Unfortunately, both the Left channel, and Right channel share tubes.
For example V1 has two triodes in the same glass envelope, one is for the Left channel, and one is used for the Right channel.
All the tubes are shared that way, two triodes in one glass envelope, one for the Left channel, one for the right channel.
That means you can not put one tube in for the Left channel, and a different tube in for the Right channel.
So, put in one tube, warm up the preamp, listen. Power it off.
Change to another tube, warm up the preamp, listen.
The problem:
It is an arguable point, but many consider "Audio Memory" to be very poor when comparing tubes.
The solution:
Purchase a 2nd identical preamp, and use different tubes than are in the first preamp.
Now, compare LIVE, with a Double pole, double throw switch box to change back and forth, quickly and easily (eliminate the "Audio Memory" effect).
Other than that, I reccomend finding a different project to spend your time on.
Case Solved
(Just My Opinion).
Would anybody else please give an opinion on this?
For example V1 has two triodes in the same glass envelope, one is for the Left channel, and one is used for the Right channel.
All the tubes are shared that way, two triodes in one glass envelope, one for the Left channel, one for the right channel.
That means you can not put one tube in for the Left channel, and a different tube in for the Right channel.
So, put in one tube, warm up the preamp, listen. Power it off.
Change to another tube, warm up the preamp, listen.
The problem:
It is an arguable point, but many consider "Audio Memory" to be very poor when comparing tubes.
The solution:
Purchase a 2nd identical preamp, and use different tubes than are in the first preamp.
Now, compare LIVE, with a Double pole, double throw switch box to change back and forth, quickly and easily (eliminate the "Audio Memory" effect).
Other than that, I reccomend finding a different project to spend your time on.
Case Solved
(Just My Opinion).
Would anybody else please give an opinion on this?
I appreciate the thinking on blind comparison testing. There are real, valid challenges. Perhaps a more pointed question: Would you expect to observe differences if such a test were properly conducted?
SoaDMTGguy,
Consider the preamps circuitry that has individual self bias, local negative feedback, multiple stage negative feedback, etc.
Then use different sets of tubes that are reasonably close to the tube data sheet values (no bad tubes).
And no tube that for some reason oscillates in the preamp circuitry.
Use the same type number sets of tubes, not "equivalent" tube type numbers.
Given all the above . . .
No, I would not expect a properly conducted double blindfold listening test to allow the listeners to determine which set of tubes sounded one way, and the other set of tubes sounded different. No repeatable statistical determination.
Just my opinion
Consider the preamps circuitry that has individual self bias, local negative feedback, multiple stage negative feedback, etc.
Then use different sets of tubes that are reasonably close to the tube data sheet values (no bad tubes).
And no tube that for some reason oscillates in the preamp circuitry.
Use the same type number sets of tubes, not "equivalent" tube type numbers.
Given all the above . . .
No, I would not expect a properly conducted double blindfold listening test to allow the listeners to determine which set of tubes sounded one way, and the other set of tubes sounded different. No repeatable statistical determination.
Just my opinion
SoaDMTGguy,
Unless your tubes are bad, the best tube tester in the world is the circuit they are operating in.
Things like shorted tubes, thermal run-away tubes, etc., might destroy the circuit they are in.
Most tube testers do not test the tubes at the quiescent conditions that they will be used in a preamp, or power amp, etc.
Shorted tubes should show up on most tube testers.
Thermal Run-away tubes my not show up on most tube testers.
New, Modern microprocessor controlled tube testers check a very large number of characteristics (but not all of them).
I know the people at Eurotubes.com
I know the many tests they run.
I know some of the designers of the testers, including one person outside of the company.
Eurotubes does extensive re-testing of JJ tubes that come from Slovakia.
Whenever I am designing an amplifier, I always try and use tubes that are manufactured by JJ.
In more recent years, I have moved away from tubes that are New Old Stock, and types that JJ does not manufacture.
I no longer work for a major Test and Measurement company; am retired.
So my test equipment is more limited than it used to be.
I use a digital scope with time domain measurement functions and FFT (rms, peak, min, rise time, phase, etc.; as well as cursers in the time and spectral domains).
I have a CD player and a Denon Audio Technical Test CD (frequency response, test tones, 2nd order IM tones, 3rd order IM tones, Impulse, etc.).
I have a fast rise square wave generator.
