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Old 27th Oct 2015, 6:12 pm   #81
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Default Re: HMV 904 prewar television restoration

Hi Catkins,
I've also enjoyed reading your write up of the 904 restoration.

I'm just getting to grips with my own 905 which has no TV components remaining on the chassis However the fact that there is only light rust present and that the remaining solder tags are ok work in its favour (a bit).

I notice the readings of focus coils that you mentioned. I'm currently trying to source focus and scan coils for my set. In my researches I have found that the earlier focus coil had a smaller hole diameter (still large enough for the 33.5mm CRT neck). I suspect that the later focus coil design was introduced when the 709/907 was introduced. The HMV 907 manual shows the focus coil as being 6000 ohms.

I also noted in an earlier post you mentioned the lack of deflection that was found in Hugo Holden's set. That is probably due to the fact that he was using an RCA 5FP4 CRT which has a deflection angle of 53 degrees. The 3/1 has a lower deflection angle, though I don't know the actual figure. In place of a 3/2 I'm planning to use a Russian 18LK5B, which has a 52 degree deflection angle, so if 53 degree CRT just about works then a 52 degree one should work...

Anyway, thanks for the write up, it is very inspirational

Cheers
Andy
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Old 27th Oct 2015, 6:17 pm   #82
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Default Re: HMV 904 prewar television restoration

Quote:
Originally Posted by merlinmaxwell View Post
Nice to know there are some proper manufacturing companies still in existence. Do they punch them or use water/laser cutting?
I assume that they punch (from their name, perhaps) but I don't know for sure what process they use.
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Old 28th Oct 2015, 1:49 am   #83
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Default Re: HMV 904 prewar television restoration

Quote:
Originally Posted by beery View Post
Hi Catkins,
I've also enjoyed reading your write up of the 904 restoration.

I'm just getting to grips with my own 905 which has no TV components remaining on the chassis However the fact that there is only light rust present and that the remaining solder tags are ok work in its favour (a bit).
I'm Catkins' brother. Yes, we both saw the 905 being used as a stand on ebay, and it appears we weren't the only ones! I did enquire but got back a rather rude message so didn't go any further. Congratulations on actually persuading the person to sell The way to look at it is once it's all done it will be a real achievement - I'm really impressed with how my brother kept up with his restoration, and the results have been worth it...

Quote:
Originally Posted by beery View Post
I notice the readings of focus coils that you mentioned. I'm currently trying to source focus and scan coils for my set. In my researches I have found that the earlier focus coil had a smaller hole diameter (still large enough for the 33.5mm CRT neck). I suspect that the later focus coil design was introduced when the 709/907 was introduced. The HMV 907 manual shows the focus coil as being 6000 ohms.
I've just checked some documentation I have and both the 5" Emiscope 3/1 and 7" 3/2 have the same neck diameter (one book says 33mm the other 33.5mm). Both agree that the 9" 3/3 in the 907 was 42.5mm.

The scan and focus coils did appear to be different sizes between the TVs but I didn't know that one was earlier than the other. I remember Eckhard Etzold initially used a 7BP7 radar tube in his Marconi 707 and to do this he had to use the coils from a 5" Marconi 706 as the original coils wouldn't fit...

We also have a Marconi 706 with a broken CRT. I started to work on this and obtained a 5FP4 and the scanning coils only just fitted - I had to remove the card tube from the centre to do it

Quote:
Originally Posted by beery View Post
I also noted in an earlier post you mentioned the lack of deflection that was found in Hugo Holden's set. That is probably due to the fact that he was using an RCA 5FP4 CRT which has a deflection angle of 53 degrees. The 3/1 has a lower deflection angle, though I don't know the actual figure. In place of a 3/2 I'm planning to use a Russian 18LK5B, which has a 52 degree deflection angle, so if 53 degree CRT just about works then a 52 degree one should work...
None of the documentation we have show the deflection angle either. How close is the appearance of the 18LK5B to the Emiscope? I ended up using the 5FP4 but was never very happy with it as the face is too flat, and it doesn't look correct. However, with the demise of RACS there's not a lot of choice...

Thanks,
Rob.
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Old 28th Oct 2015, 1:54 am   #84
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Default Re: HMV 904 prewar television restoration

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I remember Eckhard Etzold initially used a 7BP7 radar tube in his Marconi 707 and to do this he had to use the coils from a 5" Marconi 706 as the original coils wouldn't fit...
Found a thread on his TV where he mentions it:

https://www.vintage-radio.net/forum/...ad.php?t=29285
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Old 28th Oct 2015, 3:13 am   #85
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Default Re: HMV 904 prewar television restoration

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Yes, we both saw the 905 being used as a stand on ebay, and it appears we weren't the only ones! I did enquire but got back a rather rude message so didn't go any further.
Hmmm. Not wanting to give the wrong impression, I've tried to find what annoyed me and I can't (the messages I've found seem to be reasonable). The person said it was fairly valuable and I had to see it in person. As I was busy at the time this is probably what scuppered things. I remember thinking I knew exactly what it was, but considering the condition seeing it in person was right.

Rob.
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Old 28th Oct 2015, 3:50 am   #86
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Default Re: HMV 904 prewar television restoration

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Originally Posted by beery View Post
Hi Catkins,
I've also enjoyed reading your write up of the 904 restoration.
Thank you for your kind words.


Quote:
Originally Posted by beery View Post
I'm just getting to grips with my own 905 which has no TV components remaining on the chassis However the fact that there is only light rust present and that the remaining solder tags are ok work in its favour (a bit)..
I saw and read your thread earlier this week! (my brother mentioned the thread earlier but I was avoiding the forum at the time due to guilt at my long gap in posting).

