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In Reply to: RE: Hickock Plate Voltage Measures High posted by Steve O on August 06, 2014 at 12:42:58
yeah but usually it seems to affect filament voltage more and it is used to compensate for heavier current draw with larger tubes.
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The line adjust affects everything. It is in series with the AC line.
My 600A has around 190VDC plate voltage also. I believe that was a design change that was made when they went from the 600 to the 600A.
Hi Al - That explains it. I knew the line adjust affects all the voltages, the puzzle was why all of them were close to spec except the plate. Actually, at first, I thought the Grid Signal Voltage was off too - I was getting ~2.5vAC instead of ~5vAC - then I read that this was a change made in the later versions of the 600A. The later versions also have a function that reduces the Screen Voltage to 56v with the push of a button, which mine also has. Apparently, at some point, they also increased the Plate Voltage, bringing it closer to actual operating voltages.
The voltages in mine are still just a tad high with the line adjust set, but they are consistent with each other. I'll just need to either adjust the meter a bit or compensate when I test tubes. While I realize that all testers have their limitations, I'm looking forward to having a "better" tester. I will still use the Eico 666 too - one of its advantages is that it tests interelement leakage directly - but I've always been frustrated by the numerous errors and conflicting set up data contained on the Eico's various charts. Perhaps there are errors in the Hickock data too, but I think they were in wider use and most of them have probably been spotted. Mine came with a couple of extra roll charts - earlier ones I suspect. I was also able to find and download a compilation of setup data that includes "obsolete" and foreign tubes. Lots of good Hickock resources online.
Thanks again for the info about the Plate Voltage!
. . . Charlie
Al - Well, functionally you were right, there is no problem with the ~190v reading but it's not because they changed it in later versions of the 600A.
I failed to mention that I didn't follow the testing procedure exactly (DOH!) in that I used a DMM without adding a shunt resistor. The instructions suggest a 250k "in parallel with the input" when using the 250v scale. Does that mean it's connected between the red and black meter leads??
I found the info on the Antique Radios forum at the link below.
. . . Charlie
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