Buildind a ECC83/12AX7 valve tester

[Kuga]

Hi all

I'm building a valve tester to test ECC83/12AX7 as ECC81,82 valves. This is a prototype. I copyed power suply from a Madamp J5MK1because I have same value parts on my bench. I have 250 Vca on secundary HT side on this transformer as It have on my Madamp. I use a 12 Vdc power suply for heater. You can see on picture B+ voltage and anode current on one triode side. What do I more tests on this circuit to get a proper ECC83/12AX7?
Do you have an schematic to add on this one?
Thanks

 

[Jon Snell]

When you get fed up with the thump noise, switching the Fat on and off, place a 100k resistor between each wiper and ground of SW3.
How do you plan to adjust the cutoff point in your valve tester ... use a -ve DC source and a pot. Then you can measure the current flow and thereby calculate the valve characteristics.

You will be able to make a tester from the information in this AVO 160 schematic. Chopped AC is used, not DC for the anode voltage. Hence the little dual diodes.
Don't bother with switchable voltages if you only want to test one type of valve. It is just the current and result after adjusting the bias and anode voltage. Otherwise just use it as an amplifier to see if the valve works.

 

[Kuga]

When you get fed up with the thump noise, switching the Fat on and off, place a 100k resistor between each wiper and ground of SW3.

I'm sorry I don't undestand what you mean

 

[Jon Snell]

I'm sorry I don't undestand what you mean

The switch shorting the lower valued capacitor will return the voltage actoss that capacitor to zero from probably 2 -3volts. That will discharge through the contact directly through the larger valued capacitor and cause a thumping sound or bang in the speaker.Placing a 100k resistor across the lower value resistor, stops the voltage from rising whilst has no effect on its purpose, and stops the voltage surge that results in the thump noise.

 

[Kuga]

The switch shorting the lower valued capacitor will return the voltage actoss that capacitor to zero from probably 2 -3volts. That will discharge through the contact directly through the larger valued capacitor and cause a thumping sound or bang in the speaker.Placing a 100k resistor across the lower value resistor, stops the voltage from rising whilst has no effect on its purpose, and stops the voltage surge that results in the thump noise.

There is any switch on this circuit yet. I plug HT transformer and 12Vdc transformer on a protected wall socket. I will Install a switch on transformer primary side. Also a fuse on 12VDc for valve filament and other one on HT voltage. Some voltage displays and meter test points too.

 

[TassieViking]

Have you read up on any DIY valve tester articles ?
Here are some simple ones that are easy to make yourself:

A low cost, easy to build diy valve/tube tester | Valve Heaven

valveheaven.com

The Valve Wizard

Project 165

ESP Audio Project 165 - Output Valve Tester for servicing

sound-au.com

 

[Kuga]

Have you read up on any DIY valve tester articles ?
Here are some simple ones that are easy to make yourself:

A low cost, easy to build diy valve/tube tester | Valve Heaven

valveheaven.com

The Valve Wizard

Project 165

ESP Audio Project 165 - Output Valve Tester for servicing

sound-au.com

No. Thanks for your input. I'll take a look. I own a Maximatcher II power tube tester. I just want a ECC83/12AX7 tube tester to check preamp tubes but will be great built one to test rectifier valves as EZ81 and GZ34 too.

I'll know anode voltage and anode current in each triode on that one I'm bulding. Is enough information to check a doble triode valve as ECC83/12AX7? Do should display filament current too?

 

[Kuga]

I test ECC83/12AX7 valves as same operating conditions in an amplifier on this one. I use prety the same Madamp J5MK1 amplifier power suply.

Average results on a no brand chinesse ECC83/12AX7.
B+ 325Vdc.
Anode voltage about 205 Vdc and anode current about 1,25 mA on each triode. Filament current cold 310mA. Filament current hot 150 mA.

I'll Install voltage/current displays meters for anode results on a box. I'll use a 5V cell phone battery charger for the displays meters power suply.
A voltage/current display meter for the valve filament will be easy to ad on It.

