Bell radio (NZ)

[arjoll]

If you followed my thread on the Antone Cadet you may recognise this one! After researching the Antone it turned out that the company went on to become Bell Radio Ltd.

One of my wife's friends commented that her old radio was playing up a bit - apparently not staying on station - so my services were volunteered to check it out. Tania picked it up today and it is a Bell.

Sure enough, this wee Bell set is very similar to the Antone - similar case, speaker, chassis, output transformer. The valve lineup is different, updated a few years - EZ40, ECH81, EF41, EBC41 and what I think is an EL41. While the Antone was mostly octal with a token B8A, this is B8A with a token B9A!


The ECH81 has quite a lot of metallisation and the EL41? is in quite a sorry state - more about that in another post - but my main plan of attack is to replace the caps and see how I go from there.

First, though, some shots of the set. No 4ZA on the dial so its probably pre-1956; as a comparison the Antone was 1949/50.

[arjoll]

First query - I'm pretty sure this is an EF41. The pin connections look right, similar kind of circuitry to the Antone (although I'd like to trace both sets out in a bit more detail) and I can make out a lot more of the markings on this than on the Antone.

The valve looks quite sorry for itself though. I'm not sure what the discolouration is - its right by the mains transformer but the cap just behind it looks fine. The fact that the set has been used reguarly until the last couple of weeks would tend to indicate that there's probably not too much wrong with it, so maybe it just needs a careful clean.

Which gets me to my next problem - what's the best way of extracting the valves from this kind of B8A base? The Antone as easy - pop off the clip - but these holders don't seem to have the same kind of clip and those bases aren't wanting to let go of the valve. If I need to force it I'd rather know what way before breaking something!

Also what's the impression on the state of this valve - do you think just 50 years of heat discolouration etc?

[arjoll]

Finally, the coupling cap and a few others are these tubular chaps. Values are 10000pF and 5000pF (10nF, 5nF). They are quite hard, almost like a ceramic.

There are a couple of waxies in there, 0.05 and 0.1, which I'll replace anyway and I'll do the coupling cap regardless (it is one of these, 5nF which seems a little low), but was wondering if anyone recognised the type.

The other caps around the RF stage are not the flat mica or disc ceramic I'd expect but some kind of box type - again I'd be keen on info on these!

Thanks

[arjoll]

Just checked here (which I should have done before posting) and it looks like those caps are the ones about 5 down, which Paul has found to be pretty reliable - so I might just replace the waxies and grid coupling.

I'm also in two minds about the smoothing can, may leave it in there and see how I go. Jaycar don't do high voltage 105C caps anyway so I'll end up ordering those through a local repair outfit from TradeTech if they do need replaced.

[newlite4]

Dont worry about damaging the valves during extraction, they are quite strong at the base and should slip out with a slight wiggle followed by a gentle tug. If they are a little reluctant, just use a small screwdriver to tease back the metal tangs of the base clamp a bit. This is a similar treatment to releasing the other type of B8a base where the retaining ring/clip is pulled out slightly.
Neil

[Steve_P]

That valve is probably OK. If your main problem is tuning drift, check and change the ECH81 or whatever it is. It probably drifts as it warms up, so clean the tuning cap and then change any caps round here. Then try it.

Cheers,

Steve P.

[paulsherwin]

Just pull the valves out. They may need a good tug - this is normal.

The valve lineup would be typical for a European radio made in the early and mid 50s. The only oddball is the ECH81, though you do find some mid 50s sets with B8A and B9A mixtures. None of the valves are especially difficult to source, though you may find them scarce in NZ. All these valves are generally long lived. What is the brand?

As Steve says, a poor ECH81 can cause tuning drift during warmup. Here we'd just sub another valve as these are very common indeed, but this may be less easy for you.

The discolouration looks external, though I've not seen anything similar. If you clean it off you will probably clean off the markings as well, though this may be worthwhile given the current disgusting appearance. You can write the valve number on the bottom where it will be hidden by the valveholder clip. If there are *internal* white deposits, this indicates that the valve is probably gassy.

The ceramic caps in the radio are likely to be OK. The electrolytics shouldn't need reforming if the radio has been used recently and may be fine.

Good luck, Paul

[Radio Fixer]

Want a schematic? Have several for these models.

I have the sets in cream, green and best of all blue. But not the pillar box red that is very rare and fetches high prices.

If you can give me an e-mail, by PM, I will send you pics of my under chassis work (think I have those). They work very well by the way.

Gary

[arjoll]

Originally Posted by newlite4

Dont worry about damaging the valves during extraction, they are quite strong at the base and should slip out with a slight wiggle followed by a gentle tug.

I'll give that a try, just wanted to make sure there was nothing else holding them in!

Originally Posted by Steve_P

It probably drifts as it warms up, so clean the tuning cap and then change any caps round here.

The only waxies in the set are around that area so I will replace them and see how it goes.

Originally Posted by paulsherwin

All these valves are generally long lived. What is the brand?

I'll check tonight. They were all 'made in Holland' but I didn't note the brand!

Originally Posted by paulsherwin

As Steve says, a poor ECH81 can cause tuning drift during warmup. Here we'd just sub another valve as these are very common indeed, but this may be less easy for you.

