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Old 15th Jan 2021, 3:59 pm   #1
NewbieBrian
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Default Newbie Seeking guidance on PYE P76

Hello everyone.
My first post here.
Yesterday I got down a PYE 76 from the loft in the hope that I might be able to get it going again.
It came to me a number of years ago with the message that it had been working when last used except for the lamps.
Back then I turned it on briefly and it produced a mains hum but nothing else.
It has resided in the loft ever since. Until yesterday that is!
I found this site when browsing the web for information.
I also found and downloaded the service sheet.
After taking a look at the sheet and a bit more browsing I removed the chassis gave the case a polish and made a repair to the cloth on the front to stop a tear getting worse.
I should say here that I have no experience of electronics, just normal everyday things like sorting out car electrics etc when needs must.

After taking a look at the guide on here I have had a look at the components on the chassis and made a few basic that I could with a multimeter.
Here is what I have found so far:
It looks to my untrained eye as if it is in original condition.
The valves fitted are correct.
I could see no signs of any overheating or leaky/ bulging capacitors.
Wiring all seemed intact.
Checking the mains transformer I got the following readings:

LHS (numbered 1 to 4 top to bottom viewed from under knobs up)
4 & 3, 262 ohms
4 & 2, 2 ohms
4 & 1, 273 ohms

RHS (numbered 1 to 4 top to bottom viewed from under knobs up)
4 & 3, 32 ohms
4 & 2, 36 ohms

Output transformer (viewing from above front Left to right no 1 to 5 , white, black, brown, blue, bare)
Brown to blue, 557 ohms (speaker click heard when testing)
Brown to black, 24 ohms

From the diagram I was not certain which terminal was which but a number of the readings seem to correlate with those on service sheet.

Mains switch:
Testing resistance between mains lead wires as on switch operated - a value of a few hundred ohms is seen initially dropping to 36 ohms after a second or so.

Does this seem right?

I also checked the following resistors which I understand to be on the HT side:
R13 5.95 K Ohms (HT decoupling) specified value 4.7K
R6 30.8 K Ohms (S.G. HT feed) " " 27K
R19 1.53k (HT Smoothing) " " 1.6K

Are these within acceptable range?

Regarding the capacitors I am not sure how valid, if at all the following checks would be but I checked the resistance in circuit with the following results.

Capacitors: (Tested on 2000k range)
C28 Resistance low and rises I stopped at 1300K ohms after 35 secs
C8 Resistance low rapidly rises and goes open circuit 5 secs
C26 " " " " " " " 2 secs
C17 Resistance low and rises I stopped at 690K ohms after 35 secs


I read about rigging up a 100w lamp in series to give a visual indication of current when initially powering the radio and would intend to do that.
What I am wondering is what steps I should take before I attempted that?

As I said I have no prior experience of this and I freely admit that most of what I read on here is totally over my head.
Basically I would like, if possible to undertake whatever I need to in order to try powering up the beast and take it from there.
I have no doubt that if there are any but simple faults it will be beyond my pay grade but if there are some things I can do I am happy to try.

Brian
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Old 15th Jan 2021, 4:54 pm   #2
mark pirate
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Default Re: Newbie Seeking guidance on PYE P76

Quote:
Back then I turned it on briefly and it produced a mains hum but nothing else.
This sounds like the main smoothing cap, this will require replacing, as well as the wax covered caps under the chassis.

This is an AC only set, so a lot safer for a novice to restore than the AC/DC live chassis sets.


Mark
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Old 15th Jan 2021, 5:04 pm   #3
NewbieBrian
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Default Re: Newbie Seeking guidance on PYE P76

Quote:
Originally Posted by mark pirate View Post
Quote:
Back then I turned it on briefly and it produced a mains hum but nothing else.
This sounds like the main smoothing cap, this will require replacing, as well as the wax covered caps under the chassis.

This is an AC only set, so a lot safer for a novice to restore than the AC/DC live chassis sets.


Mark
Thanks.
From what I see that is the metal can one behind the mains transformer.
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Old 15th Jan 2021, 5:14 pm   #4
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Default Re: Newbie Seeking guidance on PYE P76

These are good beginner's sets and fairly easy to work on.

The values you have measured seem OK. Resistors can be quite a way off value and still work perfectly well.

You say you are going to make a lamp limiter. That is a very good idea and will prevent all sorts of switchon disasters. You don't need anything fancy or sophisticated, just some method of connecting a 100W incandescent bulb in series with the power supply. When you apply power, the bulb will initially glow very dimly, then get brighter as the valves warm up. If it glows very brightly then there is a problem which needs investigation.

A loud constant hum does suggest the smoothing capacitors have failed. You may be able to reform them (search the forum for info) or you can replace them with modern components under the chassis.

