Where would they have come from ? some batch of other double tetrodes and markings removed ? all Chinese script so scrubbed off ?
4 presumably ECC83 in a Laney (not originals) all test bad C/H leakage and bad/ low or marginally good gain. Not a trace of any marking , as low power valves, presumably no marking originally. They look like any other ECC83, no bad cut metal/ broken mica or any other indication of bad manufacture.
-- Diverse Devices, Southampton, England electronic hints and repair briefs , schematics/manuals list on
I once knew a number of ways to 'raise' the lettering in those cases. Thanks to the ravages of time and the apparent death of important brain cells, I only remember one:
Cool the tube and fog the surface with your breath.
Others will be along soon to elaborate on their techniques.
Jonesy
--
Marvin L Jones | jonz | W3DHJ | linux
38.24N 104.55W | @ config.com | Jonesy | OS/2
* Killfiling google & XXXXbanter.com: jonz.net/ng.htm
I have just carried out an inventory of my old (new) valve stock ex on-the-road service engineer. Quite a lot of them have no - partly visible lettering. I suspect this was due to our practive of removing them from their individual wrapping and carrying them in the vehicle in compartmented cardboard boxes.
measured on avo tester with settings as ECC83. just tried looping ptfe tape around the envelopes and fingernail pressure but not the slightest lettering appeared. All the valves have an unusual cloudy appearance within the glass where the leads go through, so presumably all the same batch/make despite different impressed letter/numbers in the flat base glass sections of the valves. No Mullard type tiny code numbers on the envelopes.
-- Diverse Devices, Southampton, England electronic hints and repair briefs , schematics/manuals list on
Back to your question, do you need help with identifying tube holes? I have the PDF for that amp. I actually have the whole amp too. Came to me with burned AOT. Replaced with a Fender Bassman OEM I had stocked. It's one of my fav Brit sounding amps.
Yes snipped-for-privacy@petitmorte.net. I use TMDA (the mail delivery agent) so you will get a confirmation email to respond to before I get yours. The reason being is spammers don't reply to confirmations and I can safely post my address in public.
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