[R-390] Second R-725 on ebay

[rbethman]

Well,  as I wrote Tom directly -

> Then again, *I* could be wrong!
>
> So do NOT take it as Gospel!
>
> Hell, I'm Polish! (ROTFLMAO!)
>
> I "mentally" keep the terms filament and heater separated ESPECIALLY 
> when talking R-39Xs!
Bob - N0DGN

David Wise wrote:
> Er, I _am_ talking about the filament, Bob.
> Frequently referred to as "heater" in indirectly-heated
> tubes.
>
> If the PTO was having FM hum problems, any AC in
> the area would certainly be anathema.  It's the
> biggest source of residual FM in the General Radio
> 1009 Standard Signal Generator.  There, the 
> power transformer's magnetic field changes the
> tuning slug's permeability.  I don't think the
> R-725 uses a DC oven, so in that case I have
> to guess that the combination of inner shield
> and (incidentally) field-cancelling wrap-around
> oven winding design minimizes the effect.
>
> Dave 
>
> -----Original Message-----
> From: rbethman [mailto:rbethman at comcast.net] 
> Sent: Monday, May 11, 2009 12:29 PM
> To: r-390 at mailman.qth.net
> Cc: Tom Bridgers; David Wise
> Subject: Re: [R-390] Second R-725 on ebay
>
> Tom,
>
> Dave is NOT talking about the FILAMENT.  He is talking about the HEATING 
> ELEMENT wrapped around the PTO inside the can.  Thereby taking AC away 
> from the PTO innards!
>
> Bob - N0DGN
>
> Tom Bridgers wrote:
>   
>> David,
>> How does one "float" the vfo tube's filament up to a positive dc potential?
>> Does that mean we should do the same thing to our R-390A's PTO tube's 
>> filament?
>> Thanks,
>> -tom
>>     
-- 
Bob - NØDGN