HMV 1124 - Has Been Tested And........

[pwdrive]

NM, something would get hot, resistor/rectifier/mains transformer if fitted, possibly a fuse would blow if the radio had one, if no fuse then it would usually mean permanent component damage.


Most of the hard wired radio chassis had the wires wrapped at least half a turn around the connection points, dry joints were the most common problem, caused by poor soldering techniques including oxidization of component leads and connection points etc prior to soldering, it got worse when printed circuit boards were introduced.

Lawrence.

[Nowhere-Man]

You've got the HMV going, that's good, some radios are pigs to work on some aren't so bad, keep at it.

Don't forget to post a question If there's anything regarding to radios etc that you're not too sure of.

Lawrence.

Thanks, Lawrence. To be honest, I had a hard time believing it.  The first time I powered on, I didn't get much of a result. The dim bulb tester was a bit red so I assumed something was wrong and that I'd screwed up somewhere. I'd gotten a bit of a hum from the speaker but no sign of stations. Later I found out if the dim bulb tester only goes orange and doesn't glare, it should be O.K. to plug into full voltage so I did. I finally connected the aerial lead and then I did get the one station and was pretty stunned. It was Radio 4 but there was a bit of hum and the volume was weak. Still, I was very happy to have gotten some result.

After that, I was checking the aerial and started to check resistances and joints. I finally planned to just work my way through the circuit with a hope to improve on reception as I plodded ahead. I was in no rush.

The test that was most productive was the Volume Potentiometer readings on the grid of the DDT. Placing the meter on the Megohm setting, you can hold one probe to the volume pot lug and the other probe to the grid. As the volume rises with the turn of the switch, the Ohms will creep up to 500 K. I eventually found there were capacitors in the circuit around here so their function was quite important for bypassing R.F. I tried changing one in the grid circuit plus another capacitor elsewhere and that then solved the problem of poor volume and partial reception.

It was hard to believe I finally had a working radio because I was a bit sceptical over not having access to much of the set and the fact I was limited by my approach not to fully dismantle the set. However, fortunately, it all worked out.

The work done is as follows:

(1) Repair of mains supply to transformer and fuses + holders (which were too dirty to conduct).

(2) Cleaning of wiring and components as well as chassis and all switches. Full cleaning of chassis that was covered in dust and dirt. Cleaning of tube bases.

(3) New potentiometer to replace one that was broken and corroded.

(4) Rewiring of rectifier tube.

(5) New 16mF smoothing can as former had been sparking and seemed dodgy.

(6) New AF coupling capacitors and all worn or suspect capacitors changed, except the Picofarad types.

(7) New wiring where necessary.

Work To Be Done Is:

(1) Restoration of cabinet.

(2) Need to stencil in 2 glass waveband slats with lost data.

(3) Restringing of tuning mechanism.

(4) All scale lamps to be replaced and holders cleaned.

[Nowhere-Man]

NM, something would get hot, resistor/rectifier/mains transformer if fitted, possibly a fuse would blow if the radio had one, if no fuse then it would usually mean permanent component damage.


Most of the hard wired radio chassis had the wires wrapped at least half a turn around the connection points, dry joints were the most common problem, caused by poor soldering techniques including oxidization of component leads and connection points etc prior to soldering, it got worse when printed circuit boards were introduced.

Lawrence.

Well, the HMV had two 1 amp fuses between mains supply and transformer, mounted on the rectifier platform. I thought that was a good idea.

I tried using cable ties where I soldered a high voltage supply wire so if the solder joint ever came off, the wire wouldn't drop. I can only assume if that ever happened there would be a rapid equalisation of polarity between chassis and H.T. + with the 80 watt circuit in the middle. It must have happened scores of times in past years. One snag was there was no way to earth the chassis to an RCD as I think most radio chassis will have some voltage and current, even if small.

[pwdrive]

You got a result and lived to tell the tale so you're on the right track, try downloading a few Trader sheets (schematics) for a few models from different manufactures and print them out if you can, you will be able to see circuit configurations that will be common, you will probably be able to recognize those fairly quickly, if you can then that means it's all sinking in, you will also see circuit configurations that are not common to them all and maybe are new to you, the challenge then is to figure out those differences and the reason they were implemented, all that will help your understanding of this radio stuff a lot.

The practical side such as component replacement in awkward places etc will come with practice and various tips you can pick up along the way.

Lawrence. EDIT: this post was a reply to post#112.

