Pye P45 - any known issues?

[G8HQP Dave]

I have just bought a non-working P45, and downloaded the trader sheet for it. There is not much on the web about it, but the circuit looks fairly conventional: ECH42, EBF80, EL41, EZ40. Are there any known 'gotchas' with this set? (P46 uses the same chassis).

I was told that this set worked fine 30 years ago, but when switched on recently the valves glowed and there was some hum but no signal. So far I have found that one of the tags on the smoothing C has corroded away - explains the hum! The EL41 looks like it has been running hot, but as this is a short superhet the usual suspect coupling C is not an issue. The main smoothing resistor R18 has been replaced at some time by a pair of hefty RS wirewounds - the adjacent capacitor C28 shows signs of external heating. Also, the mains voltage was switched to the 200-220 tapping. And the mains transformer has dripped most of its wax. So I guess something (EL41?) was taking too much current which overheated R18 - the wrong mains tap would not have helped.

Apart from replacing the smoothing electrolytics, is there anything else I should check before applying mains via a lamp limiter?

[paulsherwin]

These sets are full of Hunts Mouldseals and there's no point in powering up before replacing them. The smoothers will almost certainly need reforming and it may be better just to replace those too.

Paul

[G8HQP Dave]

Thanks. I didn't spot any Hunts, but I will have a closer look. There are a few wax covered tubular capacitors which I planned to replace. I just did a quick look under the chassis when I got it home to see if I dared switch it on - and decided No!

If one section of the main smoother C is gone, should I assume the other two sections are suspect too? I haven't yet worked out which tag has come off, but I suspect it will be the reservoir one as that does the most work.

All the wiring uses white insulation, so tracing things is difficult. Is this common? I suppose it saved a few pence at the factory but must have made life difficult for the repairer.

[paulsherwin]

The Mouldseals are normally in the 0.001uF-0.01uF range and are used for coupling and decoupling applications. They can be mistaken for resistors if covered in decades of crud. The waxies should be bigger, 0.02uf-0.1uF and will be knackered too. It's better to spend an hour changing these than endlessly chasing faults in the future.

I'm not sure if you're saying that the smoothers are physically damaged, not working, or both. My inclination in a set like this would be to replace them with modern electrolytics out of sight underneath the chassis, but some people go to enormous lengths to retain the original electrolytics, even in a basic 50s set like a P45.

These sets do perform well for a short superhet once all the faults are cleared.

Good luck, Paul

[G8HQP Dave]

One of the three +ve tags on the smoother has become detached, due to some electrolyte leakage. I haven't yet traced which section it is. This is a 24+24+24uF can. I'm unlikely to get an exact replacement, but maybe I can find a two-section can so I only have to add one more underneath the chassis somewhere. I'm more interested in getting it working than preserving appearance, but it would be nice to achieve both.

Thanks for your advice. I will put a note on here about progress, when I have made some!
Dave.

[kestrelmusic]

I worked on one of these a few months ago. The tone control switch has some unusual RC combinations and one of the caps was leaky, so there was some voltage on V3 grid which had overrun the valve and caused the output transformer primary to fail. C45 had also leaked (chemically) all over the place.

Another fault on the one I had was IFT2 - I never found out exactly what was wrong with it, but I replaced it and the whole set came to life. In the old one, no adjustment of the cores made the slightest difference to the alignment!

However, it's worth working on this. Like most Pye offerings, despite the lack of a separate AF amplifier valve it is a good, well made set and you should get some good results from it.

What's the case like on yours? Mine was in a shocking state.

[phase_splitter]

EL41s are prone to hk shorts.
I've binned two (yes two) Mullard EL41s today.
If the voltage readings around the EL41 are not as you would expect, might be worth a trying a new valve.

I've repaired many Pyes over the years; generally, they were built and performed well.
Definately change the waxies.

[G8HQP Dave]

Thanks for comments. I was looking at the tone control circuit and managed to convince myself that it needed at least two capacitors to go leaky before it would cause trouble. But I guess two leaky caps is actually quite likely! The case on mine is not too bad - a few stains, and some wear round the knobs.