There are lots of potentially leaky wax capacitors in there. You will probably need to change all of them, but do them one at a time, starting with the one connected to the EL41 control grid. Only values between 0.001uF and 0.1uF are suspect.
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Old 15th Jan 2021, 5:35 pm   #5
Simon Gittins
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Default Re: Newbie Seeking guidance on PYE P76

This will need a few feet of wire connected to the "Aerial" socket; something that is often forgotten nowadays!
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Old 15th Jan 2021, 5:46 pm   #6
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Default Re: Newbie Seeking guidance on PYE P76

Simon is right. The more wire you can hook up the better, particularly for LW use.
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Old 15th Jan 2021, 5:50 pm   #7
NewbieBrian
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Default Re: Newbie Seeking guidance on PYE P76

Quote:
Originally Posted by paulsherwin View Post
These are good beginner's sets and fairly easy to work on.

The values you have measured seem OK. Resistors can be quite a way off value and still work perfectly well.

You say you are going to make a lamp limiter. That is a very good idea and will prevent all sorts of switchon disasters. You don't need anything fancy or sophisticated, just some method of connecting a 100W incandescent bulb in series with the power supply. When you apply power, the bulb will initially glow very dimly, then get brighter as the valves warm up. If it glows very brightly then there is a problem which needs investigation.

A loud constant hum does suggest the smoothing capacitors have failed. You may be able to reform them (search the forum for info) or you can replace them with modern components under the chassis.

There are lots of potentially leaky wax capacitors in there. You will probably need to change all of them, but do them one at a time, starting with the one connected to the EL41 control grid. Only values between 0.001uF and 0.1uF are suspect.
Thank you.
I have already ordered two 0.047 uF 630v polyester capacitors.
I was going to replace C28 first (AF coupling) and take it from there.
Did I read diagram correctly that is the one connected to the EL41 Control grid?
I must tread carefully as these terms were double Dutch to me this time yesterday.

Also I spotted this (attached image) on eBay: Does that look the correct replacement for the smoothing capacitor?

When should I try connecting through a lamp in series?
Should I wait for the replacement for the 0.05uF to come and replace that before firing up. Or should I get the replacement smoothing capacitor as well?

I don't know if there is any life in it so don't want to go too far down the road but also do not want to do any further damage.
i would certainly be ready with the off switch anyway!
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Old 15th Jan 2021, 5:52 pm   #8
NewbieBrian
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Default Re: Newbie Seeking guidance on PYE P76

Quote:
Originally Posted by Simon Gittins View Post
This will need a few feet of wire connected to the "Aerial" socket; something that is often forgotten nowadays!
It had a few feet of wire on a plug in the back.
I guess I will put a longer length on that!
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Old 15th Jan 2021, 7:40 pm   #9
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Thumbs up Re: Newbie Seeking guidance on PYE P76

Quote:
Originally Posted by NewbieBrian View Post
It had a few feet of wire on a plug in the back.
I guess I will put a longer length on that!
I think a few feet will be enough at this stage, Brian, while you get it going.

There is some useful guidance here: https://www.vintage-radio.com/repair...ion/index.html, including a section on applying power for the first time.
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Old 15th Jan 2021, 8:57 pm   #10
Simon Gittins
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Default Re: Newbie Seeking guidance on PYE P76

Quote:
Originally Posted by NewbieBrian View Post
I was going to replace C28 first (AF coupling) and take it from there.
Did I read diagram correctly that is the one connected to the EL41 Control grid?
Yes, C28 (on the Trader sheet) goes to the EL41 Control grid via R18.

Quote:
Originally Posted by NewbieBrian View Post
Also I spotted this (attached image) on eBay: Does that look the correct replacement for the smoothing capacitor?
A double 32uF is the correct original type but I hope you are not thinking of replacing it with a genuine 1949 component! If you do replace it (and that may not be necessary) a two new suitable 32uF capacitors would be much better.


The more components you change at once, the more chances of a mistake. One possibility is to replace C28 and then try the set via the lamp limiter. If there is a loud hum with the volume turned down then two new 32uF capacitors to replace C34 and C29 would be the next step.
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Old 15th Jan 2021, 9:56 pm   #11
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Default Re: Newbie Seeking guidance on PYE P76

I agree with Simon.
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Old 15th Jan 2021, 11:23 pm   #12
NewbieBrian
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Default Re: Newbie Seeking guidance on PYE P76

Quote:
Originally Posted by Wellington View Post
Quote:
Originally Posted by NewbieBrian View Post
It had a few feet of wire on a plug in the back.
I guess I will put a longer length on that!
I think a few feet will be enough at this stage, Brian, while you get it going.

There is some useful guidance here: https://www.vintage-radio.com/repair...ion/index.html, including a section on applying power for the first time.
Ok what I currently have will suffice for now then.

Lots of information via that link.
Thank you.
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Old 15th Jan 2021, 11:29 pm   #13
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Default Re: Newbie Seeking guidance on PYE P76

Hi Brian,

The 32uF supply caps should be replaced for sure (it is possible sometimes to recondition them, but I would leave that to a future project) and I would suggest not applying power until you have done that.

