[Boatanchors] 1625 tube(s)

[Pete Lancashire]

a side question. If one was building a 40 M xmitter from scratch for
fun would one want to use a 807 or a 1625 ?

any reason one over the other .. I can't think of any.

-pete

On Wed, Mar 23, 2011 at 11:36 AM, Richard Knoppow
<1oldlens1 at ix.netcom.com> wrote:
>
> ----- 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
>
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