Digital tube tester

I must have over 50 small triodes of 6SN7, 12AU7, 6N1P and others I still use from time to time. And with the Peak on main duty I expect the tubes to go fast so a tube tester would be great. The usual suspects need knowledge and skill I don't have.
Came across this on ebay randomly a few weeks ago and bought one after finding favourable posts on forums.

I'll configure it for one octal and one nine pin socket. Filaments with dc voltage from 12V DC input. Some thoughts:
-it doesn't come with the sockets or the metal plate as in the picture. Just the board with display and two pots, everything already soldered and connected
-it can run from 9V batteries, tried and worked. You still need the heater supply.
-can run up to 450V so covers all my needs
-great support, I chatted with the seller,he sent me the manual before the purchase so I can have a look and even included an octal socket and some custom resistors already soldered so I can use the heater directly from the input. In the end I chose to use LM2596S regulators.
-might give good numbers for transconductance and plate resistance.
-microprocessor
Did a test run this morning, soldered everything up with a switch for the individual triode and a test button.
I planned to use my HDPlex LPS for the 12V input but in the end I found a random switching psu from some appliance 12V,3A



Worked from first go, no issues. I really like the test button as a press to apply the B+ and read the results at the same time.



Tested a couple of 6SN7 tubes. A new tube tests at 9.0mA for those settings.
Melz bought tested NOS and on spec with results. Tested at 9 and 9. Great.
6SN7A from langrex tested NOS, no results but promised balanced sections. Tested 8.8 and 8.8.
Sylvania 6SN7GT from ebay tested at 7.1, 7.3. Got 7.1 and 7.3
Differeny 6SN7GT from same batch/seller tested at 8.9 and 8.1, got 7.3 and 7.9
Tested a couple I knew were used and they hovered from 6.5 to 7.1 and mostly unbalanced sections but I don't hear any difference in volume.

This looks like a winner. For me the hard part will be to build a proper chaises. I'm going for a bottlehead build with everything on the top plate. Made a sketch and printed on 1:1 size so I can trace everything out. Ordered some stuff and God have mercy on my first case.

 

That looks pretty interesting. I have a box of 300+ tubes I need to test... I may have to get one of these.

 

Looks like a much less expensive alternative to Amplitrex. We've been using a digital tube tester/curve tracer from a now-defunct Italian company, and I've been eyeing an Amplitrex for when it finally expires. Hmmmm.

 

They do have a curve tracer module as well. If this works out I might do a bigger one with it and 6080/2A3 testing. That will cover all the tubes I use except rectifiers.

 

Nice! If you don't mind stainless steel you can use lasergist.com. It's actually not too expensive. But if you screw anything up on your drawings then your can forget about any sort of rework.

Any way to export data for curves?

 

When you buy the module you get a CD with software, win only. RS232 output with usb adaptor.
There's also this.

 

Ooh, cool. I've been looking at the uTracer and eTracer as potential future projects but I haven't seen this eBay special before.

Looks like it's reading back current at a chosen operating point? You would get a rough idea of typical tube parameters (Gm, Rp, Mu) if you combine multiple points. This would be a better measure of matching than a single bias point.

edit: link to eTracer https://www.essues.com/etracer/

Oh, I see the plotter/tracer module now as well. Neat.

 

I prefer to kick it old school, Seco Model 78 style...



Think it's from 1959 or something. Not sure if it would do any good if I finally send in the registration card...

Although to get back on topic, would be cool to have a digital tester!

 

I've had some good time over the weekend to work on it. I'd much rather solder than do chassis work. First time with a dremel, didn't work as well as I expected, might give it another go with another sheet.


It looks quite good in a case. I'm also doing a proper cad design for laser cutting if my handywork doesn't pan out

 

Went back to the drawing board and got a new plate to cut. This time I got a digital caliper for precise measurements and went much better. This plate has a different smell when cutting and didn't melt as easily.
6 hours later I managed to even install all the components. Hopefully soon I'll be able to wire everything and test it.

 

Man, this really felt like a bottlehead build, I've been wanting to do something like this for a while now.

Went with the flow and soldered everything in. Made a mistake on the 9 pin and the current display but testing caught that before going live. It felt like code development, buildPowerStuff(),validateAgainstSchema(), catch{}.



