Help with Stark 9-66 Calibration
Hello,
I noticed a few new Stark 9-66 owners in this thread, and some I have seen in some others (so please ignore if I have rattled your email again).
I have a question for you relative to my newly acquired Stark 9-66, and was wondering if you might be able to help me. The tester I purchased has some pretty good age to it (has the yellow/brown tweed covering on what is left of the case) and has been used hard. Even so, it is pretty much a sound unit. I am trying to calibrate it, and have uncovered some anomalies. Key to these reside in the bias circuit.
First off, my 3000 ohm R7 bias pot has been replaced with a linear one. I believe I can work around this since I have received the ohm readings of a tapered pot from another Stark/Hickok unit.
My bigger concern has to do with my bias voltage. At full clockwise rotation (bias setting of 100) the DC Grid Bias voltage should read munus (-) 39 V, plus or minus 1 volt. Mine reads 45 Volts; clearly out of speck. On sister Hickok units (533 and 600) the 6000 ohm R6 power resistor has a sliding tap and is adjustable to bring this in line. The R6 power resistor in the Stark unit is a fixed resistor.
I had a relatively high ohm (33K) resistor connected in parallell to the outside most posts of R7, but this did not show on the schematic so I removed it. I have (on a temporary basis) placed resistors of varying magnitude across these outside posts in an effort to bring the overall DC Grid Bias voltage back to the -39V it is supposed to be, but this doesn't seem to be working very well since it reduces the overall resistance of R7 significantly.
Do you know how I am supposed to get the -39V DC Grid Bias voltage on the Stark 9-66 aligned properly? Any help with an answer to this or any other info on the care, feeding and calibration of my Stark 9-66 would be greatly appreciated.
Dave
Hello,
I noticed a few new Stark 9-66 owners in this thread, and some I have seen in some others (so please ignore if I have rattled your email again).
I have a question for you relative to my newly acquired Stark 9-66, and was wondering if you might be able to help me. The tester I purchased has some pretty good age to it (has the yellow/brown tweed covering on what is left of the case) and has been used hard. Even so, it is pretty much a sound unit. I am trying to calibrate it, and have uncovered some anomalies. Key to these reside in the bias circuit.
First off, my 3000 ohm R7 bias pot has been replaced with a linear one. I believe I can work around this since I have received the ohm readings of a tapered pot from another Stark/Hickok unit.
My bigger concern has to do with my bias voltage. At full clockwise rotation (bias setting of 100) the DC Grid Bias voltage should read munus (-) 39 V, plus or minus 1 volt. Mine reads 45 Volts; clearly out of speck. On sister Hickok units (533 and 600) the 6000 ohm R6 power resistor has a sliding tap and is adjustable to bring this in line. The R6 power resistor in the Stark unit is a fixed resistor.
I had a relatively high ohm (33K) resistor connected in parallell to the outside most posts of R7, but this did not show on the schematic so I removed it. I have (on a temporary basis) placed resistors of varying magnitude across these outside posts in an effort to bring the overall DC Grid Bias voltage back to the -39V it is supposed to be, but this doesn't seem to be working very well since it reduces the overall resistance of R7 significantly.
Do you know how I am supposed to get the -39V DC Grid Bias voltage on the Stark 9-66 aligned properly? Any help with an answer to this or any other info on the care, feeding and calibration of my Stark 9-66 would be greatly appreciated.
Dave
If you don't ask, you don't get...
Yes, it's well worthwhile keeping an eye on Physics building junk. I (legitimately) acquired a Tek 570 curve tracer from the University of Liverpool Physics building. I saw it in a pile of junk in a corridor, so I asked if I could have it. I had to write a disclaimer saying that I wouldn't sue them if it killed me, and a couple of staff members (who hadn't been as enterprising) were a bit peeved. Dragging it home on the train was hard work though. It weighs 70lb.
Back on topic, the AVO VCM163 is a nice valve tester. But be prepared to fix a few faults.
gingertube said:
Yes, it's well worthwhile keeping an eye on Physics building junk. I (legitimately) acquired a Tek 570 curve tracer from the University of Liverpool Physics building. I saw it in a pile of junk in a corridor, so I asked if I could have it. I had to write a disclaimer saying that I wouldn't sue them if it killed me, and a couple of staff members (who hadn't been as enterprising) were a bit peeved. Dragging it home on the train was hard work though. It weighs 70lb.
Back on topic, the AVO VCM163 is a nice valve tester. But be prepared to fix a few faults.
Re: Help with Stark 9-66 Calibration
Remember that the -39V DC bias specification was written in the days of moving coil meters. I'll bet you measured with a DVM. The answer that a DVM gives to unsmoothed rectified (probably half-wave) AC is not necessarily the same as a moving coil meter. I had exactly this problem with my VCM163.
Edit: I removed your email address from your post. You don't really want the spambots deluging you with offers of cut-price Viagra, do you?
thennagain said:
Remember that the -39V DC bias specification was written in the days of moving coil meters. I'll bet you measured with a DVM. The answer that a DVM gives to unsmoothed rectified (probably half-wave) AC is not necessarily the same as a moving coil meter. I had exactly this problem with my VCM163.
Edit: I removed your email address from your post. You don't really want the spambots deluging you with offers of cut-price Viagra, do you?
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