HMV 1621 radiogram

[jfisheresq]

Hello All, I've recently picked up a HMV 1621 Radiogram, which is not working. I am new to radios, my background is in wind up gramophones... I'm wondering whether there are folks here that are kind enough to help me to find out whether this unit is something I can bring back to life. I'm conscious that there must be lots of 'newbies' asking for help, so if people could perhaps recommend some reading I could do to get familiar with the basics, that would be a good start.

What I can tell you about the gram is very limited.... I have switched it on, just to see what happens. The valves all light up, but there is no audio to the speaker at all. No crunching when changing between wavebands, and nothing from the pickup. I've got wiring circuits for the 1622, which I understand might be the closest I can find, and I have carefully removed the two chassis, one being the radio receiver and the other presumably an amplifier. Any advice would be gratefully received, I'm keen to learn.
Many thanks,
Jason

[Nuvistor]

This is a good place to start, lots of information about how radios work and how to repair them.

http://www.vintage-radio.com/repair-...ion/index.html

[Simon Gittins]

I notice that the loudspeaker on the 1622 is connected using plugs and sockets; it's worth checking this connection. It's likely to need other work if it's unrestored though.

[Edward Huggins]

If this Radiogram has not been altered, the original Plessey 3 speed autochanger's cartridge may well have failed. Also, these are very difficult to fix mechanically so I don't envy your task!

[jfisheresq]

I am guessing though, that even if the cartridge had failed, this wouldn't affect the functioning of the radio. Because everything is dead am I right to try to focus on the amplifier chassis as a first port of call? I'm not worried about the mechanical side of the record changer at all - that will be fine to sort out, my weakness is in understanding the electrical side of things, which I really want to improve. I'm going to build a simple unit with a 100watt bulb so that I can use that in series with the power supply before I start trying to diagnose anything, but any advice on where to start would be so helpful. I have checked the speaker, which works well and have cleaned all of the plug and socket connections, but it is still completely silent when the radio is powered up. I'm assuming that the fact tht all of the valves are glowing is a good sign ??

[Simon Gittins]

Yes, the amplifier is the place to start and glowing valves are a good sign. The link in Post 2 is a good place to start and the lamp limiter is also a good idea (must be an old-style incandescent bulb).

HT checks and checking for electrically leaky coupling capacitors (which can cause output transformer failure) would be the next stage. You could also check the resistance of the output transformer primary (with the set unplugged and after making sure the HT capacitors are discharged).

Do you have the Manufacturer's service sheet or the Trader one? The circuit references are different.

[mark pirate]

I would check the output transformer for open circuit primary windings, I take it you have a multimeter.
If OK, you may have no/low HT.

Mark

[jfisheresq]

Thanks for the advice guys, I will let you know how I get on with the checks mentioned above. Yes, I have a multimeter, and I'm looking at the manufacturer's service manual... so if you can identify any of the components I need to look at on there, that would be a huge help. And I will do some tests when I get chance.
Thanks

[paulsherwin]

If this radiogram is unrestored and has been out of use for many years, it is likely to have multiple faults, both mechanical and electronic. These can all be fixed, but you should think carefully if you want to learn the skills needed, as it is a big commitment for a beginner. It's not simply a matter of someone telling you to 'change component X' after which everything will start working.

Of course, you could pay a professional to restore it for you, but that is a skilled job so won't be cheap.

[Radio Tech]

Paul is quite correct, and for what its worth I wouldn't have applied any power to the set as quite a lot of damage can result. I would have been inclined to study the circuit diagram and check all the main components out such as smoothing cap (most likely a 32 + 32uf) replace coupling caps, these are the ones that link one stage to another. As it seems there is no output, look at the voltages around the anodes of the stages

Ken

[jfisheresq]

Duly noted, I suppose I was just keen to see whether it worked or not, and lacking in any experience with these things. I don't think having it restored professionally is something I'm after, I was hoping the challenge of trying to bring it back to life would be fun. I am very aware that I'm dipping into a world which I know nothing about, but I am also keen to learn about it... I'm not expecting simple fixes, but some guidance on other people's starting points is interesting and useful to me. I've got a lot of reading to do, I think, before I do anything else.

Is the fact that I don't have access to a circuit diagram for the amplifier section going to be a big problem? I can see that, for someone with no experience, that might make things quite difficult. Are the primary windings on the output transformer likely to be the same as the model 1622 for example?

[paulsherwin]

It seems to be a fairly complex design with push-pull output and FM, so not an ideal project for a beginner. There's no reason in principle why you shouldn't have a go at sorting it out though, and members here will certainly advise you. My concern is that you may not really be interested in the electronic side of things, and will find the work a tedious chore once the novelty wears off. Only you can make the call.

