[Boatanchors] Tube filaments

[Carl]

That doesnt seem to happen with indirectly heated filaments that have a long 
and reliable history in mobile enviroments.

In fact a tube such as the 6V6 which is known to be prone to heater cathode 
leakage resulting in hum in AC sets merrily chugs away on DC.

Carl
KM1H




----- Original Message ----- 
From: "ronw8" <w8ron at sbcglobal.net>
To: "Singley, Rodger" <rbsingl at ilstu.edu>
Cc: <boatanchors at mailman.qth.net>; "Ed Berbari" <eberbari at indy.rr.com>
Sent: Saturday, December 05, 2009 7:31 AM
Subject: Re: [Boatanchors] Tube filaments


> Running DC on filaments would cause the filament material to migrate to
> one side with early failure.  No issue with AC.
> ---
> Ron
>
>
> Singley, Rodger wrote:
>> Tektronix used DC for the filaments in their vertical plug-ins on the 500 
>> series "lab" scopes.  In this case the filaments are in series and few 
>> from one of the regulated B+ supplies.
>>
>> Given the desired performance of these scopes and the selling price (many 
>> of the plug-ins sold for as much as a typical ham receiver/transmitter 
>> setup) it was possible to justify the cost of this circuitry.  But that 
>> wouldn't be the case for typical consumer gear.
>>
>> I seem to recall reading somewhere that filaments (tubes or light bulbs) 
>> are more prone to developing localized "hot spots" on DC as compared to 
>> AC.  Anyone else recall this potential problem?
>>
>> Rodger WQ9E
>>
>>
>> -----Original Message-----
>> From: boatanchors-bounces at mailman.qth.net on behalf of Ed Berbari
>> Sent: Fri 12/4/2009 7:46 PM
>> Cc: boatanchors at mailman.qth.net
>> Subject: Re: [Boatanchors] Tube filaments
>>
>> I would like slightly change the direction of this discussion on tube
>> filaments.  My background is in medical electronics and when I first got
>> started in this field tube amplifiers for biophyscial measurements (ECG,
>> EEG, etc) were still common.  A leading company was Electronics for 
>> Medicine
>> (E for M, now defunct) and they used DC voltages for filament supplies. 
>> It
>> was their way to limit 60 Hz hum from interfering with these low level
>> signals.  I always wondered why this practice was not used with receivers
>> and other low level signal circuits.  Instead we are burdened with 
>> numerous
>> bypass capacitors and other means to limit 60 Hz interference.  Any 
>> wisdom
>> or thoughts out there on this approach?
>>
>> Ed, W9EJB
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>
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