I've heard that EL41 can be troublesome. I've not got any spares of those yet. Given that they seem to be a bit pricey these days I was toying with the idea of changing the base to B7G and using N78 instead. Has anyone tried this?

[kestrelmusic]

I like to keep sets as authentic as I can, consistent with safety. Rather than replace the valve holder, it should be possible to construct an adaptor to hold a replacement valve of a different base type but similar characteristics. I've done this:

1. Take a dead valve of the correct base type. Tie a piece of string round it fairly near to the base, soak the string in methylated spirit and set light to it. When the flame goes out, plunge the valve into cold water. If you are lucky, the valve will separate into two pieces with a reasonably clean break.
2. Remove the electrodes and clean up the wires where they pass through the glass base. Solder short lengths of copper wire onto the pins, then fill the base with something to keep them secure - I use Isopon.
3. Solder the wires onto the appropriate pins of a valveholder of the correct type for the replacement valve. Plug in the valve and off you go! If your replacement is in a frequency changer or IF stage you might need to re-align the set to take account of different capacitances either within the replacement valve or stray capacitances within the adaptor.

I've done this with a couple of rare valves including an X78 (B7G) which I replaced with an X79 (Noval). The soldering is a bit fiddly, but the only really tricky bit is getting the old valve to break cleanly in the right place. It's much easier, of course, with octals - you just remove the whole glass section, clean out the base and re-solder new wires into the pins.
Good luck!

[paulsherwin]

I haven't found EL41s to be particularly unreliable, so yours may well be fine.

If you don't want to buy another EL41, a conversion to an EL84 would be easiest. See the UL41-UL84 conversion described here: http://www.vintage-radio.com/recent-...bush-ac11.html

It's possible to use a wide range of common 6.3V B9A output valves, including the pentode section of the cheap-as-chips ECL80. You will need to adjust the cathode resistor.

An EL42 is a plug in replacement, but the valve is less powerful so the cathode resistor should be increased appropriately.

Paul

[G8HQP Dave]

Just a quick update. I've cleaned up the chassis, and changed some capacitors: electrolytics and screen decouplers. After reforming the HT caps, powered up and got some sound out of it. Voltage checks showed that the EL41 had low emission and too much grid current, so I changed that. Other valves seem OK.

It is quite deaf on MW, LW bands so at the very least needs realigning. I found that the MW aerial coil has a broken core jammed in it so I need to extract it and find a replacement - I should have a suitable core somewhere in my junk box. The rubber mounts for the tuning capacitor have perished so it is leaning forward and the drum is scraping the back of the metal tuning scale plate. I hope that I can use some grommets to fix that.

Not yet a success story, but better than it was. One peculiarity is that the speaker hums as soon as it is switched on, before the valves have warmed up. Is this magnetic coupling between mains and output transformers?

[MichaelR]

Hi Dave,

Be very careful of those RF coils , they are very easy to break and not so easy to fix

Regards
Mike

[G8HQP Dave]

Thanks for the warning. I'm finding that on some coils the wax holding the core in place is stronger than the core itself! I've managed to extract and replace the MW aerial core, but now have the LW and 49m ones to do too.

Some cores seem to have a strong brass end, but the ferrite (or dust iron?) ones are very fragile.

[paulsherwin]

Originally Posted by G8HQP Dave

One peculiarity is that the speaker hums as soon as it is switched on, before the valves have warmed up. Is this magnetic coupling between mains and output transformers?

I don't have a P45, but a number of Pye sets from this era do suffer from coupling between the transformers. You can confirm this by removing *all* the valves and powering up. If the hum is still there, and definitely coming from the speaker rather than the transformer itself, then that's the cause.

It's odd that Pye made so many sets with what is basically an obvious design fault, but people seem to have been less sensitive to mains hum then and viewed some hum as normal.

Paul

[peter_scott]

Originally Posted by kestrelmusic

Tie a piece of string round it fairly near to the base, soak the string in methylated spirit and set light to it. When the flame goes out, plunge the valve into cold water.

Thanks for that. It sounds like a good trick.

Peter