Newbie Seeking guidance on PYE P76 - Page 3 - UK Vintage Radio Repair and Restoration Discussion Forum

NewbieBrian · 20th Jan 2021, 1:06 pm

Quote:

Originally Posted by Simon Gittins

Lawrence is right. That 110V reading across C17 is a bit higher than expected. There is a mains selector input on the back; if this is set to the 200 to 225V setting, try setting it to the 226 to 250V setting.

I will give that a try and see what the result is.
I did replace C8 AGC decoupler with the remaining 0.047uF I had but again no difference. I am waiting for more replacements to arrive.
Still trying to understand what goes on under the hood and relate the circuit diagram to what I see.
Thank again to everyone for the suggestions.

ms660 · 20th Jan 2021, 1:43 pm

The higher than normal voltage across C17 might be due to the AGC reacting to that horrendous noise signal in your sound clip, as a matter of interest disconnected the antenna and measure the voltage across c17 again and see what change there is.

Lawrence.

NewbieBrian · 20th Jan 2021, 1:52 pm

Quote:

Originally Posted by ms660

The higher than normal voltage across C17 might be due to the AGC reacting to that horrendous noise signal in your sound clip, as a matter of interest disconnected the antenna and measure the voltage across c17 again and see what change there is.

Lawrence.

I will try with antenna disconnected and report back.

In response to Simon and Lawrence:
So far I have had the jumper set in the 225 to 250v position.
In that position when I tested again last night it was seemed to settle at around 98 to 100 v
I have just been out and tried it in the 200 to 220v position.
As I turned it on I had a brief glow from the lamp and then it settled down to a perceptible glow (I unfortunately only had a pearl 100w bayonet and previously I had to look closely to see if the lamp was glowing at all. Once the DC voltage had risen it settled at 68 to 70V with a perceptible glow still to the series limiter.

While I was checking the postman came and so I now have the following if required:

Polyester

630v)
C23 AF Coupling 0.01uF
C33 Negative feedback 0.25uF (replacement 0.22uF)

Electrolytic (450v)
C27 HT decoupling 2uF (replacement 2.2uF)
C30 V4 Cath By-pass 50uF (replacement 47uF)

still waiting for:

C17 SG Decoupling 0.05uF
C25 Part tone control 0.002uF
C26 AF Coupling 0.05uF

Not sure which the best order would be to try replacing them.

NewbieBrian · 20th Jan 2021, 2:21 pm

Results:

In each case I saw the voltage rise up to the region of 240 before dropping back down and settling.

Jumper set to 225 to 250V
Ariel connected 84v
Ariel disconnected 75V

Jumper set to 200 to 220v
Ariel out 75v
Ariel in 85v

so no difference in voltages when I change the jumper but circa 10v difference when ariel removed.

When I was checking 200 to 220v ariel in all of a sudden the speaker fell silent ( or it seemed after all the crackling) thinking something may have popped I shut down.
When I powered up again set to 225 to 250v it came on as normal with crackling.

With the ariel disconnected in both cases the loud interference was absent.

John10b · 20th Jan 2021, 2:24 pm

I listened to your audio clip and it sounds like “interference” , to me.
In your post #31 you tried another set, and it was interference free, interesting! What set did you use and did you plug it into the same socket? Thanks.
John

NewbieBrian · 20th Jan 2021, 2:38 pm

Quote:

Originally Posted by John10b

I listened to your audio clip and it sounds like “interference” , to me.
In your post #31 you tried another set, and it was interference free, interesting! What set did you use and did you plug it into the same socket? Thanks.
John

From the brief try without the ariel I am inclined to agree.
Maybe experiment with ariel.
i did use the same socket to plug in the other radio.
Not a valve radio just an old radio cassette player from the house.

Mr 1936 · 20th Jan 2021, 2:59 pm

Hi Newbie Brian

If your "Other" radio is a radio/cassette player it is almost certain to use an internal ferrite rod aerial.

This type of aerial tends to pick up less electric field interference from very local sources in a domestic situation, which is part of the reason they were adopted from about the mid 1950's. This may explain why it works better.

I suspect that your wire aerial is just responding to the "smog" of local interference generated by all the various electronic devices in your house, with the mains wiring all helping to radiate it. You are not alone in facing this problem.