 

[stratfordade]

I recently constructed the ‘simple valve tester’ designed by Grant Wills and it’s proved to be very handy and accurate. You could easily adapt his design to test ECC83 types only and omit the Noval and octal bases from his tester. Because the published design covers power amp valves it meters up to 200mA. You could use a lower max say 10mA to get higher resolution of the much lower ECC8X current, making it possible to test the two triode sections for matching if necessary. Also if you use a separate transformer for heater filament it can be much lower power as doesn’t have to supply higher current for EL34 etc types.

 

[Ralf_M.]

If I were still interested in the maintenance of analogue equipment, I would not test individual tubes, but the entire package, e.g. an amplifier. What you need in such a case is a very simple isolating transformer to be galvanically isolated from the mains. Favourably, your multimeters are already galvanically isolated thanks to battery operation. However you proceed, you will need an isolating transformer either way. In other words, an isolating transformer is needed before the power supply unit of your "test circuit"!

 

[Ralf_M.]

What exactly do you mean by "protected wall socket"?
Unintentional suicide and measurement accuracy can depend on something like this.

 

[Kuga]

What exactly do you mean by "protected wall socket"?
Unintentional suicide and measurement accuracy can depend on something like this.

It has 1A switch on It. If a short ocurs at 1A It open Vca on the wall socket. I know 1A can kill you.

 

[Kuga]

If I were still interested in the maintenance of analogue equipment, I would not test individual tubes, but the entire package, e.g. an amplifier. What you need in such a case is a very simple isolating transformer to be galvanically isolated from the mains. Favourably, your multimeters are already galvanically isolated thanks to battery operation. However you proceed, you will need an isolating transformer either way. In other words, an isolating transformer is needed before the power supply unit of your "test circuit"!

I use a triple shield isolated transformer and a Furman power conditioner.
All my valve test were using this equipament. I have a variac as well. Someday I will buy an osciloscope.

 

[jack Cole]

I recently constructed the ‘simple valve tester’ designed by Grant Wills and it’s proved to be very handy and accurate. You could easily adapt his design to test ECC83 types only and omit the Noval and octal bases from his tester. Because the published design covers power amp valves it meters up to 200mA. You could use a lower max say 10mA to get higher resolution of the much lower ECC8X current, making it possible to test the two triode sections for matching if necessary. Also if you use a separate transformer for heater filament it can be much lower power as doesn’t have to supply higher current for EL34 etc types.

I'll second that, I built it several years ago and and it is indeed very useful and accurate.
It's also simple to build and certainly at the time I built it, Grant was very helpful with any queries/issues.

 

[stratfordade]

Yes I had a query about the protection diode across the ammeter and Grant was really helpful and also very encouraging about my build. NB since completing the version shown here I’ve replaced the grid bias meter with a 50V FSD for more accurate setting of bias typically in -7.5 to -20V range. @Kuga the socket for double triodes is at top right.

 

[TassieViking]

I'll second that, I built it several years ago and and it is indeed very useful and accurate.
It's also simple to build and certainly at the time I built it, Grant was very helpful with any queries/issues.

I don't have a valve tester at the moment but I have started to gather parts to build Grants "Simple Valve Tester" that he published on the Valveheaven.com website.
I am only lately getting into valve pedals so I thought I should make myself a good little tester.
I haven't touched any valves for over 30 years and that was in industrial machines when I was a maintenance electrician, but I intend to build myself a couple of small tube practice amps to use with all my Sushi Box tube pedals I am making for myself.

Sushi Box FX – High quality tube pedals built with unbridled sass.

Conspiracy to Commit Electronics

Tube-based effects for the DIY community

c2celectronics.com

 

[Jon Snell]

There is any switch on this circuit yet. I plug HT transformer and 12Vdc transformer on a protected wall socket. I will Install a switch on transformer primary side. Also a fuse on 12VDc for valve filament and other one on HT voltage. Some voltage displays and meter test points too.

I am refering to your attachment for the Madamp.

 

[Kuga]

I am refering to your attachment for the Madamp.

Ok. Thanks a lot.

 

[Kuga]

 

[stratfordade]

That looks excellent with those panel meters!

What’s the difference between the points in the circuit measured by ‘HT’, ‘B+’ and ‘anode’?