Good afternoon,

I spent some time yesterday repairing and recalibrating my AVO mark II tube
tester (one of the diodes had failed in the grid voltage circuit). When
everything was complete, I decided to test a couple of KT88's on the Mark II
and compare the results with the same KT88's on my VCM 163 tester. The anode
and screen voltages were set at 250v each and the grid voltage was set at
-19.2 (measured by a digital volt meter to ensure both testers were set the
same).

For the Mark II I got:
Tube 1: 70mA, 8mA/V
Tube 2: 100mA, 30mA/V

For the VCM 163 I got:
Tube 1: 60mA, 8mA/V
Tube 2: 60mA, 8mA/V

What I cannot understand is the differences in the results between the two
testers!!?!

It seems that the each tube tester is quite different in their operation so
this might be the reason for the variance in results. For example, the Mark
II service manual says that with the anode voltage selector set at 250v, the
anode voltage measured at the tube socket is 275v AC. Compare that with the
service manual for the VCM 163 which says that with the anode voltage selector
set at 250v, the anode voltage measured at the tube socket is 153v DC.

Any ideas?

Kind Regards
Andrew

In article , "Chris Berry" wrote:

Any ideas?

Maybe clean the switches? sometimes, they go high... Just had a 1962 amp
that did that.
cb



Thanks I'll try that. I also might have to check out all the remaining
doides, capicitors and resistors too.....

Andrew

wrote in message
...
Good afternoon,

I spent some time yesterday repairing and recalibrating my AVO mark II
tube
tester (one of the diodes had failed in the grid voltage circuit). When
everything was complete, I decided to test a couple of KT88's on the Mark
II
and compare the results with the same KT88's on my VCM 163 tester. The
anode
and screen voltages were set at 250v each and the grid voltage was set at
-19.2 (measured by a digital volt meter to ensure both testers were set
the
same).

For the Mark II I got:
Tube 1: 70mA, 8mA/V
Tube 2: 100mA, 30mA/V

For the VCM 163 I got:
Tube 1: 60mA, 8mA/V
Tube 2: 60mA, 8mA/V

What I cannot understand is the differences in the results between the two
testers!!?!

It seems that the each tube tester is quite different in their operation
so
this might be the reason for the variance in results. For example, the
Mark
II service manual says that with the anode voltage selector set at 250v,
the
anode voltage measured at the tube socket is 275v AC. Compare that with
the
service manual for the VCM 163 which says that with the anode voltage
selector
set at 250v, the anode voltage measured at the tube socket is 153v DC.

Any ideas?

Maybe clean the switches? sometimes, they go high... Just had a 1962 amp
that did that.
cb