Newbie. Pye P75. - UK Vintage Radio Repair and Restoration Discussion Forum

mofanman · 23rd Oct 2016, 6:23 pm

Hi Y'all.

Just bought a 'working' Pye P75 for my new electronics workshop/radio shack. Of course it doesn't work, some signs of life initially but soon faded out. Looks like I just got yet another electronics project as if I didn't have enough..

As a newbie to vintage radio restoration I could do with a few pointers. I have the relevant circuit diagrams and some info. I was going to start by giving it a good clean. replacing the valves and some of the larger caps. Anything else I should consider doing?

Iain

'LIVEWIRE?' · 23rd Oct 2016, 10:00 pm

I doubt that any valves will need replacing, but all waxed paper capacitors will need replacing, in particular the one referred to as 'That capacitor'. I dont have the P75 circuit in front of me, but 'that capacitor' is the one which couples the anode of the Audio preamplifier valve to the control grid of the output valve. This component must be replaced before the radio is powered up again, to prevent damage to possibly irreplaceable components such as the output valve, output transformer, and maybe even the mains transformer.

music-centre · 23rd Oct 2016, 10:20 pm

Hi,
I did some work on one of these recently, the capacitor mentioned that must be changed before you do anything else is C20 - .005uf (if you are using the trader sheet diagram)
I think they are a nice set to repair and work very well once restored.
The valve pins needed a good clean on mine to make it reliable.

Oldelectronics · 23rd Oct 2016, 10:25 pm

Hi Iain if you put Pye P75 into the 'search the website' at the top of the page there is a lot of info on this set including problems and fixes.
regards

Kev

AC/HL · 24th Oct 2016, 12:09 am

Service data here: http://www.service-data.com/section.php/6656/1/p75

Station X · 24th Oct 2016, 9:20 am

You'll find lots of useful information on repairing radios here:-

http://www.vintage-radio.com/repair-...ion/index.html

MurphyNut · 24th Oct 2016, 10:28 am

Contact cleaner, I like to call it "Magic spray" this is always worth using on wave change switches and volume/tone controls.
This can often correct almost failed controls back to perfectly working units.

Sideband · 24th Oct 2016, 2:00 pm

Quote:

Originally Posted by mofanman

I was going to start by giving it a good clean. replacing the valves Anything else I should consider doing?

Yes...don't consider replacing any of the valves yet! This is a common misapprehension by people new to vintage radio. Despite what you may have heard in the past about valves 'being unreliable' it's a complete fallacy and anyone here who has been restoring sets for any length of time will say that many of their sets still have most (or all) of their original valves. Some of the sets can be over 80 years old.

As stated, concentrate on the wax paper capacitors first. If you are not sure which ones these are, come back and we can put you on the right track. Nothing wrong with giving it a good clean-up in the process. Basically get the set going first and the valves can be assessed then. If any are needed, it may just be the output valve or rectifier since these work the hardest.

dazzlevision · 24th Oct 2016, 2:29 pm

Hello,

As an aid to identifying probably faulty capacitors, take a look at this thread:

https://www.vintage-radio.net/forum/...ad.php?t=98964

The ones you are likely to find in your radio are: wax coated, metal cased (but wax impregnated inside), brown or black coloured "Hunts" Moldseal and Dubilier "bumblebee" type with coloured rings and looking like a resistor (but they aren't!).

Regards,

Dazzlevision

HamishBoxer · 24th Oct 2016, 4:29 pm

The ones you are likely to find in your radio are: wax coated, metal cased (but wax impregnated inside), brown or black coloured "Hunts" Moldseal and Dubilier "bumblebee" type with coloured rings and looking like a resistor (but they aren't!).

Except when leaky!

mofanman · 25th Oct 2016, 1:51 pm

Hello,
Thanks for all the advice.
I shall give it a good clean and replace caps C21 and C24 to C32. (Pye service sheet no.s) They are all marked as 'tubular' or electrolytic. The rest are mica and ceramic which I assume are probably OK.
You never know that might be all it needs but if not I'll then check the voltages on the valves as per the circuit analysis sheet.
Ea i presume is anode voltage..
Ia anode current, in mA I hope!
Not sure what Es and Ek are but I'll cross that bridge when I come to it.
I have no experience with valves (born in 1967) apart from using my HF linear amp for my ham radio stuff but I can research the rest hopefully.
For now I just think of them as Voltage devices rather than current and I think I should be able to work the rest out.
No doubt I will repost in a week or so with some problem or other though!

Iain

'LIVEWIRE?' · 25th Oct 2016, 7:13 pm

Es & Ek are Screen grid, respectively, and Cathode Voltages, Ia will be in mA. With an output pentode valve, the Cathode curren (Ik) should be the sum of the anode & screen voltages. Despite being involved with electronics for almost half a century, I don't remember why E is used for voltage, or I for current, nor for that matter, why K is used to denote Cathode. A (anode) and G(grid) are straight forward. Where multi-grid valves are used, G1 is the control grid i.e. the signal input, G2 is the screen grid, and G3 the suppressor grid.

