B&W 5100A ?

[Don, W2DL]

Hello all,
Has anyone heard of a B&W 5100A?  I have a 5100B (w/ 51SB unit) and I just picked up a unit marked 5100 (no letter). This latter unit is significantly different in some of the power, bias and switching circuitry from both my 5100B and the schematic for a 5100 I downloaded from BAMA.com. Did they make a 5100A ? I can't find any data on one. That said, mine is marked 5100 (no letter) and it sure doesn't match any circuit I have for this series. I'd like to talk to anyone who has - or has a schematic for - a 5100A. I've got a problem getting this thing to work and the proper schematic would help a lot!!
I can be contacted via "reply", or lawshd@blair.edu, or twisted pair 908 362 8502.

Thanks in advance!

[Pete, WA2CWA]

There was no 5100A. However, in some B&W documentation, there was a reference to a "5100-S".

If the original owner of the 5100 bought a 51SB sideband adapter, besides receiving the equipment, there were three modification kits for use with the 5100 transmitter. One kit was used to modify the multiplier and RF unit so that the 5100 could be used with the 51SB adapter. The second kit was for modifying the crystal oscillator and buffer unit to eliminate backwave on the 80 and 40 meter bands. The third kit was for modifying the negative bias supply to facilitate the adjustment of the bias voltages. Also, included with the original 5100 manual, was ADDENDA SHEET #1 which documented changes to the circuitry that were not included on the original schematic.

Later production of the 5100, which was to be used specifically with the 51SB, the factory installed these "mod"/"kits" into the transmitters. The tag, "5100'S" came about but there was no relabeling of the front panel. Likewise they did not, as far as I can tell, updated the 5100 schematic to include all these additions. Soon after this activity, the 5100B was introduced.

[Don, W2DL]

Thanks Pete, that answers some of my questions abouf produced models and I guess I'll just have to try and trace out the entire cableing system used (with all the same color white wire!) and see what's where. My unit has a 5U4G under the chassis by the PA unit, and a diode and some resistors mounted in front of that. This appears to be a somewhat variable bias supply, there is a pot adjustment on the chassis top. However, it is not the dual bias adjustment later 5100B's used. The 5V4 of the 5100 apparently is now the 5U4 of mine (Hammy Hambone might have just switched the tube from 5V4 to the 5U4G, same pin-out) freeing up the "V17" socket to be used with the 51SB. All of the changes clearly are factory done.

Back to the bench!
Regards,
Don, W2DL

[Jim, W5JO]

Don if you need any help or advice Mark, K3MSB knows a lot about the units.  He has refurbished both the 5100 and the B.  All the circuit changes and service notes are on BAMA courtesy of him. 
http://www.k3msb.com/