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Old 18th Jan 2021, 11:43 pm   #21
NewbieBrian
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Default Re: Newbie Seeking guidance on PYE P76

Thanks to all for the helpful comments. Much appreciated.
It sounds encouraging so far from your comments.

The Ariel that came with it was about four feet of coax fitted into a wander plug.
I do have a drum of coax in the shed so i could cut a longer length of that or single wire - whatever would be best.

Regarding the valves I take it then that the 'tiny spark' appearance is ok at this stage. I must admit I was expecting more of a glow. (Childhood memories of looking through the ventilation slots on the back of the TV.) The lack of that made me wonder if the voltage was perhaps too low for them to fully come on.

On the subject of hum. It did not seem to me like a mains hum, more like static.
I did only turn it on for a few minutes though as I did not want to take any chances and it took me some of that time for the penny to drop that it was on and tone on the first rotary and volume on the next!
If I power it up for longer I should get a better handle on it.
I do have a double 32uF on its way in case I need to change the smoothing capacitor.

It did reassure me that the lamp limiter bulb only glowed faintly, but I did wonder if it should have glowed a little more as the set warmed up.

I did in fact try checking at the panel lamp sockets but could not read any voltage there. I imagine it may have just been due to bad contact as from looking at the transformer secondary tappings and circuit diagram that is off the same as the heater circuit for the valves.

I was hoping to (with great care) check the voltage from the other take off from the coil but from the information sheet I could not see what I should be looking for. It did mention valve voltages though.

I admit I have not got my head around how the valves work yet so will have to read up on it. Am I correct in thinking though that on this set V5 (EZ40) is basically acting as a rectifier and feeding DC to the circuit?
So in effect the ac only goes as far as the transformer and EZ40?

I am wondering what sort of voltage I should be looking for and the best/safest places to read it from. I was thinking in terms of hooking up meter prior to turning on. I dont want to start probing the innards whilst live. At least not yet.

I should state that for the initial test I used the already fitted 2 core mains cable and kept my distance.
Would it be best to straight away fit a 3 core supply cable and connect the earth directly to the chassis?

I do hope you forgive my many questions.

Edit:
Just discovered this resource:

http://www.r-type.org/index.htm

And have downloaded information on the valves I have fitted.

Last edited by NewbieBrian; 18th Jan 2021 at 11:54 pm. Reason: additional text
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Old 19th Jan 2021, 12:27 am   #22
NewbieBrian
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Default Re: Newbie Seeking guidance on PYE P76

Quick update:
I have just switched the set on again after changing the wire in the Ariel socket to about a ten foot length of coax with both inner and outer joined in wander plug.
I did manage to pick up a couple of stations on medium wave.
The speaker is crackling rather than humming and this gets much worse in some parts of the tuning than others.
I also noticed that both the tone control and the band selector switch seem to affect the amount so I suspect they could do with a good clean.
Would a good spray with contact cleaner and a twiddle be the way to go here or is there an approved method?
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Old 19th Jan 2021, 12:48 am   #23
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Default Re: Newbie Seeking guidance on PYE P76

Cleaning switch contacts is always a good first step.

If you are using coax as an aerial wire, you must use the copper braid screening rather than the internal conductor.

I suspect you almost have a working radio. The remaining problems will be down to leaky capacitors.
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Old 19th Jan 2021, 1:03 am   #24
Graham G3ZVT
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Default Re: Newbie Seeking guidance on PYE P76

Looking good.
Yes give the volume and tone pots a good squirt of contact cleaner, there is usually a gap where the terminals are. then work the controls to and fro and the crackling should subside. Likewise the band-switch contacts, and also the valve bases if needed. Use a proper switch cleaner like Servisol Super 10, definitely not WD40.
If the tuning gang is crackling when moved, you can carefully put some switch cleaner on the earthing springs where they make contact with the spindle between the sections.
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Old 19th Jan 2021, 3:17 pm   #25
NewbieBrian
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Default Re: Newbie Seeking guidance on PYE P76

The smoothing capacitor arrived this morning so I have just fitted that.
It does not seem to have made any difference to the sound.

Here is a link to an mp3 of what I am hearing when tuned to a station on MW in case it provides any clues.

https://drive.google.com/file/d/1zVq...ew?usp=sharing

It gets more prevalent as the on/off tuning knob is turned further clockwise. As this knob is turned anti clockwise the overall sound volume is reduced.

On the up side I have found signals on MW, LW, and Trawler Band, But nothing on SW.
When the band selector is set to either Gram or SW the noise is hardly perceptible. It is also a lot less on TB.

