Do driver tubes need to be matched?

[shellylh]

Short version:  Do the 6SN7 tubes in the Woo Audio WA5LE (300B SET topology - see pic below) need to be matched? 

 

Long version: I am getting ready to sell my Woo Audio WA5LE to make room and money for the future BHSE.  However, one of the stock "matched" driver tubes that Jack sent me with the amp (a cheap Tung Sol 6SN7gtb) was very noisy and tested much much lower than the other when I got it.  Since I never planned to use the stock tubes, it wasn't a problem.  Now that I am selling it, I am thinking of selling the amp with an option to buy the amp stock (without "upgraded" tubes) and so I feel that I should include one pair of cheap 6SN7 tubes.  I do have another Tung Sol 6SN7gtb that came with my Apex Peak amp that is unused and probably good (but certainly not "matched" to the other TS 6SN7gtb that came with the WA5LE and is a completely different date).  Would it be ok to use those together (an "unmatched pair") in the amp? 

 

Here's a picture I found of one at HF - it may have upgraded parts though.

 

Edited August 18, 2013 by shellylh

[ironbut]

Although it's nice to have a pair of "matched" input tubes for channel balance, for the most part, as tubes get "burned in" that matching will get better or worse back and forth thoughout the life of the tubes.

I think in the case of providing tubes for an amp to sell, just let the buyer know that these are not matched and leave it at that.

If he/she is going to be particular, they'll probably want to tube roll anyway.

[shellylh]

Yeah, I guess I shouldn't worry too much since they will probably be "throwaway" tubes.  It turns out that the one I got with the Peak doesn't test new either.  Don't know how noisy it is. Oh well. 

[n_maher]

Shelly, if you can't hear a difference left to right it's good enough to sell as "stock" with a disclaimer about them being cheap, get you started tubes.

[Audiojunkie]

Shelly, if you can't hear a difference left to right it's good enough to sell as "stock" with a disclaimer about them being cheap, get you started tubes.

 

Agreed. And "matched" tubes are typically only matched when they're new. They could decay separately from each other so after a while they won't be as "matched".

[nikongod]

SET amps do not require matched tubes. 

Any 2 tubes that test well, and are nominally the same thing (same physical construction) will be fine. 

After that there is no real need for matched tubes in an SET amp. 

[Dusty Chalk]

Most tube stores charge extra for matching tubes, so no, there is no obligation to match the "throwin"/"freebie" tubes.  If they want matched tubes that you don't have, just send them here.

[shellylh]

Thanks everyone. The main problem is that one of the original tubes (the one that tests new) is a bit noisy - like a bit of static. Maybe if it were used more, it would be ok. I have only used it to test the amp when I first got it and to test the tube in the amp just now.

I tested the other Tung Sol S6N7gtb (from the Peak) and it tests similar to the one that is not noisy (both test lower than the other noisy one). I assume that two recent issue Tung Sol 6SN7gtb (one from 04 and one from 11) should be the same - or close enough to use together. They look similar inside (although the color of the bases are slightly different and the dimples on the top are slightly different).

Earlier, I remembered that I had a pair of practically unused matched EH 6SN7 and thought I would throw those in instead. Turns out that one of those is noisy too though (they do test similar and very high though). I am putting way too much time into this sale already.

Edited August 19, 2013 by shellylh

[dsavitsk]

one of the original tubes (the one that tests new) is a bit noisy -

 

...

 

 

Turns out that one of those is noisy too

 

Are you sure that it isn't one side of the amp that's noisy?

[ironbut]

If these are tubes that haven't been used in a long time, they may have oxide build up on some of the pins (this includes tubes that have sat on distributor's shelves too).

Try cleaning the pins. A little tarnish remover, metal cleaning paste to shine them up a bit (you don't have to go crazy). If you have some Pro Gold, a little after polishing will hold off more oxidation from forming.

I use Mother's Aluminum and Mag Cleaner on Q tips I've cut down and put in my Dremel.

I've "saved" a lot of tubes that were headed for the circle bin with this.

In sensitve positions, you can knock off a few dB's of the kind of noise you described.

[shellylh]

Are you sure that it isn't one side of the amp that's noisy?

It changes sides when I switch the tubes and it doesn't happen with all my 6SN7. That said, this amp certainly does not have a black background with any of my tubes which is the the one thing that bugs me about the amp.

[deepak]

ironbut offers sound advice. I went through a bunch of 6DJ8s when I had a Melos wondering why so many tubes were noisy.  On the majority of them it turned out it was the pins oxidizing.

[spritzer]

That will drive you mad with loktals.  Huge problem with the smaller pins... 

[shellylh]

If these are tubes that haven't been used in a long time, they may have oxide build up on some of the pins (this includes tubes that have sat on distributor's shelves too).

Try cleaning the pins. A little tarnish remover, metal cleaning paste to shine them up a bit (you don't have to go crazy). If you have some Pro Gold, a little after polishing will hold off more oxidation from forming.

I use Mother's Aluminum and Mag Cleaner on Q tips I've cut down and put in my Dremel.

I've "saved" a lot of tubes that were headed for the circle bin with this.

In sensitve positions, you can knock off a few dB's of the kind of noise you described.

 

Can I just use a bit of sandpaper or do I need some tarnish remover and metal cleaning paste?

 

I just saw that 99% Iso Alcohol is recommended.  I have some of that.  Will that work just as well? 

[ironbut]

Can I just use a bit of sandpaper or do I need some tarnish remover and metal cleaning paste?

 

I just saw that 99% Iso Alcohol is recommended.  I have some of that.  Will that work just as well? 

If they were $$$ tubes I'd say no on the sandpaper but try the alcohol first and if that doesn't work, try using an eraser. If none of those work, lightly sand the pins with 220 grit or finer.

[shellylh]

OK.  Also, thanks for the Dremel tool trick!

[wink]

I used to use an ink rubber in the day when I used valves.

 

You used to be able to purchase a rubber/eraser that was half pencil eraser and half ink eraser.

 

You could use a emery board for nails, steel wool etc.

 

Deoxit and Deoxit Gold as a finish is excellent.

 

Something like this, but a heck of a lot cheaper.

 

http://www.ebay.com.au/itm/Faber-Castell-Natural-Rubber-Ink-Rubber-Eraser-X-5-Fountain-Pen-Typewriter-/221196935107