[ARC5] 1625 question

[Kenneth G. Gordon]

On 6 Feb 2018 at 7:03, jeepp wrote:

> 
> The old PH linear, etc. amp used 4 1625s at about a kv.  I recall that one had to use certain 
> physical variants of the tube such that one could drill onto the side of the tube base and tie pins 
> together to change the tube to either a triode or tetrode?  807s could not be so modified, however.  
> But, 1625s are cheap....still.
> Jeep K3HVG

What the deal there is, is that the beam-forming plates are connected internally to the 
cathode, making the tube, really, unusable as a GG linear amp tube.

One could cut into the bases of certain versions of the 1625 to break that connection, so 
that all "grids" could be grounded.

BTW, that amp was first described in QST magazine, then P&H brought out the amp 
commercially. I think Hallicrafters had one too.

Ken W7EKB

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