[Boatanchors] 1625 tube(s)

[Richard Knoppow]

----- Original Message ----- 
From: "rbethman" <rbethman at comcast.net>
To: "Boatanchors Mail List" <boatanchors at mailman.qth.net>
Sent: Wednesday, March 23, 2011 9:34 AM
Subject: [Boatanchors] 1625 tube(s)


> I've had to go back as far as a copy of the 1941 Radio 
> Handbook
> published by the ARRL to find a "proper" tube diagram that 
> clearly shows
> the "beam forming plates".  However, this stopped at 
> listing of the
> 1621, (not its diagram.), and it did not list the 1625.
>
> This simply leaves myself and others in the *elifIknow* 
> mode!
>
> Then again, I have no intent of using 1625s in GG.  I 
> don't have a thing
> here that even uses them.  I *DO* have equipment that uses 
> 807s.  That
> would be the BC-610 and the T-213.
>
> So we have beat it to death, and find the tube manuals 
> "LACKING"!
>
> Bob - N0DGN

     FWIW, the RCA receiving tube handbooks all have a 
section describing beam power tubes with a drawing and 
explanation. I am not sure when the standard tube diagrams 
stopped indicating the plates and replaced them with the 
pentode symbol. I thin it was a simplfication of required 
symbols.
     The beam forming plates act in some ways like a virtual 
suppressor grid since the field they produce eliminates 
secondary emission and the negative resistance 
characteristic found in tetrodes. I am not certain what sort 
of characteristics the plates have as far as being able to 
modulate the electron beam. It may be they have enough 
effect to function as a modulation grid or perhaps not. Beam 
pentodes seem to have originated around 1935. They have 
better efficiency than power tubes employing a third grid 
such as the 6F6. The 1625 and 807 are very similar in 
construction to the 6L6 but have plate caps which lowers the 
interelectrod capacitance and extends the maximum frequency 
considerably.


--
Richard Knoppow
Los Angeles
WB6KBL
dickburk at ix.netcom.com