Pye P45 Chassis

[Pye4T]

Hi,

I've heard that some vintage valve radios used to operate with a live chassis(!). I have a PYE P45 model which seems to have a live chassis - but I don't think it should have! Can anybody confirm?
Thanks - and sorry for the newbie question 

[Refugee]

Welcome to the forum
What are you using to test it with?
Those neon screwdrivers often give a false positive.

[joebog1]

IS there a transformer connected to the power cord, probably through a power switch on the volume control ?.

Joe

[roadster]

I have had a look at the service sheet. The P45 has a mains transformer, so is not a "live chassis" type.

[Mike Watterson]

A Pye P45 should be an isolated chassis. https://www.radiomuseum.org/r/pye_p45p_4.html
I had one or bits of one. See mains transformer in 2nd photo.

There are several faults that can make the chassis live.


A Pye 45A is likely live. https://www.radiomuseum.org/r/pye_45a45.html A 200mA series chain. The EF39 takes 200mA though also a 6.3V type often in parallel isolated chassis.

[Geordie McBoyne]

The power supply and output stage in the Pye P45.
Note the switched tone control system.

Geordie McBoyne.

[Pye4T]

Thank you for all your responses – very kind.

I have since realised that it would be crazy for the chassis to be live as the radio user was encouraged to plug in a simple aerial. Chassis contact would be inevitable.

And yes, it is a neon screwdriver that’s giving me the warning sign. I used a series lamp limiter to test the set. It seems to be dead. Interestingly, P1 & P2 lamps do not light (they both tested good). I have replaced some of the capacitors and a resistor (before switch on), but this problem is slightly beyond my comfort zone and experience. Not sure what to do with it as it is an iconic set.

[ppppenguin]

We can help you bring your set back to life but we need to know a few things first.

1: Can you solder (presumably yes as you've replaced some components)
2: Do you have a test meter? Simple digital multimeters are available for under £10.

You've used a lamp limiter and that's good. Did the lamp light up brightly? Or at all?

Which components did you replace and why? Generally you shouldn't do this as it risks making mistakes which will then be much harder to find.

Where are you in "SW"? If you're within reach of Falmouth there's a member there who may be able to help you in person.

The Trader sheet for the P45 can be downloaded here: https://elektrotanya.com/pye_p45-p46.pdf/download.html If you're using Pye's own service data the component numbers will be different (confusing!) so we all need to be working from the same information in order to help you.

[Pye4T]

Yes to solder and multimeter questions. The lamp limiter light did not shine at all, nor did anything in the set (although I couldn’t see the valves properly as I had the back cover on for safety). There was no hum from the set. The only “life” was from the safety screwdriver when I touched the chassis with it.

Yes, I could have made a mistake replacing components.

I replaced C7, C19, C23, C28 and C29 because – well look at them!

I also replaced R18 with 2 resistors to mimic the centre-tapping requirement – it looked like someone had already been at it and added an extra resistor to the original. It didn’t make any sense as the original centre-tapped resistor was open circuit and the extra resistor was not centre-tapped.

I have attached some photos – underside before and after, what I removed and one of the topside (which looks a little grim now I see it again – maybe I’m expecting too much from it!).


               

[joebog1]

The two resistors you replaced the BIG wirewound with are too small I would suggest.
The big centre tapped one looks to me to be at least 10 watts, you have used, again only by sight, maybe one watt metal films.

They are the main filter/dropper resistors for the whole set, and supply all the HT for the radio.

Geordie has loaded the schematic, so I suggest you download the pic, and print it out. Unfortunnately its only a JPG so it wont be possible to make it much larger than it already is.

It contains the power supply circuit and thats the bit I am specifically discussing with regrads to the big wirewound resistor.

Joe

edit: C37, C38 and C39 may be the reason thhat big resistor went open circuit.
The voltages there will give a VERY nasty boot, so take care!!!.

j.b.