The AM Forum

I recently purchased a B&W 5100. I replaced all the electrolytic and paper capacitors and the unit turns on, but V2 and V3 (Buffer Xtal Osc - 6BJ6) and V6 and V7 (Multiplier - 6AQ5) filaments do not light. I verified 6.3 VAC present at pin 2 of J4 and pins 1 and 2 of J5. I verified continuity within the buffer/xtal osc module and multiplier module. When transmitting in phone, the plate is at 230 mils and the grid is at 8 mils with no RF output. The loading, exciter, and plate controls have no affect during tune up. I am at a loss here and would appreciate any help pointing me in the next direction of troubleshooting.

73,
John
KJ7USA

John,

I am not familiar with the 5100.  However, just recently I happened across the web page by K3MSB detailing his restoration of a 5100, which can be found here:  http://www.k3msb.com/bw5100/bw5100.html (http://www.k3msb.com/bw5100/bw5100.html)  There is a link near the top of that page to service notes, which may be of interest.  He also has a page devoted to his 5100B.

73,
Brad K4RT

sounds like several problems .... an oscillating final either needing neutralizing or parasites ... what type 6146 is in there ? .... connection problem for fil voltage .... you might consider a frame off type restoration at this time

Sounds as if you have lost the connection to filament winding on T4.  For those particular tubes filament is on a 6.3 volt 1 amp winding separate from the rest.  Measure the voltage at that winding, they are the brown leads out of T4.

You mentioned that this is a 5100 and I assume it is not the B model

UPDATE: For some strange reason, maybe from reseating some connectors, V2 and V3 are lit now. Just V6 and V7 are out. I have voltage at J5, so the problem must be within. Looks like a bear to take this comportment apart.

K4RT - I have seen K3MSB's website. I will send him an email as well.

W4BFS - I have a 6146 and 6146A in the final and modulating with two 6146B tubes.

W5JO - I verified 6.3 VAC from the transformer to the connectors leading to the buffer and multiplier compartments.

Thank you all for replying and helping me out with this.
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You might to try and re-seat V6 and V7 several times. There may be some crud on the tube pins or some crud in the socket terminals. Could also be a cold solder joint on the filament pin terminals.

Thanks Pete! I reseated the J5 connector several times and they all lit up. Tuned her up and have full output. I'll clean everything up real good and start enjoying it. Thanks to all!

Performed the alignment on the B&W this morning and was playing with it today. I noticed that there is a pretty big variance in plate current from one end of the band to the next. Sometimes I would be able to load 220 mils, and then sometimes not even 200. Is this normal for this rig or am I missing something? If I wanted to peak it's performance on the frequency I use most, would I set the VFO to that freq and then align it instead of the freq listed in the manual?

The plate current variance is not normal.  Right off the top of my head it sounds like the multiplier section is aligned wrong.  But to find out, put a scope on the VFO output and tune from one end to the other, the output should not vary much.  Then reattach the VFO to the buffer and do the same thing with the scope.

My guess is you are seeing the loss in the upper bands.  If that is the case you have the multiplier misaligned.  They can bet just a bit tricky to get right.

A little more maintenance might be needed for connectors and controls and the tube sockets. Use DeOxit to help clean and revive the contact areas. Selector switches too. Clean up excess spray.
Sounds like you are on the air!!

Well, got her on the air and all set up on the rack today. Performed another alignment and everything seems to be working fine. Thanks again for all the help!