I have non-inductive 8 Ohm load
My very old tube tester is never used any more (used to test the status of unknown aging hours of old tubes).
My amplifiers are my tube testers.
Where do you plan to go with this "project" from here?
Unless your tubes are bad, the best tube tester in the world is the circuit they are operating in.
Things like shorted tubes, thermal run-away tubes, etc., might destroy the circuit they are in.
Most tube testers do not test the tubes at the quiescent conditions that they will be used in a preamp, or power amp, etc.
Shorted tubes should show up on most tube testers.
Thermal Run-away tubes my not show up on most tube testers.
New, Modern microprocessor controlled tube testers check a very large number of characteristics (but not all of them).
I know the people at Eurotubes.com
I know the many tests they run.
I know some of the designers of the testers, including one person outside of the company.
Eurotubes does extensive re-testing of JJ tubes that come from Slovakia.
Whenever I am designing an amplifier, I always try and use tubes that are manufactured by JJ.
In more recent years, I have moved away from tubes that are New Old Stock, and types that JJ does not manufacture.
I no longer work for a major Test and Measurement company; am retired.
So my test equipment is more limited than it used to be.
I use a digital scope with time domain measurement functions and FFT (rms, peak, min, rise time, phase, etc.; as well as cursers in the time and spectral domains).
I have a CD player and a Denon Audio Technical Test CD (frequency response, test tones, 2nd order IM tones, 3rd order IM tones, Impulse, etc.).
I have a fast rise square wave generator.
I have non-inductive 8 Ohm load
My very old tube tester is never used any more (used to test the status of unknown aging hours of old tubes).
My amplifiers are my tube testers.
Where do you plan to go with this "project" from here?
Last edited:
I guess my next step is to decide if I should replace the tubes in my old gear, or if I want to anyway for fun. I have a preamp and power amp set that are ~40 years old, and the preamp at least seems to have the original tubes.
Are JJ tubes not made by New Sensor?
Are JJ tubes not made by New Sensor?
I added edits to my Post # 45, after you posted # 46.
Please go back and re-read my post # 45.
JJ tubes are made in Slovakia
Most if not all New Sensor tubes are made in Russia (as far as I know, correct me please, if anybody knows better).
I think this thread has already discussed multiple times, opinions on whether to replace the old tubes or not.
Sit Back, Relax, and Enjoy listening to your favorite music.
Please go back and re-read my post # 45.
JJ tubes are made in Slovakia
Most if not all New Sensor tubes are made in Russia (as far as I know, correct me please, if anybody knows better).
I think this thread has already discussed multiple times, opinions on whether to replace the old tubes or not.
Sit Back, Relax, and Enjoy listening to your favorite music.
Try to think about tubes like you think about tires.
Would you change your tires just for fun?
Would you change your tires if they were working fine?
Would you change your tires if somebody told you there were much better tires?
Would you change your tires just for fun?
Would you change your tires if they were working fine?
Would you change your tires if somebody told you there were much better tires?
That may be a bad analogy for me… 😂
1. No, not for fun
2. No, except pending 3
3. Yes, if I thought there was an advantage. I replaced all-terrain tires on my truck with highway tires, and I would put new tires on a car I bought if it had been fitted with mediocre or poor-quality tires.
1. No, not for fun
2. No, except pending 3
3. Yes, if I thought there was an advantage. I replaced all-terrain tires on my truck with highway tires, and I would put new tires on a car I bought if it had been fitted with mediocre or poor-quality tires.
Solid state devices vary as much as tubes in their characteristics. Even more, in some ways.
Engineers design circuits that can accommodate the inherent wide variations in all active devices.
Because we have to.
Way back in EE101, when there were only discrete devices available for design, we were taught how
to make a circuit design insensitive to such unit to unit variations, because otherwise it just wouldn't work.
All EEs have seen circuits that worked fine with one particular device, but would not work with another sample.
Of course, there are circuits around that do not follow good design practice, and are hampered by such variations.
The discerning EE will recognize these circuits, and avoid them like the plague.
Engineers design circuits that can accommodate the inherent wide variations in all active devices.
Because we have to.
Way back in EE101, when there were only discrete devices available for design, we were taught how
to make a circuit design insensitive to such unit to unit variations, because otherwise it just wouldn't work.
All EEs have seen circuits that worked fine with one particular device, but would not work with another sample.
Of course, there are circuits around that do not follow good design practice, and are hampered by such variations.
