Gm emulator for calibration

[astouffer]

Doing some searches about tube testers shows mention of someone using a "Gm emulator" for calibration instead of an actual tube. Anyone else ever tried this? It sounds like a FET or two and maybe some passive parts would be all thats needed.

[bembel]

Hi,
What tubetester model please ? Different patented topologies exists.

On Hickok transconductance meters, a isolation transformer with a variac are used to feed directly the tube pins , thus simulating a tube under test for calibration purpose.

Maybe this is your "Gm emulator" ?

[astouffer]

So its just an AC voltage thats applied to simulate a tubes Gm reading? This is the page that got me thinking.

http://item.express.ebay.com/Industr...mdZExpressItem

[Yvesm]

Me understand that they offer a service, not a product

Yves.

[bembel]

Astouffer

As Yves, I understand that they offer a "renewing & calibration" service. (helped by their own calibrated original test purpose tubes)

They also sell beside 5Y3GT(a) & 83 solid state replacement.


I wonder what's inside their 83 replacement, as I'm working on this project for a just found TV7/U, planned to be accurate & bulletproofed (I've yet worked on a digital readout like 120.0, & By now replaced the 83 by 2 TV damper diodes, with 2 150R res. But hope to find time to simulate something with zeners)

Prices seems fair...so far (If you don't like grease)

PS: yes it's just an AC voltage (IIRC at the most skilled calibration level)

[Brian Beck]

Astouffer,

I've heard of what you're asking about and have looked for one myself. Many tube analyzers needed a calibrated 6L6 for their own calibration, but I've heard of gm emulators too. I think it could be whipped up using an opamp plus a HV power FET to make a transconductance device whose gm would be set accurately by precision feedback resistors. You could use the AC heater supply to feed a small bipolar power supply for the opamp. It almost sounds like I'm close to drawing a schematic, doesn't it? If I have time, I may sketch something up. In the meantime, if you find something out there, let us know.