I have equipped my Pre-amp project with 4x used 6n23p tubes (Russian eq. of E88CC/6922). I had the opportunity to make some simple tests in an OVO tester and the results was not so nice to see. The spread in measures where significant.
As the tubes are used and from unknow origin was this perhaps not to unexpected. Tube #2 are scraped, #3 doesn't look so good either.
My first thought was to buy another set of 5pc, test them and try to match 4 out of my 5+5. After some reading do I understand that the Russian tubes have big variations from the factory. There are also a risk of buying a lot where someone else already has sorted out the the best tubes and resold the not so good ones to me.
There are sellers who claim to have NOS 6p23N: What kind of variation can be expected?
If I buy NOS Philips: What kind of variation can I expect?
If I buy new JJ: What kind of variation can I expect?
As the tubes are used and from unknow origin was this perhaps not to unexpected. Tube #2 are scraped, #3 doesn't look so good either.
My first thought was to buy another set of 5pc, test them and try to match 4 out of my 5+5. After some reading do I understand that the Russian tubes have big variations from the factory. There are also a risk of buying a lot where someone else already has sorted out the the best tubes and resold the not so good ones to me.
There are sellers who claim to have NOS 6p23N: What kind of variation can be expected?
If I buy NOS Philips: What kind of variation can I expect?
If I buy new JJ: What kind of variation can I expect?
+ - 25% is expected unless you pay for "matched/balanced" tubes.
The "old folks" that designed tube equipment knew this and made designs that would work with any tube.
The "old folks" that designed tube equipment knew this and made designs that would work with any tube.
As stated, +/- 20% is normal for new tubes. After a long period of no use they could be worse. High Gm tubes are usually worse case.
Let each tube operate for a few hours with cathode current flowing. A few on-off cycles may also be beneficial. Then test again.
Tube # 2 does look bad if it doesn't recover after some on time. #3 looks OK to me unless you need better matching for a specific purpose.
Let each tube operate for a few hours with cathode current flowing. A few on-off cycles may also be beneficial. Then test again.
Tube # 2 does look bad if it doesn't recover after some on time. #3 looks OK to me unless you need better matching for a specific purpose.
Test them in a real circuit, could be as simple as a common cathode stage. Measure the gain and DC values. That's what I usually do.
Generally,
Self bias often makes a lot of tubes work surprisingly similar to each other.
The really bad tubes will show up, the self bias voltage will be way out of range of the others.
My favorite tube tester is . . . working amplifiers.
$0.03
adjusted for inflation
Self bias often makes a lot of tubes work surprisingly similar to each other.
The really bad tubes will show up, the self bias voltage will be way out of range of the others.
My favorite tube tester is . . . working amplifiers.
$0.03
adjusted for inflation
In a preamp if it's well designed it won't matter much, as others have said test them in a real circuit. A valve is a high voltage low current device that means any difference in I or V over a small value anode resistor won't result in any great loss of amplitude. Same for high gain valves with large Ra, the change in I is very small.
With any NOS valves the main issue's tend to be SC between electrodes or other mechanical faults. Also datasheet specs are for optimum operating conditions of the best valve, it's a sales leaflet as well as a datasheet.
Tektronix used to "burn" in their valves for their scopes in big racks, see - https://w140.com
With any NOS valves the main issue's tend to be SC between electrodes or other mechanical faults. Also datasheet specs are for optimum operating conditions of the best valve, it's a sales leaflet as well as a datasheet.
Tektronix used to "burn" in their valves for their scopes in big racks, see - https://w140.com
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Sounds prommising. I know that the pre-amp has quite strong feedback. The gain are defined by the feedback, not the valve.
I got an offer for measured Tesla E88CC for reasnable price. They are almost in the 5% range.
I got an offer for measured Tesla E88CC for reasnable price. They are almost in the 5% range.