Post by davidballantynezl1tfg on Oct 20, 2018 19:50:18 GMT 12
Sorry can't help with a 6E7 but it's in RCA valve manual RC-20 but not in several earlier ones I have. If you get a dud one how about fitting its base to a 6U7. Plenty of them about. Presume not too tall? Good luck. David Ballantyne
It seems the 6D6, as you have found, is equivalent but has the wrong base - is the 7-pin base on the 6E7 a standard one from that era? You could potentially frankenstein a dead 6A7 or similar base onto a 6D6, wrap it in foil and attach that to the cathode pin and paint it grey for effect... if foil isn't your thing apparently weld-through primer is heavy in zinc and works well as a modern spray-shield alternative - although I've never tried it.
There is an interesting section in JWS's valve book (p.179-181) on Grigsby-Grunow and how they set up their own valve manufacturing in 1930 (ended in 1934) with completely non-industry-standard part numbering (it seems they didn't even stick to their own part numbering since the shielded valves started out with an S in the code, but the 6E7 doesn't have that). JWS postulates that they made their own identification system up simply to keep customers using G-G valves and make it hard, if not impossible, to use anything else.
Have you tried Gary (TwentyB on Trade Me)? He often has some oddball stuff and his prices are generally pretty reasonable.
There are no personal problems that can't be solved with the liberal application of high explosives
Thanks everyone for your replies. As Macbeth said to the witches regarding his suspicions of Banquo "Thou hast harped my fears aright ".The 6E7 is a 7 pin valve and fits a 7 pin socket.The Riders schematic showed a lineup of 6E7 6A7 6E7 6C7 42 6Y5
As found the set had what were stenciled 6D6s in the 6E7 sockets. So there has been some substitution . That's ok , I thought, I have a couple of 6D6s should either prove to be absent on leave. One did so prove.A phone conversation with a very learned person in the ChCh VRS ,though, suggested that there must have been a socket change , as the 6D6 fitted a 6 pin socket whereas a 6E7 was a 7 pin valve.On the walk back to the shed I remembered that the sockets are all original i.e riveted. Then followed some careful counting of pins on these sockets. Sure enough they are 7 pin sockets , original and riveted . So how come it's 6 pin 6D6s in 7 pin sockets? I began to think I knew.
Closer examination suggested that both 6D6s had been de- soldered from their original 6 pin bases and re- soldered onto 7 pin bases,as you would if an original 6E7 was made from unobtainium.(Thank you David for your suggestion of using a 6U7. I certainly have more of those than 6D6s and will probably have to follow that course). There were other clues. The soldering on the pins looked less than factory, shall we say , and masking tape 200 years old had once helped to hold the glass envelope to the bakelite base on one of the now suspiciously faux 6D6s. Similarly there is presently a " 75 " in the 7 pin socket which should be occupied by a 7 pin 6C7, also made from unobtainium. That 7 pin base base may also need to be "frankensteined" (thank you Steve!) onto a 6Q7 envelope as the 75 seems to be no go even with its cathode connected to a cathode bias resistor (see note later) . As suggested by Steve , when made by Grigsby Grunow the third pin on these valves was for their famous sprayed on screen.The replacement valves in this set as found were protected from "stray oscillation" by Goat shields though not actually earthed through the usual Goat spring clipped bases.In fact not earthed at all.Perhaps that was the point of the spray paint. (See note later) If you have ever seen or worked on a Majestic Model 118 set you will realise why the previous repairer went to the trouble of frankensteining" 3 valves.It would take a complete rebuild of the set to change sockets. The set was made to fit into the glove box of a 1934 Ford V8,said box being roughly triangular in shape. Guess what shape the set is?
And on this set someone has helpfully sprayed the chassis with silver paint to provide multiple leakage paths.The original vibrator has long since passed on so a "normal" vibrator has been removed from its can and squeezed into the top of the black box power pack after being tucked back into its now gooey sponge rubber hat.All wire joins are carefully insulated with that lovely tarry insulating tape we used to get before the war.The cathode wire for the 6C7/75/soon to be 6Q7 went nowhere. On the bright side the 42 does pass a signal and the old e.m. speaker has been replaced by a nice new p.m. substitute,which means less battery draw.So, watch this space! Thanks again for the replies and cheers.
Last Edit: Oct 21, 2018 19:53:09 GMT 12 by trombone