Not quite sure of the best next step to take.
I do have more capacitors on the way and was wondering if the symptoms are indicative of any particular part of the circuit.

I should add that I have taken the advice regarding cleaning of potentiometers, the tracks/contacts on the band switch and the contacts on the spindle of the variable capacitor. It is certainly a lot better when switching bands.

Last edited by NewbieBrian; 19th Jan 2021 at 3:34 pm. Reason: additional text
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Old 19th Jan 2021, 3:51 pm   #26
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Default Re: Newbie Seeking guidance on PYE P76

You are picking up electrical interference. This can come from a switch mode power supply or anything with a digital processor in it. It is worse because you are using a very minimal aerial.

Try turning off everything in the same room as the radio at the mains - computers, lights, routers, TVs etc. I bet the interference goes away, or at least reduces.

This radio is basically working.
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Old 19th Jan 2021, 4:10 pm   #27
NewbieBrian
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Default Re: Newbie Seeking guidance on PYE P76

Quote:
Originally Posted by paulsherwin View Post
You are picking up electrical interference. This can come from a switch mode power supply or anything with a digital processor in it. It is worse because you are using a very minimal aerial.

Try turning off everything in the same room as the radio at the mains - computers, lights, routers, TVs etc. I bet the interference goes away, or at least reduces.

This radio is basically working.
I have been testing it on the bench in the shed.
I tried it with the lights (fluorescent tubes) both on and off.
Nothing else was on in the shed with the exception of the lamp limiter.
There is a wifi router in the house and a wifi extender I will try with those switched off.
I cannot of course do anything about other Wifi signals in the area (of which there are a number) but they are weaker of course.
I could also try with a longer ariel wire and see if that makes a difference.
I will make one move at a time.
Thanks for your help.
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Old 19th Jan 2021, 4:14 pm   #28
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Default Re: Newbie Seeking guidance on PYE P76

See what others think, but that sounds very like interference to me.
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Old 19th Jan 2021, 4:57 pm   #29
NewbieBrian
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Default Re: Newbie Seeking guidance on PYE P76

Quote:
Originally Posted by paulsherwin View Post
See what others think, but that sounds very like interference to me.
I have just tried it again with router and wifi extender in house switched off.
My mobile left in the house and the lights off in the shed.
There was no noticeable difference.

I then got a longer a reel of coax and connected the outer braid to the Ariel socket and laid out the coax with the reel on another shed roof.
Still the same result.
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Old 19th Jan 2021, 5:04 pm   #30
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Default Re: Newbie Seeking guidance on PYE P76

Can you see what reception is like on a different radio in the same location?
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Old 19th Jan 2021, 5:22 pm   #31
NewbieBrian
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Default Re: Newbie Seeking guidance on PYE P76

Quote:
Originally Posted by paulsherwin View Post
Can you see what reception is like on a different radio in the same location?
I just took a mains radio out there and it was fine on MW.
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Old 19th Jan 2021, 6:27 pm   #32
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Default Re: Newbie Seeking guidance on PYE P76

You are making good progress.
Quote:
Originally Posted by NewbieBrian View Post
I did in fact try checking at the panel lamp sockets but could not read any voltage there. I imagine it may have just been due to bad contact as from looking at the transformer secondary tappings and circuit diagram that is off the same as the heater circuit for the valves.
Worth trying that again for practice; was the meter set to AC volts for that measurement?
Quote:
Originally Posted by NewbieBrian View Post
Am I correct in thinking though that on this set V5 (EZ40) is basically acting as a rectifier and feeding DC to the circuit?
So in effect the ac only goes as far as the transformer and EZ40?
Yes to both.
Quote:
Originally Posted by NewbieBrian View Post
I should state that for the initial test I used the already fitted 2 core mains cable and kept my distance.
Would it be best to straight away fit a 3 core supply cable and connect the earth directly to the chassis?
Opinions differ on that question! https://www.vintage-radio.net/forum/...ad.php?t=67587
Quote:
Originally Posted by NewbieBrian View Post
I am wondering what sort of voltage I should be looking for and the best/safest places to read it from. I was thinking in terms of hooking up meter prior to turning on. I dont want to start probing the innards whilst live. At least not yet.
Connecting the meter with the set switched off is a very good idea. The key voltages are on the Trader sheet that you have. I would suggest that a good point to start would be the screen volts for V1 and V2. This is a common supply to both valves and should be 63V. If you measure significantly less than this then C17 would be a good capacitor to replace.
C8 is the AGC decoupling capacitor and may well improve performance.
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Old 19th Jan 2021, 6:57 pm   #33
NewbieBrian
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Default Re: Newbie Seeking guidance on PYE P76

Simon:
I had the multimeter set to DC volts when I checked at the lamp holders.
I have noticed that although on the circuit diagram it shows as being fed from the same source as the valve 6.3 v supply that at one end of the chassis it comes from a different tapping on the secondary coil. The other end it comes from what i assume is the 6.3v feed to Valve 1. I will have to take a closer look.

