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

[Nowhere-Man]

Here is the circuit for the HMV1124 the 2 resistors Terry mentioned are arrowed, on the manufacturers circuit they are listed as R17 680R and R20 750R.
My bet it is either the resistor R20 or a dry joint. Try re-flowing the solder joints with good clean multicore 60/40 solder.




By the way I use these types of capacitors. You cant get much cheaper, and they do have a fairly decent length of lead, it saves having to solder wires onto those little stubs on the Wima caps. The caps you are using are intended for printed circuit use.
http://www.ebay.co.uk/itm/291569440252?_...2749.l2649&ssPageName=STRK%3AMEBIDX%3AIT
Mike

O.K. thanks. I'll have to check this all through tonight as I won't be doing anything till it's 100 per cent clear. I had this problem before with potentiometer wiring on the last set and it took me a while to clear it up.

To "recap" (pardon the pun).

There is a red lead HT voltage supply lead from rectifier cathode to one lug of the first big can. This jumps up to 400 volts and holds a lot of charge for a time.

There is another lead from the rectifier to the second lug of the HT can but this has a break in the circuit. That is, why do I have a floating cathode voltage on a busbar?? I measured this today but it leads nowhere and does nothing.

[Crackle]

Dont worry about the discussion over audio quality and capacitors.
The 2 resistors R17 & R20 are shown on these 2 diagrams.
       

Mike

[Nowhere-Man]

In terms of audio quality they're impressive. On the G.E.C. the audio quality is terrific so long as there is some grounding of the earth wire.

What makes you think these caps are responsible for good sound quality? Even in the realms of top quality hifi the "sound" of capacitors is mostly snake oil. On a humble radio the exact type of cap will make no difference. Obviously a faulty (usually leaky) cap can give problems with sound quality.

That may be the least of my troubles.... I think tonight I'll spend some time triple checking the H.T. supply layout just to be sure.

[Nowhere-Man]

Dont worry about the discussion over audio quality and capacitors.
The 2 resistors R17 & R20 are shown on these 2 diagrams.


Mike

Here is what has me confused:

First H.T. can has 3 lugs. One of them should be ground.

One of the lugs is energised and has direct supply from the rectifier cathode pin. It charges up.

Should the other lug (not the ground) also have a supply from cathode? I have a floating cathode wire and I assumed this must connect to the second lug on the can. Otherwise I'm baffled as to why my 2nd cathode wire measures 400 volts and is soldered onto an empty terminal on a connector block..

[Nowhere-Man]

Just found a similar thread where someone was asking about H.T. Can terminals and was hesitant. What throws me is whether they put resistors inside the can itself so you can't physically see them. I won't be doing anything just yet till I'm 100 per cent certain. Will have a wade through info on HT cans tonight..

[Crackle]

The resistors are NOT in the electrolytic can.
There should be a wire from the 16uf terminal C35 which goes to R20 (this may be fed direct from the rectifier HT output as a second wire, maybe this was not replaced when you were fiddling with adding silicon diodes, or was that a different radio, I cant remember now). Then there should be a connection from the other end of R20 to the 8uf terminal C34 on the other smoothing can located in front of the tuning capacitor..

Check the layout diagrams I added to my last post, you will see that the 2 main smoothing caps are in different cans.

Do you have your own copy of these diagrams.

Mike

[Crackle]

..................... I have a floating cathode wire and I assumed this must connect to the second lug on the can. Otherwise I'm baffled as to why my 2nd cathode wire measures 400 volts and is soldered onto an empty terminal on a connector block..

This "floating" wire maybe the one which needs to connect to R20 and then another wire from R20 goes to C34, which is in the other smoothing can in front of the tuning cap, follow it and check, if so reconnect it to the rectifier output and you may have HT to the rest of the set.

I find it helps to take photos or make a quick sketch on paper before dismantling anything.
Mike

[Nowhere-Man]

..................... I have a floating cathode wire and I assumed this must connect to the second lug on the can. Otherwise I'm baffled as to why my 2nd cathode wire measures 400 volts and is soldered onto an empty terminal on a connector block..

This "floating" wire maybe the one which needs to connect to R20 and then another wire from R20 goes to C34, which is in the other smoothing can in front of the tuning cap, follow it and check, if so reconnect it to the rectifier output and you may have HT to the rest of the set.

I find it helps to take photos or make a quick sketch on paper before dismantling anything.
Mike

It has to be very specific for me or I won't understand. Detail is everything. I spent some time searching online and simply wasn't getting the specifics I needed for this. I was forced to go about it a different way.

Taking the GEC as an example, some time ago I used a silicon rectifier and capacitor/resistor network and fed the cathode D.C. ripple to the corresponding lug on the single smoothing can. I tested this can last night and found I had the same 3 lugs or terminals, one being ground. I found the voltage on the supply feed lug was about 280. However, the voltage on the second lug was about 200 volts. So definitely two potentials at work, the latter being dropped across the circuit.

Suffice it to say, the design around the can is quite different from what appears to be the case with the HMV.

To further clear a few things up, I took the first 16 mF smoothing can out of circuit, except ground. I then manually charged the first terminal "A" of the capacitor for a few minutes. On measuring with the a meter, "A" was holding the voltage of the charge. "B" was zero potential. Negative was at ground.

Next, I manually charged terminal "B". After a few minutes, "B" was holding charge without any problem.

Between "A" and "B" was zero potential difference, as was expected as both had been charged.
That's what I needed to know.

The resistors mentioned I tested some time ago - one is between the two cans.

It seems as if someone has messed with the rectifier circuit junction bridge and removed some small junction wires.

It now seems wise to test the second smoothing can out of circuit.

[Nowhere-Man]

I wish textbooks would give a bit more detail over smoothing cans. This is the first set where I've had two instead of one. I never found any comments made in any of the books about testing the cans. I did hear of the odd case where the cans exploded. In such cases shrapnel has a habit of embedding itself in ceilings and walls....

Some people bypass the old cans altogether and may even fit motor runner capacitors instead.

[Nowhere-Man]

My feeling is the voltage is a bit high so this may have to be looked into later. The manual data does give about 390 from the rectifier with an AVO but it's a lot to be feeding into a set that's been dormant maybe for years.

Have been working hard on this the last 2 days so could use a day or to chill out as I can get mental blocks. However, it won't be long hopefully till the next test.

Will need about 4 6 volt scale lamps as I think all of them are kaput and the holders rusted.