Pye M78F questions

[stevehertz]

Now that I've finally managed to acquire one, I have a few of questions about the PYE M78F if any owners or enthusiasts can help please?

Firstly, to build a suitable power supply. Spec? Circuit? Construction? Fit internally or externally?

Any common faults or issues to look out for?

Looking at photos on the internet there seems to be quite a range of colours that they were available in. Bearing in mind that it's difficult to differentiate photos from different sources (hues etc) and I may well be getting confused, I've identified the following colours where the first colour is the main body and the second is the sides:

Cream/black
Pale cyan/white
Pale green/cream
Cream/pink
White/black
White/cream
White/pink

Any comments or corrections?

Also, some appear to have black plastic handles and others translucent.

Thanks.

[stevehertz]

I've found this ready built power supply specially developed for use with AM valve radios: https://www.ebay.co.uk/itm/90-Volt-B...v/174525122023

[Lloyd 1985]

You could make up a battery pack using 9V batteries and a single 1.5v cell for the filaments, or build an inverter that runs from 6V, with a reed relay used as a current sensor in the LT circuit to switch the HT on and off, I’ve built a couple of those, but they do generate a little noise on the audio.

I’d love to get one of these little radios, I’ve only ever seen one in person, they are a little out of my price range these days though!

Regards
Lloyd

[Ed_Dinning]

Hi Steve, beware of inverter drive battery eliminators; in some sets they work great, in others they generate a lot of hash that is difficult to filter.
A battery stack works well, as does a small mains powered unit for demo purposes (Unless you want to take the set on picnics)

Ed

[Cobaltblue]

The HT on these is 67.5 v and LT is via a single D cell.

It's hard to get more than 7 PP3's in the small space.

That's just 63V but it doesn't make much difference to it's performance.

I would tend to run it on batteries if possible this sets performance isn't great.

On the question of the handle the only ones I have seen that look to be genuine are translucent.

Cheers

Mike T

[stevehertz]

Originally Posted by Ed_Dinning

Hi Steve, beware of inverter drive battery eliminators; in some sets they work great, in others they generate a lot of hash that is difficult to filter.
A battery stack works well, as does a small mains powered unit for demo purposes (Unless you want to take the set on picnics)

Ed

Well, that's what I was thinking, so I asked the question of the seller. He replied:

"Hi

It is linear, using two power transformers for LT & HT
HT is semi regulated at 90, 67 and 45v and LT is fully regulated at 1.4v"

So, seems like he knows his onions?

[Herald1360]

FWIW if it's the:

https://www.ebay.co.uk/itm/90-Volt-B...v/174525122023

It looks from the pictures like a well engineered (perhaps even somewhat overkill) linear power supply unit. The price reflects the non trivial cost of the components used let alone any reasonable profit for the maker!

Onions known, in other words

[Lloyd 1985]

Certainly looks better than the Amplion ‘Convette’ battery eliminator that I’ve been using! The 2 transformers were probably quite pricey, especially if they weren’t off the shelf items. It would certainly be a good unit if you don’t want to go down the build it yourself route.

The inverter power units I’ve built do make a bit of noise, somewhere in the region of 20-30hz, which can come through on the audio as a quiet purring noise in the background, on the sets I’ve used it on it can normally disappear into the background with the volume turned up, i have one that I use in a Bush BP10 which by the design of the radio it has to sit right in the middle of the frame aerial, so it had to be quiet! I’m no expert at inverter design, so I just experimented with adding chokes and different capacitor values until it was acceptable.

Regards
Lloyd

[stevehertz]

Maybe I'm worrying about nothing, but he says that the LT is 1.4V, not 1.5V. I guess it's neither here nor there.

[ms660]

Originally Posted by stevehertz

Maybe I'm worrying about nothing, but he says that the LT is 1.4V, not 1.5V. I guess it's neither here nor there.

1.4 volts is what it should be for parallel heaters:

http://www.r-type.org/pdfs/dl92.pdf

Lawrence.

[vinrads]

Hi Steve much better to make it self contained for this radio, you need eight x pp3's =72 volts and one d cell , construct a B101 battery box , available as a download , the main thing is the set may need work and they are not the easiest sets to work on, as I was telling you earlier ,the vol cont is a special 2meg ohm , I had to graft a track onto the original housing ,Mick.

[stevehertz]

Mick, I don't want to make one out of batteries, it'll only last a finite time. With its limited performance characteristics it's not as if this will be a regular 'go to' set for daily listening purposes. I want a reliable, mains power supply that I can use on the occasions that I may want to fire it up or demonstrate it. I'm thinking more and more about an external unit that can lie away from the set, like the one that's on eBay in fact and I will probably go for. I'll see if anything else crops up on here.

That's a lovely looking green and white set there!

[Cobaltblue]

You could build this one adapting parts you have.


https://www.vintage-radio.com/projec...y-set-psu.html

Cheers

Mike T

[vinrads]

In that case I would go for the one with proper mains transformers , not a switch mode one ,as Chris suggested post 7. good luck with it , Mick.

[stevehertz]

Originally Posted by vinrads

In that case I would go for the one with proper mains transformers , not a switch mode one ,as Chris suggested post 7. good luck with it , Mick.

Well yes, fearing SMPSs myself, that's the link that I proposed back in post 2. Chris repeated it. Cheers.

[stevehertz]

Originally Posted by Cobaltblue

You could build this one adapting parts you have.


https://www.vintage-radio.com/projec...y-set-psu.html

Cheers

Mike T

Cheers Mike, that looks an excellent build. How would I reduce the HT to around 67v as required by the Pye?

Now, I have to ask myself, do I want to spend hours building my own to save a few tens of pounds, or buy that new one? Hmm. I really do love building stuff but already have a mountain of restorations and other home projects on my hands..

[Cobaltblue]

You could try using a 12 12 transformer instead of the 15 15 that should give you the lower HT

It would also reduce the amount of waste in the LT circuit.

Cheers

Mike T

[stevehertz]

Originally Posted by Cobaltblue

You could try using a 12 12 transformer instead of the 15 15 that should give you the lower HT

It would also reduce the amount of waste in the LT circuit.

Cheers

Mike T

Thanks Mike. So reduce the value of R4?

[ajs37]

I have 2 of these radios - and they are among my favourites for their appearance. They were not cheap - one from Ebay and the other from an RWB auction (one does have an original black handle - see photos). As Mike says - not great performers - I have tried them on batteries and using an eliminator and I can see why they were withdrawn from circulation (besides the Rising Sun controversy)!
They sit in a glass cabinet, in my study - away from the little fingers of my grandchildren (there are enough robust radios on open display for them to play with).
I don't plan on 'restoring' the two I have, which is unusual for me, as I normally like my radios to work! As can be seen in the photos, one has a replacement baseplate - quite well done as well!
Good luck with yours Steve!
Cheers
Andy

[HamishBoxer]

I built 2 of those vintage Radio power supplies and they are first class I add. Used all RS components.

Just a point , all DKDL etc 1.4V valves never saw that figure due to batteries being 1.5 v of course. Unless I am wrong.