[Collins] 32 s 1 self oscilation

[Carl]

----- Original Message ----- 
From: "Dr. Gerald N. Johnson" <geraldj at weather.net>
To: <collins at mailman.qth.net>
Sent: Saturday, April 21, 2012 7:11 PM
Subject: Re: [Collins] 32 s 1 self oscilation


>
>
> 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.

That is only one of the benefits. It can also tame a stubrorn low frequency 
oscillation or a not perfect neutralization. Very common in many HF 
circuits. Unless a circuit is already drive starved it shouldnt affect 10M 
at all.




>>
>> 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.


I used the 32S1 schematic on collins.org


>>
>> 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.


No different in a receiver where it overides the AGC voltage and in extreme 
cases drives the grid positive with severe signal overload and sometimes 
oscillation the result.
I see this in receivers, transmitters and transceivers on a regular basis.

Carl
KM1H


>>
> 73, Jerry, K0CQ, Technical Adviser to the Collins Radio Association
>>
>>
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