Pye CB01X4T (P131MBQ) portable radio

[telstar]

Yes this is a really nice radio. The plastic clad wire that links the frame aerial to the radio had suffered badly on my example and was replaced with the type of coloured wire that you can buy at the N.V.C.F meetings (it does not look too bad).
Cheers
Mike

[Luxman1050]

Cheers for that I'm measuring from ground and got 4.3v.
I think I've been getting confused as the last set I worked on which I think you helped on Lawrence was the Philips AC/DC set with no mains transformer. So with this set I've been measuring as A/C not D/C but for reference I've measured in both.
Firstly the schematic indicates measurement on mains is taken from the 200/210 tap which is set to 240/250 tap so I would assume this could affect readings as per schematic.
Anyhow here's some readings.
MR 191 volt not 184 as per sheet.
Neutral on mains tap is 33.8vac Live on switch 152.6vac.
Pins 1&7 VDC
V1 1.13v
V2 1.07v
V3 1.07v
V4 2.26v

Pins 1&7 VAC
V1 2.9mA
V2 3.2mA
V3 3.2mA
V4 35.9mA

Pin 5 referenced to ground
0.4mA VAC
4.4v VDC

Smoothing cap reading across R13 80.1vdc dropped to 68.4VDC which is fine.

So those are figures.

[Luxman1050]

Not sure what the N.V.C.F meetings are Mike.

[ms660]

Replies in Bold

Originally Posted by cdm1christopher

Cheers for that I'm measuring from ground and got 4.3v.
I think I've been getting confused as the last set I worked on which I think you helped on Lawrence was the Philips AC/DC set with no mains transformer. So with this set I've been measuring as A/C not D/C but for reference I've measured in both. Yes you are getting totally confused, the Philips AC/DC receiver can operate from either an AC or DC supply, that would be the mains supply option. Your present receiver can also operate from an AC or DC supply but in this case it's only AC mains not DC mains, the DC option being provided by HT and LT batteries
Firstly the schematic indicates measurement on mains is taken from the 200/210 tap which is set to 240/250 tap so I would assume this could affect readings as per schematic. The manual states that the measurements when operating from the mains were taken with the mains transformer tap selected for 200 to 210 volts input and that the mains supply was 205 volts at the time the measurements were taken, the fact that yours is set for 240 to 250 volts input shouldn't affect the measurements too much providing your actual mains voltage is somewhere between 240 and 250 volts, all the voltages quoted in the manual when the receiver is set for mains operation were taken with reference to chassis and are DC voltages except the voltage at the rectifier cathodes which was measured between the cathodes and is an AC voltage
Anyhow here's some readings.
MR 191 volt not 184 as per sheet.
Neutral on mains tap is 33.8vac Live on switch 152.6vac.
Pins 1&7 VDC
V1 1.13v
V2 1.07v
V3 1.07v
V4 2.26v
If the 191 volts measured above is AC and was taken between the two cathodes of the Metal Rectifier I would say that voltage was ok, however, to me the DC voltages across the valve filaments seem low, I would expect something approaching 1.4 volts for V1, V2&V3 and 2.8 volts for V4, having said that the correct way would be to set the filament current, from memory I think Mullard recommended something like 24mA for series operation.....

…..I've included a link below to some Mullard technical documents with regards to series filament chains for the types of valves fitted in your receiver.

Pins 1&7 VAC
V1 2.9mA
V2 3.2mA
V3 3.2mA
V4 35.9mA
Not sure what's going on with your meter....whicheverways the filament voltages should be measured with your meter set to measure DC volts...Not AC

Pin 5 referenced to ground
0.4mA VAC
As previous comment
4.4v VDC
See the comment pertaining to your DC filament voltage measurements

Smoothing cap reading across R13 80.1vdc dropped to 68.4VDC which is fine.
If your mains voltage matches the mains transformer tap selected then 80 volts HT seems a little low, the receiver should work ok at that voltage but it might be worth measuring the total HT load current and if it's not excessive then replacing the metal rectifier might increase the HT to the 90 volts (ish) that would be expected (a series limiting resistor will be needed if replacing the metal rectifier with silicon diodes)

So those are figures.

Lawrence.

[Luxman1050]

Thanks Lawrence I'll have a read later be very helpful I think for me it is the abbreviations used for voltage readings in tube data sheets books etc there not always the same but have the same meaning. So it gets a bit confusing. Well for a hobbyist like myself.
It's interesting as the other radio has components layed out slightly differently and has used a completely different speaker not the Celestion as used in mine. Maybe it is a newer model?
Cheers Chris

[AC/HL]

Originally Posted by cdm1christopher

Not sure what the N.V.C.F meetings are Mike.

https://10times.com/nvcf
Now rebranded as RetroTechUK: https://www.retrotechuk.com/

[Luxman1050]

Oh well back to the drawing board. I changed a resistor and mica cap on waveband switch turned her on nothing. So re installed originals still nothing although I cannot see that affecting voltage through unit.
Eventually current got through and on mains it has shot up to 167v and the MR anode to anode shot up to 127v.
No readings on pins 1&7 on all valves. Two of the caps in can both reading 127v no drop across the resistor R13 and the 3rd cap in can no reading at all. No voltage drop across R20 127v either side.
So she's completely dead and I think all that testing yesterday has either caused a short or the MR has failed and the triple can is shot. Plus could be some of the resistors gone OC. Have not checked all that yet. The valves still have same ohm readings as from beginning so don't think it's them.
I suppose having it running nearly all day yesterday and quite a while the day before is gonna eventually fail if some components are on the brink.
So voltage coming in high no volume and no radio just quiet hum from tranny.
Any ideas most welcome.
Cheers Chris

[ms660]

Check the filament series string for DC voltage at various points with reference to chassis, start from the point of known voltage (output side of R20) and follow on down the series circuit.

