[ARC5] Modifying 1625s

[Glen Zook]

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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