[NJARC] BC-348

[John Ruccolo]

Scott,

Sorry about the B-24. But, seriously....

So you ARE running the 348 off the dynamotor, correct? I assume the dynamotor "spins up" as it should? Did you measure the B+ output from it?

How loud is the hum? You said you hear it regardless of vol control setting....hmmm. What happens if you stick an audio signal on the grid of the output stage? Or measure the plate voltage at the output stage, for starters.

Did you try "jamming" a signal into the antenna via an RF generator? Is so, what happened? If not, try that too.

JR


--- On Tue, 11/4/08, Scott Roberts <ng19delta at yahoo.com> wrote:

> From: Scott Roberts <ng19delta at yahoo.com>
> Subject: Re: [NJARC] BC-348
> To: "NJARC Radio Club" <njarc at mailman.qth.net>
> Date: Tuesday, November 4, 2008, 2:17 AM
> Visit our web site - See http://www.njarc.org
> _______________________________________________
> 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
> > 
> > _______________________________________________
> > NJARC mailing list
> > NJARC at mailman.qth.net
> > http://mailman.qth.net/mailman/listinfo/njarc
> _______________________________________________
> NJARC mailing list
> NJARC at mailman.qth.net
> http://mailman.qth.net/mailman/listinfo/njarc