[Boatanchors] Suppressor grid modulation

[WA5CAB at cs.com]

Close.  But the deal was that some 1625's had the beam forming plates (not 
suppressor grid) connected to the cathode inside the glass envelope whereas 
others had the separate wires run through the glass and tied together 
externally at the cathode base pin.  The latter could be modified by separating 
the wires whereas the former could not.

The 837 also has a 12.6 volt heater.  It's used as the PTO tube in the 
T-47/ART-13 and as the output tube in the TBX.  Which is why the TBX hand crank 
generator, alone AFAIK of all the pre-war, WW-II and post-war units, outputs 
12.6 VDC instead of 6.3.  The 807 is the 6.3 volt heater tube.  But it only 
has a 5-pin base so it's a moot point whether the beam forming plates are 
connected internally or externally.

In a message dated 1/28/2010 12:43:10 AM Central Standard Time, 
revcom at wbsnet.org writes: 
> In the early days of SSB amps (economical ones) the 1625, by some
> manufacturers had the suppressor on a seperate pin, while those, if I
> remember right by RCA, the JAN tubes did not.  You ground a hole in
> bakelite base and carefully disconnected the screen grid wires and
> rerouted it. That way you could operate them in a Grounded Grid amp.
> 
> P&H had an smp using them, about 400W. I think the 837 was about the same
> but did not require modification and had a 6V filament.  Memory gets
> cloudy after all these years.
> 
> Sure made good use out of all the surplus 1625s laying around.  Used to be
> able to buy them by the 100 lot fairly cheap.
> 
> Rod
> KØEQH
> 
> 
> 
> >On Wed, 27 Jan 2010, Al Klase wrote:
> >
> >>In addition, you need a pentode with the suppressor grid brought out to
> >>a separate pin, as opposed to being internally connected to the cathode.
> >>
> >This ticked a faint memory of some article about tubes, 807 or 1625,
> >and in some brands there was something connected internally, but in
> >others there were two separate wires going to the same pin on the base.
> >So if you had that kind you could carefully remove the base and
> >separate the two wires and do something useful with it.
> >
> 

Robert & Susan Downs - Houston
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