Cordovox CG Trouble Shooting Unlit Tubes

[VASANTORO]

Hi All
None of the six tubes in the "Quality Control" section of my tone generator (see tube chart attached) will light up.
Opened the tube panel to examine wiring and rear of tube sockets. There is no evidence of failure or damage.
Any advice on trouble shooting this issue is greatly appreciated!
Thanks in advance...

I am the original owner of this instrument ....purchased in May of 1965

 

[Ventura]

that is basically the audio pre-amp section

none/zero of the tubes heater elements lighting up would indicate
the 12 volt power supply voltage is not reaching that shared circuit

that is not like a superheterodyne tube radio where the
total heaters circuit = 110 volts.. in the c-vox if one tube is
burnt out that is the only one out, the rest of the heater
circuit is not dependent on every tube element being whole

i am assuming the 6x8 and 6fh8 (6 volt) tube sections
DO still light up, further indicating this is not a catastrophic
power supply failure, but a localized one

you should be able to use tube pin-out info to help you
focus on the heater part of the circuit, then trace it out
and test back toward the power supply to find the
open component

there was a schematic posted by CAPS on the forum, if you can
find that it will help a lot