[Collins] 32 s 1 self oscilation

[Dr. Gerald N. Johnson]

On 4/21/2012 11:54 AM, Carl wrote:
> long with the other suggestions Ive tamed an unruly S1 and others with a 22
> Ohm 1/2W carbon resistor right at the grid pin of V-7 and a 100 Ohm 1/2W
> right at at Pin 8&3 with C58 at the tube side and C59 at the other and both
> with very short leads.

Those can be most effective at preventing VHF parasitic oscillations at 
some possible cost of gain on 10 meters.
>
> For the finals be sure R119/120 and R43/48 havent drifted high and as long
> as you are at it check the cathode resistors.Next install other 100 Ohm 1/2W
> carbon resistors at pin 3 of both tubes with added .01 discs at the far end
> as with V7.

On my 32S-1 schematics, R43-48 ARE the cathode resistors of one of the 
6146 with R49-54 the cathode resistors of the other 6146. I can't find R 
119-120 on the schematic or parts list. I find them in the 32S-3 
schematic, part of added grid parasitic suppressors not shown in my 
32S-1 manual or the 1959 edition of the yellow book.

Those parasitic suppressors for the 6146 grid circuits are described as 
4 turns #20 and a 47 ohm carbon comp 1/2 watt resistor.

Traditionally the coils use the resistor for a coil form. In these RL 
parasitic suppressors, there is always a trade off in effectivity at the 
parasitic frequency vs power loss on the highest operating frequency. 
More turns increases the insertion loss at the VHF parasitic frequency 
while also increasing loss at the operating frequency. In some tubes 
that's a delicate choice requiring a higher power resistor to withstand 
the operating frequency dissipation while the tiniest of resistor would 
stop the parasitic when the suppressor is working correctly. Parasitic 
suppressors for the PA of the 821A-1 where the circulating tank current 
was a couple kiloamps were impractical to add to the plate circuit, so 
were built as capacitively coupled shunt elements in the boiler box. 
With 60 KV peak on the boiler at RF and modulation peaks, the capacitors 
had several inches spacing from the boiler and 100 watt glowbars were 
used for the resistors. The coils were substantial copper wire, maybe 
larger than #8 or 10.

There is a hint of the development process in the component numbering 
especially resistors and capacitors. I appears that the basic circuit 
was created and the components identified by R and C number. Then as 
refinements were added to make the radio buildable and to work in the 
field added components were added to the end of the parts list, not 
organized by stage as they were in the initial numbering. And if a 
component was deleted, its number was not used some where else. The 
component numbers were kept from the earliest 32S-1 through the last 32S-3A.
>
> Why Collins didnt use some of those basic stabilazation components across
> all S Lines is beyond me.

You'll have to ask Warren Amfahr W0WL about that.
>
> Also dont overlook a gassy 6AH6 or 6CL6 which would likely be running hotter
> than normal.

Also tubes with grid emission will counter act the fixed or ALC 
generated grid bias and draw more current and in pentodes the gain goes 
up as the plate current goes up.
>
> Carl
> KM1H
>
73, Jerry, K0CQ, Technical Adviser to the Collins Radio Association
>
>