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Matching tubes, what parameter to use?
Matching tubes, what parameter to use?
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Old 26th August 2019, 11:48 AM   #11
DF96 is offline DF96  England
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Quote:
Originally Posted by PRR
What parameter *matters* in YOUR circuit?
Yes, that is the first question. It could be gain, or second-order distortion, or quiescent current or something else.

The zeroth question is "what is your circuit?". Post 1 omitted this information.
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Old 26th August 2019, 07:55 PM   #12
cerrem is offline cerrem  United States
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Matching Phase-Inverter halves can be critical in Non-Feedback amps such as AC30 circuit.. However it is not as critical in feedback amps like Marshall, since the tail of the phase inverter is receiving error correction feedback that will push the signal into balance...Provided that things are not grossly out of wack in the first place....
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Old 26th August 2019, 08:19 PM   #13
6A3sUMMER is offline 6A3sUMMER  United States
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TonyTechson,

I use Eurotubes.com for my tubes. They take JJ tubes, and retest them, match them, etc. They do very extensive testing of several factors. I know the test equipment they use, and also the designers of some of those measurement devices (all specifically made to test tubes).

Eurotubes works very closely with JJ, and a couple of them there have been at JJ in Slovakia several times.

I call Eurotubes, tell them what I want, and then because I am so lucky (blessed), I just drive over and pick them up.

I have had excellent performance results and reliability of those tubes.

Given all those facts . . . With very few exceptions, I will not design a tube amp that does not use any thing but JJ tubes from Eurotubes. (a few tube types I use are not made by JJ).

When I design a circuit that needs a phase invertor, I always use a pair of triodes, tie the cathodes together, use an extremely high impedance solid state current source, match the plate load resistors, and match the grid resistors of the next stage. That intrinsically matches the gain of the two phases.

If there is any need for further matching, it is the output stages that are not as intrinsically matched. I use well matched output tubes, but if they are not, I can slightly un-balance the phase invertor by putting an additional resistor in the plate load of only One side of the invertor. Find out which phase amplitude needs adjustment to balance the sum total of the invertor and outputs. A low Ohms rheostat in series with the plate load, or a high Ohms rheostat across the plate load. When I do that, I measure the fundamental, 2nd harmonic, and 3rd harmonic in real time on an FFT. Tweek, look, find the null, done! And done rhymes with fun. Time to listen.

Oh, if you are going to use negative feedback, be sure to do the null test without negative feedback. Make the amp linear before applying negative feedback. Negative feedback hides a multitude of bad characteristics, but do not make negative feedback have to work harder than necessary.
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Old 26th August 2019, 10:50 PM   #14
TonyTecson is offline TonyTecson  Philippines
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Matching tubes, what parameter to use?
@6A3sUMMER , i did not expect those JJ's to match up like that tbh, i am just glad that they did...
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Old 27th August 2019, 12:16 AM   #15
HarryY is offline HarryY  United States
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Matching tubes, what parameter to use?
Quote:
Originally Posted by 6A3sUMMER View Post
I use Eurotubes.com for my tubes.
I'll have to check them out.

Thank you
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Old 27th August 2019, 05:02 AM   #16
6A3sUMMER is offline 6A3sUMMER  United States
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Eurotubes caters to both Guitar people and to Hi Fi people. They do sell online.

Eurotubes does some really good extra testing of the tubes when they get them from JJ in Slovakia.
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