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Old 20th Nov 2020, 7:13 pm   #1
Radio Tech
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Default Hmv 1125

Hi folks

I recently got this set and have started to restore it, the wooden part of the cabinet has of course the famous HMV logo on the top of the set but the stain and varnish are very bad and needs to be re done, saying this, the HMV logo will get destroyed if I strip the surface, is there any way I can save the logo then re-apply it to the woodwork after. Same goes the plastic part of the cabinet, this needs to be re worked so all the chipped marks are gone and re sprayed, the plastic section I had to repair on one corner so I will have to be gentle with this. I have yet to start work on the actual chassis as I had to do a bit of re gluing of the various parts of the wood to secure the wooden part of the cabinet, I think I have my work cut out for the winter alright. I noticed that the first valve which is supposed to be an X78 is an ECH81, obviously at some stage someone has been a bit clever and changed the base but what bothers me is is the performance of the modification going to match that of the X78. More on this to follow with pictures.

Regards

Ken
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Old 20th Nov 2020, 7:55 pm   #2
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Default Re: Hmv 1125

These are a great radio - well I would say that because I've got one. They're not the nicest in the 'looks' department (in my opinion), but they are an excellent performer - well, when there were still worthwhile stations to receive on AM, that is! It was, I think, my first ever 'proper' valve radio, given to me by my grandmother when I was a young kid in the early 60s. She's had it from new and when it went wrong she rented another from Radio Rentals rather buy a replacement, so she gave me this set to 'play around with'. I remember sitting on the floor of her Walthamstow flat with it plugged in and the back swung open, while my parents and her were chatting about whatever. I was tapping around the innards with the handle of a screwdriver when it suddenly burst into life - everyone was amazed! Unfortunately this didn't last long, as when it was switched off and allowed to cool down and then switched back on, it didn't work again. Tapping round again with the screwdriver I found that clonking one of the valves caused it to spring back into life again. After taking the radio home and sending off for a replacement valve, the radio performed without fault ever since - I only replaced the grid coupling capacitor sometime in the last decade and that's the only component other than that valve that's ever been replaced in the entire life of the radio.

Unfortunately, it caught a dose of woodworm while in loft storage a few years ago and had to be treated and the holes filled in, which somewhat spoiled it - HMV plywood with its animal glue is known to be a bit of a magnet for woodworm, so watch yours!

I think that front surround is possibly cream painted brown Bakelite and the paint does flake off making the set look tatty - I've never done anything with this, but did think about removing all the cream paint and polishing up the Bakelite instead. It's now back in storage in the loft, due to the lack of AM stations available to listen to nowadays.

I can't comment on the valve substitution, as I've not compared the differences at this time of writing, but may have a look later if I get time, although someone else will probably chip in with advice...you could even check yourself if you look up the data on both and compare.

Last edited by Techman; 20th Nov 2020 at 8:00 pm.
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Old 20th Nov 2020, 8:10 pm   #3
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Default Re: Hmv 1125

I have a 1125, 1126 (brown bakelite front) and a spare chassis. i also like the 1122 with
the oval front speaker opening. Like the 1121 these EMI sets must have been the first
to use an elliptical loudspeaker. As there is a tone control if you would like a bit more top
connect a 1uF cap across the N78 cathode resistor.

The HMV logo is available on here you just need to print it on waterslide paper.
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Old 20th Nov 2020, 8:42 pm   #4
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Default Re: Hmv 1125

HMV and Marconi were using Elliptical speakers before the war.

The Marconi 219 from 1936 uses an elliptical speaker.

Cheers

Mike T
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Old 20th Nov 2020, 9:34 pm   #5
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Default Re: Hmv 1125

Hi Ken, the substitution of an ECH81 for an X78 seems a reasonable choice to me; the characteristics of the 2 valves are similar, the principal difference being that the screen (grid2/4) of the ECH81 requires a higher voltage than the X78. However, I'm not sure if this is likely to have any adverse effect since in the 1125 circuit the anode voltage is running at only 175v so I would think it is OK to leave as-is. However, as always I stand ready to be shot down! Certainly the ECH81 is readily available and although you can still find X78 some of the prices have gone daft. Cheers, Jerry
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Old 21st Nov 2020, 11:20 am   #6
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Default Re: Hmv 1125

I ran some tests on a good used ECH81 on the Avo VCM163 valve characteristics meter. Here's the detail:
Using test parameters from the Avo manual (Va=250v, Vg2=100v, Vaosc=100v), gave the results as follows (spec values in brackets):
Triode (Vg=-3v) Iaosc=4.4mA (5.0) gm=1.6mA/v (2.3)
Heptode (Vg=-2v) Ia=4.2mA (6.5) gm=1.1mA/v (2.4)
Using the supply and bias conditions as close as poss to the HMV1125 circuit (Va=175v, Vg2=60v, Vaosc=90v) gave the results as follows:
Triode (Vg=-3v) Iaosc=3.3mA (5.0) gm=1.5mA/v (2.3)
Heptode (Vg=-2v) Ia=1.3mA (6.5) gm=0.5mA/v (2.4)
This test indicates that although the triode oscillator should work OK, the gain of the Heptode mixer is likely to be considerably reduced and therefore the set might sound deaf. Things can be improved simply by increasing the screen (g2) voltage from 55v to 100v: using this value, still with Va=175v, gives for the Heptode:
(Vg=-2v) Ia=4.2mA (6.5) gm=1.1mA/v (2.4). Increasing the screen (g2) voltage can be achieved by replacing the grid2 potential divider resistors R3 (15k) with 8.2k and R4 (12k) with 39k. So if the set is deaf then I would give that a try. Cheers, Jerry
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Old 21st Nov 2020, 3:14 pm   #7
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Default Re: Hmv 1125

Thanks everyone for their input so far, as promised here are some photos I took of it in the process of restoration.

