Question about output tubes

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Question about output tubes

Postby erigmo » Wed Jan 30, 2013 9:50 am

Hi all, a couple newbie questions.

Is it OK to replace a quad of output tubes with 2 sets of matched pairs?

And, is it really necessary for output tubes to be matched?

Thanks for your inputs.
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Re: Question about output tubes

Postby Jon Agner » Wed Jan 30, 2013 10:50 am

erigmo wrote:Hi all, a couple newbie questions.

Is it OK to replace a quad of output tubes with 2 sets of matched pairs?

And, is it really necessary for output tubes to be matched?

Thanks for your inputs.


They need to be closely matched if you want both channels to be perfectly balanced. Replacing a set of matched quad with 2 matched pairs is possible if your amp has balance controls, or separate volume controls for the left and right channels.
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Re: Question about output tubes

Postby tony » Wed Jan 30, 2013 11:04 am

erigmo wrote:Hi all, a couple newbie questions.

Is it OK to replace a quad of output tubes with 2 sets of matched pairs?


yes....


And, is it really necessary for output tubes to be matched?

Thanks for your inputs.


yes, if using cathode/self bias in the output, this is where you can just plug in the tube and listen, a "plug and play" if you will.....best to check the
documentation of your amp..

no, if using fixed bias since you can adjust bias on the tubes individually....

fact is no two tubes are exactly alike, there will be variations, what tube matching does is merely get two tubes as close as possible in characteristics, static or dynamic...

there are even situations wherein a slight mismatch s desirable, some like the sound coloration it brings... ;)
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Re: Question about output tubes

Postby narayan » Wed Jan 30, 2013 11:24 am

Eric,

The Jolida JD707a is fixed bias. BTW, all 4 of the output tubes have been recently biased at the recommended bias level of 400mv by audio amplified's technician.
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Re: Question about output tubes

Postby tony » Wed Jan 30, 2013 12:38 pm

the next time you will have to worry about biasing is when you replace them, tubes have at least 1000 hours of life so that at a daily listening of say 3 hours, that tube should be good for about a year, but even after that the tube can still be good.....so just sit back and listen to the music and set aside worriying about matching tubes.... ;) enjoy....... 8)
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Question about output tubes

Postby erigmo » Wed Jan 30, 2013 1:23 pm

Thank you guys for your replies-- very informative indeed. I'm new to tube amplification so I'm in the process of trying to learn as much about it as I can.

Tony, I've had the Jolida for only a couple of days and yes I'm enjoying it very much! It's very different from my previous solid state amp. The music is sweeter! I believe I made the right choice with this acquisition. Many thanks to sir Obet!
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Re: Question about output tubes

Postby tony » Thu Jan 31, 2013 3:33 pm

erigmo wrote:Thank you guys for your replies-- very informative indeed. I'm new to tube amplification so I'm in the process of trying to learn as much about it as I can.

Tony, I've had the Jolida for only a couple of days and yes I'm enjoying it very much! It's very different from my previous solid state amp. The music is sweeter! I believe I made the right choice with this acquisition. Many thanks to sir Obet!


my recommendation is to live with it for months listening and learning how it sounds, resist all sulsol about changing tubes just as yet.... 8)
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Re: Question about output tubes

Postby narayan » Thu Jan 31, 2013 3:37 pm

tony wrote:
my recommendation is to live with it for months listening and learning how it sounds, resist all sulsol about changing tubes just as yet.... 8)


Very sound advice Tony 8)
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Question about output tubes

Postby erigmo » Thu Jan 31, 2013 4:05 pm

Hehehe! OK I will! Many thanks for all the advise.
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Re: Question about output tubes

Postby tony » Thu Jan 31, 2013 4:10 pm

there will come a time when you are grown accustomed to the sound of your amp, when that time comes, then that is the time to roll....having another amp like a classD, or an ss amp that you can try from time to time is also a good way to appreciate your tube amp....
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Re: Question about output tubes

Postby Jon Agner » Thu Jan 31, 2013 4:36 pm

tony wrote:
erigmo wrote:Thank you guys for your replies-- very informative indeed. I'm new to tube amplification so I'm in the process of trying to learn as much about it as I can.

