[Boatanchors] And Now for Something Competely Different: Zenith

[J. Forster]

It would only be possible if the cap were in a grid circuit somewhere,
obviously, so that the tube bias is badly off.

-John

===============



> Hmmm...  Have heard reports of this before but what capacitors in what
> part of the circuit?  Can't imagine a screen bypass cap in an
> oscillator circuit  requiring this treatment for ex.  Caps in the
> tuned circuit maybe?  Doesn't make sense from an engineering
> standpoint in any case, would need to see the schematic.
>
> Dennis D.  W7QHO
> Glendale, CA
>
> ************
> On Mar 30, 2013, at 12:46 PM, Glen Zook wrote:
>
>> One thing that I have found in restoring receivers from especially
>> the 1930s is that some circuits, especially oscillator circuits,
>> fail to work when a modern capacitor replaces an old paper type.  It
>> seems that some leakage through the capacitor was needed for the
>> circuit to work.  In those cases, a resistor from around 470K to 2.2
>> meg has to be put in parallel with the capacitor to get the circuit
>> operational.
>>
>> Most circuits work fine with the new capacitors.  However, one can
>> definitely go bald from "pulling their hair out" when the oscillator
>> fails to oscillate trying to locate the problem.  I found that
>> adding a high resistance in parallel with the capacitor suddenly got
>> the circuit working again just by trial and error having tried about
>> everything else.
>>
>> Glen, K9STH
>>
>>
>> Website:  http://k9sth.com
>>
>>
>> ________________________________
>> From: Joe Connor <joeconnor53 at yahoo.com>
>> To: Glen Zook <gzook at yahoo.com>; "Charlie , W5COV" <cvest at cox.net>;
>> David Stinson <arc5 at ix.netcom.com>; "boatanchors at mailman.qth.net"
>> <boatanchors at mailman.qth.net
>> >
>> Sent: Saturday, March 30, 2013 1:02 PM
>> Subject: Re: [Boatanchors] And Now for Something Competely
>> Different: Zenith
>>
>>
>> The quality and sound from these radios is pretty amazing. My theory
>> is that after we restore them, they perform better than they have
>> since they left the factory.
>>
>> Here's why: back in the '30s, capacitors were a high-failure item
>> even when new. A lot failed quickly and a lot more probably suffered
>> leakage even then. A radio with a dozen or so caps that are leaky to
>> one degree or another isn't going to sound as good as it should.
>> It's sort of a cumulative degradation. If there was one particular
>> cap that shorted or caused a noticeable problem, the repairman would
>> replace it but I've never heard of any repairman back in the day
>> replacing all the paper caps. It would probably have cost more than
>> a new set. Instead, the set was written off as "old" and "tired" and
>> relegated to a dusty attic.
>>
>> Now, we come in and replace all the caps with high-quality modern
>> caps. We replace the out-of-spec resistors and align the IFs with
>> precision (thank you, frequency counter). The end result is that the
>> radio performs the way it was designed to perform, probably for the
>> first time since it left the factory.
>> ______________________________________________________________
>> Boatanchors mailing list
>> Home: http://mailman.qth.net/mailman/listinfo/boatanchors
>> Help: http://mailman.qth.net/mmfaq.htm
>> Post: mailto:Boatanchors at mailman.qth.net
>>
>> List Administrator: Duane Fischer, W8DBF
>> ** For Assistance: dfischer at usol.com **
>>
>>
>> This list hosted by: http://www.qsl.net
>> Please help support this email list: http://www.qsl.net/donate.html
>
> ______________________________________________________________
> Boatanchors mailing list
> Home: http://mailman.qth.net/mailman/listinfo/boatanchors
> Help: http://mailman.qth.net/mmfaq.htm
> Post: mailto:Boatanchors at mailman.qth.net
>
> List Administrator: Duane Fischer, W8DBF
> ** For Assistance: dfischer at usol.com **
>
>
> This list hosted by: http://www.qsl.net
> Please help support this email list: http://www.qsl.net/donate.html
>
>