Can't find a tube checker for a 407A

<< < (2/2)

PA0NVD:
Quote from: wb1ead on September 20, 2018, 01:33:15 PM

Hi Tom..yup give it a go..not sure on ur TV-7DU unless the tube you tried to check cudda been a dud or one side gonzo??..here BTW are two more from the 8CJ family..6386 and 7861..b/4 you do check them please take a moment and compare the two basings 407A and 8CJ just so you will see the almost identical diagrams of these two..it'll assure you I think..the only oddball thing on the 407A is that one tube manual lists the fil voltage as 20v AND 40v..??..I'm thinking misprint or maybe two together in a series string??
                           Anyhoo the other 6 I have say 20v filament/heater..let us know if and how it works and if ur tester is like mine in any respect at least the test switch to check gain is fused and spring loaded..to eliminate AH OH!!   73 de DAVE


The filament connections are a little odd. When you power the filament between pin 1 and 9, it needs 40 Volts. When you tie 1 and 9 together and power between these pins and pin 5 (CT of the filament), you need 20 Volts

KA0HCP:
Won't using the CT method help eliminate AC hum, just like in a transformer?  Seems like a advantageous method.

PA0NVD:
The CT is more to be able to use the tube at 20 or 40 volts. The main application of this tube was a negative resistance amplifier to amplify telephone lines bi-directional. The filaments could be powered by the 24 or 48 Volts system battery of the telephone central or repeater station. Many thousands of these negative resistance amplifiers were in use in the years 50. So hum wasn't a problem, they were powered by DC

Navigation

[0] Message Index

[*] Previous page