Re: {Collins} Tough problem in 32S3 ALC semi-fixed



Tony - very good point. Different manufacturers would make tubes with slightly different inter-electrode capacitances and even though they would all test 'good', they didn't result in same behavior in the radio. That's why if you ever get hold of a Drake, Collins, Hallicrafters or Hammarlund receiver that has not been used in many years, you will see that they tended to use the same brand or have the manufacturer stamp the tube with the company name (especailly Hallicrafters). The ones Drake used to use in my experience were Sylvania brand. The other one commonly used was RCA (like the famous RCA 6EA8's used in the S-line radios), and less commonly GE. So always good idea if you have a squirrely problem you can't figure out  to sub with a different brand of tube, if you have a good one to see how it behaves. Might just fix the 'problem'.

73,Bob K3AC
In a message dated 8/12/2019 2:08:22 PM Eastern Standard Time, collins@xxxxxxxxxxxxx writes:

Hi gang,
    This is a “for what it’s worth” comment. I was working on the AVC circuit of a Drake 2B. After removing someone’s workaround add-ons everything looked normal but still no AVC. It turned out to be one of the tubes that was being controlled by the AVC voltage was loading down the high impedance circuit and not the AVC circuit itself. The tube tested good but changing it out cured the problem. I know this is an ALC problem but what is being discussed here keeps reminding of the surprising outcome of my experience. A kind of the tail waging the dog scenario where the solution ended up out to be “of the box”. 

Just a thought. 
          73
Tony - W9JXN 

Sent from my iPad

> On Aug 12, 2019, at 11:51 AM, Doug Millar via Collins <collins@xxxxxxxxxxxxx> wrote:
> 
> Grayson, Thank you. A heroic job of troubleshooting. My round emblem TX has some of the same problems.  Doug K6JEY
> 
> 
> 
> 
> 
>  On Monday, August 12, 2019, 8:17:21 AM PDT, Grayson Evans via Collins <collins@xxxxxxxxxxxxx> wrote: 
> 
> To all of you who helped with my “tough prolem in 32S3 ALC”, wanted to let you know that I semi-fixed it.
> I say “semi” because while it works, it is not satisfying.
> 
> I replaced every part in the ALC circuit including V6 (it is NEVER the tube).
> I found that something past the ALC rectifiers was loading the ALC circuit.  
> I seemed to isolate it to the part of the circuit that drives pin 1 of V6 through a 10K resistor R105.  When I lifted R105 from the ALC line, ALC was restored, not as much as in my winged 32S3, but enough so it worked OK.
> 
> I could not find anything in the grid circuit/tuned circuit that was causing the loading.  no shorts, opens, etc.  all voltages normal.  There isn’t much there.
> 10K in a grid circuit is a very low value unless collins was trying to kill two birds by using it to drastically lower the Q of the tuned circuit.
> SO I replaced the 10K with a 470K.  I didn’t notice any difference in tuning, but this let the ALC work and deliver ALC voltage to V6 and V3.
> 
> I am tired of working on it so this will have to do for now.
> 
> Thanks all who helped.
> 73, Grayson KJ7UM
> 
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