6681 Sylvania's...

[K-SOLO]

Hey guys,i lucked up and found an unopened 6-pk of Sylvania 6681/12AX7's in a friends father's T.V. repair shop. His dad said he has no use for them and gave them to me. I looked them up and it's said that they are "heavy-duty" 12AX7's. I have all kinds of "vintage" 12AX7's for my tube amps...and i'm going to give them a try. Have any of you guys used this pre-amp tube in your amps??? Thanks.

[Chad]

Heres what Jeff West posted about the 6681 at Metro http://forum.metroamp.com/viewtopic.php?f=13&t=11629 Hope that helps.

[Chad]

This is what was posted

Yeah, 6681 was "mobile rated", otherwise specs were per 12AX7. Mobile rated meant not only rugged and hardy in the face of repeated on-off cycles, just as stated, but also capable of performing under extreme fluctuations of filament voltage as supplied by Jeep or halftrack battery, etc. under field conditions, I believe the spec called for reliable operation w/in range exceeding 5V to 7.6V on the heater!

Numerous U.S. manufacturers marked their own tubes as 6681 on occasion, inc RCA, Sylvania, GE. It's not really clear if they differ inside from standard 12AX7s, although maybe. Here's a tip: lots of GE branded GE 6681s from 1966-67 period in the grey and orange boxes are rebranded 1966 I63 shortplate Mullards, with Blackburn etched codes from 1966, I've seen many of these, and they sound just like a '66 Mullard 12AX7 (lots of '66 GE branded 12AX7s are also '66 Mullard 12AX7s). All marked as made in Gt. Britain right on the tube.

6681 was part of a mobile rated series starting in mid-'50s that included lots of alternative inductrial numbers for common 6.3V tubes: 6679 was mobile rated 12AT7 equivalent, 6663 was 6AL5, etc.

Jeff

Thanks to Jeff West. Very Knowledgeable guy.

[David Root]

Below is the www.audiotubes.com website's offering. Your tubes are worth $270 in the marketplace!

I haven't used one but they are I think pretty rare these days, I've never even seen one before.


6681/12AX7 early longplate industrial GE OR Sylvania greyplate
New Old Stock in white box. This is a very fine industrial 12AX7 type, with the rare early longplates. Can withstand many on off cycles, and filament voltage variations, without any loss in output. Originally made for mobile communications equipment, they are super sweet tubes in guitar amps and hifi units!
$45.00