Power Tube Matching
Can someone translate the two #’s on the tube boxes?
What does the first two digit # signify? Plate current I think. And I assume millivolts, milliamps? Or what?
And the 2nd four digit # means transconductance I gather. What is transconductance?
How far apart can these #’s be before they are considered unmatched? And if you explain with percentage, I will need to know how high the numbers go, so maybe stick to actual number increases. My point being, on the internet people just say "5% difference." This means nothing if the plate current numbers can go up to 35 million, or only 100, or maybe 50, or 120.
So, if I Bob has 3 tubes that all have the first number of 14.3.....what numbers on a forth tube would be considered matched? 17.1, 18.4, 19.0, 25.8, or even 12.3?
What happens really if Bob used an unmatched pair of tubes in an amp. And it would be nice to hear about direct experience.
Thank you for your time,
TD
Roger Modjeski designed his own proprietary computer tube testers to ensure appropriate matching of power and signal tubes. So here is a tutorial from a very knowledgeable amplifier designer and tube expert: https://www.ramtubes.com/article-5 that should address any questions you may have.
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@tonydennison No that is not what he is saying. If you read the very last paragraph Roger wrote Bias is matched within 4% and Gm (transconductance) within 8%.
The answer is 13.7 or 14.9 using our method of testing. We actually offer even tighter testing upon request. I personally would not accept anything below 14 or above 14.6. So none of the other values in your example offer a good match to the tube labeled 14.3. |
@tonydennison RAM Tubes is the company founded by Roger Modjeski and run by me since his passing. You can find it here: https://www.ramtubes.com/ |
The RAM EL34s are either from China or Russia. Roger used to purchase large volumes of raw stock from the factories or other sources. Then he would test them and only keep the tubes that tested to his desired specs. The NOS stock EL-34s we carry are Siemens from the old East German factory. During testing each tube is given a serial number and when testing is complete the machine prints a label with the test data for that tube which is then attached to the box. |
