to fade on 10
meters--but the output meter indicates far less output than before.
Also, the grid current goes below zero while the B-plus is on, but the
unit is not being modulated (i.e. I'm ot talking). This is an old
problem and I don't know what's causing it. I'm not sure I should worry
about the output, since the unit seems to work and the transmitter
output appears normal.

Is there anybody out there who is thoroughly familiar with these
sideband generators and can answer a few questions?

Thanks in advance for whatever help you can provide.

Steve, W3DEF

Hi Steve:

I am not familiar with the B&W unit in particular, although I know about
them.

The reverse grid current makes me suspect leaky coupling capacitors. I have
repaired a number of Collins 75A4 receivers with leaky mica coupling caps,
which then makes the grid voltage positive. The leakage is quite small and
it is useful to use a scope or vtvm to measure voltages. Seems to be more
common when a solid state rectifier is substituted for the vacuum tube
rectifier.

A sudden change is more likely to be capacitor related than resistor.

Good luck, that is a nice piece of history.

Colin K7FM

wrote:
I have a B&W 51SB-B sideband generator which I use with a 5100-B
transmitter. The generator worked fine until recently, when output from
the grid circuit disappeared. I discovered a faulty resistor and
replaced it, plus I replaced the two 1N34 diodes, which are nearing 50
years old and, I am told, don't age well.

The result: Grid current is up--although it seems to fade on 10
meters--but the output meter indicates far less output than before.
Also, the grid current goes below zero while the B-plus is on, but the
unit is not being modulated (i.e. I'm ot talking). This is an old
problem and I don't know what's causing it. I'm not sure I should worry
about the output, since the unit seems to work and the transmitter
output appears normal.

Is there anybody out there who is thoroughly familiar with these
sideband generators and can answer a few questions?

Thanks in advance for whatever help you can provide.

Steve, W3DEF..... Steve I have the SSb adapter and 5100 ..When you switch to SSB the 5100 grid current is now read on the grid position of the SSB unit..grid current in the 5100 is of no significance in this mode..when you are in CW or AM the 5100 grid meter will read accurately.. If you go to AM and tune up the 5100 you should see abt 60/65 watts out on watt meter..when in SSb you will probably see abt. 75 peak watts.I have never been able to get full power out using the SSB adapter,I have tried several units,they are all low in output..SSB is nice and crisp but lower than I expected.. Good Luck Harold W4PQw

Harold:

I've always been able to get 100 watts or so out of the B&W 5100 on AM
up through 20 meters. It drops off after that, and on 10 I get perhaps
75 watts. On ssb, though, I've always gotten 100 watts output on peaks.
Perhaps the difference is that I am using the 5100-B and the sideband
generator designed for it. The 5100 had slightly less input power than
the later B, although the sideband generator was the same circuit as
the one I have, but used its own power supply. It was designed to be
use don any number of 100-watt rigs. The later ssb generator for use
with the 5100-B has no power supply, and gets all its power from the
transmitter.

Thanks for the info.

Steve