Help with 6v6 Tube match

[med]

Just got some tubes ordered online and opened the box's to find each base labeled with 31.0 on one and 32.1 on the other.

Should this be a matched pair?
What's the no's indicate. it's not ma's is it ?
What is a good match?

Don't want to sound stupid butt what do i know it's better than roastin an OT.
Thank you very much

Med. 8)

[Tim Swartz]

Most consider a match to be within 5mA. Those are just fine.

[med]

That's all i wanted to know.
Med

[Kevin Nybo]

My literature says, "within 7ma". Is there a correct answer? I know many amp techs think 'matching' is pure BS. I tend to agree after my own experiences.

Only once have I had a pair of tubes that exactly match. This was a set of Svetlana 6L6's(SV6L6GC). They gave an exact reading on a duel-bias probe.

Because of the minute price difference, I usually buy sets in matched pairs but, have never found a problem using a tube that was 5ma+/-.

I'd like to hear from folks like "Big Cookie" that actually do amp building/restoring.

[med]

I don't know if i'd install an unmatched pair without checking the currend.
I put new tubes from GC in my gibson sometime ago.
Just to be safe i checked the current after reading some on biasing on the ampage.
The mismatched pair had 15mA on one and 47mA on the other,they also sounded like crap .
Med

[Big Cookie]

Matching is less of an issue in a cathode biased amp like my Sewell, but in a fixed bias amp, you are going to start getting additional hum a around a 7ma mismatch.
In my Crumblers 5ma is about the largest differentiation that I will tolerate, after that the tone seems to suffer. Some wholesalers tolerate up to a 10ma mismatch, for this reason I "fired" a couple of wholesalers last year and now just deal with one, who has promised me 2ma or less tube matching. Matching shouldn't be that much of an issue at less than $2 a pair compared to what the tubes cost.

[med]

The tubes i just installed are labled around 30/31mA and sound good.
The ones i replaced were marked on the box lp39 and Gm3.900.
I am guessing this is 39mA.
This is a 33% diifference which sounds signifiant to me.
I have not noticed a big diference in sound to my tone deaf ear though should i?

Cookie whats up with your amp?
When i was last on your site it was in the works.

Med

[Big Cookie]

Henri,

They are being built and are leaving the shop slowly, thats the only way I know how to build em. I need tio update the website.

[EMan]

Hi Med. Gm is a tube parameter associated with AF (Amplification Factor). It is: (Delta) Plate Current/(Delta) Grid Voltage, and is expressed in "mho"'s. It is a number that describes the ability of the the tube to amplify (it's efficiency).

Ip is the Plate Current. Keep in mind, that the parameters will change as the tubes 'age'.

The idea of matched tubes is to insure fidelity; to insure that each have of the PP amp is running the same. Very important in HiFi applications where absolute fidelity is important.

In guitar amps...we generally think about the 'distortion' or non linear qualities as being desirable. In that case, you might expect a slight mis-match to be "toneful".

As mentioned above, matched sets are common these days, and why not just buy them that way.

PP amps have ripple voltage (AC) on the B+ supply, and is a function of the load. The OT's are designed so that the two tube's currents are flowing in opposite directions. This is what "cancels" that AC voltage (so you can't hear it). When these individual currents become too different, the "hum" is audible through the speaker.

However, a "bias balance" (ot output tube matching) pot in your amps bais supply circuit can eliminate most all the hum from lesser matched tube sets.

Okay...I'll **** up now....

[med]

I should have known what the IP was but mis read it as LP.
The tubes with my kit just had the numbers 30/31 on them.
I assume this is Ip also and was wondering if this was an indication of the state of the amps bias (hot or cold)?

In other words could i request a plate current for a set of tubes to match a set i like?

I imagine tubes brands would have thair own sweet spot for IP.
Med

[Silverface]

med - you could, but only if the plate voltage the measurements are made with are the same as the amp you're using.

One note - depending on the source, many online tube sellers (mostly of the eBay variety) match the tubes using some sort of Hickok (or other brand) tube tester. The plate voltage in these testers usually only tops out at 165-180 volts or so, making the "matching" with them pretty irrelevant for guitar amp applications.

That being said, I'm one of those that will match my own tubes with that type of tester and then check 'em with a bias probe in an amp...but I also agree with eman's statement about slight mismatches often being more toneful. Matching can be overhyped. Heck it *is* overhyped - as long as you don't have hum problems and the amp sounds good (and you're biased in a safe range) up to 10% can sound pretty darned cool in some cases.

Remember one other caveat - if your driver isn't balanced you might as well buy your tubes at the electronics swap meet. Hehe, but then sometimes I'll intentionally unbalance a driver....

It's a sickness.

[EMan]

..and don't forget any 'mis-match' in the primary halves of the OT.

It never ends, I tell ya!

[Tim Swartz]

..or the plate resistors on the PI.

[Silverface]

...that's the point. Most "buyers" get hung up on "matched tubes" and the snake-oil mysteria therein when their amps aren't set up as a platform for them anyway!

[Bluesbob]

Transconductance changes with usage.