12AT7 Testing Settings -- They Change the Voltages?!
- Thread starter thefragger
- Start date
OK, it's taken me a while to get my head around things, but here's a spreadsheet with various info on the 667 (which should also be right for the 666 Satan's Choice unit).
I've developed new settings for the 12A?7 series of tubes that make more sense than what's in the published lists, and tested them with a fair number of NOS tubes.
Please give this a try and give me feedback. There are no other links to it yet, other than this one:
New 667 Settings Spreadsheet
Thanks,
Conrad
I've developed new settings for the 12A?7 series of tubes that make more sense than what's in the published lists, and tested them with a fair number of NOS tubes.
Please give this a try and give me feedback. There are no other links to it yet, other than this one:
New 667 Settings Spreadsheet
Thanks,
Conrad
thefragger
Certified Crazy.
I just lost an hour of my life to reading the machining section of your website--awesome info! :thmbsp: I miss having regular access to a machine shop.
I'll give those settings a try when I get a chance.
thefragger
Certified Crazy.
Excellent document, Conrad--thank you!
A couple minor edits and clarifications uploaded. What I really want to do, when I have time and can look up how to make Excel branch to different equations, is completely automate the current process- give it a current and it gives you the lever and knob setting automatically. Not hard I suspect, if anybody wants to take a shot at it. The chart should also automatically give the current and power when the settings are entered. The grid setting is harder- I don't know how to get that without experimentation.
IMO, the giant charts are a PITA. I can fit every tube I'll likely ever test on a single sheet. BTW, I found a completely worthless tube in my collection, the RCA 6350. It's a perfectly good medium mu triode, but with a different pin out than the 12A?7 series.
IMO, the giant charts are a PITA. I can fit every tube I'll likely ever test on a single sheet. BTW, I found a completely worthless tube in my collection, the RCA 6350. It's a perfectly good medium mu triode, but with a different pin out than the 12A?7 series.
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Hey, this is getting to be fun! I've added a page that analyzes the current shunt because my 667 isn't as accurate as I would have thought, based on the components. The results are interesting to say the least. I've been wrong before, but I think Eico designed the current shunt and meter system for DC and forgot that it won't respond to half wave AC in the same way. The meter will read low, so actual current values through the tube will be higher than believed. Still, I could easily have missed something, so hopefully somebody will check my work. :yes:
edit- OK, I got suckered by the old zero DC sum for RMS measurements. New data coming shortly. Until then, concept = good, numbers = bad on shunt analysis page.
edit- OK, made more measurements and uploaded better numbers. These things can hammer the tubes harder than you might think!
edit- OK, I got suckered by the old zero DC sum for RMS measurements. New data coming shortly. Until then, concept = good, numbers = bad on shunt analysis page.
edit- OK, made more measurements and uploaded better numbers. These things can hammer the tubes harder than you might think!
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Did another edit to the divider page (none of this affects the tube settings part of the sheet) and I think I've got it down pretty good. My belief is that the Eico units have a built-in error of 1.6X in the stated tube currents. IOW, if you set the levers for what Eico says is 10 mA, you get about 16 mA.
That's just enough to be of concern, so I'll be expanding the sheet to account for it when time allows.
That's just enough to be of concern, so I'll be expanding the sheet to account for it when time allows.
thefragger
Certified Crazy.
Hey Conrad, the 'I,mA RMS' column in the 'New Settings!' sheet is configured for the listed current when the meter shows '100?'
:scratch2:
:scratch2:
