prewar Marconi

[ChrisW6ATV]

I am still amused how Ebay bidding usually goes. The set went from about $3400 to $7600 in the last thirty seconds of the seven-day auction.

[John Folsom]

That is because many people (including myself) use snipe bidding services.

[kx250rider]

Originally Posted by ChrisW6ATV

I am still amused how Ebay bidding usually goes. The set went from about $3400 to $7600 in the last thirty seconds of the seven-day auction.

Out of my league.... And I'm astounded that a British prewar set went that high at all! They're nowhere near as rare as USA prewar sets.

Charles

[ChrisW6ATV]

Originally Posted by John Folsom

That is because many people (including myself) use snipe bidding services.

I still bid on Ebay the old-fashioned way, "sniping" manually.

Actually, I wonder how that term started, because it implies cheating or something else negative. I figure, bidding early just exposes you as a target for anyone else to beat. There is nothing wrong or sneaky about wanting to keep your maximum price hidden.

That would be a very nice set to own, but I would much rather have a prewar set from here in the USA. Not likely to ever happen, though, with my budget...

[tubesrule]

Originally Posted by kx250rider

Out of my league.... And I'm astounded that a British prewar set went that high at all! They're nowhere near as rare as USA prewar sets.

Charles

There were certainly many more British prewar sets made, but Steve's data base shows fewer remain than American ones.

Darryl

[Sandy G]

I'm sorry, but these things just DON'T really "Excite" me...It likely won't work, & quite possibly CAN'T be made to work, either. Part of the fun of having these things is to turn 'em on once in a while, & at least show a raster to amazed guests...Or showing off the "Glorious Lollipop Color" of a well-tweaked Roundie...There IS a "Kick" from having a pre-war TV, but not THAT much of one if you can't at least show a raster...

[wa2ise]

Originally Posted by ChrisW6ATV

Actually, I wonder how that term started, because it implies cheating or something else negative. I figure, bidding early just exposes you as a target for anyone else to beat. There is nothing wrong or sneaky about wanting to keep your maximum price hidden.

I just figure how much I'm willing to spend, and I place the bid with that value. If someone wants it more (bids higher) so be it.

[Steve McVoy]

These sets can be restored to work. Standards converters are available to produce the 405 line signal. Even the CRTs can be rebuilt now.

[Penthode]

Originally Posted by Steve McVoy

These sets can be restored to work. Standards converters are available to produce the 405 line signal. Even the CRTs can be rebuilt now.

Also, VHS tape holds 405 lines pretty well (apart from the lack of drop out compensation). Considering that the bandwidth of 405 is only 2.5 to 3MHz, VHS quality looks a lot better on 405 than it does on 525 or 625.

[Sandy G]

Hmmmm...Well, I thought since Scotty has retired, that was it as far as rebuilt CRTs went. I KNOW the electronics can generally be rebuilt, & even the standards issue isn't THAT hard to overcome, if you're really determined, but I thought that the door had closed on CRT rebuilding... Its all academic for me, though, 'cause a prewar set is so totally out of my means to be not even worth considering.

[miniman82]

If it's a Pyrex tube, it would have to be sent to RACS in France for now. But I hold out hope that something will materialize with the ETF's efforts. Too bad I couldn't volunteer myself to help out with the project, I just have too much other stuff going on ATM.

[ppppenguin]

Originally Posted by jhalphen

Much skill is needed to rebuild guns and sometimes an entirely new gun must be assembled from scratch re-using the original parts: Wehnelt cylinder, G1/G2/G3 anode assemblies, etc. X/Y/Z positionning of the parts in space must match the original specs to within fractions of a millimeter so that the electron optics performance are satisfactory. This is no mean feat, and for color CRTs (Think 15G..) the amount of work is tripled.

The guns on the 9" and 12" pre-war EMI CRTs are a particularly complex hexode design. Not sure how much needs to be dismantled to replace the cathode/heater assembly.

I hadn't heard about the EHT connector problem. Possibly because the 6/6 that I had rebuilt in 1986 was pumped cold. There were 2 reasons for this. The CRT was too long to fit in the available oven and the guys doing the glassblowing were worried that the stresses caused by heating could crack the glass. I'm not sure about the stress problem, the heating might well anneal the glass and make it stronger. I admit that for that project we had a choice of 5 dead EMI 6/6 CRTs. The choice was made on the basis of which glass had the fewest bubbles and other defects.

[ohohyodafarted]

Originally Posted by ppppenguin

The guns on the 9" and 12" pre-war EMI CRTs are a particularly complex hexode design. Not sure how much needs to be dismantled to replace the cathode/heater assembly.

I hadn't heard about the EHT connector problem. Possibly because the 6/6 that I had rebuilt in 1986 was pumped cold. There were 2 reasons for this. The CRT was too long to fit in the available oven and the guys doing the glassblowing were worried that the stresses caused by heating could crack the glass. I'm not sure about the stress problem, the heating might well anneal the glass and make it stronger. I admit that for that project we had a choice of 5 dead EMI 6/6 CRTs. The choice was made on the basis of which glass had the fewest bubbles and other defects.

Jeffery,

Just out of curiosity, how long did you "cold pump" that EMI crt to get a good vacuum? WE had been considering a low temperature pump down, in the range of 450 to 500F for our 15GP22 rebuilding project, but we did not get that far. We have a special epoxy that we wanted to use to seal the leaks, but it degrades around 500F so we were considering using a low temperatur pump cycle, but we had not data as to how long it may take at a lower temperature. It would be useful to know how long it takes to pump down a crt that is at low temperature versus at 650F in a pump down oven.

Thanks!

[ppppenguin]

Originally Posted by ohohyodafarted

Just out of curiosity, how long did you "cold pump" that EMI crt to get a good vacuum?

Sorry, can't help you there. I wasn't present during most of the rebuild, I only co-ordinated the different companies that were involved. The guy who did the work is now dead (at least I assume so, he'd be about 115 now) and had vast experience. I don't know what other knowhow he used for doing a cold pump. One thing I remember is that while the gun was being rebuilt he rough pumped the tube and sealed it off. This was mainly to minimise damage to the phosphor as it was not being rescreened. I think he also used double the normal amount of getter.

For you, I suspect it's a matter of doing some tests with worthless CRTs and seeing how they respond when pumped cold. You have the additional unknown of how the epoxy will outgas during pumping so you might put a bit of that in the worthless CRT for test purposes.