I would also change C17, C27 and C30 first also.

Although the set is transformer isolated from the mains supply, it has no earth connection by default, so please add one. A new 3-core power cord with the earth fixed to the chassis is the best. And preferrably ensure the mains supply you are using has an earth leakage trip. Makes it much safer.

After that, power through the bulb limiter and check the valve voltages. Be carefull, high voltages here!

It is usually wise to replace all the wax capacitors (the yellow tube types with a sticky surface), but not all are in a high stress position so may not be essential.

Ralph
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Old 15th Jan 2021, 11:59 pm   #14
NewbieBrian
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Default Re: Newbie Seeking guidance on PYE P76

Quote:
Originally Posted by Simon Gittins View Post
Quote:
Originally Posted by NewbieBrian View Post
I was going to replace C28 first (AF coupling) and take it from there.
Did I read diagram correctly that is the one connected to the EL41 Control grid?
Yes, C28 (on the Trader sheet) goes to the EL41 Control grid via R18.

Thank you for the confirmation. I just wanted to check that I was interpreting it correctly.

Quote:
Originally Posted by NewbieBrian View Post
Also I spotted this (attached image) on eBay: Does that look the correct replacement for the smoothing capacitor?
A double 32uF is the correct original type but I hope you are not thinking of replacing it with a genuine 1949 component! If you do replace it (and that may not be necessary) a two new suitable 32uF capacitors would be much better.

I admit I was as it looked the same and I was unsure of the others I saw.

I was unsure as the original only appeared to have two terminals but I am now guessing that the third terminal, as it were is connected to the chassis and that the two capacitors C34 & C29 are in the same can. If so would the one in the attached photo be suitable?




The more components you change at once, the more chances of a mistake. One possibility is to replace C28 and then try the set via the lamp limiter. If there is a loud hum with the volume turned down then two new 32uF capacitors to replace C34 and C29 would be the next step.
Thanks. Useful information. I will do as you suggest.
Much less chance for confusion if I take it one step at a time.

There is just one other thing at the moment in that the dial lamps are both missing.
I read that on AC/DC models this can cause a problem.
As this is AC only am I good to switch on through a lamp limiter once C28 is changed or should I replace the dial lamps first?
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Old 16th Jan 2021, 12:35 am   #15
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Default Re: Newbie Seeking guidance on PYE P76

The dial lamps are just cosmetic in this set. It will work perfectly well without them.
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Old 16th Jan 2021, 12:40 am   #16
NewbieBrian
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Default Re: Newbie Seeking guidance on PYE P76

Thank you Ralph
I have one already on the way for C17 and have just ordered ones for C27 & C30.
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Old 18th Jan 2021, 9:39 pm   #17
NewbieBrian
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Default Re: Newbie Seeking guidance on PYE P76

The 0.047uF capacitors arrived today so I replaced the 0.05uF C28 (AF Coupling) capacitor.
I double checked the main power coil resistances and they appeared to be correct.
At the weekend I put together a series limiter lamp with a bypass switch so tried powering up the set via that.
When I switched on I could see after a few seconds that each of the valves had a faint spark like red glow within them.
I assume that indicates the heater circuit is working.
The lamp in the limiter circuit had a very faint glow - it remained at that level of glow.
After a brief period I found that I got crackling from the speaker as I changed the band switch.
This was louder as I increased the volume.
I tried on MW first but could find no sign of any stations.
I switched to LW and found that the background noise increased as I tried tuning on that but again found no indication of it picking up any signals.
Throughout the few minutes or so that I was checking it the valves stayed at the same level of illumination i.e. just the tiny visible spark like red glow.
Any indicators on the best way to progress would be much appreciated as I would like to get this working if I could.
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Old 18th Jan 2021, 10:20 pm   #18
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Default Re: Newbie Seeking guidance on PYE P76

Heaters glowing and background noise that varies with the volume control are good signs. You don't mention a loud hum so the electrolytic capacitors are probably ok. I take it you still have the wire connected to the aerial socket.
I think the next step is to repeat the same test and when the radio has warmed up with the lamp limiter in circuit, try the effect of the bypass switch to apply full mains and see whether you now have any stations.
If you don't get stations, voltage measurements (carefully if you are not used to taking them) would be the next step. We can guide you through this.
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Old 18th Jan 2021, 10:21 pm   #19
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Default Re: Newbie Seeking guidance on PYE P76

It is probably safe to switch out the lamp limiter now. Some radios do perform very badly with a limiter in circuit.

The first thing to do is to take some voltage readings with the radio powered up, and compare them to the values in the service data. They won't be exactly the same, but look out for any that are dramatically different. Post them here and we will advise you.

The fact that the wavechange switch is producing audible crackling is a hopeful sign.

(Crossed with Simon - great minds think alike )
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Old 18th Jan 2021, 10:29 pm   #20
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Default Re: Newbie Seeking guidance on PYE P76

Don't forget that you will need a few feet of wire in the aerial socket.
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