PYE PT.501 Marker Oscillator

[agardiner]

Hi,

I have picked up a PYE PT.501 10.7MHz Marker Oscillator, manufactured originally by Labgear Ltd. An interesting little box, very simply with an on/off switch and a banana socket for the output. It contains an OC170 transistor and a crystal. Does anyone know anything about these?

I would love to try it out, but have no idea what battery it would have originally used, and cannot seem to find any information about it.

Thanks.

[Silicon]

I believe the OC170 is susceptible to tin whisker syndrome.

[CambridgeWorks]

I think they take the 15v avo battery? I can't see a crystal in your picture. Is it there? Original was hc6/u type.
These were made for 455KHz, 2MHz and10.7MHz.
Used to zero beat the rx to carrier frequency.
I will look later to see if I have any circuit information.
Rob

[agardiner]

Originally Posted by Silicon

I believe the OC170 is susceptible to tin whisker syndrome.

Yes, I did wonder that.

Originally Posted by robinshack

I think they take the 15v avo battery? I can't see a crystal in your picture. Is it there? Original was hc6/u type.
These were made for 455KHz, 2MHz and10.7MHz.
Used to zero beat the rx to carrier frequency.
I will look later to see if I have any circuit information.
Rob

Thanks. I appreciate it. Yes, the crystal is there; you can't see it in the photo but it is tucked in on the back of the PCB.

[Radio Wrangler]

Could be intended as a centre marker for use when wobbulating.

David

[G6Tanuki]

They were used for 'zero beating' the RX crystals to the base-station transmitter in AM Pye PMR radios.

I've probably got one or two of these in the attic somewhere along with a low-band AM Westminster or three.

[trh01uk]

Virtually every engineer who had been at Pye Telecom a while had one of these in his desk drawer. They were given out well before my time (1977) so I had to make my own, I recall. As I never had one, I never saw what batteries were used....

They were principally used to adjust receiver local oscillators precisely on to frequency, with the aid of a calibrated sig gen to produce a known RF input frequency - typically a HP8640B.


Richard

[agardiner]

Originally Posted by Radio Wrangler

Could be intended as a centre marker for use when wobbulating.

David

Yes, I am hoping to try this.

[agardiner]

OK, tried powering it up with 10V from my bench supply and hooked up to my scope. Nothing initially, but a sharp tap on the OC170 brought up a nice, stable 10.7MHz waveform. So it works, and the frequency is bang on. Yes, I think this will make a good marker.

Need to sort out the tin whiskers now, plus source a suitable battery.

[G6Tanuki]

If it were mine, I would replace the obviously-whiskered OC170 with any modern general-porpoise P-N-P silicon transistor, and use a PP3 battery.

[You _may_ need to tweak the biasing but chances are you won't.)

[CambridgeWorks]

Yours is the first model, dating back to valve days, that's why some were 2MHz.
I only have the later version details, service sheet attached.
There was a series after these as well, built in a blue diecast box, about 75mm x 30mm x 30mm.
10.7/11MHz, 21.4 MHz and 23.455KHz.

Rob

[agardiner]

Originally Posted by G6Tanuki

If it were mine, I would replace the obviously-whiskered OC170 with any modern general-porpoise P-N-P silicon transistor, and use a PP3 battery.

[You _may_ need to tweak the biasing but chances are you won't.)

Yes, I am intending on trying a silicon transistor. If it doesn't work then I will try another germanium device before adjusting the bias, as I have some available. The unit is too small to fit a PP3 in the case!

Originally Posted by robinshack

Yours is the first model, dating back to valve days, that's why some were 2MHz.
I only have the later version details, service sheet attached.
There was a series after these as well, built in a blue diecast box, about 75mm x 30mm x 30mm.
10.7/11MHz, 21.4 MHz and 23.455KHz.

Rob

Thanks Rob. As you say mine is earlier than yours, but I suspect the circuit will be very similar. Will compare as I disassemble to replace the transistor.

[G6Tanuki]

If you can't wangle a PP3 in there, then perhaps a few stacked CR2032 coin-cells in series could be fitted? They probably contain more Coulombs/amp-hours of usable charge than the originally-specified zinc-carbon Leclanche cells would have managed.

[agardiner]

I was thinking of buying the correct battery as there are 15V AVO batteries on ebay for around £6. Cheaper than a stack of coin cells and the unit only draws about 2mA.

[trh01uk]

Originally Posted by agardiner

I was thinking of buying the correct battery as there are 15V AVO batteries on ebay for around £6. Cheaper than a stack of coin cells and the unit only draws about 2mA.

According to the user handbook posted by Robinshack, the correct battery is a 9V one - probably a PP3 size, though you will be best able to judge that by the space available in the case.


Richard

[CambridgeWorks]

That handbook is maybe 15 to 20 years newer model than the one Adrian has.
A pp3 will not fit width ways inside the older case, but the 15V AVO type will, just!
Rob

[agardiner]

Yes. After I measured the space, I concluded that the 15V AVO battery was probably correct and ordered one. Besides the circuit is simple enough and probably quite tolerant of a wide voltage range. It is also interesting that the on / off switch, although a slide switch type, has an internal spring so that it has to be held in the on position.

[Katar83]

Love these little gadgets, I'd use any single rechargeable that will fit in there with a mini step up converter for stable voltage and maybe even fit a mini screw on charging port.
I normally have a bunch of various size batteries though from all sort of discarded devices.