[Milsurplus] Submini tubes

[Kenneth G. Gordon]

On 4 Oct 2018 at 4:20, Jim Whartenby wrote:

> Ken and I have traded a bunch of emails almost exactly two years ago about the SRR and FRR 
> receivers; they should be in the archives if we didn't go off list.  I cannot verify Ken's assertion 
> that the SRR-13 or FRR-23 ran hot.

In the setting in which these were being used, they ran very hot. The cases would get too 
hot to keep one's hand on for very long.

>  Especially after changing the power transformer tap to the 
> 400 cycle position which lowered the power supply output voltages to as low as they can go. 

I didn't think of that at the time, but is sounds like an excellent idea.
 
> In looking at the schematic for the SRR-11, I only see one or two pentodes like the 5902 in the 
> audio module that have no screen grid resistor.  Checking the tube manual, the plate and screen 
> are both run at a typical 110 VDC.

According to the table 7-5 on page 7-58 of NAVSHIPS 91875(A), the screen voltages of all 
but one or two pentodes is exactly equal to the plate voltage: 120 VDC. And all those which 
ARE 120 VDC are in the Preamp, RF, and IF amp stages.

IMHO, no pentode or tetrode should be operated with its screen voltage equal to the plate 
voltage, except, maybe, in receiver audio output stages....maybe...

>From that table, I assumed that despite the value of the existing screen resistors, they were 
not the correct value. I installed, as I remember it, 51K resistors, maybe bigger ones, where 
smaller or no resistors were used. Again, as I remember it (1970s) that reduced the screen 
voltages to something like 70 VDC, maybe less. I think I was shooting for 50 VDC.

In any case, the heat produced was markedly reduced by doing this.

Coils were a big problem. Still are. Also, those damned pot-metal cranks.

However, I STILL see the SRR-11/12/13/13A receivers as being excellent receivers. In fact, 
I find that they are easier to use than my R-390A and seem to me to work at least as 
well....when they are at their peak of performance. I like them.

Ken W7EKB