Surprisingly enough it looks like I have got a spare one - although no idea of its condition - in my box of random pulls from stuff I threw away 10+ years ago (I'm sure everyone used to do that and regrets it now!). The ECH81 is the valve showing quite a bit of metallisation at the LHS of the chassis in the photo, so I suppose its possible that it is just getting quite tired.

Originally Posted by paulsherwin

If there are *internal* white deposits, this indicates that the valve is probably gassy.

No, just external. I'm familiar with the internal ones after nicking the glass on the EL84 in a Ferrograph bias oscillator fortunately EL84's are easy to get here thanks to guitar amps .

Originally Posted by Radio Fixer

Want a schematic? Have several for these models. I have the sets in cream, green and best of all blue. But not the pillar box red that is very rare and fetches high prices.

Thanks Gary - that is not a response I expected from a UK user for a NZ domestic set! I've seen a few red ones on Trademe recently, and could PM you links when they come up. I'd be really keen on the schematic and will drop you a PM. I don't suppose you also have a schematic for this model's predecessor, the Antone Cadet?

Thanks everyone!
Andrew

[arjoll]

An update - its almost finished! Thanks to Radio Fixer for the circuit and the others for the hints.

Caps: the two waxies, grid coupling and the electrolytics have been replaced.

EL41: the deposit was holding the valve in the socket - with a bit of force it came out, and I cleaned most of the deposit off. I suspect it was crud from the electrolytic can, which appears to have been leaking quite a bit at some time in the past (hence the new ones under the chassis).

Instability: after replacing the caps and powering up, the station burst into life, good reception on all local stations from Radio Sport 558 up to Rhema 1404. After about 10 minutes it suddenly lost sensitivity and the stations wandered around. I tried Steve's suggestion of a different ECH81, ran the set for an hour or so and no problems.

So everything's looking pretty good. I have completely forgotten to grab a replacement bulb for the dial so that will have to see if I can find one locally - no 6.3V MES at Dick Smith unfortunately.

The only thing I'm not sure about is one resistor, between the grid coupling cap and the grid of the EL41. The circuit shows 560R but the resistor in there measures about 5k. Seeing all the other resistors appear fine, and apparently Bell were reasonably 'fluid' in their designs, I'm not sure if this seems like a reasonable value or not. (as far as I can tell that band is red!)

Thanks
Andrew

[arjoll]

Last thing - two hazards.

Firstly, the incoming mains cable ran right by a high power resistor in the main HT line - 50 years on its pretty charred. I have replaced the mains cable and re-routed it so it doesn't get as close to the resistor.

Secondly, one that's probably more NZ/AU specific, the problem with the older style PDL tapon plugs. The contacts to the tapon portion can start 'letting go' after a while - hazardous when its the earth pin as in this case. If the owner had plugged anything in on top of this plug it would have been pot luck as to whether the other appliance was earthed.

['LIVEWIRE?']

I would have thought 560R(or similar low value) was about right. This component is called a 'grid stopper', whose function is to minimise the risk of parasitic oscillations. It should be mounted with leadouts as short as possible, between the grid pin and the 500k grid leak resistor/coupling capacitor junction(I assume you've already changed 'that' capacitor). An 0.5watt resistor should be OK here.
Oh, I would also try to secure the mains lead by some other means than tying a knot in it, a 'P' Clip fitted inside tthe chassis near the point of entry would be better.(Or use a clamp type cable grommet)

[arjoll]

I'll have a look at replacing it then - I had a quick look and only have 1/4w of that value in stock so will grab some from Dick Smith tomorrow (might be an early start so I can get a park this time of year!).

It is mounted between pins on the valve holder as shown in the photo.

What kind of effect would the 5k that's in there have?

[ppppenguin]

1/4W should be fine for a grid stopper. It's not as if it carries any significant current or has any significant voltage across it.

[paulsherwin]

Originally Posted by arjoll

What kind of effect would the 5k that's in there have?

I don't think you'll notice much difference. This is a high impedence circuit and a 5k resistor won't drop a lot more signal than a 560R one. Personally I wouldn't bother changing it if performance is good.

As a stopgap for the 6V bulb you can fit any suitable MES torch bulb and a resistor. You'll find bulbs will look best if underrun. One or more high brightness yellow LEDs will also look reasonable if you have some to hand.

Paul

[audiomm]

If you need parts, circuit data etc for the Bell (or any of the other NZ built radios), then I will likely have it. 6.5v Dial lamps - how many boxes do you want?. Seeing as though you are 'just down the road' from me, maybe you could PM me and I'll give you my 'phone number .

[arjoll]

Thanks for the offer audiomm - I'm actually driving through Oamaru just after Christmas (and my dad's family comes from there!). I wanted to get this off my workbench before Christmas though, and I'm pretty sure I should be able to get the lamps locally, but will drop you a PM anyway as its always handy to know where else I can get 'bits' from!

[audiomm]

Small world ain't it. Unfortunately, I won't be around here for Xmas/New Year - I'll be away on holiday.
I've PM'd you some details on where to get the bulbs (other than me )and also my contact details.