What exactly have I just bought?! A 1930s Radiogram

[deliverance]

That looks fantastic !

[EF80TVVALVE]

So I've been having a look around and there are two power supplies, one for the main radio and amplifier and the other with just a mains transformer and rectifier supplying the DC for the speaker field coil. The ammeter is fed from the DC output of the field coil supply but the volts meter looks to be fed from the main PSU although I haven't yet looked deep enough to see whether it is HT or mains.

Other than that there are a lot of extra sockets, one bayonet type and three mains sockets under the unit itself so presumably this also supplied lighting or power for extra speakers (if they were using the same speakers and DC supply in stand alone cabinets).

Another thing is it looks as though there are two rectifiers working in parallel in the main PSU, one is a U14 which I presume is original but the other is a U18/20 which is younger than the rest of the equipment. I'd imagine it should be 2x U14 so I will have to find a replacement.

As far as rectifiers go, am I likely to run into trouble keeping the original on the speaker supply board as pictured? I only ask because it looks to be made from brass and not selenium like the later types but equally I have never came across one of these before. I don't know if it is something that is likely to fail and cause damage or quite the opposite, being a robust piece of equipment.

[vinrads]

Wonderful piece of kit , do you think the cabinet was originally a wind up gram , looking at the inside of the lid it looks like it , Mick.

[EF80TVVALVE]

Hi Mick
I initially thought that it has been built into another cabinet, whether it be a gramophone or a piece of furniture but on closer inspection I think this was built for its purpose, there are no signs of it being something else before and the way it is built shows it was made to take some weight and has everything built 'in mind' too. I'll hopefully get more photos soon once I'm done cleaning it out and getting rid of the mess.

I've answered my own query regarding the plug sockets, they are all mains power to the various parts of the amplifier, not very safe as some male plugs are live when exposed so I'll be replacing with a suitable terminal block instead.

[bikerhifinut]

Originally Posted by EF80TVVALVE

So I've been having a look around and there are two power supplies, one for the main radio and amplifier and the other with just a mains transformer and rectifier supplying the DC for the speaker field coil. The amps meter is fed from the DC output of the field coil supply but the volts meter looks to be fed from the main PSU although I haven't yet looked deep enough to see whether it is HT or mains.

Other than that there are a lot of extra sockets, one bayonet type and three mains sockets under the unit itself so presumably this also supplied lighting or power for extra speakers (if they were using the same speakers and DC supply in stand alone cabinets).

Another thing is it looks as though there are two rectifiers working in parallel in the main psu, one is a U14 which I presume is original but the other is a U18/20 which is younger than the rest of the equipment. I'd imagine it should be 2x U14 so I will have to find a replacement.

As far as rectifiers go, am I likely to run into trouble keeping the original on the speaker supply board as pictured? I only ask because it looks to be made from brass and not selenium like the later types but equally I have never came across one of these before. I don't know if it is something that is likely to fail and cause damage or quite the opposite, being a robust piece of equipment.

Could you conceal a silicon rectifier somehow and leave that in situ for the look of authenticity?

A.

[PaulR]

Could you bring the rectifier up gently on a variac? Even if you don't keep it in circuit it would be interesting to know if it still works to any extent.

[Techman]

I think that when we see something like this that we haven't seen before and think that it's something unusual and possibly custom made is because no one on this forum was alive when these radios were made and because of their size, none got put into storage such as lofts, so there's hardly any left. A child that would have been around when that set was put together would have to be around 100 years old by now! When we speak with authority on these early sets, it's because of what we've read in books or been told by our grandparents etc.

Now by sheer coincidence, I happen to have a little booklet that proves that big cabinet sets like yours were probably quite commonplace in the larger family houses of the time. The picture below is taken from a vacuum cleaner instruction book dating from the early to mid thirties, that was given to me just a few days ago by a chap that I picked up a couple of old tape recorders from. In the picture the lady is using the cleaner to suck out dust from the innards of the receiver - not something I recommend doing on a decades old set now, as you don't know what unpleasant and harmful products are going to to be sucked up and pushed through the filters to be spread throughout your house, but that's another story for another day.

They could have shown any old table wireless set for a plate in a general domestic appliance instruction book, but they chose to show a large cabinet unit of a similar type to the one that you have there, perhaps proving that they were more commonplace at the time than we might think. I've got the same vacuum cleaner as shown in the picture, hence my use and need for the book.

