Ebay

mightymike · Post by **mightymike** » Thu Jul 14, 2005 6:33 am

Well the quad of Big Bottle GE 6ca7 I bought was thee most unbiasable quad I've ever seen. http://www.metroamp.com/forum/viewtopic.php?t=2618
V4, V5, V6, and V7 were 38mA, 28mA, 44mA, and 63mA. (where 38mA is desireable)
This on an amp that was 38,38,38, and 39 respectively with my previous Cryovalve tubes. Needless to say, I put the old ones back, and it's back to within 1mA again. (The more I try , the more I like those Cryos)

So I emailed the seller. He said he was "confused", and said they tested these before they shipped "Using an AVO Characteristic Valve meter and using the manuals recommended settings of, Anode/Screen volts of 250 Volts at a bias of neg 14.5 volts, each valve passing 62 to 64 ma.
The measured gm was 9 m/v for each valve." , and wanted to know how I measured it. So I explained how I measure from pin 8 to gound, using the 1 ohm shunts, 70% dissiptaion at 460v, 38 mA, bla bla bla. How my old ones are within 1 and I can make a video of the whole process If he likes. Then he said is all he can "suggest" is that I ship them back, and "if" they confirm my findings, they will replace them. He apologized and said he wants to keep his customers happy and "resolve" this, but as engineers, feel the need to check for themselves. The guy has a perfect feedback rating, and I used paypal.

I ship these back to the UK today. I hope he has some more to make a matching quad, because they are a nice sounding tube when matched.

Maybe I need to copy that THD circuit that allows you to use mismatched tubes.

Billy Batz · Post by **Billy Batz** » Thu Jul 14, 2005 7:11 am

Just add another bias pot. One for the left and one for the right set.

clarkydaz · Post by **clarkydaz** » Thu Jul 14, 2005 7:38 am

my quad from him were spot on

mightymike · Post by **mightymike** » Thu Jul 14, 2005 10:28 am

Billy Batz wrote:Just add another bias pot. One for the left and one for the right set.

Did you mean for the inner and outer pair?

clarkydaz wrote:my quad from him were spot on

Hopefully he has some more spot ons.

Billy Batz · Post by **Billy Batz** » Thu Jul 14, 2005 1:30 pm

mightymike wrote:
Billy Batz wrote:Just add another bias pot. One for the left and one for the right set.
Did you mean for the inner and outer pair?

No

mightymike · Post by **mightymike** » Thu Jul 14, 2005 3:37 pm

I'm confused.

I thought the pairs were the inner 2, and the outer 2.

Can you draw it? Nothing fancy.

Billy Batz · Post by **Billy Batz** » Thu Jul 14, 2005 7:32 pm

that thundertweak site has layouts for dual biasing

mightymike · Post by **mightymike** » Wed Jul 20, 2005 7:14 am

Update:

The seller recieved my tubes, tested and saw how they were off, then tested another quad that were good, and sent them off to me yesterday.

mightymike · Post by **mightymike** » Sun Aug 07, 2005 8:31 am

When the new set of 6CA7 arrived they were much better matched.
The seller was very honest, professional, and courteous.
Every Ebay transaction I've ever had with someone from the UK
has turned out great.
I have them in now. They are a very fine cunt hair better than the Cryovalves on the clean. Suprisingly close to the Cryovalves in tone.
How can that be?. I'd A/B them , but I broke the center pin on one of them, crazy glued it back, and it didn't break off when I installed it, so I'm not taking it out and risking breaking it again.

I have some NOS Siemens EL34 on their way. I bought another Quad of Cyros too. (I have 4 builds going on right now) They really are that good. I've never had tubes match that close before. It's nice not having to worry about drift because they are pre broken in, then matched.