Boater Sam · 25th Oct 2016, 7:33 pm

Could I suggest that you replace the coupling cap and then get the set working before doing any blanket changing of capacitors?

Then if you make an error, you know what you did last, much easier to correct then.

AC/HL · 25th Oct 2016, 8:20 pm

E will presumably refer to EMF, I interestingly is French, but adopted by us in the dim and distant past: https://www.quora.com/Why-is-I-the-s...ectric-current

25th Oct 2016, 9:17 pm

To be pedantic, E is (as said) the EMF measured in volts (V), you can't measure a unit, only how many of them there are. The resultant number should be non dimensional, so measuring an EMF in volts gives E/V the dimensions disappear and all is well in the land of maths etc.. Also if you had a column of figures for resistance it should be titled resistance/ohms assuming you are using ohms as the measurement. Unless the title was resistance and each entry had ohms after the figure implying multiplication.

This could be important where something like weight is described where many different units are used (at least two in common use). Luckily in electronics we have stuck to the same units for a while. It wasn't that long ago capacitance was measured in jars (or is that Jars?).

'LIVEWIRE?' · 26th Oct 2016, 8:44 am

Silly Me! I should have remembered Electromotive Force (EMF), though I didn't know that 'I' stood for Intensity, but then I did learn my theory a long time ago!! Regarding Capacitance being measured in Jars, I recall a now long-deceasd Scotsman with whom I worked in the early 70s telling me that was how they measured it in his younger days, around the time of WW1.

23rd Oct 2016, 6:23 pm	#1
mofanman Retired Dormant Member Join Date: Oct 2016 Location: Norwich, Norfolk, UK. Posts: 2	Newbie. Pye P75. Hi Y'all. Just bought a 'working' Pye P75 for my new electronics workshop/radio shack. Of course it doesn't work, some signs of life initially but soon faded out. Looks like I just got yet another electronics project as if I didn't have enough.. As a newbie to vintage radio restoration I could do with a few pointers. I have the relevant circuit diagrams and some info. I was going to start by giving it a good clean. replacing the valves and some of the larger caps. Anything else I should consider doing? Iain

23rd Oct 2016, 10:00 pm	#2
'LIVEWIRE?' Rest in Peace Join Date: Mar 2006 Location: N.W. Oxfordshire(Chipping Norton) Posts: 7,306	Re: Newbie. Pye P75. I doubt that any valves will need replacing, but all waxed paper capacitors will need replacing, in particular the one referred to as 'That capacitor'. I dont have the P75 circuit in front of me, but 'that capacitor' is the one which couples the anode of the Audio preamplifier valve to the control grid of the output valve. This component must be replaced before the radio is powered up again, to prevent damage to possibly irreplaceable components such as the output valve, output transformer, and maybe even the mains transformer.

23rd Oct 2016, 10:20 pm	#3
music-centre Heptode Join Date: Sep 2007 Location: Brentwood, Essex, UK. Posts: 687	Re: Newbie. Pye P75. Hi, I did some work on one of these recently, the capacitor mentioned that must be changed before you do anything else is C20 - .005uf (if you are using the trader sheet diagram) I think they are a nice set to repair and work very well once restored. The valve pins needed a good clean on mine to make it reliable.

23rd Oct 2016, 10:25 pm	#4
Oldelectronics Heptode Join Date: Jan 2016 Location: Nottinghamshire, UK. Posts: 676	Re: Newbie. Pye P75. Hi Iain if you put Pye P75 into the 'search the website' at the top of the page there is a lot of info on this set including problems and fixes. regards Kev

24th Oct 2016, 12:09 am	#5
AC/HL Dekatron Join Date: Nov 2003 Location: Heckmondwike, West Yorkshire, UK. Posts: 9,642	Re: Newbie. Pye P75. Service data here: http://www.service-data.com/section.php/6656/1/p75

24th Oct 2016, 9:20 am	#6
Station X Moderator Join Date: Jan 2003 Location: Ipswich, Suffolk, IP4, UK. Posts: 21,288	Re: Newbie. Pye P75. You'll find lots of useful information on repairing radios here:- http://www.vintage-radio.com/repair-...ion/index.html __________________ Graham. Forum Moderator Reach for your meter before you reach for your soldering iron.

