[NJARC] BC-348

[Angelo Napoli]

Scott,

Did you try a signal tracer on the various stages to see if the hum is at 
each stage to see where the hum might be present or start? You may also want 
to make sure what is supposed to be grounded or connected directly to the 
chassis is actually connected properly. It could also be a bad tube - the 
tube tests good but may have some other issues. Try swapping out the tubes 
on at a time. You may still have a bad bypass capacitor even though it is a 
replacement.

Angelo T. Napoli
251 Varsity Ave
Princeton, NJ 08540
(609) 987-2380
Email: atjnap2 at comcast.net


----- Original Message ----- 
From: "John Ruccolo" <jr6v6gt at yahoo.com>
To: "NJARC Radio Club" <njarc at mailman.qth.net>; <ng19delta at yahoo.com>
Sent: Tuesday, November 04, 2008 1:27 PM
Subject: Re: [NJARC] BC-348


> Visit our web site - See http://www.njarc.org
> _______________________________________________
> 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
>
>
>
> _______________________________________________
> NJARC mailing list
> NJARC at mailman.qth.net
> http://mailman.qth.net/mailman/listinfo/njarc