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#1
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AVO tube tester II and VCM 163 - HELP
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 |
#2
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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 |
#3
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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 |