Without going to solutions which are too exotic, I'd suggest you first try a much longer wire and try and keep the end outdoors as high as possible and as far from the house wiring as possible. Use nylon cord to support and insulate the far end of the wire. The actual wire type and diameter matters very little as long as it's strong enough. Insulation makes little difference. A decent independent earth rod may help too. That way you should be able to increase the signal by more than you increase the interference. In the old days, long aerials were needed because transmitters were weaker and receivers not very sensitive. Today, they are still a good idea but for the reasons of signal versus interference. Your set's AGC circuit will adjust the gain to suit the greater pickup.

Ambientnoise · 20th Jan 2021, 3:04 pm

I noticed some earlier references to using coax as an antenna. Even using just the outer is not optimal, especially if it is on a reel. Just use single core wire (half of bell wire/figure of eight if you have it) into the aerial socket, as long as you can (over say 10 feet) and as high as you can (and away from the floor if indoors).

NewbieBrian · 20th Jan 2021, 3:31 pm

Yes the radio I used did have an internal ariel.
Your suggestions are taking we back to when I was a boy making crystal sets up. The single wire ariel sporting pocelain egg insulators!
That is about the last time I delved into any of this until now.
I did just try a sweep of MW with the ariel disconnected.
I picked up a couple of stations. output volume was low with a slight background hiss but I would say the differential between the signal and interference was improved.
I did try with about a dozen feet of single wire just draped down onto the floor as well but still the interference.
Coming out of the shed again I was reminded of what they have installed just behind us!!!
See photo attached.
Perhaps it is not stray signals from the house after all!

Upshot is I think the radio was working 'out of the box' ( or rather loft).
At least I have changed a couple of capacitors that could prove troublesome in the future. I think I will progress with that, one at a time and check result, if any.

Seeing as the choice on the wavebands is limited in scope I may in the future try using the Gram input and see what that performs like once it is sorted.

Not sure yet if the voltages I am seeing are a cause for concern.

paulsherwin · 20th Jan 2021, 3:48 pm

I think you have found the source of the interference.

You should not be measuring voltages with the lamp limiter in circuit, as these will be misleading. No valve radio will work well with the limiter in circuit, as the valve heaters will be being underrun.

The purpose of the lamp limiter is to give some protection against switchon disasters when powering up an unknown set. Once you have established that all is well, then you don't need it any more.

NewbieBrian · 20th Jan 2021, 3:55 pm

Quote:

Originally Posted by paulsherwin

I think you have found the source of the interference.

You should not be measuring voltages with the lamp limiter in circuit, as these will be misleading. No valve radio will work well with the limiter in circuit, as the valve heaters will be being underrun.

The purpose of the lamp limiter is to give some protection against switchon disasters when powering up an unknown set. Once you have established that all is well, then you don't need it any more.

Point taken.
I did put it in series as I switched on with the lower input setting the first time.
The subsequent readings ariel in/ out on both input settings were taken with the lamp bypassed.

Simon Gittins · 20th Jan 2021, 5:16 pm

Please leave the mains selector set to the highest voltage position; I thought that it might have been in the lower position and that might have explained the slightly high voltage.
The voltages should be measured with no signal input (the Trader sheet says "with the receiver tuned to the highest wavelength end of M.W.")
At 75V with no signal the voltage across C17 is close enough to 63V so no problem there.
There is no particular order to replace the capacitors you mention, checking after each one will show you what difference changing each one makes and will confirm that you haven't made a mistake.

NewbieBrian · 20th Jan 2021, 5:36 pm

Quote:

Originally Posted by Simon Gittins

Please leave the mains selector set to the highest voltage position; I thought that it might have been in the lower position and that might have explained the slightly high voltage.
The voltages should be measured with no signal input (the Trader sheet says "with the receiver tuned to the highest wavelength end of M.W.")
At 75V with no signal the voltage across C17 is close enough to 63V so no problem there.
There is no particular order to replace the capacitors you mention, checking after each one will show you what difference changing each one makes and will confirm that you haven't made a mistake.

Thanks Simon.
I confirm it is back at the 225 to 250V setting.

I have just changed the following four and checked after each one.
C23 AF Coupling 0.01uF
C33 Negative feedback 0.25uF (replacement 0.22uF)

Electrolytic (450v)
C27 HT decoupling 2uF (replacement 2.2uF)
C30 V4 Cath By-pass 50uF (replacement 47uF)

No change but hopefully a little future proofing done.

One that I have been unable to locate a replacement for is the electrolytic on the output transformer it is rated at 0.005uF 1000V

The lamps have arrived and they worked once I put them in. Strange that I could detect no voltage there.

