Drugolf wrote:Can someone describe for me how to correctly test/check the filament voltage?
Any decent voltmeter with an AC range.
Note that the filaments on the GZ34 is elevated to +500V DC be very careful!
You could connect the voltmeter ( on pin 2 and 8 on the GZ34 ) in advance before powering up.
When powered up it should have 5VAC +-10%
Filaments on other tubes (in a st70) should be at 6.3VAC , these are located on pin 2 and 7
on the octals and 4,5 to 9 on the novals ( see tube data for the specific tube).
There is two 6.3 V windings on ST70, one for each side. On the original st70
those were connected in the octal sockets on the front, thus it was very easy to measure.
( from another post )
I have found no layout of the front octal sockets however,this is extracted from the build instructions
( it might be in error )
1 and 2 _might_ be 6.3V
3 is ground
8 bias test