When is it advisable replace PI valve?

[PelliX]

You are useful to complain about the electrical nomenclature that I use, but not to contribute a circuit or idea to this easy/modest valve tester.

I didn't mean to criticize you or your designs, I was merely providing (or attempting to provide) some constructive advice/information. As I stated, there is a *lot* of confusion and incorrect use of these notations not just by amateurs but by companies and professionals, too. In addition, please note that I did in fact compliment the designer of the circuit on his project and - indirectly - you for having implemented it in a way. What I criticized were a couple of the notions outlined in your posts(s), namely that the filament current draw or warmup time relates to the performance of the valve and the 'sales pitch' by TAD. No offense intended.

 

[Pete Farrington]

I can see If valve heater it's ok.

Why is that affected / dependent on the HT supply?

When filament is consuming about 150mA I know valve it's hot to work.

I don't know, it seems to me that when the cathode has reached working temperature then it's hot enough to work. Heater current seems unrelated to that.

I have one it's using 350mA all time. This valve don't works.

High heater current and non functional valve indicates poor vacuum. But the getter flashing should have reacted if that was the case

New ones or good condition ones show max current anode faster than worn out ones. Looks like a good one quickly is able to works. Do you think this not can be correct?

It seems irrelevant / unrelated to me.

As TAD says

Surely the total absence of any verifiable technical metrics or claims should ring alarm bells for you?
It seems total marketing BS to me.

a difference of 5% in mains voltage during the testing made a significant difference in the idle current

I'm surprised Maximatcher don't include regulated power supplies.

you should actually put a variac in front of it, and make sure to have a fixed set point for AC mains

He has
Dunno why the V AC meter is on the HT winding, rather than after the variac though.

You are useful to complain about the electrical nomenclature that I use

It would be a good idea to use that info as a learning point, rather than to take offence. Reporting data that doesn't make sense is not helpful, hence post 5.

 

[Kuga]

Great stuff. I like my Maxi Preamp 2, but having a tester like this with multiple voltage and current readings is ever cooler. I should actually remeasure all my power tubes (300+), as a difference of 5% in mains voltage during the testing made a significant difference in the idle current. you should actually put a variac in front of it, and make sure to have a fixed set point for AC mains

I use a variac at 240Vac (Vca in Spanish) on my Maxi matcher 2. At 230Vac you have different measure.

 

[Kuga]

Why is that affected / dependent on the HT supply?

No affected. This tester has three transformers. HT it's One coil at 230Vac primary side two coils at 110Vac secundary side wired in serial. I have about 259 Vac on It.
A 12Vdc 500mA transformer for heater. A 5Vdc for displays suply.

It seems irrelevant / unrelated to me.

I'm sure you are right. I'm here to learn about It. But it's curious that how two same valves (same brand same valve type) works different. The only difference is that one is very used and the other is not.

 

[Pete Farrington]

contribute a circuit or idea to this easy/modest valve tester.

I suggest to add an input socket (and grid leak, grid stoppers, and cathode bypass, possibly switched).
That allows a known test signal to be applied, the resulting output voltage measured, and hence gain calculated.
And an output socket, to enable hum, hiss and microphonics to be assessed (using an external amp etc).
As an added bonus, you could use it as a booster (may need a volume control on the output, as the 35dB gain of a good 12AX7 triode could be excessive ).

Self (cathode) bias acts to 'normalise' circuit operation such that the difference between strong and weak valves will tend to be less pronounced.
Whereas fixed bias would make the difference more apparent.
So as your goal seems to be to segregate / grade your valves, it may be better for you to use fixed bias, eg swap the cathode bias resistor for suitable diodes (forward biased).

 

[Pete Farrington]

No affected

So why not a single power switch, ie what is the benefit of a separate switch for the HT?

259 Vac

Wouldn't it be more logical for this meter to monitor the output of the variac at the mains supply?
The 'AC' (and 'DC') abbreviation needs to be capitalised. I leave a space between the V and AC, as North American readers are used to the HVAC abbreviation, and have previously assumed I've missed the 'H' off. So V AC

I'm sure you are right. I'm here to learn about It

There's a mountain of this stuff I don't know, I'm keen to learn too

it's curious that how two same valves (same brand same valve type) works different. The only difference is that one is very used and the other is not.

Maybe you've discovered something
To be more certain of the correlation, consider identifying a few test valves, then monitoring how they behave over time, as they're used, and so wear / age.

My guess is that the behaviour you're checking isn't a controlled characteristic, so the manufacturer may not monitor it. Provided that the valves' performance metrics are acceptable after eg 2 minutes warm up, it may not necessarily matter whether they were ready after only 15 seconds. So different prouction batches may end up behaving differently, and over time it may change, without the potential operational life of the valves being affected.

 

[Helmholtz]

If so, you seem to be overlooking the self balancing nature of the circuit.

Does a LTP really have special self-balancing properties?
I mean both triodes have the same Vgk bias, so if one triode has higher static transconductance, its plate current will tend to be higher.
I understand there is some negative feedback effect via the lowered plate voltage of the triode having higher Ip, counteracting the current increase.
But this current stabilizing effect lies in the nature of triodes and also happens with a normal (separate) gain stage.