Tubes/Valves+ 1930's radio renovation

[Davsop]

Hi everybody
I'm a newbie here so just a quick intro. I work for a company supplying wound components to industry but I am also still involved in tubes/valves etc.. which I used to deal in with my last company in the 1980's/1990's. (I'm always interested in buying unwanted/clearouts so let me know,I will travel to collect.)

I've just received an old 1930's radio and asked can you get this renovated for me please?
So I'm currently looking around who can help me with this project.  I'll post some pictures later for you to see.
Thanks
Dave

[PhilipPeake]

Well, real help over the internet may not amount to much, but if you want to post details of the problems that you encounter on the way I (and others) may have some ideas of where to go next.

As a starter:

Look to see that the valve heaters are glowing. If they are not, find out how they are supplied.
In better class radios there will be a 6.3v winding on the power transformer. Check that power is getting to the transformer, and that you have 6.3v (AC) on the heater winding. If no power, start looking at the on/off switch and any fuses.

Cheaper radios may not have a transformer. Instead, the heaters are wired in series, and there will be a large wire-wound resistor dropping the mains supply current feeding these. If one of the valve heaters is open circuit, non will be on. More likely, one section of the wire wound resistor has gone open circuit. You used to be able to buy replacements to just bridge over an O/C section. These days you will probably need to be more creative.

If the heaters are all running, check the HT supply, usually ~240v in the UK/EU, 120v in the US.
No HT? Start looking at the PSU.

Again, good quality radio will have a transformer, quite often a center-tap 240-0-240.
El-cheapo ones may pick off something from that big WW resistor, or even go directly to the incoming mains via a fuse...

No/low HT? Start looking at the rectifier. Possibly a valve rectifier, or just maybe a big, square (usually gray) thing with fins (selenium rectifier). If that has cooked, it will smell like a herd of cats has peed in the radio (assuming it was relatively recent, and not 50 years ago).

Better quality radios will have a couple of capacitors for smoothing, with a choke (big, iron-cored) between them. 1930's the capacitor are probably oil-filled paper. Check the choke for continuity and capacitors for shorts.

Assuming you have heaters and a high voltage supply - let us know what the symptoms are beyond that.

[james_s]

I've restored a few 30s-40s radios, in general I've found it's rare to have to replace any of the tubes although the pins and sockets sometimes require cleaning. The most common problem by far is bad capacitors, the electrolytics dry out completely and the wax paper type absorb moisture and get electrically leaky while drifting in value, sometimes dramatically. I normally replace all of those.

[@rt]

Will you travel to Australia LOL.
I’m about to send off 8Kg of valves to another fellow in a vintage radio FB group.

I’ve never found a radio valve difficult to come by if prepared to go to eBay.
As already stated, they are hardly ever bad, but often missing.

[Davsop]

Thanks for all your replies everyone. Much appreciated.
Perhaps Australia from here is a little too far this week but thanks for the message anyway
However I'm willing to still purchase and ship in tubes by courier from wherever you are. Anyway, just send me your lists/photos. The main thing is that they are in original boxes and unused.

[james_s]

If you want tubes in their original boxes and unused be prepared to pay top dollar. Realize that you are asking for 50-80 year old products that are new old stock, those are rare as hen's teeth even with relatively common tubes.

[PhilipPeake]

Scratch around and see if you can find an old valve equivalents book somewhere. Most UK radios will likely have Mullard valves. Those are even rarer than hen's teeth. There are US equivalents of most.

[Davsop]

Thanks James and Philip
Yes having dealt in tubes since the early 80's I try and keep up to date on prices etc.. Over the years I've managed to accumulate over 10,000pcs.
As you say my Mullard tubes are always requested but these are disappearing fast these days.I picked up a job lot of RCA valves last year which people are very interested in. I also had quite a few small DG7/6 Philips CRT tubes which were mainly sold to customers in the USA.

[mojoe]

Like James_S said, replace the caps. All of the electrolytics will certainly be dry by now. Also, the paper/foil caps that were dipped in bee's wax have changed in value. Replace all of the caps, without exception.

The resistors may also have changed in value. Check and replace any that have drifted high in value.

Don't spend money on tubes until the caps and resistors have been replaced, and you have tested the radio out. Chances are, most or all of the tubes are fine.

If you haven't already tried to power up the radio, DON'T. As a minimum, replace the electrolytics in the power supply first, then bring up the AC very slowly, with a variac. If you don't have a variac, build a "dim bulb" tester. A 1930's radio almost certainly had a power transformer. You risk burning it out.

Also, look closely at the wiring before applying power. If cloth covered, it may be OK. If plastic, it will probably crumble at a touch.

Speaking of plastics, other than bakelite, the few plastics of the day will have shrunk, cracked and yellowed by now. If you have bakelite or wood that is in good condition, that's one less problem. Be aware that some manufacturers used a very thin veneer over a cheaper wood (Philco was guilty of this, among others). The veneer is very easy to damage.

Depending on how much effort you want to put into keeping the radio looking "authentic", you could spend much more effort. One of the radios that I had was a 1932 Philco cathedral radio. The paper caps were inside little bakelite "bathtubs", and potted with tar. I replaced the paper caps with modern pollys (I didn't replace the tar). When re-mounted, you couldn't see the substitution. For the electrolytics, I cut open the nickel-plated copper can, soldered a new part inside, then re-sealed the can. When re-mounted, you couldn't tell it was modded.

Unless you want to get obsessive, I'd say, if it is underneath the chassis, and won't be seen, use modern parts and don't worry about the looks.

You can find lots of info and get help on www.antiqueradios.com. Years ago, there was a guy on there who specialized in selling radio knobs. I bought several. I haven't been on that forum in quite some time, so I don't know if he is still around.

Things like dial string, dial light bulbs, replacement speaker grill cloth, replacement cloth covered wire, etc. can all be found from various vendors.

One last thing. If your radio is a US model, PM me the make/model, and your email address. I probably have a schematic and alignment instructions.

[james_s]

Like James_S said, replace the caps. All of the electrolytics will certainly be dry by now. Also, the paper/foil caps that were dipped in bee's wax have changed in value. Replace all of the caps, without exception.

There is an exception in some cases, mica caps can usually be left alone. I would definitely replace electrolytics and wax paper caps though.

[mojoe]

Yep, I forgot to mention the mica caps. Good catch.

[coppercone2]

Look for the youtube channel "Mr Carlesons lab" it has like a hundred videos that mostly focus around vacuum tube radios and older equipment, with some modern stuff, but he really focuses on tubes.

https://www.youtube.com/channel/UCU9SoQxJewrWb_3GxeteQPA

There are alot of videos on full restorations (not just temporary repairs) where he goes over many details you will find fascinating