Pye CB01X4T (P131MBQ) portable radio

[Luxman1050]

Yep all the capacitors have been changed except the micas.
All caps removed where all high by around 300% plus. Very unusual. There where 6 to change. Other problem is the schematic has no voltage readings all I have is the valve data sheets.
I'm assuming it does not matter which way the mains input goes? At present live is on the switch and negative to transformer. But I think these types could go either way.
All three have a loud ring through speaker except one.
I could connect up aerial and see if anything is being picked up just worried don't cause damage elsewhere.
Plus you cannot remove these values when switched on.

[KeithsTV]

I have one of these radios which I restored a few years ago and when powered up after replacing the paper caps I had no response and a low HT. This was due to the rectifier which I replaced with a couple of 1N4007s and a series resistor to reduce the HT to the correct value.

Keith

[Simon Gittins]

It's worth double checking for mistakes when all capacitors are changed at once. They would all have been electrically leaky to some extent (dc leakage) but the high capacitance reading is something that modern capacitor checkers do in this instance.

I should get a chance to look at the circuit later; are you using the "Trader" version or the manufacturer's sheet?

[Luxman1050]

Using the service sheet it's okay but does not have voltage ratings except for bias voltage on R15. Otherwise nothing. The MR diode is working fine no shorts forgot ohms reading on it and voltage on either side was around 58v no difference. Sound wise volume is working okay slight hum on full waveband trying to tune in but I have it disconnected.
Like say just the ringing on valves.
I'll need to check the heaters values for mains operated V1 2.21mA, V2 1.33mA, V3 22uA, V4 4.55mA.
Saying MR anode to anode 184v. Not sure where you take that reading on the circuit.

[ms660]

The valve anode and screen grid voltages are given in the service sheet....read V for E.....Don't mistake the filament current values you've quoted for the "cathode" currents...Ik…..The anode to anode 184 volts for the MR should be read as cathode to cathode, the voltage will be AC.

Lawrence.

[julie_m]

Originally Posted by cdm1christopher

All caps removed where all high by around 300% plus. Very unusual.

Most capacitance meters are designed in such a way as they will read high with a leaky capacitor. It is working out the capacitance by timing how long the capacitor takes to charge to a certain voltage, at a constant current. The leakage causes the capacitor to take longer to charge, so it appears to have a higher capacitance than it really does.

Some of the more sophisticated multi-component testers can measure the leakage resistance of a capacitor, in case you need to know it (anything less than infinity is usually bad news anyway).

Surely the cathodes (pointy ends!) of the metal rectifier are connected together, and to the reservoir capacitor positive? The two ends of the power transformer secondary go to the anodes, and the centre tap goes to chassis.

[Simon Gittins]

Originally Posted by cdm1christopher

I'm assuming it does not matter which way the mains input goes? At present live is on the switch and negative to transformer. But I think these types could go either way.

It could go either way; in general I prefer to switch the live but as mains is going to a wafer on the bat/mains switch I might choose to switch neutral in this instance (especialy if I was touching something close to the switch).

Originally Posted by cdm1christopher

Using the service sheet it's okay but does not have voltage ratings except for bias voltage on R15.

You are using the manufacturer's sheet then (the other sheet has different reference numbers). That bias voltage is a handy thing to measure (5.6 volts).

Another key voltage is the DL96 anode (91 volts).

[ms660]

Originally Posted by julie_m

Surely the cathodes (pointy ends!) of the metal rectifier are connected together, and to the reservoir capacitor positive? The two ends of the power transformer secondary go to the anodes, and the centre tap goes to chassis.

In the manufactures schematic the cathodes are fed from the transformer and the anodes are both connected to chassis, the transformer centre tap is HT +ve.

Lawrence.

[Luxman1050]

Well voltages all low and then pop with a loud ring went the output pentode dead as a door nail. I knew the valves where faulty due to the microphonics hopefully no damage done I'll check the mains transformer and output.
Got another one on it's way as parts today with valves in it so will try them.
Always go by first instinct is the morale to this story ha.

The other thing confused me and again not come across this on a diagram it says voltage across r15 should be 5.35v I was getting 2.4mA? and pin connections on pentode are 1,2 & 3 I'm assuming pin 2 is the cathode?
I'm having bit of trouble working this one out.
Oh the MR was reading 184v spot on its connected straight to the mains transformer on secondary which runs of to s2B & s2A then running to frequency charger and AF amp. Their okay so V4 & V2 I reckon are knackered. As smoothing can readings well low again 95v was getting 23v.
Another interesting thing now v4 is shot I can measure the cap across output tranny and get a reading whereas before I was just getting a sound through speaker on uf readings.