Lastly, be very careful with those output valves - it'll be a show stopper if you bust them, in fact I would advise checking that all the filament strings are intact before going much further with repairs. You can easily check them by applying 4 volts and seeing if they all glow as they should. The only thing that possibly points to this set being a 'special' are those meters, but then none of us were around to actually know if this was an unusual arrangement at the time. Restoring/repairing this will test all your skills to the limit. It's not going to be easy if you haven't worked on something as old and substantial as this before...good luck with it.

[Paul_RK]

Not much doubt, I'd say, that this was an exceptional item even in its day. Certainly floor-standing radios were quite popular before WWII, and quite often homebrew sets of the '20s were built into existing items of furniture. My guess would be the set in the instruction book has a pretty ordinary three or four valve chassis, quite enough of an investment for most middle-class households. There are factors determining the proportion of a particular type of item that stays intact for eighty or ninety years to come down to us: I suspect larger high quality radiograms survived fairly well at least until the recent ravages of audiophools just by dint of their being bought for large houses where a proportion of them could be shunted aside and largely forgotten about for decades. But production runs for Dynatron machines and the largest RGD and EMI products pre-war were small, and items like this will always have been even less widely owned.

I of course agree with others here that it's a lovely beast, and had it become available to me the question would have been where, not whether, I would find it a home. Probably in the sitting room where a couple of the seven or eight radiograms currently resident would have been shunted to somewhere else...

Paul

[EF80TVVALVE]

Regarding the rectifier, I will bring it up on a variac and see what we find, according to the speaker it only requires 6v for the field coil so I can't imagine it supplies a high voltage. I can fit a bridge rectifier but I'd imagine this would also need a series resistor to drop the voltage a bit, as we all know their modern equivalent are much more efficient.

Techman, thanks for the info of the instruction booklet, I actually have one of the same cleaners too! I can imagine these types of grams were once popular to some extent to the upper classes, but I can also imagine that they may have been replaced or modified fairly quickly with the advances radio was making in the 1930s and this may be why we don't see as many now.

I can't help but think that with the amplifier and styling of cabinet it was definitely for a hotel lounge or club, the door covering the radio section also has a sliding bolt lock on the inside to keep the left door and radio covered, allowing you to open the right door and checking the mA meter. It's all very interesting and I'm looking forward to having it working.

I'll be extra careful with regards to the output valves, I work on power amps a lot so I know what can happen here and I'll be sure that it is in a faultless condition especially before I leave it playing relatively unnatended.

[Techman]

It's certainly a fantastic radiogram. That record deck is period and probably original - it's an RC something or other low number that I've forgotten at the moment, but someone will remember.

Let's hope we see this restored and not have the amplifier sold off, as happened in a recent thread with a gram with power triodes (and not for the first time) that we'd all been giving help and advice on, only for the person to announce that he'd sold the amplifier for big bucks and then had the nerve to ask for help on what to replace it with, needless to say he didn't get any help and disappeared never to be heard of again! You're a long standing member, so I don't think that you'd be the sort of person to do something like that - it's not what this forum is about (in my opinion anyway), although it's your gram and you're perfectly entitled to do with it as you like - let's hope you keep it in one piece and have a go at getting it up and running, it's certainly a very interesting piece.

I would advise carefully removing the two output triodes and wrapping them in cotton wool and storing them somewhere very safe while you're working on the rest of the electronics etc.

[EF80TVVALVE]

Yes there is no chance of it being broken up, it's uncommon to see something like this in its original state so I'm all for keeping it as it is. I would like to know if there are any less valuable valves that will work in place of the output triodes? I'm not going to sell them on but obviously they do have value and as I'm planning on using the gram a fair bit once working I don't know how I feel knowing that anything could suddenly give and kill one or both. Even if it is something with less power as I won't need the 25ish Watts that these can give, but I'll keep them for the bragging rights and give them some occasional use when I'm happy to watch it whilst running.

Just an update regarding the unit itself, the stand that the speaker was on had a damaged top panel so whilst cleaning yesterday the speaker was removed and repairs made. The speaker has been cleaned and is found to be in perfect order, I've removed the cloth cover and gave it a very careful hand wash before refitting, it's in good condition for the age with only a few small holes so I won't bother replacing it. I've also removed the whole spaghetti of mains wiring and will fit a terminal block once I'm ready to start work on it. More photos to be added once I refit the speaker.

