[Boatanchors] Tube filaments

[Carl]

Directly heated tubes with long thin filaments did develop hot spots at the 
stem seal. Some Navy transmitters had a polarity reversal switch that the 
operators had to switch at each shift so that the hot spot was on the other 
lead.

Carl
KM1H



----- Original Message ----- 
From: "Singley, Rodger" <rbsingl at ilstu.edu>
To: "Ed Berbari" <eberbari at indy.rr.com>
Cc: <boatanchors at mailman.qth.net>
Sent: Friday, December 04, 2009 9:13 PM
Subject: Re: [Boatanchors] Tube filaments


> 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
> ______________________________________________________________
> 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