[Milsurplus] 1626 Tube Base Hole

[Kenneth G. Gordon]

On 12 Mar 2006 at 18:58, B. Smith wrote:

>     I have several 1625 tubes with a 1/4  by 1/2 inch hole cut in the side 
> of the base
> right above pins 5 and 6.  Could someone explain why this was done.

Yes. Those cuts were made to enable separation of the suppressor grid 
connection from the cathode connetion so that those tubes could be 
used in a grounded-grid linear amp.

SOME 1625s had a separate EXTERNAL connection to the suppressor 
grid, and that connection, and the one to the cathode were stuffed in 
the same pin and soldered. Most 1625s had the suppressor connected 
to the cathode INTERNALLY, i.e. inside the tube envelope.

There were a couple of linear amp circuits published that used 4 of 
those "special" 1625s in grounded-grid.

One was named the Loudenboomer, and some company used that 
entire circuit for a commercial amp at some time in the past. I think it 
may have been Hallicrafters.

The 1956 ARRL Radio Amateurs Handbook has the entire article.

The amp used an ARC-5 roller coil for the plate coil. As I remember it, 
the amp covered 80, 40 and 20. I don't think it was used on 15 or 10.

Ken Gordon W7EKB