[Collins] removing and disassembling a 70E-8A PTO in a 310B?

[Dr. Gerald N. Johnson]

On Thu, 2008-06-26 at 17:22 -0400, Bob Spooner wrote:
> I recently acquired a Collins 310B transmitter. This is the first piece of
> Collins equipment that I have ever owned, and its been an interesting
> project getting it ready to put on the air. I need to remove and open up the
> PTO to replace some resistors that have changed value so that the oscillator
> output will be high enough. Can anyone give me some advice about removing
> and disassembling the PTO? I want to be sure to not loose the alignment
> between the PTO and the frequency dial, among other things.
> 
I think in that vintage PTO that the resistors and most of the
capacitors are close to the tubes, practically in a separate box from
the permeably tuned coil. Though the pictures I have in my 1948 Radio
Handbook (by Editors and Engineers) show a one piece cover.

I think those early PTO used small paper capacitors for the screen
bypass and output coupling capacitors that have had a propensity to go
leaky. So while checking resistors those capacitors should be replaced.

Aligning the dial should not be difficult, its just a matter of checking
the output frequency and moving the dial to match before tightening the
dial set screws.

Some of the early PTOs included a capsule of silica gel to keep the
interior dry, it might be worth removing that silica gel and
regenerating it (it will be pink now, should be blue when dry) in a 200
degree oven for a few hours. 

By this time the lubrication will need attention too if you desire
smooth PTO operation. Unless it already been replaced a couple times.
>  
> 
> Also, the PTO Specification Data on the CCA web site says that the output of
> the PTO should be 5.2 Volts across 33 pF. Can anyone tell me if that is rms
> or peak voltage?

I'd expect that to be RMS, most likely measured with the diode probe of
an HP 410 VTVM that actually measures peak but is calibrated in RMS.
> 
>  
> 
> Thanks in advance.
> 
>  
> 
> 73, Bob  AD3K
> 
The more common cause of low output might be the tube. Tubes were in
sockets because they did fail more often than any other circuit
components.
-- 
73, Jerry, K0CQ, Technical Advisor to the CRA
All content copyright Dr. Gerald N. Johnson, electrical engineer