Tech Talk.. New Toobs.

midnightlaundry

Well-known member
Come in a get all nerd!

So I picked up a pair of EH EL34's from Upscale Audio because they have the "Best Matching in the business" :ROFLMAO: for my Trainwreck Express build.. They burn in for 72 hours which is pretty cool.

I use the Eurotubes Pro One Bias Probe for biasing. So what I'm seeing is that on paper these tubes are pretty well matched, but according to the Probe, there's about a 4.5 ma difference between Tubes. The Bias Pot on my Amp is backed off all the way, so I can't get the higher Tube down to 43.7 ma's which is 70% dissipation.. 47.1 is about 75%, so it's not a deal breaker.

They added the Grid 2 current spec on there, so this must have a effect on why the 1 Tube pulls more current? Or did they just fluff on the match?

Thoughts?

IMG_20210501_114930918.jpg


IMG_20210501_115408370.jpg


IMG_20210501_115553345.jpg
 

blackba

Well-known member
Does the difference follow if you switch the tubes?

on my silver jubilee I have like 10mA difference between the “matched” tubes, that means one is running at 55% and the other at 70%, but the amp sounds great.
 

blackba

Well-known member
I typically like to see less than a few mA difference between tubes and most of the time that is the case, but less than 5mA in an actual amp is not out of bounds.
 

RedPlated

Well-known member
Upscale Audio sells to audiophiles with those crazy expensive stereo systems that use tubes. They do not match tubes for use in guitar circuits.

In fact, I bought a pair of kt88’s from them a few years back, I’m local. The owner told me they will be relatively close but not as closely matched in a guitar amp. 5ma is within tolerance and completely fine though.

The best matched tubes I’ve gotten are the Apex matched from Amplified Parts with the 24 hr burn in.
 

midnightlaundry

Well-known member
Thanks. Their price was really good and the guy seemed passionate in his videos.. I usually get JJ Power Tubes froim Eurotubes. All thier stuff is usually within like 2 ma's.. I just wanted to try something different.
 

midnightlaundry

Well-known member
Well live and learn.. It will be more effort to send them back than I want to deal with.
I just won't buy from them anymore and I don't think anyone who reads this will either..
I'll stick with people who deal in Guitar Amps and not rich HiFI dudes..
 

RedPlated

Well-known member
4.5ma vs 2ma spread isn’t going to change anything significant. I really wouldn’t worry about it.

All those vintage Marshalls that you’ve heard on countless recordings were probably way further apart than 4.5ma when they left the factory.
 

midnightlaundry

Well-known member
Yeah, I'm not worried about it.
But, when you make a video stating you have the best matching in the business, with custom burn in rigs at 72 hours per tube, I expected them to be tighter than that..
They were still better than Tube Depot. Fuck TD.. I bought a quad of EH KT88's and each tube was on another planet. We're talking 50ma apart.. I did write them a shit graham and I don't remember if I even got a reply because I didn't get new tubes... I will shit on them everytime they come up.
 
I've use quads that where 10 -12 mA apart in the past. I move them around until each side V4,5 & V6,7 are as close as possible when adding the mA measurements together for each pair. This way, usually the pairs only end up with a few mA difference. Always sounded good to my guitar beatin' to death ears. lol
 

Geo

Member
Some people feel the sound is better if the tubes are not matched perfectly but if you wanted matched tubes, send them back.
 

LP Freak

Well-known member
I've use quads that where 10 -12 mA apart in the past. I move them around until each side V4,5 & V6,7 are as close as possible when adding the mA measurements together for each pair. This way, usually the pairs only end up with a few mA difference. Always sounded good to my guitar beatin' to death ears. lol
Seems a lot of people aren’t aware of doing this.
 
Top