You seem to be making very good progress As others have said, most of the missing bits should be able to be found/replicated. Mike Barker did an excellent job on the audio transformer and LOPT rewinds on the 904. I expect all of that can be put into progress.

Quote:
Originally Posted by beery View Post
I'm currently trying to source focus and scan coils for my set.

I'm planning to use a Russian 18LK5B, which has a 52 degree deflection angle, so if 53 degree CRT just about works then a 52 degree one should work...
Out of curiosity what is the situation with focus and scan coils? Can these be fabricated from new similarly to EHT/LOPT transformers etc. or is it a case of finding originals that match?

You mentioned in your thread that "Another good thing about the 18LK5B is that it is extremely common in some parts of the world.". I assume that is because the CRT was (according to various web-pages) in production up to the 60s and a lot were made (over a million the web-pages say). What is the situation with original focus/scanning coils for the 18LK5B, are they possible to find?
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Old 29th Oct 2015, 2:48 am   #87
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Default Re: HMV 904 prewar television restoration

Hi Rob,

I have to say that the negotiations for the 905 were the strangest ever and it took a couple of months to secure it. Of course the extra time did alow me to save up a bit and get permission from my wife
I wonder what happened to the old coils from Eckhard's set? They would certainly suit me...
I have a 5FP4, an MW13-35 (aluminised version of the 5FP4) and a 7TP4. When I eventually get the set running I will hopefully try them all out...

Hi Catkins,

The 18LK5B is supposed to be a 7" CRT, but is in fact 6 3/4". This together with the fact that it has a ion trap means that the original CRT mounting needs to change a bit as the steel CRT clamp would normally be where the ion trap magnet needs to go. However because the CRT has a slightly smaller face this means that the focus and scanning coils need to move nearer the front of the cabinet, so some spacing pieces should provide enough gap between the neck clamp and the focus coil for the ion trap magnet.
The face of the 18LK5B is nicely curved, so not so different from the original
I'm sure I can track down more of these CRTs if needed.

Making new scan coils would normally be very hard, but the simple design of the ones in these sets should not present too much of a problem.
The focus coil assembly is another thing though as it has a lovely pressed steel doughnut shape as well as forming part of the CRT and scan coil mounting assembly.
As for the Russian focus and scanning coils, well they look very different, so I really hope to get something EMI...

Cheers
Andy
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Old 29th Oct 2015, 10:39 am   #88
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Default Re: HMV 904 prewar television restoration

From the March 1958 Practical Television magazine:
An article titled "Making scanning coils".

DFWB.
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Old 30th Oct 2015, 6:39 pm   #89
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Default Re: HMV 904 prewar television restoration

Hi David,
Can you post the whole article?

Cheers
Andy
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Old 30th Oct 2015, 8:46 pm   #90
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Default Re: HMV 904 prewar television restoration

Scan of the three page PT article "Making Scanning coils".

DFWB.
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Old 31st Oct 2015, 8:16 am   #91
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Default Re: HMV 904 prewar television restoration

Good find David!

I'm amazed how informative this magazine is.

Please note that you can download a lot of issues from this site:
http://www.americanradiohistory.com/...n_Magazine.htm

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Old 1st Nov 2015, 10:30 pm   #92
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Default Re: HMV 904 prewar television restoration

As an update to the reproduction tagstrip saga, while waiting for the tags to arrive, I made a square punch and die set (the one I ordered was discontinued) and designed a jig to punch the strips. The pictures tell the tale. I call this an incremental jig as it uses a previous hole as a datum. The metal strip with the row of holes is the starter - the holes in it fit over the reference peg (screw) and it is used for the first 3 holes and then the first hole in the new strip reaches the reference peg and so on until 12 holes are punched, all exactly 14mm apart (in theory).
The first picture shows the jig and starter and the second, punching under way.
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Old 7th Nov 2015, 2:13 pm   #93
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Default Re: HMV 904 prewar television restoration

A further update - two sample tags have arrived for approval (that was quick!). They fit the strip I have punched and look the part. I will endeavor to get one dimension changed if I can but I am very happy with the samples. Here's a couple of pictures. I will contact the company on Monday and get them under way.
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Old 7th Nov 2015, 2:31 pm   #94
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Default Re: HMV 904 prewar television restoration

Very good Brian.

What sort of press are you using?
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Old 7th Nov 2015, 2:56 pm   #95
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I have an RS 3000lb bench press which I bought second-hand off ebay. However, I have just negotiated buying a 5000lb version of the same press so that I can work with 1.6mm steel. It should be arriving next week and then I will sell the 3000lb version (RS stock No. 541-309).
I deal directly with the importer: RS mark the 5000lb model up by nearly 70% and the tools are cheaper from them (Manuform Ltd. - no connection other than satisfied customer).
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Old 7th Nov 2015, 3:04 pm   #96
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Default Re: HMV 904 prewar television restoration

Thanks for that Brian and the tip about buying from the importer.

I've never liked the look of the cheap arbor presses you see advertised and reckon they'd need a lot of work to make them usable for precision work.
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Old 7th Nov 2015, 4:00 pm   #97
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Default Re: HMV 904 prewar television restoration

Hi Brian,

They look amazing

Cheers
Andy
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Old 7th Nov 2015, 4:59 pm   #98
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I've never liked the look of the cheap arbor presses you see advertised and reckon they'd need a lot of work to make them usable for precision work.
You're absolutely right. The so called "Arbor Presses" are totally unsuited to punching and forming. The punch would always be hitting the die with disastrous consequences! I know, I've tried it.
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Old 30th Nov 2015, 2:00 pm   #99
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Default Re: HMV 904 prewar television restoration

I've finally got the 1000 tags and very good they are too. However, the company "forgot" to plate them so I will be getting that done locally, this week sometime, I hope.
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