Pye CB01X4T (P131MBQ) portable radio

[Luxman1050]

I've just bought one of these in immaculate condition although have not yet picked it up.
Has anyone got any background info on this particular model as I have not been able to find anything. Had a look on here but there's no info either.
Cheers Chris

[Paul_RK]

I don't know where the seller found that number, but when I put it through a search engine I see a P131MBQ - a very popular model with info readily available.

https://www.radiomuseum.org/r/pye_p131mbq.html

Paul

[Luxman1050]

Cheers Paul that's the exact model thanks for that. Not surprising could not find it! It's no where near the model code unless they found it on case or a component somewhere very odd.

[AC/HL]

Interestingly, it's being repeated on many sites, those that just re-post auction details. Illustrates beautifully how misinformation spreads.

[Luxman1050]

Yes that's very true such as the RARE quote when suddenly theres hundreds of them.
Mind you I'm not complaining as I got it cheap and it's complete handle grubby and chrome needs a clean plus those original caps will need replacing and I've read the MR rectifier usually needs replacing aswell. So it will keep me busy for a while although she said not working not sure how she tested it?
Nice bit of kit by looks of it.

[Luxman1050]

Well just picked it up.
I'll have a good look later hopefully all valves are okay.
Handle needs re clothing but there's an upholster up high street reasonable prices I'll get him to do that.
Luckily I have a 2 pin female bulgin plug so will be able to run off the mains.

[Luxman1050]

Okay quick inspection valves okay mains transformer okay output tranny okay and speaker fine. Valves look okay not tested yet.
Will need to desolder mains cable and the aerial which will allow me to completely remove unit. Not happy with those connected whilst refurbing easily damaged.
If your all interested I'll keep you posted on progress.
Mind you I have a Sanyo DCA1400 on the go as well. I know not valve gear but a lot easier to work on.

Oh and she said it did not work well not surprising since one of the mains cables is detached from solder point ha.

[Luxman1050]

Okay time to start pulling apart and see what's going on.
The panel at back of case houses the aerial picture supplied for reference. Very well made hence no reason for an external one.

[Luxman1050]

I'll start a new thread with correct title as it's not going to come up for any future reference.
Not sure how to create a link from here if a moderator could help be most welcome.
Cheers Chris

[Luxman1050]

Oh it's been done thank you.

[Luxman1050]

Pulled from case but something I've not encountered before on testing ohms on output there's static and when I try and measure cap on output transformer there's high pitched tone going through speaker. Does that mean it must have recently been charged? Odd!!!.
Another interesting thing which never encountered is R19 sliding track resistor 750ohm. Why would you need that is it to reduce/increase voltage?

[Biggles]

The variable resistor adjust the current through the series connected valves. Do not adjust this until you have read and followed the service info. You could damage the valves if it is not set correctly. The buzzing sound through the speaker when testing the capacitor could just be the ohm meter injecting an ac signal while it tests. Assuming you were doing this while the set was switched off. These radios are attractive but because of the series connected valves, they are a little more complicated to work on than the usual battery sets. Do not be tempted to remove the valves while the set is switched on. They also have live mains connections exposed to be aware of where the lead enters the set if I remember correctly.
Alan.

[Luxman1050]

Thanks for that Alan
so it's a bit like an AC/DC set which has the dropper resistor as opposed to the transformer in this one.
I Tested pins 1&7 on each valve 3 of which are 15 ohms and one which is around 33 ohms so I would assume there testing good.
Oh I never thought of that with the meter sending signal through output as I said I've never encountered that before as I was testing for continuity, ohm ratings and the capacitance of the capacitor which is way too high 0.002 reading 0.007 replaced. The output transformer ohm ratings are all within schematic spec so another good sign.
Yes the set was not switched on. I will replace caps and test all resistors before winding her up on the variac.
The smoothing can all reads good all well in spec.
The sliding resistor has not been touched and there's no sign of it being moved its actually in great condition.
It looks like someone has put a new cord on and spring and I must say they have done a great job. Otherwise untouched.
I'll need to find that metal rectifier and test as I read somewhere they tend to be faulty.
No I don't intend to remove the valves whilst she's switched on.

[Biggles]

The set has a mains transformer as far as I know, but the valve filaments are run in series through a dropper resistor network from the HT supply, at about 25mA if I remember correctly in this set. I have one of these sets myself but it's been a long while since I repaired it.
Alan.

[Luxman1050]

It's a nice little set worth getting out.
I wanted to get the front panel off give it a good clean but too much work needed to remove as you either remove output transformer or speaker but the bottom nut is tucked behind the transformer. The dial panel would need removing and some additional wiring. So I'll clean as is I think.
I removed the 4 caps all of which where triple there original spec. Plus one which is on v3 bl..dy nightmare to get too.
Put new mains cable on as the original was too short.
Another tip if you want the unit out of the case just desolder the aerial situated under the suitcase back panel much easier than trying desolder on main chassis. Also make sure you cover the end wires otherwise you'll end up breaking them.
Pic attached but also there are two mica wax caps which are both well out of spec one 560pf reading 18.2pf and other 470pf reading 6.2pf both are 2%. So I will need too change them as well. Any ideas on voltage rating for these as there are no ratings on spec sheet. I thought maybe 150v? Both situated by the MW LW switch so not much voltage there I would have thought.
Waiting on a new 0.5uf cap once put in I'll fire here up see what happens oh the resistors are fine and the main triple electrolytic can.

[Biggles]

One thing I have noticed when checking the value of mica capacitors is make sure you have made a good connection to the capacitance meter probes. Sometimes the presence of wax on the leads gives an open circuit or low reading. Give them a good clean as they tarnish too. Mica capacitors don't give much bother as a general rule so it is unusual to find two with such low values. I would say a working voltage of 100 volts or so would be ample. The HT is only 90V max anyway. Valve holder contact to valve pin connections can be intermittent too, giving all sorts of problems. Something to watch out for.
Alan.

[Luxman1050]

okay cheers Alan.

[Luxman1050]

Well I'm not sure what solder they have used on this unit but it's a nightmare to try and remove. Heating at 350°c applying a bit of solder to get it moving but as soon as you remove the heat it goes rock solid. So your having to apply more solder etc. I assume it's lead but does it have a higher melting point?
Problem especially on pin bases you can end up doing more damage than good.
Any tips?

[Luxman1050]

Well fired her up slowly through variac upto 240v have sound and tuning static aerial not connected. No valves light up not sure if that's the norm for these valves? Anyhow V1 V3 and V4 are all microphonic each one sends loud ring through the speaker when gently tapping which could also explain why I was getting a sound through output transformer when measuring the cap. So I'm gonna need 3 new ones or just replace all 4. Plus mains transformer was only reading 50v at 240v.
Turned off as I did not want to cause a short.
Any thought?
Cheers Chris

[Simon Gittins]

Yes, normal for these valves is hardly any visible glow.
It's unlikely that all 3 are microphonic to the point of being unusable.
If the HT is low then that's the first thing to investigate; have you replaced the audio coupling capacitor yet?