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Vintage Amateur and Military Radio Amateur/military receivers and transmitters, morse, and any other related vintage comms equipment.

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Old 10th Feb 2019, 3:28 am   #1
vu2nan-nandu
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Default Drake TR-4C - PTO problem

In the process of troubleshooting a faulty Drake TR-4C, years ago, the root cause was traced to a non-working PTO.

A visual examination of the mint-condition PCB revealed nothing. Component checks with a multimeter also showed nothing amiss.

Then 'Eureka'! A continuity test showed that the PTO coil was isolated from ground.

A closer examination of the PCB, with a magnifying glass, revealed a dry-solder connection at the ground end of the PTO coil.

Just one solder touch-up and the old workhorse was back in business!

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Nandu.
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Old 10th Feb 2019, 12:24 pm   #2
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Default Re: Drake TR-4C - PTO problem

Excuse me for asking, but what's a PTO coil?

To me PTO denotes Power Take Off as used by tractors.
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Old 10th Feb 2019, 12:42 pm   #3
g4aaw pete
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Default Re: Drake TR-4C - PTO problem

Permeability tuned oscillator. AFAIK all the '4' series Drake rigs used this tuning method.
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Old 10th Feb 2019, 12:51 pm   #4
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Default Re: Drake TR-4C - PTO problem

Thanks Pete.
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Old 10th Feb 2019, 1:08 pm   #5
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Default Re: Drake TR-4C - PTO problem

Hi Graham,

Yes, as Pete says, PTO refers to 'permeability tuned oscillator'. Thanks, Pete!

Permeability tuning is variable-inductance tuning effected by the movement of a ferrite slug in the coil.

Linear tuning is achieved with a variable-pitch coil.

All Drake rigs use a PTO as VFO.

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Old 10th Feb 2019, 1:53 pm   #6
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Default Re: Drake TR-4C - PTO problem

Yes. I'm familiar with permeability tuning as it was often used in car radios having mechanical pre-set tuning. I just hadn't heard the term PTO used in this context before.
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Old 10th Feb 2019, 2:10 pm   #7
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Default Re: Drake TR-4C - PTO problem

Thanks for the enlightenment about variable pitch inductor winding to linearise the tuning.
I have some Swan rigs that use these and I always wondered how they got it so good.
I have never taken one apart - maybe I should now
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Old 10th Feb 2019, 2:26 pm   #8
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Default Re: Drake TR-4C - PTO problem

Quote:
Originally Posted by Station X View Post
Yes. I'm familiar with permeability tuning as it was often used in car radios having mechanical pre-set tuning. I just hadn't heard the term PTO used in this context before.
Thanks, Graham, for rekindling old memories - I plumb forgot about vintage car radios with permeability tuning!

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Old 10th Feb 2019, 5:00 pm   #9
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Default Re: Drake TR-4C - PTO problem

Quote:
Originally Posted by Jon_G4MDC View Post
Thanks for the enlightenment about variable pitch inductor winding to linearise the tuning.
I have some Swan rigs that use these and I always wondered how they got it so good.
I have never taken one apart - maybe I should now
Most welcome, Jon.

Real great rigs were the Collins, Drake & Swan!

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Old 10th Feb 2019, 5:13 pm   #10
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Default Re: Drake TR-4C - PTO problem

Drake used a permeability tuned oscillator, the Ten Tec Corsair sports one, but the famous user was Collins i a lot of their professional and amateur classics.

In lieu of a gearbox, a screw thread gave lots of reduction.

Artful variation of the spacing of the turns along the former could give a nice linear tuning scale.

Wear of the screw can be a problem

David
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Old 11th Feb 2019, 12:13 am   #11
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Default Re: Drake TR-4C - PTO problem

Hi,

I have a Drake SPR-4 receiver with a PTO, Unfortunately there is wear
on the threads, and tuning can be a bit of a lottery!

Kind regards
Dave
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