At least it should look better with the tuner lit even if the sound is off.
I thought I might try this to see what it actually sounds like.

https://joefreeman.weebly.com/connec...age-radio.html

I will see if I can sort something out regarding the ariel.
Not sure how it will work out with what we have behind us though.
In the words of Del Boy "What a Plonker". I should have realised that but have got so used to it being there over the years it became invisible.
It certainly seems to have sprouted more appendages since I last looked!

Brian

Simon Gittins · 20th Jan 2021, 6:15 pm

Sounds like a good result there, well done.

Quote:

Originally Posted by NewbieBrian

One that I have been unable to locate a replacement for is the electrolytic on the output transformer it is rated at 0.005uF 1000V

The lamps have arrived and they worked once I put them in. Strange that I could detect no voltage there.

The 0.005uF 1000V capacitor isn't an electrolytic (although it may look like one).
I think you said your meter was on a DC range when measuring the supply to the lamps and it's AC. They are now lit and that makes all the difference to the look of a radio.

Mr 1936 · 20th Jan 2021, 6:34 pm

Hi

I wouldn't worry about the tower behind you. The chance of professional microwave kit built in properly screened cases inside a screened building causing interference at Medium Wave frequencies is negligible.

I think your interference source(s) are much more likely to be closer to home. If you can get a battery powered MW portable, try tuning it off station and taking it for a walk round your house and get it close to any power supplies, lamps etc. You may identify more than one source of noise. Such things are often in unscreened plastic cases and have minimal filtering on their cables. You will be lucky if they even scrape through the legal emissions tests, which are not especially onerous.

Neil Purling · 20th Jan 2021, 6:59 pm

I was reading your thread from the beginning. I am glad to read that you have got some sound, even if it is cursed with interference.

Hybrid tellies · 21st Jan 2021, 2:14 pm

Before I come in with some aerial advice which you might find useful can someone confirm that the Pye P76 is an AC radio and not AC/DC.
I think it is an AC only radio but not 100% sure.

paulsherwin · 21st Jan 2021, 2:22 pm

Yes, E series valves.

https://www.radiomuseum.org/r/pye_p76p_7.html

NewbieBrian · 21st Jan 2021, 3:12 pm

Next time I am 'Home Alone' I will try turning off everything and bring items into play one by one to see if I can locate source of interference.
I can only try.
I am sure we must have a battery powered radio somewhere, not so sure we have batteries at the moment. I will certainly try that when I can.
I was interested to read some threads here where people were discovering neighbors with noisy equipment using this method.
Aerial advice, that sounds good. I have been searching on here and reading various threads on the subject.
I have also been reading up on the subject of earthing the chassis via 3 core mains lead.
I did try running an earth lead for the signal from the socket on the radio to see if it helped but detected no perceptible improvement.

What has been of great assistance was my purchasing the 9 page service data via download.
I found the circuit diagrams in that very much clearer and easier to follow. The two page service sheets diagrams are rather blurry and much more difficult to follow, especially if like me you initially had no idea of what you are looking at!
It is a pity the component numbering on the two sheets differs though.
With the two sheets and the valve specifications I have downloaded I think I have the information needed.
I just need to process it!
I am looking forward to once again hearing the sound of a well sorted valve radio. It may be nostalgia, but there was some quality of the sound that I loved.

NewbieBrian · 21st Jan 2021, 4:33 pm

I have just checked the resistor R1 that links between the aerial and earth sockets.
The resistance in the service data is 22K ohms.
The readings I get are 25.6K with the Band switch in the following positions Gram, LW,TB.SW
In medium wave it is showed open circuit. when I lowered the range on the multimeter I got a reading of 17 Ohms.

I have had a look at the data sheet but have not been able to work out why I should get this result.

20th Jan 2021, 1:43 pm	#42
ms660 Dekatron Join Date: Apr 2011 Location: Cornwall, UK. Posts: 13,454	Re: Newbie Seeking guidance on PYE P76 The higher than normal voltage across C17 might be due to the AGC reacting to that horrendous noise signal in your sound clip, as a matter of interest disconnected the antenna and measure the voltage across c17 again and see what change there is. Lawrence.

