WTB Matched pair of Mullard EL34s!!!!

Sigs

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If you buy 2 separate unused Mullard EL34 valves, not matched but they measure almost exact readings, is this classed as a matched pair ?
 

Dblgun

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I would guess it would depend on what almost exact readings means. I suppose you could have two tubes that once placed into a given piece of equipment provided extremely similar readings. These tubes could be from two different suppliers but still be considered matched. I have always thought of a "matched pair" as two from the same maker and series that provide very similar readings and performance.

Kind of like a pair of socks you got out of the drawer and put on in the dark. They feel and work the same but they may not match!

I'm sure that those putting together pairs or quads today have a tolerance that they desire to stay within. So I would think two Mullards of the same design which provide very similar results in a given environment would be considered a matched pair.
 

Matthews Guitars

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For my purposes, I consider a set of tubes to be matched if they're within 5 percentage points of each other, measuring bias current. Tighter is better, of course. I'd love it if they all measured identically in a set. But that's what apex matched pairs and quad are for. Not applicable to old/used/NOS tubes, generally.

Too much variance between the tubes will cause hum. But that takes a lot of imbalance.

I have yet to encounter a scenario where somebody has a set of four tubes and one goes bad and is replaced with another good one, right out of the spare tubes bag, and it was so badly mismatched that it made the amp hum.

Dare I say it: The importance of output tube matching is usually overrated. Yes there are times when you want a tight match. For recording, yes, keep that imbalance hum to a minimum. If the amp has an ultralinear output transformer, it is very sensitive to output tube matching, and WILL hum if there is a small match imbalance.
 

StingRay85

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I can tell you, even on new out of the box tubes, there can be a large variation on idle current at realistic plate & screen voltages (e.g. 400V). If you use 5% as a guide line for matching, a 30 mA tube should match with a 31.5 mA tube at most. But on my tester, which uses 400V and -36V bias, a good healthy tube can measure anywhere between 22-23 mA and 50+ mA. So matching really isn't that easy unless you really have many tubes. Especially for Mullard tubes the getter flash is a much better indicator of the hours it has been used. Personally I see no reason why not to match Xf2 with Xf3 or Xf4. But in this case you shouldn't rely on matching measurements at 250V -13.5V bias, because the tubes could be much further apart when they are placed in an amp running at 480V.

Check the chart on this page: https://www.marshallforum.com/threads/blackburn-mullard-el34.120020/page-2

Although a bit outdated, I have many more in the meantime, it gives a good idea on distribution
 

StingRay85

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By the way, here's an ebay listening for a nice pair of Mullard EL34 Xf2

https://www.ebay.ca/itm/334294702088?hash=item4dd5845808:g:CYMAAOSw3y9h7RXe

I'm not affiliated with the seller, but these tubes appear to be well matched, and I'm quite sure they are really new based on the appearance of the getter flash. Hard to come by and I've only seen junk posted on Reverb lately, listed for a lot more
 

Springfield Scooter

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StingRay85

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They appear new. I don't think in your lifetime you will find new Xf2 Mullard tubes listed for much lower than 100 a piece.

EDIT: I checked the listing again, and price went up from 198 to 298. WTF happened there??
 

AndyD

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They appear new. I don't think in your lifetime you will find new Xf2 Mullard tubes listed for much lower than 100 a piece.

EDIT: I checked the listing again, and price went up from 198 to 298. WTF happened there??
Appreciate the heads up! At 198 I might have tempted!
 

neikeel

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I did a blitz of testing EL34s on my AVO CT160 at Christmas after recalibrating it. Mainly mullard xf3 and xf4 and assortment of RFTs and some 6550s and KT66s.
Noticeable that a lot of the older tubes did rattle a bit (I actually thought it was the support plates.
Of course the AVO is old school and only uses 250v or 300v and some fudge factors. But it helped me put some current and Gm figures to them and bin quite a lot of rubbish. Managed to find a few ‘matched’ pairs but ideally need to plot curves for them but too much else going on in life! I’ve been contemplating making a u-curve tracer but same reasons get in the way.
 

StingRay85

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AVO CT160 is one of the older Dutch AVO testers. But I guess it's a respectable tool for the job. Most of them measure emission at 250V -13.5V bias. IIRC ranges for those tubes should be between 60 mA and 110 mA. With respect to the rattle, this is indeed sometimes a problem with the Mullard tubes. You should really put it to the test in an amp, and see if it is a problem or not. Some of them rattle noticeably at certain (lower) frequencies and are not suited for use anymore, unless for recording with UA Ox IRs or something similar, or on stage where the sound levels greatly exceed the rattle. Buyer beware
 

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