24th Oct 2016, 10:28 am	#7
MurphyNut Heptode Join Date: Apr 2016 Location: Croxley Green, Hertfordshire, UK. Posts: 979	Re: Newbie. Pye P75. Contact cleaner, I like to call it "Magic spray" this is always worth using on wave change switches and volume/tone controls. This can often correct almost failed controls back to perfectly working units. __________________ Clive

24th Oct 2016, 2:29 pm	#9
dazzlevision Dekatron Join Date: Sep 2003 Location: Near Swindon, North Wiltshire, UK. Posts: 3,612	Re: Newbie. Pye P75. Hello, As an aid to identifying probably faulty capacitors, take a look at this thread: https://www.vintage-radio.net/forum/...ad.php?t=98964 The ones you are likely to find in your radio are: wax coated, metal cased (but wax impregnated inside), brown or black coloured "Hunts" Moldseal and Dubilier "bumblebee" type with coloured rings and looking like a resistor (but they aren't!). Regards, Dazzlevision Last edited by dazzlevision; 24th Oct 2016 at 2:33 pm. Reason: Added text.

24th Oct 2016, 4:29 pm	#10
HamishBoxer Dekatron Join Date: Aug 2007 Location: W.Butterwick, near Doncaster UK. Posts: 8,932	Re: Newbie. Pye P75. The ones you are likely to find in your radio are: wax coated, metal cased (but wax impregnated inside), brown or black coloured "Hunts" Moldseal and Dubilier "bumblebee" type with coloured rings and looking like a resistor (but they aren't!). Except when leaky! __________________ G8JET BVWS Archivist and Member V.M.A.R.S

25th Oct 2016, 1:51 pm	#11
mofanman Retired Dormant Member Join Date: Oct 2016 Location: Norwich, Norfolk, UK. Posts: 2	Re: Newbie. Pye P75. Hello, Thanks for all the advice. I shall give it a good clean and replace caps C21 and C24 to C32. (Pye service sheet no.s) They are all marked as 'tubular' or electrolytic. The rest are mica and ceramic which I assume are probably OK. You never know that might be all it needs but if not I'll then check the voltages on the valves as per the circuit analysis sheet. Ea i presume is anode voltage.. Ia anode current, in mA I hope! Not sure what Es and Ek are but I'll cross that bridge when I come to it. I have no experience with valves (born in 1967) apart from using my HF linear amp for my ham radio stuff but I can research the rest hopefully. For now I just think of them as Voltage devices rather than current and I think I should be able to work the rest out. No doubt I will repost in a week or so with some problem or other though! Iain

25th Oct 2016, 7:13 pm	#12
'LIVEWIRE?' Rest in Peace Join Date: Mar 2006 Location: N.W. Oxfordshire(Chipping Norton) Posts: 7,306	Re: Newbie. Pye P75. Es & Ek are Screen grid, respectively, and Cathode Voltages, Ia will be in mA. With an output pentode valve, the Cathode curren (Ik) should be the sum of the anode & screen voltages. Despite being involved with electronics for almost half a century, I don't remember why E is used for voltage, or I for current, nor for that matter, why K is used to denote Cathode. A (anode) and G(grid) are straight forward. Where multi-grid valves are used, G1 is the control grid i.e. the signal input, G2 is the screen grid, and G3 the suppressor grid.

25th Oct 2016, 7:33 pm	#13
Boater Sam Banned Join Date: Dec 2013 Location: Middlewich, Cheshire, UK. & Winter in the Philippines. Posts: 3,897	Re: Newbie. Pye P75. Could I suggest that you replace the coupling cap and then get the set working before doing any blanket changing of capacitors? Then if you make an error, you know what you did last, much easier to correct then.

25th Oct 2016, 8:20 pm	#14
AC/HL Dekatron Join Date: Nov 2003 Location: Heckmondwike, West Yorkshire, UK. Posts: 9,642	Re: Newbie. Pye P75. E will presumably refer to EMF, I interestingly is French, but adopted by us in the dim and distant past: https://www.quora.com/Why-is-I-the-s...ectric-current

25th Oct 2016, 9:17 pm	#15
Guest Guest Posts: n/a	Re: Newbie. Pye P75. To be pedantic, E is (as said) the EMF measured in volts (V), you can't measure a unit, only how many of them there are. The resultant number should be non dimensional, so measuring an EMF in volts gives E/V the dimensions disappear and all is well in the land of maths etc.. Also if you had a column of figures for resistance it should be titled resistance/ohms assuming you are using ohms as the measurement. Unless the title was resistance and each entry had ohms after the figure implying multiplication. This could be important where something like weight is described where many different units are used (at least two in common use). Luckily in electronics we have stuck to the same units for a while. It wasn't that long ago capacitance was measured in jars (or is that Jars?).

26th Oct 2016, 8:44 am	#16
'LIVEWIRE?' Rest in Peace Join Date: Mar 2006 Location: N.W. Oxfordshire(Chipping Norton) Posts: 7,306	Re: Newbie. Pye P75. Silly Me! I should have remembered Electromotive Force (EMF), though I didn't know that 'I' stood for Intensity, but then I did learn my theory a long time ago!! Regarding Capacitance being measured in Jars, I recall a now long-deceasd Scotsman with whom I worked in the early 70s telling me that was how they measured it in his younger days, around the time of WW1.