Lawrence.

[Luxman1050]

Okay I think r20 is knackered 128v either side no drop there was before around 40volts thats going to c23 which is reading 128v. Reading across r13 connected to c21 and c23 reading is 128v either side so no voltage as before it was around 45 volt drop. No voltage at c22 which goes to pin 7 on V2 which is connected to pin 7 on V1 again no readings.
There are no readings on all pins 1&7 on valves.
So I think C22 is knackered and since no voltage drop across r13 connected to c23/c21 must be faulty as well.
All references to ground.
Now that's the only not cap replaced.
So R20 may need replacing and main smoothing cap.
Pre R20 as I said MR is now think it was 127v and main in to switch is 168v which seems about right to me.
So changing that mica and resistor was just a coincidence.
Hope that eligible.
Cheers Chris

[ms660]

Originally Posted by cdm1christopher

Okay I think r20 is knackered 128v either side no drop there was before around 40volts thats going to c23 which is reading 128v. Reading across r13 connected to c21 and c23 reading is 128v either side so no voltage as before it was around 45 volt drop. No voltage at c22 which goes to pin 7 on V2 which is connected to pin 7 on V1 again no readings.
There are no readings on all pins 1&7 on valves.
So I think C22 is knackered and since no voltage drop across r13 connected to c23/c21 must be faulty as well.
All references to ground.
Now that's the only not cap replaced.
So R20 may need replacing and main smoothing cap.
Pre R20 as I said MR is now think it was 127v and main in to switch is 168v which seems about right to me.
So changing that mica and resistor was just a coincidence.
Hope that eligible.
Cheers Chris

I don't think I'm alone in saying that I find your posts difficult to understand.

There will be no voltage drop across R13 unless the valves are working, the valves won't work unless the filaments have a power supply, eg: voltage.....When working properly the voltage drop across R13 should be approx. 16.3 volts according to the currents quoted in the valve table in the manual.

Anyways, that aside, why would you think R20 is knackered when according to your measurements you have HT on either side of it.....If there's no voltage on any of the filament pins of the valves then I would be looking for a discontinuity between pin 7 of V4 and the output side of R20 where you have already said that HT is present, a discontinuity could be caused by the switch contacts on switch S2a, open circuit R19 (in effect) or a poor connection along that circuit.

Lawrence.

[Luxman1050]

I must admit being an hobbyist my terminology is not great but hopefully it makes some kind of sense.
For me I always thought that a resistor reduces current/voltage so if you have 250v going in I would not of thought that 250v would come out the other side due to the internal resistance of the winding internally even if there is a break in the circuit. I thought it would go open 0v open.

Anyhow had a quick look at R19 and you were spot on the slider has come lose so the strap was not making contact with the exposed winding on resistor which I will tighten up, which as you said goes to s2a. Well done and many thanks Lawrence.
Hopefully it has not moved too much.
Pic attached what I'm going on about.

[Herald1360]

A current through a resistor will generate a voltage across it. V=IxR
Applying a voltage across a resistor will cause a current to flow through it. I=V/R

You will see the same voltage at the end of a resistor as applied at the other end if nothing is connected to the end you're looking at other than the meter as long as the resistance of the meter is >> than that of the resistor. (Technically a bit lower since there will be some voltage dropped across the resistor by the current taken by the meter).

[Luxman1050]

Ah thanks for that so technically there should be a slight drop. Interesting.
Have you substituted V for E?
V=I×R voltage equals amps times resistance
I=V÷R Amps equals volts divided by resistance.

Is that right?

Cheers Chris

[ms660]

Yes, check out the Ohms Law triangle:

https://www.electronics-tutorials.ws...its/dcp_2.html

Also here's a calculator for a potential divider:

https://www.electronics2000.co.uk/ca...calculator.php

In that link (the first set of boxes) use the value of R20 in your receiver to put into the R1 box (enter 3.2 and select Kilohms) Then enter 10 in the R2 box and select Megohms (10 megohms is a typical input resistance for a digital meter)

Next enter 125 into the V1 box and select Volts, the voltage between the 0v rail and V2 will now be displayed towards the right, subtract that voltage from the 125 volts input and you will see that the voltage dropped across the 3.2k is very small in comparison.

It's worth book marking that link as you might find it could come in handy from time to time.

Lawrence.

[Luxman1050]

Thanks Lawrence I'll do that.

[ms660]

Also try different values of resistances and voltages so's you get the hang of it....you might find it more convenient to use lower value resistance figures for that, then to prove the results add the value of the two resistances together and divide that total into the supply voltage in order to determine the current flowing through them (remember that in a series circuit the current flowing through all the circuit elements is the same) then do the Ohms law calc for the voltage drop across R2 (the bottom resistor)….within a figure or two the result should be more or less the same as that obtained by the online potential divider calculator, do that a few times and your understanding should be streets ahead of what it was a while back.

Keep at it.

Lawrence.

[Luxman1050]

Yep will do must admit I do find it interesting. Even now when I look at the physical circuit then the schematic I'm now able to link it whereas before it made no sense at all.

So it's slowly sinking in.

Cheers Chris

[Luxman1050]

Anyone good any ideas the fabric used to cover the case the radio sits in? It's s lizard skin design.
It's a textured sort of nylon with fairly rigid backing not very thick.
I'd like to recover if possible.
Pic posted.

[music-centre]

Just my opinion but I think it would be a mistake to recover it, you loose the originality and it doesn't look bad at all in the photo, I would just give it a gentle clean.
Steve.

[Luxman1050]

Good point Steve.