[Simon Gittins]

The other thing confused me and again not come across this on a diagram it says voltage across r15 should be 5.35v I was getting 2.4mA?

The table has 2 sections; the top has voltages when on batteries when voltage across R15 should be 5.35V, the next section is for mains operation with 5.6V across R15. Where is the 2.4mA current reading coming from?

The valve base connections are in Fig. 4 (looking at the base from below chassis).

[Luxman1050]

Taken across R15.
I got her working last night aerial connected sounds okay apart from the middle bandwiths lot of static. Might be those mica caps? Volume bit staticty too. Problem is removing front panel alot of work. Need to do that to get proper access to the pot and wafer switches.
I'll check voltages again today and go through input on thread again.
Valves don't light up so hard to tell if working or not visibly plus no bulb to light up screen.
I do find schematic bit odd as heater pins don't seem to tally with schematic and it also looks like the grids are connected to one of the heaters on think 3 valves!!!

[Cobaltblue]

If your looking at the PYE service sheet those are not the pin numbers of the valves on the circuit diagram, the filament pins are 1 and 7 on this series except where there is a filament tap (DL96) which is pin 5.

The Pin numbers/function of the valve are shown in the table on the second page.

They really don't light you might just see at the right angle a dull red glow in a blacked out room on some of the valves.

Cheers

Mike T

[Luxman1050]

Cheers Mike no wonder I'm getting odd readings. Yeah seen those but v1 says pin 7 also seems to have grid 5 attached aswell is that correct and if so am I actually gonna get a proper volt reading?
Pic of schematic I'm using attached no voltage measurements anywhere. Maybe they need filling in for future reference.0

[ms660]

Originally Posted by cdm1christopher

I do find schematic bit odd as heater pins don't seem to tally with schematic

The numbers shown against the filament connections in the schematic are not supposed to be valve pin numbers, they're to show in which order the filaments are connected, eg: 3 to 3, 4 to 4, 5 to 5.

All the suppressor grids except for V1 are connected to the valves filament -ve, the suppressor grid for V1 is connected to the valves filament +ve.

Here's the relevant info for reference:

V1...Schematic ref. 5 = pin 1, schematic ref. 4 = pin 7

V2...Schematic ref. 4 = pin 1, schematic ref. 3 = pin 7

V3...Schematic ref. 6 = pin 1, schematic ref. 5 = pin 7

V4...Schematic ref. 3 = pin 1, schematic ref. 2 = pin 5, schematic ref. 1 = pin 7

EDIT: Post crossed.

Lawrence.

[ms660]

Originally Posted by cdm1christopher

Cheers Mike no wonder I'm getting odd readings. Yeah seen those but v1 says pin 7 also seems to have grid 5 attached aswell is that correct and if so am I actually gonna get a proper volt reading?
Pic of schematic I'm using attached no voltage measurements anywhere. Maybe they need filling in for future reference.0

You can annotate the schematic with the voltages given in the valve voltage and current tables given in the manual.

The grids that are attached to one side of the filament are the suppressor grids, remember that the filament is also the "cathode" in directly heated valves.

Lawrence.

[Cobaltblue]

Yes the Suppressor grids are connected to one or other filament connections on all of the valves these would in most cases be connected to the cathode on a mains powered valve.

The voltages are given in the table.

it may be convenient to write them on the circuit I don't usually bother.

They should be correct no voltages for the suppressors are given only Screen grids and Anodes.

Don't forget G2 (pin3) is effectively the OSC "anode"

Crossed with Lawrence

Cheers

Mike T

[Simon Gittins]

I got her working last night aerial connected sounds okay apart from the middle bandwiths lot of static. Might be those mica caps?

That's good news! If you are getting results at both ends of the tuning scale but only crackles in the middle, that points to a problem with the tuning capacitor. You could prove that by resistance checks with the set unplugged. If this is the case, ideas for clearing shorts are here: https://www.vintage-radio.net/forum/...ead.php?t=1144

[Luxman1050]

Cheers Guys everything written down so will start tests in a minute.
Thanks for link for tuning cap.
Cheers Chris

[Luxman1050]

Just out of curiosity has anyone got a set of these dials as the other one I bought cheaply for spares is untouched and in very good condition apart from one dial missing and central gold missing on the other three. Don't want to butcher it too good condition and worth restoring.
Thanks Chris

[ms660]

Originally Posted by cdm1christopher

The other thing confused me and again not come across this on a diagram it says voltage across r15 should be 5.35v I was getting 2.4mA?

Just a warning, a meter connected across R15 that's set to a current range could damage the valve, in effect it would be connecting one half of the valves filament across the whole of the filament supply

Lawrence.