Matched tubes or not matched

[pointy]

you will want to match labels because the metal (parts) will be different from make to make. and they will move apart from each other in use
and also match the rating so they age the same ( ie. not one side dying and the other bright.)

 

[richwalters]

Please don't say no one does matching of Gm - I do.

Responding to the other posts...

1. It's not an economic issue. Matched tubes cost more because of the time invested in the matching process. I could do much better productivity-wise if I didn't have to match tubes. Yes, the matched tubes are SLIGHTLY higher priced (maybe a buck or two for a quad), but it doesn't cover the costs of doing it. So Miles, your accusation doesn't hold water, at least as far as I'm concerned.

2. Why no matched 807s? As Tom Bavis said, there aren't enough out there to match them. There is no sinister unethical reason I have KT-88s matched and not 807s!

3. Actually, the current production tubes are as tight as the old stock in terms of "out of the box" matching. But both will have variances of as much as 100% in cathode current and 30% in Gm.

4. Stu Hegeman (the Citation series designer) said there was a statistical probability of matched tubes aging more evenly than unmatched tubes. He was pretty darn smart. I give his statements credence.

Honestly, it really bothers me when people accuse me (by making broad sweeping generalizations) of borderline thievery:



The people YOU deal with may overlook them, but I don't. And I don't appreciate that sort of comment... there are people out here who do a very good job, the sort of comment you made is inaccurate and just serves to damage the reputations of good vendors.

I can't speak for others, but don't go painting me with that broad accusatory brush. I don't deserve it and you have no basis to say it does.

Your da*n right I'm mad.

...Miles .you copied my name in your last quote which wasn't all my damage....
.....the problem, if we as customers have unknowingly dealt with suspect traders, then it is good you come forward to hold your reputation..

richy

 

[hilbert_mostert]

Well, its clear to me... if i am going to build an PP amp based on 807 type valves i am going to use 829B valves, these have two valves in one package and look quite alien too

I know there is no sinister goal behind matching but was just wondering why it was. For those who put afford in matching tubes, keep up the good work, its a lot of work and clearly worth the extra money.

 

[Miles Prower]

Me Thinkest Thou Doth Protest Too Much

So Miles, your accusation doesn't hold water, at least as far as I'm concerned.

Honestly, it really bothers me when people accuse me (by making broad sweeping generalizations) of borderline thievery:

Show me where I accused you of anything in this, or any other, thread.

I can't speak for others, but don't go painting me with that broad accusatory brush. I don't deserve it and you have no basis to say it does.

Your da*n right I'm mad.

Nobody in this thread posted word one about you. That you get this uber-defensive leads me to ask why that is. Until this little rant of yours, I had no idea who you were, or that you were even a member here. I don't recall ever seeing anything you ever posted here before. Furthermore, I couldn't care less even if you paid me.

 

[Rod Coleman]

Ah, this makes things interesting, I have a Hughes and Kettner Tube 50 guitar amplifier with a matched pair of EL34s and this story makes sense to me. Does your guitar amplifier have fixed bias with or without potmeters for bias control?

The Vox AC30 has auto-bias (using a 50 ohm cathode resistor shared by all 4 cathodes), but the problem is almost the same - if your valves are working very hot, then 20% or more current variation makes one valve too hot -burns out!

 

[Jim McShane]

Re: Me Thinkest Thou Doth Protest Too Much

Show me where I accused you of anything in this, or any other, thread.

You made the usual sweeping generalization, and did it in a way I found inappropriate. "They" can charge more, "they" overlook all the nasty little problems. And so on...

Nobody in this thread posted word one about you. That you get this uber-defensive leads me to ask why that is. Until this little rant of yours, I had no idea who you were, or that you were even a member here. I don't recall ever seeing anything you ever posted here before. Furthermore, I couldn't care less even if you paid me.

Whatever. Of course, if you couldn't care less then why did you respond? I suspect it's because - just like me - you felt wronged.

FYI, I've posted here for a number of years, I've had nice dialog with a number of people here - Kevin Kennedy, Tom Bavis, Eli Duttman, and others.

What I didn't find here before was the snarkiness and cynicism that your post (and response above) exhibited IMHO. To say some vendors do a poor job of matching is fine, it's true some do horribly; but not all are as inept as you'd have people believe. Some do a very good job. Please don't paint us all with the same broad brush.

In any case it's time to move on, and we can have peace and tranquility...

 

[Wavebourn]

The Vox AC30 has auto-bias (using a 50 ohm cathode resistor shared by all 4 cathodes), but the problem is almost the same - if your valves are working very hot, then 20% or more current variation makes one valve too hot -burns out!

This type of bias, with a common resistor, highlights differences. Use 4 separate 200 ohm resistors, and all 4 of them will be happy no matter who and when built'em.

What I didn't find here before was the snarkiness and cynicism that your post (and response above) exhibited IMHO. To say some vendors do a poor job of matching is fine, it's true some do horribly; but not all are as inept as you'd have people believe. Some do a very good job. Please don't paint us all with the same broad brush.

In any case it's time to move on, and we can have peace and tranquility...

Sure, if to view Miles' posting as a valuable source of information about your competitors you know now how to make the difference, right? Just state what did you match, and how well they are matched.

 

[Geek]

Is it correct to state that when using an auto bias circuit, tube matching isn't necessary anymore?

Correct.

When I made that statement, I didn't realize you were referring to CATHODE bias.

This is what I know as autobias:
http://www.tubecad.com/2005/May/blog0046.htm

Cheers!

 

[Rod Coleman]

This type of bias, with a common resistor, highlights differences. Use 4 separate 200 ohm resistors, and all 4 of them will be happy no matter who and when built'em.

True, and I make them like that for a new amp. But you should not do it to a customer's (vintage) Vox AC30 (Beatles amp!)

In this case a matched quad is easy to buy and fit. Also, I like matched sets from a good vendor, because they will have been tested again, and the bad ones rejected. I don't mind paying a bit extra for that.

 

[Wavebourn]

True, and I make them like that for a new amp. But you should not do it to a customer's (vintage) Vox AC30 (Beatles amp!)

In this case a matched quad is easy to buy and fit. Also, I like matched sets from a good vendor, because they will have been tested again, and the bad ones rejected. I don't mind paying a bit extra for that.

Sure, in order to play and sing like Beatles they need to experience exactly the same troubles Beatles did.

If to change bias resistors Hot / Cold switch has to be changed as well.

There is a reissue with lots of opamps inside, but still with the same bias of output toobs...