20th Jan 2021, 2:21 pm	#44
NewbieBrian Triode Join Date: Jan 2021 Location: Aldershot, Hampshire, UK Posts: 29	Re: Newbie Seeking guidance on PYE P76 Results: In each case I saw the voltage rise up to the region of 240 before dropping back down and settling. Jumper set to 225 to 250V Ariel connected 84v Ariel disconnected 75V Jumper set to 200 to 220v Ariel out 75v Ariel in 85v so no difference in voltages when I change the jumper but circa 10v difference when ariel removed. When I was checking 200 to 220v ariel in all of a sudden the speaker fell silent ( or it seemed after all the crackling) thinking something may have popped I shut down. When I powered up again set to 225 to 250v it came on as normal with crackling. With the ariel disconnected in both cases the loud interference was absent.

20th Jan 2021, 2:24 pm	#45
John10b Nonode Join Date: Nov 2016 Location: Aberaeron, Ceredigion, Wales, UK. Posts: 2,884	Re: Newbie Seeking guidance on PYE P76 I listened to your audio clip and it sounds like “interference” , to me. In your post #31 you tried another set, and it was interference free, interesting! What set did you use and did you plug it into the same socket? Thanks. John

20th Jan 2021, 2:59 pm	#47
Mr 1936 Heptode Join Date: Mar 2017 Location: Romsey, Hampshire, UK. Posts: 521	Re: Newbie Seeking guidance on PYE P76 Hi Newbie Brian If your "Other" radio is a radio/cassette player it is almost certain to use an internal ferrite rod aerial. This type of aerial tends to pick up less electric field interference from very local sources in a domestic situation, which is part of the reason they were adopted from about the mid 1950's. This may explain why it works better. I suspect that your wire aerial is just responding to the "smog" of local interference generated by all the various electronic devices in your house, with the mains wiring all helping to radiate it. You are not alone in facing this problem. Without going to solutions which are too exotic, I'd suggest you first try a much longer wire and try and keep the end outdoors as high as possible and as far from the house wiring as possible. Use nylon cord to support and insulate the far end of the wire. The actual wire type and diameter matters very little as long as it's strong enough. Insulation makes little difference. A decent independent earth rod may help too. That way you should be able to increase the signal by more than you increase the interference. In the old days, long aerials were needed because transmitters were weaker and receivers not very sensitive. Today, they are still a good idea but for the reasons of signal versus interference. Your set's AGC circuit will adjust the gain to suit the greater pickup.

20th Jan 2021, 3:04 pm	#48
Ambientnoise Heptode Join Date: Feb 2006 Location: Marlborough, Wiltshire, UK. Posts: 915	Re: Newbie Seeking guidance on PYE P76 I noticed some earlier references to using coax as an antenna. Even using just the outer is not optimal, especially if it is on a reel. Just use single core wire (half of bell wire/figure of eight if you have it) into the aerial socket, as long as you can (over say 10 feet) and as high as you can (and away from the floor if indoors).

20th Jan 2021, 3:31 pm	#49
NewbieBrian Triode Join Date: Jan 2021 Location: Aldershot, Hampshire, UK Posts: 29	Re: Newbie Seeking guidance on PYE P76 Yes the radio I used did have an internal ariel. Your suggestions are taking we back to when I was a boy making crystal sets up. The single wire ariel sporting pocelain egg insulators! That is about the last time I delved into any of this until now. I did just try a sweep of MW with the ariel disconnected. I picked up a couple of stations. output volume was low with a slight background hiss but I would say the differential between the signal and interference was improved. I did try with about a dozen feet of single wire just draped down onto the floor as well but still the interference. Coming out of the shed again I was reminded of what they have installed just behind us!!! See photo attached. Perhaps it is not stray signals from the house after all! Upshot is I think the radio was working 'out of the box' ( or rather loft). At least I have changed a couple of capacitors that could prove troublesome in the future. I think I will progress with that, one at a time and check result, if any. Seeing as the choice on the wavebands is limited in scope I may in the future try using the Gram input and see what that performs like once it is sorted. Not sure yet if the voltages I am seeing are a cause for concern. Attached Thumbnails

20th Jan 2021, 3:48 pm	#50
paulsherwin Moderator Join Date: Jun 2003 Location: Oxford, UK Posts: 27,944	Re: Newbie Seeking guidance on PYE P76 I think you have found the source of the interference. You should not be measuring voltages with the lamp limiter in circuit, as these will be misleading. No valve radio will work well with the limiter in circuit, as the valve heaters will be being underrun. The purpose of the lamp limiter is to give some protection against switchon disasters when powering up an unknown set. Once you have established that all is well, then you don't need it any more.

