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Old 5th Sep 2010, 11:13 am   #6
deco-doctor
Tetrode
 
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Join Date: Mar 2006
Location: Brackley, Northants. UK.
Posts: 53
Default Re: Homebrew valve curve tracer.

Hi All

In response to some questions.

Firstly, as I said in my original post the curve tracer is based on a ready built PCB module with a PIC processor that is supplied with the Windows software. I purchased mine from a supplier in France, so I make no claims at all for originality or genius!!

The supplier sells these PCB modules on Ebay for 65 Euro plus P&P. The module comes built, tested and calibrated with the software on a CD rom.

All you need to do to get a working curve tracer is provide a 24v AC supply, a (preferably variable) AC HT supply, a heater supply for the valve under test and (if you want to test/trace pentodes) construct a suitable stepped DC screen voltage supply. The 24 vac supply and the HT ac supply must be in phase.

I opted to add a little complication by arranging a selection of different valve bases with the associated switching, but a more simple arrangement could be adopted without the switching.

It is necessary to keep the wiring as short as possible as the tracer works in a pulsed mode with the PC software which can cause instability with high mu valves. I placed small ferrite beads on the grid and anode connecting wires near to the PCB module.

The module works best when using the supplied software and a PC, but you can use it to trace curves with X&Y input on a scope as well.

Using the software you set some parameters for the test:

The minimum grid voltage (ususally 0V), the maximum negative grid voltage, the maximum anode voltage, the maximum cathode current, the target test cathode current and the valve type ie triode or pentode. (screenshot attached)

Then you start the measurement and the module sweeps the curves at steps of one volt on the grid from the selected maximum negative grid voltage to zero grid volts up to the maximum anode voltage and the maximum cathode current selected.

The RP, GM & Mu are then calculated from the results of the sweep.

The Ebay seller of these modules is 'rimlok' he is currently auctioning some of these modules link below:

http://cgi.ebay.co.uk/MODULE-LAMPEME...item3a560c3719

The seller has very good communication in English. He sent me PDF's of the operating manual and connection diagram before I made a purchase. Usual disclaimers apply, I have no association with the seller etc etc.

Martin
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Last edited by deco-doctor; 5th Sep 2010 at 11:19 am.
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