Hickok Testers and Dynamic Conductance

[Shannon Parks]

Can someone give me a dumbed down explaination of how the Hickok's measure mutual conductance? The schematics are difficult to read.

Secondly, can anyone explain Eico's method of measuring dynamic conductance? The Eico 666 schematic is much easier to understand, but I don't quite get what is going on. I see the meter is sensing current at the plate, but how does this correspond to gm?

Thanks in advance, gurus!

Shannon

[erichayes]

Hi All,

Shannon, I've renovated the shop to the point that it scares me. I'll send you pix and would be beholden to you if you'd post them. Please give me about a week and a half, and I'll have my 752 completely RE'd; I can tell you how everything works in a Hickok up to the meter, but that's what has been baffling me.

Now that I have bench space and (finally) first rate equipment at my disposal, I can joyously bound about the diytube meadow and provide services and answers to the members. I'll elaborate on that in the future (it will be free); stay tuned.

[Shannon Parks]

Thanks, Eric, glad to hear this!

Update to my original question:

I went ahead and spend a week a month ago completely going over Steve Bench's RAT tube tester. I transcibed the schematic and even have a partial layout. It was a good exercise. Ultimately, I wanted to add a 12-bit data acquistion circuit and DB-25, but the project started to get too complex. That's too bad, but the need to have semi-automated data gathering for new tube curves and mu/gm/rp charts (plopped into nice Excel charts) is the only thing that would make manufacture practical.

That said, some simpler things might be done. I think accuracy can be gained with a digital meter, ala this gents. And the new AudioXpress has a nifty Gm standard for 'calibrating' the Hickok. Worth the read!

Shannon

[Rick]

The dynamic conductance tube tester places different voltages on the grids and plate of the tube under test and then checks the emission of the tube. It is a deluxe emission type tester. The simple emission tester ties all of the tube grids and plate together and then checks the emission. The Hickock Mutual conductance tube tester places a signal on the control grid of the tube under test and measures the tubes performance (GM).