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Vintage Television and Video Vintage television and video equipment, programmes, VCRs etc. |
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17th Aug 2005, 11:25 pm | #1 |
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Re-gunning TV tubes - can it still be done?
Hi all I was looking at old books for the 50s regarding regunning of tubes, it looks like it would have cost about £600/ £800 then to buy the equipment to carry this out on a small scale.
From further reading it seems quite a few small tv repairers carried this out on a small scale with this equipment which would have allowed them to regun about 30 tubes a week. Of course they would have been able to buy in new guns with no problems. What a pity this equipment no longer exists along with the guns, but no doubt new guns could be fabricated, today but no doubt most of all the old equipment has been junked. Last edited by Mike Phelan; 26th May 2007 at 5:48 pm. Reason: Legibility |
18th Aug 2005, 10:45 am | #2 |
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Re: re gun tv tubes
I had an MW43-64 rebuilt last year. I tried to find a rebuilder in the UK, but no-one seems to do it anymore. I ended up using Hawk-Eye in the USA who did a superb job. http://www.hawkeyepicturetube.com/index.html It wasn't cheap - $250 for the job plus carriage. I used the cheapest tariff I could find - up to 3 months for delivery each way. The only thing Hawk-Eye got wrong was that they fitted a 600mA heater instead of 300mA, so it has to be powered by a small transformer.
There has however been a side effect on my Pye C17 set (similar to CTM17T series). This is one of the few 405-line sets with a proper gated AGC system. I had noticed that there is an RC network giving a lot of DC attenuation in the video feed to the CRT. Not being able to see the point of this, I had shorted it out, resulting in a nice stable black level. Now however I can see why they put this network in as a mod on the later sets. If there is a scene with high average level, there is increased load on the line output stage. This results in the AGC gating pulse reducing in amplitude slightly. The effect of this on the AGC system, is to increase the contrast. This in turn results in a higher beam current... you get the idea. This just doesn't happen with a knackered tube as it simply can't produce a high beam current, but a nice bright rebuilt tube is another story! |
18th Aug 2005, 10:55 am | #3 |
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Re: re gun tv tubes
Hi David,
Maybe I'll regunning my MW43-69 too. It is possible to cut the heater for the odd systems. With a resistor parallel I can heat it with 0,3A. I think. What kind of gun did you get for your MW? BTW only aluminized tubes can be regunt with a system without ion trap. So I was lucky to have a CRM 93. Kind regards Darius |
18th Aug 2005, 12:17 pm | #4 |
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Re: re gun tv tubes
Hi all/Darius, CRM 93 tubes can be got hold of here,the best source being the Ekco Tmb 272 tv, there still seem to be a few of these sets coming up for sale, I have seen about a dozen, in various sales in the last year, of course as in the case of every 405 tv bought the tube may be no good, but if you have not paid to much you still have a good load of spares, from the coments made so far it seems that no one here is reguning tubes, which is a great shame as I am sure there would be some sort of market be it a bit limited
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18th Aug 2005, 12:24 pm | #5 |
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Re: re gun tv tubes
Display Electronics in Uxbridge (not the surplus equipment dealers of the same name) were probably the last UK based tube regunners. I don't know if they still exist. I doubt it. They did most of the work for the EMI 6/6 that I wrote up for Television in the mid 1980s.
$250 + carriage would be a bargain for a 6/6! I imagine doing one of these would be a lot more expensive and the transit risks would be horrendous. Even $500+ would be well worthwhile for a prewar tube. |
18th Aug 2005, 2:17 pm | #6 | |
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Re: re gun tv tubes
Quote:
Jeffrey, Hawk-eye charge a flat rate for all 'antique' tubes. I don't know if the type you referred to is all-glass, but they do say the chances of success are not so good with glass/metal types. Also some early tubes were made of Pyrex glass which makes rebuilding more difficult. Last edited by David_Robinson; 18th Aug 2005 at 2:19 pm. Reason: Added reference to Pyrex |
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18th Aug 2005, 3:12 pm | #7 | |
Tetrode
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Re: re gun tv tubes
Quote:
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18th Aug 2005, 3:17 pm | #8 |
Hexode
Join Date: Jul 2004
Location: Michigan USA
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Re: re gun tv tubes
Hi Jeff/All,
It is true Hawkeye will not rebuild pre-war Pyrex crt's, but they do a wonderful job on post war ones. There is an effort underway over here to rebuild the Pyrex crt's. It is being headed up by Steve McVoy and you can read about it here: http://www.earlytelevision.org/prewar_crt_rebuild.html Clinton is the only place anyone has found that would invest any time into looking into this process, and even then it has not gone well, but there is still some hope as you can see from the web page. If anyone does know of a rebuilder anywhere that is capable of handling the Pyrex, please let Steve know. As you noted Jeff, there are usually flaws in the glass of these Pyrex crt's, and there is a good chance they will not survive, but if the crt is dead, and it's a spare, it might be worth the risk. It's also interesting that Clinton feels they can aluminize the tubes and still have them work with the low EHT potential of these sets. That would be wonderful for all the electromagnetic sets with ion burn! Thanks, Darryl |
18th Aug 2005, 3:53 pm | #9 |
Pentode
Join Date: Feb 2004
Location: Columbus, Ohio, USA
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Re: re gun tv tubes
There was one successful rebuild of a 9AP4 prewar tube in the 80s using a couple of different glasses between the Pyrex and a modern soft glass tube. The process is difficult and very time consuming, so no rebuilder will try it again.
