[NJARC] BC-348

[Scott Roberts]

Well, I haven't had any replies yet...

I added a pair of filter caps and a choke to thw 28VDC power supply I cobbled together, but no change in the hum. So, I am going to replace the caps in the dynamotor and see what that does. After that, ? I guess I just start fiddlin with stuff.

Any help still appreciated!
Thanks!
Scott


--- On Mon, 11/3/08, Scott Roberts <ng19delta at yahoo.com> wrote:

> From: Scott Roberts <ng19delta at yahoo.com>
> Subject: [NJARC] BC-348
> To: "NJARC Radio Club" <njarc at mailman.qth.net>
> Date: Monday, November 3, 2008, 2:24 PM
> Visit our web site - See http://www.njarc.org
> _______________________________________________
> Hi Everybody-
> I am messing about with my BC-348P(Not my Uncle's, but
> the one I picked up at the swap meet a few months back) and
> am setting it up for its original power supply. Dave Sica
> did me a great favor, and swapped me a BC-348 dynamotor and
> mount in exchange for a radio I had he was interested in. I
> cleaned & relubricated the bearings on the dynamotor,
> and put it into the de-modified chassis after testing. My
> test rig is simply a 25.2 VAC transformer, rectified through
> 4 1N4007 diodes, but no filter caps. (This tuning units, see
> nothing may be important...)
> 
> The dynamotor tested out nicely- on 25.2 VDC(rectified) it
> was putting out around 230 VDC. The few caps in the
> dynamotor are original, one a nice metal one, the other a
> paper cap. (It is a DM-28-Q, from a BC-348-Q) Caps have not
> been replaced in the dynamotor, but all caps were redone in
> the BC-348-P.
> 
> When I switch the unit on, in either AVC or MVC mode, with
> the proper impedence headset, or speaker, I get a hum, but
> no indication of volume control- no scratchiness, nothing,
> but a hum. I have tried running it through the FL-30-M
> filter(similar to FL-8-A) but it has no effect. Could this
> be a hum from my cheap-a** power unit(literally thrown
> together to form a circuit) that could be solved by a couple
> filter caps before it comes into the radio?(If so, would
> 47/450Es be about right?)
> 
> I have been rechecking my wiring repairs, and, other than
> tearing out the tuning units and looking into them I see
> nothing obviously missed. Tubes have all been tested on my
> Precision tester, and check out fine.
> 
> Ideas?
> 
> Thanks!
> Scott
> 
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