-9 pin is wired for 6.3V
-I've left a 3mm hole in the chassis to adjust the voltage on the heater regulator. My OCD demands having an exact voltage.
-heater digital voltage display
-heater digital current display
-separate heater on/off switch.
-adjusting the plate and grid can be tricky as mm turns are needed
To operate it I have to switch the main on/off switch, this turns on the module and the heater voltage is displayed so I can adjust it before turning on the heater. With the heater switch on the current display turns on(mA). I see it starts from 900 and goes to 600+-20 in a few seconds. Interesting to see some tubes draw more than others.


I'll still try a laser top plate for another build to get perfect margins, maybe even a solid colour with a triode symbol on it.


Now total cost.
Module with shipping - 90
On-Off push button switch -1.79
On-On 6 pin switch x2 - 5
On-On 9 pin switch - 2.49
DC female connector - 1.69
Digital display voltage - 4.5
Bakelite kob x2 - 3.9
ammeter - 4.3
DC-DC converter x 2 - 10
M3 screws,nuts and risers - 10
M2 screws for digital display - 1.4
Case - this fits the bottlehead quickie case since that's what I used as my base. 40$ from bottlehead + shipping but let's say 40
Acrylic 3mm plate - 7
---------------------------------
182.07£

In addition I had to buy a dremel for 40£ and I had a cordless drill.
Around 10 hours total but I recon I can get it done it around 5 now. Half that maybe without carving up the plexiglas.

Now I have to test against tested tubes to compare. I'll be checking if wall wart vs hdPlex makes a difference.

A good Saturday overall.

 

Well done! Looking very cool

Once you're fully done would be great to have a detailed BOM and schematic for any of us that might want to try it as well.

Thanks

 

Earlier this week I found out the 6080 family of tubes has the same pinout as the 6SN7. Ordered a 5A DC converter for the heater supply, best 2 pounds I've spent in a while. The stock one could work if you put a heatsink on it but it would be at the limit.
This now covers 80% of the valves I use and will probably use for the next 20 years.

This little thing works great for output tubes, the confirmed NOS tubes I have tested NOS and the dodgy ebay ones tested all over the place. One such example reported at 100%, tested new on one half and failed on the other.
With 6SN7 I get about same output reading after 30 seconds or 30 minutes but these take a good couple of minutes to settle down. Bendix WB needs 10+ minutes.
Using 100V and -30 where a Va of 100 is new value.

Today is gec testing day.

 

I saw someone who had a really nice utracer build, that seems like the best value for performance. At LTA we had MaxiMatcher testers and a burn-in station, which are great for functional testing but don't do curve traces and require a frustrating amount of adapters. Eventually I built my own burn-in stations.

 

Hmm, the seller says its available assembled in a luggage upon request, I've sent them a message.

Sure would be nice to test the 396As for the AF.

 

Would gave gone for the suitcase myself but the size was a massive turn off, price as well.
I assume you're referring to this one? https://www.radioelec.com/en/-xml-352_387-1507.html

 

Seems like it yes.

It's not cheap, but neither is the time I'd have to spend to make a container for it, given that I've never done anything of the sort for electronic equipment. And also I'm lazy.

 

At one point I was thinking to try and build a couple but it would end up just 130 less than the case. I was aiming for half but that doesn't even cover the BOM. Surprised the suitcase doesn't do 12V without a center tap. 12SN7 and such cannot be tested.

 

Can you expand on the burn-in station? What is its purpose?
I've had NOS tubes that changed their sound for the better in 5-10 hours but I'm more interested in the so called conditioning where you apply just heater voltage to NOS tubes for better life expectancy.

 

I haven't heard of the life-expectancy conditioning. Burn in stations are useful for two reasons that I know:
1. If you're testing large lots of tubes, you can put them all on the burn-in station to warm up, so that you don't have to wait for them to warm up and give accurate results on the tester. This is especially useful for power tubes.

For this use, you don't really need a real burn-in station that does both heater and plate voltage, you would just need the heaters.

2. We used them because we were using NOS tubes in manufacturing, which were purchased in large, untested lots, and after sitting unused for decades there is some internal settling of sorts. After a few days of being live again in a circuit, tubes sometimes became noisy or, more often, would no longer match. Burning them in for a few days before testing and matching them led to more consistency in manufacturing, and fewer instances of having to replace tubes when final testing revealed imbalances or noise.

Tubes also generally required the longest burn-in time to sound their best, so giving them a head start before the finished unit burn-in led to a better sounding amp at first unboxing.