The discerning EE will recognize these circuits, and avoid them like the plague.
In the case of a preamp I would hook up the output to an ADC and do a recording of three or four reference tracks so you have something to compare. I do that when doing circuit changes to compare measurements with the subjective.
Purchase:
The "Educational" low cost entry level Tektronix Digital Oscilloscope.
The Denon Audio Technical CD
An 8 Ohm non-inductive load resistor
. . . And measure.
This method does not require "Perfect Listening Audio Memory".
Or,
Purchase a new preamp for Equal $, or more $$ than the above test gear.
And, you will need "Perfect Listening Audio Memory", unless you purchase a DPDT switch to quickly switch back and forth, so you can compare one channel of the old preamp to one channel of your new preamp.
Or,
Do both of the above (a second opinion of the results can be helpful).
Solutions are not always simple or inexpensive.
But to do any kind of testing that does not have a snowball's chance of even coming anywhere near to being definitive is a waste of time.
Just my opinions
Have Fun!
The "Educational" low cost entry level Tektronix Digital Oscilloscope.
The Denon Audio Technical CD
An 8 Ohm non-inductive load resistor
. . . And measure.
This method does not require "Perfect Listening Audio Memory".
Or,
Purchase a new preamp for Equal $, or more $$ than the above test gear.
And, you will need "Perfect Listening Audio Memory", unless you purchase a DPDT switch to quickly switch back and forth, so you can compare one channel of the old preamp to one channel of your new preamp.
Or,
Do both of the above (a second opinion of the results can be helpful).
Solutions are not always simple or inexpensive.
But to do any kind of testing that does not have a snowball's chance of even coming anywhere near to being definitive is a waste of time.
Just my opinions
Have Fun!
You can get an entry level Picoscope for around $130, if you have a suitable computer to use with it.
Completely adequate for beginner use. Software includes an AWG.
Completely adequate for beginner use. Software includes an AWG.
The old "output mode" switches that used to be ubiquitous on every receiver through the 1980's were very handy for "fast flipping" right/left channels to compare differences in balance/tone. With such a switch you can flip between left mono or right mono making it easy to compare tubes as you "roll along". Unfortunately this switch seems to have disappeared from most commercial amps. Here is what I mean, you've all seen one!:
https://goldpt.com/mode.html
https://goldpt.com/mode.html
Attachments
Casual listeners would play around with the knob when they bought it, and end up
leaving it unknowingly in mono or L only, and listen to it that way for years.
leaving it unknowingly in mono or L only, and listen to it that way for years.
As Count Basie once said: "One More Time!"
Comparing the Left versus Right channel does not work if the dual triodes are in a single glass envelope.
That is the case of the preamplifier of this thread.
(One triode for Left channel and one triode for Right channel, all in the same glass envelope).
In this case, even if that preamp has a left and right channel switch, even that 1% is useless.
Back to the drawing board . . .
Build a DPDT switch box with RCA phono connectors on it.
Then get an identical 2nd preamp with different tubes in it.
Input the Left channel of A signal source to the switch box, and switch the output to the original preamp's Left channel, then to the 2nd preamp's Left channel.
Back and Forth, Back and Forth.
No long term "audio memory" required.
I am not talking about a double blindfold test anymore.
I am talking about instant switching A-B-A-B testing.
Simple but Expen$ive (A second identical preamp with different tubes).
If you can not hear the difference when testing that way, what is the point?
Comparing the Left versus Right channel does not work if the dual triodes are in a single glass envelope.
That is the case of the preamplifier of this thread.
(One triode for Left channel and one triode for Right channel, all in the same glass envelope).
In this case, even if that preamp has a left and right channel switch, even that 1% is useless.
Back to the drawing board . . .
Build a DPDT switch box with RCA phono connectors on it.
Then get an identical 2nd preamp with different tubes in it.
Input the Left channel of A signal source to the switch box, and switch the output to the original preamp's Left channel, then to the 2nd preamp's Left channel.
Back and Forth, Back and Forth.
No long term "audio memory" required.
I am not talking about a double blindfold test anymore.
I am talking about instant switching A-B-A-B testing.
Simple but Expen$ive (A second identical preamp with different tubes).
If you can not hear the difference when testing that way, what is the point?
This lead me to a thought... Would it be technically possible to wire two single-triode tubes into one dual-triode socket?