6C4s--experiences with 2 brands

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Received a conrad-johnson MET1 yesterday. Had previously bought some 6C4/EF90s thru eBay.
The 10 6C4s were NOS WWII-era National Unions (linked), and at $5 each are certainly affordable. I also won four British-made Mullard EC90/6C4s. All arrived promtply and appeared to be new. All tested well in my transconductance-type tester.
I plugged a set of 6 into the MET1, turned it on, and when it unmuted I sort of thought I had connected a sinewave generator, the tubes rang all by themselves so much. It was difficult to determine which tube was worse, so I started over and tested all of them one at a time, with 5 original Mullard M8080s. Long story made short--9 of the 10 NUs were so microfonic they're unusable, while 1 of the Mullard EC90s was somewhat microfonic. The 1 'good' NU started hissing and popping after it warmed, so I'm now zero for 10 on NUs and 3 for 4 on Mullards.
I have some RCAs coming--hope they do better.
I wonder how much c-j's replacement set costs?

http://cgi.ebay.com/ws/eBayISAPI.dll?ViewItem&ssPageName=ADME:B:EOIBSAA:US:31&Item=5881460382 (Open in New Window)

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Topic - 6C4s--experiences with 2 brands - jeffreybehr 19:34:40 04/18/06 (7)

Six more arrived today, marked CV 133. Carton was labeled 'VALVE ELECTRONIC'... - jeffreybehr 22:24:48 04/26/06 (0)

Four more NUs of later era arrived yesterday. They're as microfonic (and useless)... - jeffreybehr 14:21:37 04/23/06 (0)

5 NOS RCAs arrived today. After identifying the channels belonging to those 6 tubes... - jeffreybehr 20:35:36 04/19/06 (2)

Shouldn't you break in the unit - unclestu52 21:54:44 04/19/06 (1)

The MET1 does not have the teflons in it; the ACT2 and the CT5 do. This MET1 and the $4500 2-channel CT6 use... - jeffreybehr 00:08:12 04/20/06 (0)

Try Herbie's tube dampers before you chuck em. - hukkfinn 21:32:00 04/18/06 (0)

Re: 6C4s--experiences with 2 brands - Jimmy 20:00:52 04/18/06 (0)

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