Clinton is attempting to use Pyrex tubes and a Pyrex stem. If they are successful they should be able to do any prewar tube with a 35mm neck. Clinton is using a very thin aluminized phosphor to allow it to work with the 6-7 KV EHT of prewar sets. This should solve the ion burn problem with these tubes. Last edited by Steve_McVoy; 18th Aug 2005 at 4:00 pm. |
18th Aug 2005, 4:48 pm | #10 | |
Rest in Peace
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Re: re gun tv tubes
Quote:
http://www.dundee.ac.uk/biocentre/se...assblowing.htm And:- http://www.chemistry.ohio-state.edu/...lass_shop.html Regards, Mick. |
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18th Aug 2005, 6:14 pm | #11 | |
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Re: re gun tv tubes
Quote:
The reason the CRT would have died if turned face down is that one of the getters fell off during processing and would have landed on the screen if turned face down. |
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18th Aug 2005, 7:48 pm | #12 |
Dekatron
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Re: re gun tv tubes
Hello,
Most if not all of the skilled tube rebuilders have now unfortunately passed on. From a young age I was very lucky to know and work alongside one of the very best. He rebuilt all types including E.M.I., Metal cone, Twin panel, Rimbands and colour. He retired some years ago and unfortunately died of a heart attack about five years ago. His name was JOHN BROWN and his company was CENTRAL TUBES. He used to get the standard gun assemblies together with the 'pan' getters from Italy. They were the only source of supply. The old MW43-64/69 tubes were later fitted with a 100 degree gun, the same as the then current A50-120WR 20" tube. The results were superb. Pages could be written about the re-gunning process and a great deal of skill is required. Mercury seal vacuum pumps were used and tubes pumped whilst still in the ovens to eliminate all gas molecules [or at least most that were humanly possible] This was the system used by MULLARDS and resulted in a very long tube life. [Most of the 9" MW 22-16 type tubes are still good after 60 years. Mazda produced one of the best screens and their tubes produced the shapest pictures but they never seemed to overcome the gun problems that were mainly down to heater cathode shorts and an open circuit cathode connection. Large tubes such as the 27" Cathodeon used in the schools receivers took 48 hours to cool and the only way to stop them imploding was to switch the ovens off at the end of the evacuation process and let them cool VERY slowly. The huge getters were fired by R.F. heaters made by PHILIPS Eindhoven. Most modern tube rebuilders fit a new heater assembly and recoat the cathode with a new emissive serface. The Sony Trinitrons were done this way as of course no guns of any sort were available. Some firms re screened their tubes [Re-View] but the pictures always appeared slightly GREEN!! John said that the best combination was a MAZDA screen and a MULLARD type gun. The old gun assembly was cleanly removed from the neck by passing a current through a thin wire that was placed tightly around the neck. This formed a neat crack and allowed the air to enter overnight and prevent the screen coating being 'blown away'. Colour tubes were filled with argon to replace the vacuum rather than air. The use of 25kv created problems with flash over and any impurities took a while to settle but this resulted in internal flash overs when the tube was first run up. This lasted about 10 mins but could do damage to the silicon if not prevented. I will not bore you further but if you have any questions..thats if you have not fallen asleep you are very welcome to thread. Regards. JOHN |
20th Aug 2005, 6:56 pm | #13 |
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Re: re gun tv tubes
http://www.pgo-online.com/intlframes/glas_list_set.html
Here is some information about PYREX. All in my neigbourhood. Kind regards Darius Last edited by oldeurope; 20th Aug 2005 at 6:59 pm. Reason: link |