[NJARC] BC-348 Hum

[Scott Roberts]

Well, I had an idea tonight while working on solving the problem of the BC-348P hum. First, I checked to be sure I had a jumper in place on the 2 & 6 connections, in place of the tx relay, and I had none(a friend reminded me of this need). So I added one, but still no soap on any signal, and the hum is still persistent. So I tried a reverse substitution- As many may recall, I spent considerable time last year demodifying my late Uncle Bill's BC-348Q to its original wiring configuration, except that I had it set to accept a transformer setup in place of the dynamotor. Well, I pulled the transformer setup out, and changed the last two wires needed to convert it completely back to a dynamotor.(I checked band activity, etc first- set was working well, & receiving on several bands, no hum)

I installed the dynamotor I've been working with, and hooked it up. At first, there was no hum at all, but once things warmed up it was back, however- it is nowhere as loud as in the 348P. I am thinking it must be in the power supply I built, so I guess I need larger caps(I am using 47/160 electrolytics) and a larger choke(I have no idea its Henrys- it is a small one from an engine whine suppression kit) If I can get it cleared out entirely in the 348Q, then I can test it in the 348P. I am also thinking there may be other issues with the P- it seems the RCA 991 glow regulator is not glowing- so I need to check through all the tube wiring, and ensure I missed nothing.

I may attempt to wire my solid state power unit (from the 348Q) in, and see if there is any action there- another substitution to test things!

Any ideas/suggestions?

Thanks!
Scott