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!

Regards,

Nandu.

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.

Re: Drake TR-4C - PTO problem
 

Permeability tuned oscillator. AFAIK all the '4' series Drake rigs used this tuning method.

Re: Drake TR-4C - PTO problem
 

Thanks Pete.

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.

Regards,

Nandu.

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.

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 ;)

Re: Drake TR-4C - PTO problem
 

Thanks, Graham, for rekindling old memories - I plumb forgot about vintage car radios with permeability tuning!

Regards,

Nandu.

Re: Drake TR-4C - PTO problem
 

Most welcome, Jon.

Real great rigs were the Collins, Drake & Swan!

Regards,

Nandu.

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

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