Regards

Ken
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Old 21st Nov 2020, 4:09 pm   #8
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Default Re: Hmv 1125

Nasty looking bodge tape on the mains transformer. I wonder what that is concealing? Jerry
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Old 23rd Nov 2020, 4:42 pm   #9
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Default Re: Hmv 1125

The 'bodge tape' was to prevent me touching bare leads , when I was checking it over recently and can be easily removed. ( I sold this to Ken as I knew it had potential and I was never going to do it). Also , I have read of other sets , fitted with a ECH81 from new.
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Old 23rd Nov 2020, 6:18 pm   #10
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Default Re: Hmv 1125

Hi Folks

I am currently in the process of replacing electrolytic capcitors, I am a little confused when looking at the ERT service sheet which indicates the the large canned capacitor has three capacitors inside which are C22 16uF C25 32uF C26 32uF but coming off pin 4 G2 of the output valve V4 is another electrolytic capacitor marked up as C25 of a value of 32uF, can anyone tell me what the correct value of that cap is off pin 4 of the output valve please.

Regards

Ken
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Old 23rd Nov 2020, 6:23 pm   #11
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Default Re: Hmv 1125

I think that just an error in the drawing.

They drew the power supply conventionally but had already put the same capacitor next to the screen grid.

There is only one C25 so just rewire it as it was.

Cheers

Mike T
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Old 23rd Nov 2020, 8:20 pm   #12
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Default Re: Hmv 1125

Quote:
Originally Posted by Radio Tech View Post
Hi folks

I recently got this set and have started to restore it, the wooden part of the cabinet has of course the famous HMV logo on the top of the set but the stain and varnish are very bad and needs to be re done, saying this, the HMV logo will get destroyed if I strip the surface, is there any way I can save the logo then re-apply it to the woodwork after. Same goes the plastic part of the cabinet, this needs to be re worked so all the chipped marks are gone and re sprayed, the plastic section I had to repair on one corner so I will have to be gentle with this. I have yet to start work on the actual chassis as I had to do a bit of re gluing of the various parts of the wood to secure the wooden part of the cabinet, I think I have my work cut out for the winter alright. I noticed that the first valve which is supposed to be an X78 is an ECH81, obviously at some stage someone has been a bit clever and changed the base but what bothers me is is the performance of the modification going to match that of the X78. More on this to follow with pictures.

Regards

Ken

Hi Ken, re the hmv logo, if you damage it and are struggling with a DIY solution, you can buy really good quality waterslide decals from e-bay. They come from Peru (yes really!) and aren't cheap though. I haven't used them myself but I've seen pictures and they look great. The seller is epj24. Screenshot will give you the details you need.

Gabriel
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Old 24th Nov 2020, 3:11 pm   #13
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Default Re: Hmv 1125

Thanks Mike T for the conformation over the drawing, that does clear the confusion up, I have housed the new electrolytic capacitors in the old can, I used wire in ones and got the three in the can.

And thanks to you Gabriel for the decal info.

Will be repraying the front bakelite panel in the morning but got to either get hold of a six inch round LS or a replacement 10 x 6 elliptical one

More to follow

Ken
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Old 27th Nov 2020, 1:41 pm   #14
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Default Re: Hmv 1125

Following on with the progress of this set here are a few more pictures of the set. I haven't done the varnishing of the woodwork yet as I have still got to print off the HMV decal and water slide it on to the top.

So here goes with pictures

Ken
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Old 27th Nov 2020, 7:59 pm   #15
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Default Re: Hmv 1125

A word of caution regarding the mounting of that speaker - I would strongly advise removing that grille cloth, or whatever it is, that's directly in front of the speaker, as on loud volume the cone will come forward and come into contact with it and destroy the surround in the same way as your original one. You never, ever see speakers mounted that way and that's the reason why. Any grille cloth should be on the outside of the baffle board only, in fact you shouldn't need it as you've got the original gold painted metal grille on the front of the radio anyway. The original speaker is the 'making' of the sound/tone from these radios, coupled with that N78 output of course. You really should have tried to repair the original, unless it really was too far gone.
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Old 30th Nov 2020, 9:48 am   #16
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Default Re: Hmv 1125

Hi Folks

Thanks techman for the info on the LS, I could repair the original so had to put a different one in as you saw, yes I did take the rubber away, and the set is back in its case working fine on all bands with good volume and selectivity.

Regards

Ken
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Old 30th Nov 2020, 2:50 pm   #17
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Default Re: Hmv 1125

I'm really pleased it has worked out well and that you bought it from me.
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Old 30th Nov 2020, 6:21 pm   #18
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Default Re: Hmv 1125

On E-Bay, I found a woman in Peru making great new HMV water slide decals for a low cost.
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Old 1st Dec 2020, 9:15 am   #19
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Default Re: Hmv 1125

Hi folks

Here is the picture of the set with all of the front panel done and the set on

Regards

Ken
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Old 4th Dec 2020, 3:51 pm   #20
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Default Re: Hmv 1125

Does it work Ok on LW without a long aerial? Apart from caps , what else did you do to the set alignment wise?
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