Tube Matching Question

[rockable]

As I was sorting through my tubes and tryng to get the best matched set for my new SIII, I hit on something that confuses me. (I know all of you don't agree on tube matching, so let's don't debate that.)

I have a Weber bias rite which I decided to use to try to match EL84s in my new amp. I had already tested them for transconductance and they were all close.

I tried a set of "matched" JJs and found the current to be about 10 ma apart. I had 6 other RCA's and I tried to match them up. Most pairs I measured would give me a reading about 10 ma apart. If I took the lowest reading tube of two given pairs and put them in the amp together, I still got about 10 ma separation, even though both of them had read 35 ma when matched with the other tubes.

I have one pair that almost exactly matched but I couldn't get any of the others to get closer than about 10 ma.

What's up with that? I just doesn't seem logical to me. Thanks.

[dartanion]

These details need not be sweated. A 10ma mismatch is favorable for a guitar amp. It adds harmonic complexity whereas perfectly matched tubes sound sterile. Matching is a carry over from the HiFi world and need not be applied to guitar amps.

To explain that variations in measurement, look to the tolerance of the components that you built the amp with. Variations of 5-20% are not uncommon and this will throw off actual measurements of a tube in the circuit. You could be so anal as to match every component as close to spec as possible by buying the lowest tolerance components available, and then QAing every last one. However, this is best left to the HiFi fanatics as it really doesn't matter hugely in a guitar amp unless the component is so far off spec that it degrades performance.

I select sets of tubes the old fashion way, with my ears

[T-bones]

Well said, yes thats a big hifi thing and as far as matching in a guitar amp is pretty much a waste of time. A lot of folks eat that matching pair stuff up and quite frankly there spending much more for tubes that are matched for plate current. Although in hifi practices it is most important for the overall sound to stay clean no distortion, yes sterile. About time someone has spoken to clear the myth from reality. T-bones

[Plexi]

I kinda like tubes matched for current.. in amps that are run on the verge as the 18s. it will keep one tube from taking all the heat so to speak.
And hopefully as time goes by,they will wear more evenly.

Richie