Problems with valve radio

In article , Rob Morley scribeth thus

How's that going to happen?..

In message , "Dave Plowman (News)" writes

Thank you all for the comments. I really don't think I'm brave/confident/knowledgeable enough to poke around and actually repair this radio. First step, I think, is try to find someone local.

The paper capacitor feeding the grid of the output valve leaks positive volts on to the grid and the resulting high anode current is too much for the primary winding. The Bush DAC90A transformer in particular is known to be fragile. With a 500k to 1M grid leak resistor it does not take much capacitor leakage to overcome the couple of volts negative bias.

I'd guess a coupling cap putting serious voltage on the grid of an output valve

But tyhat foesnt net you 'no hum'

Dead rectifier does tho

If you say roughly what "local" is, you may find someone here has a suggestion. Our town has a "Local Stuff" facebook page, if you have something similar a post there might work too.

snipped-for-privacy@gmail.com wrote on 31/08/2018 :

..and some used resistance wire in the mains lead in place of a dropper.

When I was a lad, I was given a transformerless radio. The chassis was connected to the mains live, rather than to the neutral. Whether it was meant to be like that or just that someone had wired the plug the wrong way round, I can't remember, but I discovered it the painful way when trying to set up an earth wire to the chassis!

The 'glowing' of a valve only tells you the filament is intact, it could have other issues.

Given the radio has been unused for 20 years, my first thought was be a fail capacitor- especially as you probably just plugged it in. (Not a criticism, without being rude, if you don't know the tricks it is what you do.)

Old capacitors can fail in several ways, some 'dry out' and go short circuit or low resistance, others need to be 'reformed' after long periods of disuse.

Someone with a multimeter and basic radio/electronics knowledge could probably find which one(s) have failed. It is possible, especially if one in the PSU section has failed and the rectifier isn't a valve, the rectifier has been damaged.

You could try to find a local amateur radio club, someone there may be able to help.

There are people on the internet who restore radios but I've no idea what they charge. Assuming it is just capacitors, the parts aren't expensive- a few pounds at most.

Some old radios are worth (semi)serious money, you may want to look on the internet to see what it is worth- assuming it isn't a sentimental thing- before you invest money in labour etc.

There are other possibilities but, if I was presented with such a radio, I'd try to isolate the fault to a stage then check the caps.

Oh yes, the infamous AC/DC sets.

Some even had special mains leads which were not low resistance and 'dropped' the mains voltage for the HT.

As a youngster I tinkered with countless old valve radios, how I survived those years is a bit of mystery.

Thanks Brian. Yes, very much a sentimental thing, which is why I am not tempted to fiddle, despite the excellent advice available here. Amateur radio clubs is a good idea, if there is one locally. Will search. My first idea was local Facebook groups.

In message , newshound writes

Aberdeenshire. Yes, we have local FB groups, and that is my next idea, following Brian's amateur radio groups.

No need to give up so quickly when a few simple checks may help resolve the problem.

First, do you have a digital Muli-Meter (DMM). Despite some earlier comments about quality, although desirable, any one of the very cheap ones that around these days will suffice for this set.

Second, check the valve numbers: is the first letter an 'E' or a 'U'? If it is an E, the set should be mains isolated but if it is U, which is highly likely with a lot of Bush sets, it will have a 'live' chassis. Don't panic - just use the resistance range of your meter to ensure that the neutral pin of the mains plug is connected to the chassis.

Third, work in an earth free area and, if you are right handed, make sure your left hand never gets within range of the set as it is shocks across the body from one arm to the other that kill.

One of the valve numbers should start EZ or UY. Near it will be a largish aluminium can, usually with three tags on the yop, one wich is connected to earth. Clip yje negative side of your meter to the chassi, switch on and wait for it to warm up. Then, with the DMM set to its highest DC voltage range, connect it to each of the other two tahs in turn. Note voltages and report them here together with the set's model number.

Another useful forum you can try is

Which you will find very friendly as well as being useful.

Here is one in Aberdeen- I saw your other post:

Not a club I know, I've visited quite a few when running training courses but not that one.

curtain burners are rare though. They were all miniatures.

NT

Might help if you tell us what model it is.

NT

In message , Brian Reay writes

Thanks Brian. Yes, I had found them, and will try a plea on a local group first, and if that fails, will try the club.

If you get stuck, there is an Email address on my website. I can perhaps 'talk you through' some checks.

g8osn.net

More recently that method has been used so the girlies can use their originally US made hair straighteners on 240V, with consequent overheating when they are used with the lead wound up.

In the vintage forum there is at least one member who does repairs just North of Aberdeen.