[Nowhere-Man]

Well done, it is surprising how difficult it is to find a fault like a little wisp of wire touching where it shouldn't.
It may be possible manufacturers fitted components into "modules" like your double tag strip, and then fitted these into the set. It may have saved time.

This is a component board in a radio I am repairing at the moment, I would not be surprised if this was assembled outside the set and then wired in. There is another row of solder tags for the other end of the component leads the opposite side of the board (which indecently is only made of cardboard) hidden under the rest of the wiring. But this method of fitting components is probably easier to work on whilst carrying out repairs than the tag strips you had in the HMV.



Mike

My strip had the capacitors twisted onto lugs and then soldered as well. I had to cut them out with wire cutters and could only solder in the new component. There was no access to actually thread the wire through. Therefore, the headache was to solder onto just a small bit of copper wire and get a good enough joint. It tended to be easier if I used quite thin single strand wire but I also used thicker wire that was wrapped around the frame a turn. Don't think I ever want to go through that again to be honest. I much prefer just going from pin to pin with decent access.

[Nowhere-Man]

You got a result and lived to tell the tale so you're on the right track, try downloading a few Trader sheets (schematics) for a few models from different manufactures and print them out if you can, you will be able to see circuit configurations that will be common, you will probably be able to recognize those fairly quickly, if you can then that means it's all sinking in, you will also see circuit configurations that are not common to them all and maybe are new to you, the challenge then is to figure out those differences and the reason they were implemented, all that will help your understanding of this radio stuff a lot.

The practical side such as component replacement in awkward places etc will come with practice and various tips you can pick up along the way.

Lawrence.     EDIT: this post was a reply to post#112.

The best site for schematics I found is Radio Workshop and there I locate whatever schematic I may need. I currently have 3 radios stored at a friend's garage and 3 in my other boat, plus a German set. Given I work very slowly and sporadically this will take some time.

Yes, this thread has finally reached its finish but I do have the nasty job of stringing the tuning mechanism. This is the flywheel type with side pulleys and I don't particularly like fiddly work but we'll have to see.

Possibly my next job could be a 1939 battery TRF where my soldering wasn't up to scratch as I'd just started out at the time.

For now, I've been unwinding with some music. The latest thing that kept me busy is working out TV scores. That is, the backing music you hear on seventies TV series or even films. Last night it just happened to be the Six Million Dollar Man. This actually has some neat bass in the background. So, I was busy last night trying to duplicate some of the background score and finally made a recording. Music is the one thing that totally relaxes me.

[Joe]

'Freddy Got Fingered' is a lousy film but has a damned good sound-track.

— Joe

[Nowhere-Man]

'Freddy Got Fingered' is a lousy film but has a damned good sound-track.

— Joe

I thought The Beach had a pretty good soundtrack. That was the movie with Leonardo DiCaprio. It was a great film as well.

As I seem to be in an incredibly lazy state of mind and physically sluggish (partly due to the weather), most of my radio work now is theory. Someone gave me a very early Radio Engineer's book that was first published in The Thirties. It shows a lot of illustrations of 120 volt accumulator batteries and tubes like pepper pots on radios. I figured it would do no harm to get new perspectives by starting even at some of the beginning chapters. Sometimes one explanation can give perspectives others didn't.

The chapter I was on last night had me up a bit late. It was kind of fascinating. Back in the early Forties it seems Radio Engineers would use a Milliameter with a full scale deflection of 5 Milliamps. It then turns out they used shunt resistors to produce readings up to 2 amps in the circuit but with the meter still only passing 5 Milliamps. It even tells you how to make the shunt resistors. I mean, back then there was no cheap East Asian meters to buy in a local Wilko store for a fiver. Even the 5 Milliamp meter cost 30 Shillings.

I got out my calculator and then my troubles began. Trying to work out the shunt resistances at a deflection of 5 Milliamps to get readings up to 2 amps.

I might try and get my hands on the other classic Radio Engineers Vest Pocket Book as well.

[Joe]

I remember having to calculate shunt resistances at college. You need to know the resistance of the meter coil or the voltage needed to give full-scale deflection.

— Joe

[Nowhere-Man]

I remember having to calculate shunt resistances at college.  You need to know the resistance of the meter coil or the voltage needed to give full-scale deflection.

— Joe

Yes, I found that out over the last 2 nights. I decided it would be a good idea to explore how the very early radio engineers had to get by.