[ARC5] Modifying 1625s

[Dennis Monticelli]

I can only add to the discussion that RCA tubes cannot be modified.
Their beam forming plates are tied internal to the envelope.

Dennis AE6C

On 1/10/12, Glen Zook <gzook at yahoo.com> wrote:
> The secret to modifying 1625 tubes to be used in grounded-grid is to get the
> "right" brands.  Some brands have the beam forming plates connected inside
> the glass envelope and some brands have the beam forming plates connected
> outside of the glass envelope.  The latter can be modified and the former
> cannot be modified.
>
> Glen, K9STH
>
>
> Website:  http://k9sth.com
>
>
> ________________________________
>  From: Kenneth G. Gordon <kgordon2006 at frontier.com>
> To: ARC5 at mailman.qth.net
> Sent: Tuesday, January 10, 2012 11:49 AM
> Subject: Re: [ARC5] Modifying 1625s
>
> On 10 Jan 2012 at 1:31, hwhall at compuserve.com wrote:
>
>> >Just curious. How do you modify a 1625 ??
>>
>>  Certain brands had the beam forming grids brought out of the glass &
>>  connected to the cathode inside the phenolic octal base. You could
>>  remove the base or cut a hole in it and rewire the beam forming grid
>>  to a separate pin, for three independent grids. I think the standard
>>  practice then was to ground all the grids & run the tubes as grounded
>>  grid amplifiers that typically needed no neutralization.
>
> Yes. Exactly. In fact, that entire procedure and the amp that
> resulted was the subject of an article in at least one ARRL Handbook
> of the period. Used 4 ea "modified" 1625s in GG and the ARC-5 roller
> inductor in the front. It was a nice-looking little amp and,
> apparently, worked quite well.
>
> As I remember it, it was good for about 300 watts input.
>
> Since, at the time, many of the hams who were experimenting with SSB
> were using such exciters as the CE-10 and CE-20 with 10 and 20 watts
> output respectively, this provided a significant improvement in power
> at relatively low cost.
>
> I have a CE-20A and the factory "458" VFO which was built on an ARC-5
> transmitter, the BC-458.
>
> The combo is a nice little phasing rig with a lot of good features.
>
> Ken W7EKB
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