[NJARC] Power Supply Question

[njarc@mailman.qth.net]

Aaron,
       Bravo.  You hit it right.  I returned the correct caps to their place 
in the circuit then considered your idea.  The tubes were also checked again, 
on a tube tester and I tried Johns suggestion to check the tubes with an ohm 
meter.  All is OK.  I had also read this and was wondering myself about this. 
 In fact, it was something that I thought about early on.  When I first 
started working on this radio, I had noticed that it had been worked on 
before and the speaker connections were also touched before.  Two of the 
connections had been resoldered.  I had assumed that they were connected 
correctly previously, and followed what was there.  I have a noticeably lower 
hum now.  Since I'm not sure how much hum to expect from this radio, I'll 
bring it to the meeting and take opinions.   There may be something else that 
I've missed.   

Thanks again for everyone's help.
Joe 



In a message dated 1/4/03 5:41:06 PM Eastern Standard Time, vv7-3@rcn.com 
writes:


> Joe
> 
> Was the speaker ever disconnected?  Seems to me I remember hearing the 
> voice coil
> and electromagnet had to be in phase with one another.  Maybe one of the 
> windings
> had been reversed inducing hum into the voice coil instead of canceling it. 
>  The
> electromagnet is normally used as part of the power supply filtering 
> circuit.
> Does anyone else have knowledge or experience with this?
> 
> Aaron
> 
> TrainBee@aol.com wrote:
> 
> > Jim,
> >        Thanks for the advise.  Unfortunately, I don't have any extra 35's 
> or
> > 47's to substitute.  I've tried the 27's and 80 with no changes.  Tapping 
> the
> > tubes, chassis, etc..., produces no noise.
> > The tube complement for the Sparton 15 is:
> > 27 x 3,
> > 35 x 3,
> > 47 x 1,
> > 80 x 1.
> >        I'll go back to the original caps and bring it to the meeting next
> > week.  I'm sure other sets of eyes will see what I'm not.
> >
> > Thanks again.
> > Joe



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