It should be a good performer if and when you fix it. It would have been an upmarket radiogram when new.

https://www.radiomuseum.org/r/hismas...gram_1621.html

[Simon Gittins]

I don't know what the differences are between the 1621 and 1622 but as a circuit for the 1621 doesn't seem to be readily available the 1622 seems at least a good starting point.
As you have the manufacturer's service manual then you do have the circuit for the amplifier section it's just not shown as a separate diagram; if you follow the line of the PL1/SK1 connections the amplifier and power unit is the part on the right. The drawing A.F. UNIT - TOPSIDE VIEW shows the output transformer (TR1) to the left of the valves. As has been suggested, a good starting point would be to check (with the unit unplugged) for a resistance reading of about 125 ohms for each section of the primary.

[Techman]

It almost looks too old to have FM, but it seems it does. I quite like that typical HMV setup with the N78 output valves. They always seem to work well and sound good.

If you look at the RM link you'll see the speaker plug setup, typical of HMV at the time and you can see where the plug is supposed to be for normal internal speaker.

It should be very easy to determine why there's nothing other than valve heaters glowing. Once you've done this you can then decide whether the job is going to be either too expensive, or beyond you.

So first check that the speaker is properly connected via that yellow plug, then work out the connections for the output transformer primary and measure it for continuity - you can work this out from the valve data sheet for the N78...download it. The two anodes will basically go to each end of the transformer primary.

There's another way you could go about things, and that's by taking voltage readings, but doing it that way is potentially more dangerous for both you and the gram, as under a fault condition, damage could result if left powered up for too long. I might do it this way, but I would take the readings very quickly, probably in under thirty seconds and then switch it off - not recommended for a beginner! As has already been said, it depends on how dedicated and interested you are.

What has already been said about the deck and cartridge is also very valid, but first things first to get the state of play and then decide what you're going to do after that.

[Herald1360]

Watch out if you're using a DMM rather than analogue meter. Some go haywire on ohms when presented with a high inductance like a transformer primary. Open circuit will still be open circuit though.

[Simon Gittins]

I should have seen that the 1621 uses N78 output valves so you don't have the correct circuit diagram for the amplifier section after all.
A continuity check of the output transformer primary is still probably your best first step, you may even hear a crackle from the speaker as you do so (depends on the meter type). Each section of the primary may not be 125 ohms but both should be about the same.
Let us know what you find and we can consider the next steps.

[PaulR]

As someone new to this I think you need to follow the advice already given. Put the radiogram to one side and read up on how valves and superhet radios work, why electrolytic capacitors can be problematic but not necessarily need to be replaced, and Ohm's Law This site is a mine of information. I have learned a huge amount from the experts on here and by reading previous threads.

If you don't do this the circuit diagram will just be a jumble of lines and symbols and you won't understand the advice given or stand much of a chance of repairing the set. As I have found, working by yourself you can't just ask quick questions and be shown techniques as an apprentice would have done but you can take things slowly and ask questions on here.

Starting from a low knowledge base I still would not consider myself to be anything like an expert and would not dream of giving technical advice but I would be fairly confident in tackling your radiogram so you can do it with a willingness to learn - and a camera to record how it was before you started!

[jfisheresq]

Thank you to everyone who has replied - I'm very grateful. So... I've traced the wires coming from the output transformer primary windings, two of which go to the N78 valves. Testing the resistance between each of these at their connections to the valve anodes and the third wire, one section gives a reading of 17.6 ohms (am I reading that correctly?), and there is a definite crackle through the speaker. The other section though seems to be open...no crackle and no reading on the meter. So I know this is bad news - I'm assuming that if the transformer is bad then there's not much I can do without sourcing a replacement, if that is even possible.... I'm fairly sure I'm testing it correctly, so it looks like this might be the first of many problems.

[paulsherwin]

You are right, this is bad news assuming you have measured the resistance correctly. If you are very lucky, the connection will have failed near the solder tag and you can repair it. Otherwise you will need to source another transformer (it doesn't have to be exactly the same type) or rewire the amp so that it operates in class A rather than push-pull. The latter is certainly achievable even for a beginner, but again you need to decide if you really want to bother doing it.

[jfisheresq]

Thank you Paul. I really do want to bother, yes. I will have a careful look to see whether I can see where it has failed without disturbing too much. I have done this with transformers before with success. Replacing it would be something I'd be happy to do, my soldering skills are fine. "Rewiring to operate in class A rather than push-pull" means nothing to me, so I will do some reading up about it, but if someone is willing to talk me through it or if it is described elsewhere on this forum, that would be great. As others have said, more reading on my part is needed I think.