[Techman]

I wouldn't worry too much about wearing out the triode output valves, they actually go on forever so long as the heaters aren't overrun and they don't get any sharp physical knocks. I run a radiogram in my living room with Mazda globe power triodes and have done for many years without any failure, other than a heater connection within one of the pins in one of them needing re-soldering about 12 years ago. You see, these valves don't have any cathode as such, the heater strings being the actual cathode 'emitter', being known as 'directly heated' types. There isn't anything else that can be used without modification, the particular problem being that anything that you could triode strap and adapt would need a 6.3 volt heater and your gram is all 4 volts. There was a forum member who used to pretend that he kept getting sets with the output triodes missing, but I found out that he was actually removing them and selling them. He got quite a lot of advice on modifications to use other valves - I'm not going to mention any names, but I'm sure you'll be able to find these old threads and have a read if you do a search...something to think about if you find there's a problem with the ones that you have. Great to hear that you're going to do the right thing by the radiogram, it's a fantastic item!

[Uncle Bulgaria]

Wonderful. Add my name to the list of people looking forward to seeing this come back to life. After lockdown eases, time for a swing-dance party with this providing the music, I think!

[EF80TVVALVE]

Thanks for the advice, really my only concern is the Ferranti 'dog bone' resistors used for the biasing, they're wirewound and measure okay but all it will take is for a faulty contact on the holders to cause problems, I'll just have to ensure that all connections are cleaned and in perfect order here before even the first power up.

I'll have to make some videos of it up and running once it's back in a good working condition, it would be great to take it somewhere such as retrotechUK (NVCF) and have it singing away, but as you can imagine this is a very awkward thing to move!

[EF80TVVALVE]

A rather crude photo of the speaker now refitted, I don't have much space to work around it really so photos are rather difficult at the moment until I move things around a bit. I'll be looking at the PSU this evening and hopefully get some photos of that too. I'll need to find suitable replacements of the huge Parmeko oil filled capacitors, I really don't want to keep these in as I'm sure they'll give off a good bang should they fail and one is already leaking an possibly hazardous oil, but I'd like to find something that is similar in looks although this may be a difficult task.

[Uncle Bulgaria]

I thought paper in oil capacitors were one of those things like cockroaches that are supposed to survive anything. Is that wrong? I'm sure you can find other PIO capacitors of the same value if one is leaking - don't people buy ex-USSR ones for their guitar amplifiers? I've got some big old ones somewhere as well.

[Techman]

Originally Posted by EF80TVVALVE

I'll need to find suitable replacements of the huge Parmeko oil filled capacitors, I really don't want to keep these in as I'm sure they'll give off a good bang should they fail

No!

There's nothing wrong with those caps!

My radiogram is full of them, all original and still going strong from the 1940s.

This whole subject has just been discussed today in the thread linked to - have a read-
https://www.vintage-radio.net/forum/...d.php?t=177185

The leaking one if it's the one I can see in an earlier photo probably isn't leaking and just had something waxy melted and dropped on it - check it again carefully.

If you're worried about them you can always test them at HT voltage with a high value series resistor and check volts drop across it.

If one really is leaking, then handle it with some of those blue nitrile disposable gloves - I use them all the time when working on such things.

[EF80TVVALVE]

Thanks for the advice, I'll give it a second check but when I first looked over them I noticed it looked as though it was weeping from a corner seam. I can take them out and test them on a separate psu I have access to and see if they're short/leaky. I figured after almost 90 years they wouldn't be too trust worthy especially working on the HT line but I'm perfectly happy to be proven wrong!

[Techman]

Yes, look at it closely, if it does turn out to be leaking then you'll have to deal with it.

You could test them in situ by just disconnecting them one at a time and use flying leads with a series resistor from your PSU.

Definitely try to keep it as original as possible. If you do find a faulty one, you can fit a replacement (which will be physically smaller) under the chassis and leave the original disconnected, but still in place.

[Ed_Dinning]

Hi Bren, if the cap is leaking oil and is otherwise OK electrically it should be possible to carefully clean it and reseal with a clear epoxy. Soldering could be attempted but not a good idea to heat the cap.
In a set of this age the oil is most likely a mineral type and not the highly toxic PCB that was expensive and I believe came in later.

Ed