[NJARC] BC-348 Hum

[Al Klase]

Scott,

I wouldn't worry about the filter downstream from the dynamotor at this 
point.  If you have hum, like 60 or 120 cycle hum, it's not coming from 
the dynamotor.  The filter is designed to take care of the typical 
"whine" of the dyno.

Do you have an oscilloscope?  I sense you're just floundering around 
here.  As someone else suggested you need engage in signal tracing.  
It's like plumbing:  The trouble lies between the last place you have 
water pressure and the first place you don't.

Start by grounding the center terminal (wiper) of the audio gain 
control.  (There are two pots in tandem, you have to figure out which is 
AF and which is RF.  Read the schematic etc.)  Does the hum go away?   
If not, look at the plate and screen with the scope.

Al

Scott Roberts wrote:
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> 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
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-- 
Al Klase - N3FRQ
Jersey City, NJ
http://www.skywaves.ar88.net/