The search for 12FQ7's

joerest · « **on:** 12 Aug 2014, 06:08 am »

Looked into the old tube cabinet and found only 3 12fq7's left. They were cleartop Philips made in Italy. Well
in a short time they all went bad. For some reason the tops turned pure white. Looks like air infiltrated into the tube. Later found out that this $9.95 tube is selling for $30 by quicksilver's own mike sanders. I ordered some from internet vendors only to find they were all out of stock. My preamp was looking obsolete at this point. A very good friend knocked himself out and acquired some for me through eBay. Thanks pal-of-mine. We'll to make a short story long, one of the eBay tube is a very old magnavox, claiming to be NOS. Put it in the line stage of my full featured Quicksilver (over 25 year old ) preamp, and was flabbergasted. 'The 12fq7 is not a critical tube in this preamp and yet it was like hearing it for the very first time. This tube is nothing short of magic. It is somewhat old-world sounding, yet with loads and loads of extension and detail. It reminds me of my father's old magnavox console, I grew up with. After 45 years in this hobby I am still learning stuff. That's why I am addicted to audio. Thanks for reading. Joe.

tonyptony · « **Reply #1 on:** 12 Aug 2014, 03:49 pm »

I wonder where else the 12FQ7 was used? Given how infrequently it's mentioned on the various sites it seems like a tube that didn't make its way into a lot of audio designs. I could be wrong, though. It certainly seems to get the job done as part of a good design. I've heard the Quicksilver FF preamp and it is a thing of beauty.

From what I understand there also isn't a one for one substitute for the 12FQ7.

Steve · « **Reply #2 on:** 13 Aug 2014, 12:38 pm »

I have over 500 tubes with lots of audio tubes, a full caddy with new "tv" tubes, worked in tv repair part time back in the late 70s, and I do not believe I have ever used a 12FQ7 tube. There are plenty of 6FQ7/6CG7 tubes though.

Cheers

Steve

tonyptony · « **Reply #3 on:** 13 Aug 2014, 02:48 pm »

That's really something, Steve.

joerest · « **Reply #4 on:** 14 Aug 2014, 02:39 am »

Dear Steve. Good to hear from a tube professional. I was getting excited there for a minute thinking you had loads of 12FQ7's.

Was able to locate 2 12FQ7's for 5 bucks apiece. One is a Sylvania made in USA (real nice) and the other is a crappy international service master. I have a personal theory of these international's but really don't know anything about them. Except they mostly don't work out of the box. Does anyone know about these tubes? Are they basically factory rejects? Any background would be appreciated. Joe.

Steve · « **Reply #5 on:** 14 Aug 2014, 07:41 pm »

Quote from: joerest on 14 Aug 2014, 02:39 am

Dear Steve. Good to hear from a tube professional. I was getting excited there for a minute thinking you had loads of 12FQ7's.

Was able to locate 2 12FQ7's for 5 bucks apiece. One is a Sylvania made in USA (real nice) and the other is a crappy international service master. I have a personal theory of these international's but really don't know anything about them. Except they mostly don't work out of the box. Does anyone know about these tubes? Are they basically factory rejects? Any background would be appreciated. Joe.

Hi Joe,

They are rare, as the RCA tube manual does not list a 12FQ7, just an 8FQ7/8CG7 and 6FQ7/6CG7. Evidently, only one or two
manufacturers may have produced them. I have one 8FQ7 and a couple of 6FQ7s if there is some way to use them.
I also have a couple of 12BH7s, which is close to the 6FQ7/6CG7 tubes.

Filament would be the same, Mu is 16.5 for CG vs 20 for FQ. Transconductance is quite close. Plate dissipation is slightly greater for
both sections than the CG. For one section, the same. If you are interested, PM me.

Cheers

Steve