DIY-ing a Simple Power Tube Tester

[schmidlin]

Hi All,

Looking to take an old PS chassis and wire it up to check current draw on power tubes.  ~400 B+, fixed neg bias, just need my own numbers for tube current draw comparisons and match up some sets.

First, do I need an OT or can I hook the plates right up to the B+?

Or maybe there's a schematic floating around I could go from.

Thanks in advance.

 

[mad.ax]

You don't need an OT.
What you need is a load, and a meter or two.
Making the bias variable would be useful, and allows you to measure 'S' in mA/V...

Which power tubes do you want to measure?
Do you have a schema of your actual PS/chassis?

Axel

 

[abbey road d enfer]

You'll find a couple of schemos there
http://www.one-electron.com/FC_TestEquipment.html
You don't need an OT, you don't even need a real load. You want a good meter and a variable bias. And some overcurrent protection.
I would also have provision for variable G2 bias.
The most complicated thing in these commercial tube testers is the ratsnest of tube sockets.

 

[schmidlin]

Thanks Gang,

I was thinking B+ to plate --> 1K to screen grid, control grid to B-, suppressor and cathode to 1 ohm 1% resistor to ground.  Cathode MV will give me my current rating.  See any possible issues?  Not looking for transconductance.

Looking to do the standards: 6L6, 6550, EL34, 6V6, etc.  For the B- I would select a 'sweet spot' and take all my measurements from there for each tube type.  (looking at 4 or 5 sweet spots here)

I'm really doing this for my 7868's which don't fit into my currents testers, so we are looking at at least 2 sockets.