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Old 4th Sep 2010, 6:32 pm   #1
deco-doctor's Avatar
Join Date: Mar 2006
Location: Brackley, Northants. UK.
Posts: 53
Default Homebrew valve curve tracer.

Hi All

I have just finished my homebrew valve curve tracer. I thought there maybe some folks here that might be interested.

The curve tracer is based on a small ready made PCB module with a pre-programmed microprocessor and some software that runs on a Windows PC connected by an RS232 link.

The completed project has set of various valve sockets, a valve socket pin switching system that uses the same switch settings as an AVO valve tester, a power supply with the HT voltage controlled via a variac, a regulated screen supply, and an adjustable AC heater supply.

Small signal triodes and power valves requiring up to 100mA anode current can be traced. The characteristic curves, the plate resistance, the mutual conductance, the Mu and the reference anode current and voltage at 0 grid volts of the valve under test are all displayed on the PC. I have also included a switch to quickly swap between each half of a double triode.

I have attached some pictures and an example of the results screen when tracing a 7193 (2C22) single triode.

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Old 4th Sep 2010, 8:10 pm   #2
Join Date: Jan 2004
Location: Newcastle on Tyne, Tyne & Wear, UK.
Posts: 4,141
Default Re: Homebrew valve curve tracer.

Hi Martin, great project and I like the panel layout. Will you be publishing the circuit and software listings?

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Old 4th Sep 2010, 9:50 pm   #3
Guitarist28's Avatar
Join Date: Dec 2009
Location: Hockley, Essex, UK.
Posts: 463
Default Re: Homebrew valve curve tracer.

Hi Martin,
This looks a super build, congrats.
I agree with Ed, it would be great if you would be so kind to share the design/schematic with us.


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Old 4th Sep 2010, 9:51 pm   #4
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Join Date: Apr 2009
Location: Aylesbury, Buckinghamshire, UK.
Posts: 1,521
Default Re: Homebrew valve curve tracer.

Wow what a super piece of kit.
I assume you set and enter the negative grid volts then sweep the anode voltage up to the maximum, the anode voltage and current communicated to the computer through the A/D. The curves are then compiled from the results, can it display other curves from the same results such as Ia vs. -Vg1 for a fixed anode voltage? Genius, can you give more detail on the A/D and programming required please. Do you check tetrodes / pentodes strapped as triodes, or with a fixed screen supply?
We have done so much, for so long, with so little, we are now qualified to do anything with nothing.

Last edited by glowinganode; 4th Sep 2010 at 9:57 pm.
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Old 5th Sep 2010, 8:44 am   #5
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Join Date: Jul 2008
Location: Maidenhead, Berkshire, UK.
Posts: 6,190
Default Re: Homebrew valve curve tracer.

Whats the PCB PC link board?
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Old 5th Sep 2010, 10:13 am   #6
deco-doctor's Avatar
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:

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.

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Last edited by deco-doctor; 5th Sep 2010 at 10:19 am.
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