05-02-2020, 01:05 PM
Lawrence, perhaps I 'm being thick but not quite sure what you're getting at. 21 ohms would be the resistance of a 6.3V 300mA heater. This CRT is actaully 6.3V 150mA but I still don't understand.
Mark, I've never explored the measurement capabilities of my Rigol 1054Z scope so thanks for the reminder. Just had a quick look and it's got RMS capability. Just need to be careful because the heater supply is sitting at about +30V so I'll have to disconenct that to make the meaurement. I'd rather not float the scope though it wouldn't be the first time that somebody had disconnected a safety earth to make a measurement.
Thanks also for the offer of the 8290A which would give a true RMS reading until hell freezes over. I think this is overkill.
Incidentally, the DU1-12 minitors were acquired by the BECG for the planned refit of the ABC-Thames truck. https://becg.org.uk/projects/abc-thames/ They are not quite authentic but close enough. It's not often that we would have the opportunity to acquire a decent set of identical small monochrome monitors. We also got some very nice black alloy framework from the same installation which we can use to make the stack. We need 18 for the truck but I think we've got nearer 30 so I took a few for experiments. All have been in an area that wasn't quite dry. A few in a different area have been downright damp.
Of the 6 I've now got, 2 work well, 1 emits magic smoke, 2 work really badly with nasty high voltage noises and one did work until something went pop and the picture went funny. I think it's in the 110V supply which is derived from the LOPT. There seem to be at least 2 versions, an earlier one with 4 knobs and a later 1 with 3. The basic circuit seems to be identical, it's mainly mechanical and cosmetic changes.
For my 405 experiments I've decided on one of the workers, which has a slightly less good CRT than the other.
Assumning my experiments go well, I'll keep 1 or 2 here as lab 405 monitors. Another will go to Dulwich to replace the unreliable Prowest PM14/1A. I've promised 1 to Frank Cuffe who, astonishingly, did all his Hedghog converter work without a 405 monitor. There may be 1 or 2 more available for a donation to the BECG.
Mark, I've never explored the measurement capabilities of my Rigol 1054Z scope so thanks for the reminder. Just had a quick look and it's got RMS capability. Just need to be careful because the heater supply is sitting at about +30V so I'll have to disconenct that to make the meaurement. I'd rather not float the scope though it wouldn't be the first time that somebody had disconnected a safety earth to make a measurement.
Thanks also for the offer of the 8290A which would give a true RMS reading until hell freezes over. I think this is overkill.
Incidentally, the DU1-12 minitors were acquired by the BECG for the planned refit of the ABC-Thames truck. https://becg.org.uk/projects/abc-thames/ They are not quite authentic but close enough. It's not often that we would have the opportunity to acquire a decent set of identical small monochrome monitors. We also got some very nice black alloy framework from the same installation which we can use to make the stack. We need 18 for the truck but I think we've got nearer 30 so I took a few for experiments. All have been in an area that wasn't quite dry. A few in a different area have been downright damp.
Of the 6 I've now got, 2 work well, 1 emits magic smoke, 2 work really badly with nasty high voltage noises and one did work until something went pop and the picture went funny. I think it's in the 110V supply which is derived from the LOPT. There seem to be at least 2 versions, an earlier one with 4 knobs and a later 1 with 3. The basic circuit seems to be identical, it's mainly mechanical and cosmetic changes.
For my 405 experiments I've decided on one of the workers, which has a slightly less good CRT than the other.
Assumning my experiments go well, I'll keep 1 or 2 here as lab 405 monitors. Another will go to Dulwich to replace the unreliable Prowest PM14/1A. I've promised 1 to Frank Cuffe who, astonishingly, did all his Hedghog converter work without a 405 monitor. There may be 1 or 2 more available for a donation to the BECG.
www.borinsky.co.uk Jeffrey Borinsky www.becg.tv
