[ARC5] Modifying 1625s

[Dennis DuVall]

All,

More accurately beam "confining" plates.  This subject comes up about  
once a year.  For more than you ever wanted to know about beam  
tetrodes see <http://www.r-type.org/static/btet.htm>

Dennis D.  W7QHO
Glendale, CA

******************
On Jan 10, 2012, at 10:41 PM, Dennis Monticelli wrote:

> 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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