Thank you for confirming about the AC/DC.

I will have a look at the link at decide what to do when better informed.

Re measuring the DC voltage: I will see what i get there.

Thank you.

I just connected the voltmeter up and measured the DC from the terminal on the valve that C17 connects to and the chassis where the other end of C17 is grounded to.
On switching on the set the voltage climbed to 116 volts then dropped back to circa 110 volts. this was all in about the time it took for the speaker to come to life.
I then switched off. The voltage dropped over a few seconds.
Seems a bit higher than stated - unless I was measuring the wrong place.

Last edited by NewbieBrian; 19th Jan 2021 at 7:21 pm.
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Old 19th Jan 2021, 7:05 pm   #34
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Default Re: Newbie Seeking guidance on PYE P76

If you are still feeding the radio via the lamp-limiter, it will not 'see' full voltages and this is likely to mean it will struggle a bit.

The lack of anything on SW could be due to this - with the limiter in-place the HT voltage will be low, and the frequency-changer's heater will also be cooler than it should be - both of which could mean the local-oscillator will not oscillate.

Finally, remember that on MW there will probbaly be only 3 or 4 stations receivable at good strength: you will probably be able to get TalkSport, 5Live and another couple. On LW you might get RTE and Radio4... but it has to be admitted that MW/LW broadcasting isn't what it was.
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Old 19th Jan 2021, 8:04 pm   #35
NewbieBrian
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Default Re: Newbie Seeking guidance on PYE P76

I do still have it connected through the lamp limiter.
I have used the bypass switch a few times to see if it made any difference but as it did not appear to most of the time I have left it going through the limiter lamp as an indication to shut it down if it should start glowing brightly at me.

I think that I am receiving reasonably, as you say there is not much about nowadays !
My problem is that the amount of interference/ background noise is at pretty much the same level as the station.

In respect to the HT voltage as in my previous post it appears rather high - unless I messed up reading it. That reading was taken with the limiter lamp in circuit.
All rather confusing to a Newbie. Good fun though.
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Old 19th Jan 2021, 8:29 pm   #36
Simon Gittins
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Default Re: Newbie Seeking guidance on PYE P76

The voltages given in the Trader sheet are what would be measured using an AVO 8 of similar vintage to the radio. A modern DVM has a much higher resistance so voltage readings on valve electrodes will often read higher than those listed. It doesn't look as though C17 is significantly leaky and it's not working at a particularly high voltage so it could be left as it is or you could change it to see whether the voltage increases slightly; it probably won't improve the performance at the moment but changing it would avoid the original capacitor failing in the future.

SW performance often improves after dark.
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Old 19th Jan 2021, 8:46 pm   #37
NewbieBrian
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Default Re: Newbie Seeking guidance on PYE P76

That is encouraging regarding Voltage.
I do have a capacitors coming to replace the original toffee ones.
At the moment I have one 0.047uF I am thinking I may use that to replace C8 AGC de coupling as has been suggested and see if that makes any difference.
One step at a time.
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Old 19th Jan 2021, 9:05 pm   #38
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Default Re: Newbie Seeking guidance on PYE P76

Using a DMM there's only one voltage that will read noticeably higher (but not by a lot) compared to the voltages given in the service information and that's the voltage on the anode of V3's triode, and that's on the assumption that the DMM has an input resistance of 10 megohm, some DMM's have an input resistance of 1 megohm and in that case that voltage won't read higher it will read lower....

Avo 8 on 250 volts DC range (the range used in the service information for that measurement) has an input resistance of 5 megohm.

Avo 7 is quoted as a 1,000 ohms per volt meter but it's input resistance is actually 500 ohms per volt.

Lawrence.
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Old 19th Jan 2021, 9:27 pm   #39
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Default Re: Newbie Seeking guidance on PYE P76

As you’re making good progress it may be worth checking the resistors too, unlikely to have much effect on the performance unless very high but worth checking whilst you’re in there.
You may have to take any suspect ones out of circuit (or remove a valve to break the circuit) to test properly.

Just something I do routinely, not sure others think?

John
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Old 20th Jan 2021, 12:21 pm   #40
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Default Re: Newbie Seeking guidance on PYE P76

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.
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