20th Jan 2021, 5:16 pm	#52
Simon Gittins Heptode Join Date: Jan 2006 Location: Cornwall, UK. Posts: 506	Re: Newbie Seeking guidance on PYE P76 Please leave the mains selector set to the highest voltage position; I thought that it might have been in the lower position and that might have explained the slightly high voltage. The voltages should be measured with no signal input (the Trader sheet says "with the receiver tuned to the highest wavelength end of M.W.") At 75V with no signal the voltage across C17 is close enough to 63V so no problem there. There is no particular order to replace the capacitors you mention, checking after each one will show you what difference changing each one makes and will confirm that you haven't made a mistake.

20th Jan 2021, 6:34 pm	#55
Mr 1936 Heptode Join Date: Mar 2017 Location: Romsey, Hampshire, UK. Posts: 521	Re: Newbie Seeking guidance on PYE P76 Hi I wouldn't worry about the tower behind you. The chance of professional microwave kit built in properly screened cases inside a screened building causing interference at Medium Wave frequencies is negligible. I think your interference source(s) are much more likely to be closer to home. If you can get a battery powered MW portable, try tuning it off station and taking it for a walk round your house and get it close to any power supplies, lamps etc. You may identify more than one source of noise. Such things are often in unscreened plastic cases and have minimal filtering on their cables. You will be lucky if they even scrape through the legal emissions tests, which are not especially onerous.

20th Jan 2021, 6:59 pm	#56
Neil Purling Nonode Join Date: Jul 2005 Location: Hull, East Yorkshire, UK. Posts: 2,087	Re: Newbie Seeking guidance on PYE P76 I was reading your thread from the beginning. I am glad to read that you have got some sound, even if it is cursed with interference. Last edited by Neil Purling; 20th Jan 2021 at 7:06 pm.

21st Jan 2021, 2:14 pm	#57
Hybrid tellies Nonode Join Date: Jan 2004 Location: 1966-1976 Coverack in Cornwall and Helston Cornwall. 1976-present Bristol/Bath area. Posts: 2,965	Re: Newbie Seeking guidance on PYE P76 Before I come in with some aerial advice which you might find useful can someone confirm that the Pye P76 is an AC radio and not AC/DC. I think it is an AC only radio but not 100% sure. __________________ Simon BVWS member

21st Jan 2021, 2:22 pm	#58
paulsherwin Moderator Join Date: Jun 2003 Location: Oxford, UK Posts: 27,944	Re: Newbie Seeking guidance on PYE P76 Yes, E series valves. https://www.radiomuseum.org/r/pye_p76p_7.html

21st Jan 2021, 3:12 pm	#59
NewbieBrian Triode Join Date: Jan 2021 Location: Aldershot, Hampshire, UK Posts: 29	Re: Newbie Seeking guidance on PYE P76 Next time I am 'Home Alone' I will try turning off everything and bring items into play one by one to see if I can locate source of interference. I can only try. I am sure we must have a battery powered radio somewhere, not so sure we have batteries at the moment. I will certainly try that when I can. I was interested to read some threads here where people were discovering neighbors with noisy equipment using this method. Aerial advice, that sounds good. I have been searching on here and reading various threads on the subject. I have also been reading up on the subject of earthing the chassis via 3 core mains lead. I did try running an earth lead for the signal from the socket on the radio to see if it helped but detected no perceptible improvement. What has been of great assistance was my purchasing the 9 page service data via download. I found the circuit diagrams in that very much clearer and easier to follow. The two page service sheets diagrams are rather blurry and much more difficult to follow, especially if like me you initially had no idea of what you are looking at! It is a pity the component numbering on the two sheets differs though. With the two sheets and the valve specifications I have downloaded I think I have the information needed. I just need to process it! I am looking forward to once again hearing the sound of a well sorted valve radio. It may be nostalgia, but there was some quality of the sound that I loved.

21st Jan 2021, 4:33 pm	#60
NewbieBrian Triode Join Date: Jan 2021 Location: Aldershot, Hampshire, UK Posts: 29	Re: Newbie Seeking guidance on PYE P76 I have just checked the resistor R1 that links between the aerial and earth sockets. The resistance in the service data is 22K ohms. The readings I get are 25.6K with the Band switch in the following positions Gram, LW,TB.SW In medium wave it is showed open circuit. when I lowered the range on the multimeter I got a reading of 17 Ohms. I have had a look at the data sheet but have not been able to work out why I should get this result.