Tony, I've had the Jolida for only a couple of days and yes I'm enjoying it very much! It's very different from my previous solid state amp. The music is sweeter! I believe I made the right choice with this acquisition. Many thanks to sir Obet!


my recommendation is to live with it for months listening and learning how it sounds, resist all sulsol about changing tubes just as yet.... 8)


Agree to that :)
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Re: Question about output tubes

Postby endrik35 » Thu Jan 31, 2013 7:31 pm

Hi Eric, happy to find a fellow Angelicum alumni here in WS. Yes, enjoy your present tubes first so you'll be familiar with it's sonic character before tube rolling. Tube rolling has it's rewards but could prove expensive and disastrous at times. Happy listening! ;)
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Question about output tubes

Postby erigmo » Thu Jan 31, 2013 7:45 pm

Tony I'll take your advise. Actually, I really have no plans of tube rolling yet. I'm just trying to understand what tube matchings are all about as I've been hearing (or reading) a lot about it on the net. My knowledge of tube amplification is practically zero.

Jon many thanks for your comments.

Doc Endrik, tayong 2 lang ba tiga-Angelicum dito?
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Re: Question about output tubes

Postby narayan » Thu Jan 31, 2013 9:54 pm

erigmo wrote:Doc Endrik, tayong 2 lang ba tiga-Angelicum dito?


Dagdag mo na yung tatay ng tiga Angelicum :lol:
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Re: Question about output tubes

Postby carbondated » Fri Feb 01, 2013 12:39 am

erigmo wrote:
Hi all, a couple newbie questions.

Is it OK to replace a quad of output tubes with 2 sets of matched pairs?

tony wrote:yes....



I didn't know that! How does this work? Say with a push-pull amp that uses a quad of EL34s, would you have AA on left channel and BB on right, or AB and AB? What about if parallel single-ended?
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Re: Question about output tubes

Postby tony » Fri Feb 01, 2013 6:57 am

carbondated wrote:
erigmo wrote:
Hi all, a couple newbie questions.

Is it OK to replace a quad of output tubes with 2 sets of matched pairs?

tony wrote:yes....



I didn't know that! How does this work? Say with a push-pull amp that uses a quad of EL34's, would you have AA on left channel and BB on right, or AB and AB? What about if parallel single-ended?


there are fixed bias circuits that that have just one bias pot per channel, in this case matched pairs is indicated, AA and BB, if the fixed bias circuit allow for individual grid bias adjustments, then you do not need to buy matched quads at all....

in case of parallel single-ended, matched pair is desirable, again if individual grid bias adjustment is provided then no.....

so it really depends on the circuit used in your amp....the object of matching tubes in push pull is to minimize 3rd harmonic distortion, in parallel single ended, 2nd harmonics can be affected.....
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Re: Question about output tubes

Postby tony » Tue Feb 05, 2013 12:29 pm

narayan wrote:Eric,

The Jolida JD707a is fixed bias. BTW, all 4 of the output tubes have been recently biased at the recommended bias level of 400mv by audio amplified's technician.



come to think of it, tubes may be biased "hot" or "cold"......hot implies classA, say an EL34 rated for plate dissipation of 24watts, then having a B+ of 400 volts, then 60mA is the cathode current, if the cathode has a 10ohm resistor, then 600mV can be read across the resistor....cold implies classB, tubes are very hard to cut-off, so choosing 2.4watts plate dissipation at idle, then 6mA and 60mV is read on the resistor......classAB biases the tubes somewhere between the extremes, so at 40mA bias, that means 16 watts or about 67% of plate....

the main diasvantage of ClassA is shorter tube like and higher power consumption.....the main disadvantage of classB is cross-over distortion....so classAB takes the middle ground....
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Question about output tubes

Postby erigmo » Wed Feb 13, 2013 7:35 pm

Hi Tony,

This is the output tube section of the Jolida JD707A. Am I correct in thinking there are 4 bias pots (one for each tube)? So does this mean I don't have to buy matched tubes at all?

Sorry for my ignorance but I would really appreciate your inputs.

Thank you very much.

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Re: Question about output tubes

Postby tony » Wed Feb 13, 2013 8:41 pm

^it does look that way, 4 pot affair has a set of 2 pots per channel, one pot to set bias voltage and another to set balance currents between pair of tubes per channels.....but i'd rather that we look at the schematics to be sure.....

yes in this case, no need to buy matched tubes at all.....
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Question about output tubes

Postby erigmo » Wed Feb 13, 2013 9:11 pm

Thanks Tony. Appreciate very much your comments.
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