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The 6FQ7 / 6CG7 in the Audio Research D70

daveyf,

In my view, in buying the Audio Research D70, you've gotten one of the best audio bargains. Although I enjoy the extra power of it's close cousin- the D115, the D70 actually some things better- I can't think of a batter Chamber ensemble/Lieder amplifier- smooth, articulate, natural timbre, transparent- does everything well. I once thought of adding two D70 as L/R monoblocks to run the high and mid drivers of the Vandersteen 2C's and have the D115 work the woofers.

6FQ7's in the D70: In the last 10 years I bought quite a number of NOS tubes, but had neglected a couple of important types until nearer the end of the collecting, the 6FQ7's was among them. The D115 is my only use of this type (4 )

Rsearching the 6FQ7, it seems they were derived from the 6SN7. The 6SN7 was repinned, the bottle made more compact and to compensate fro those big, big plates proximity, an centre electrostatic shield was added between the plates- and it was called the "6CG7". Later, the shield was removed- cost reasons- and the 6FQ7 was born. You'll see tubes marked "6FQ7/6CG7" but the real 6CG7 has the centre shield.

In NOS, I often prefer to buy the earlier and/or military versions of tubes, and while I bought some CA 6FQ7/6CG7- “cleartop”, I concentrated on buying centre shield 6CG7's:

6FQ7/6CG7 (4) TOTAL: 9

5- RCA 6FQ7/6CG7- “cleartop” - NOS
4- RCA 6FQ7/6CG7- cleartop- TNOS

6CG7 (4) TOTAL: 51

13- RCA 6CG7- “cleartop”- center shield- US- NOS [5,8
5- RCA 6CG7- "chrometop" black plate, D gtr, cn shd- NOS [8, 14
1- GE 6CG7- center shield- NOS [5*
11- Omega by Hitachi- black plate- square gtr- cnt shd-NOS [3
2- Tung Sol- US- TNOS
7- Westinghouse 6CG7- blk pl, D gtr- NOS [1.5
8- Westinghouse 6CG7- blk pl, D gtr- Used? [1.5
4- RCA 6CG7- grey pl, halo gtr, cn shd- TNOS [6


The "[5,8" are the prices paid, so you can see this type was inexpensive 5 years ago!. The most unusual tubes are the Hitachi's. These are my only Japanese tubes and they are black plate with a square getter! I have no idea of their age.

-As time went on, I discovered there are special favourites among 6CG7s and the competitin was between the RCA 6CG7- “cleartop”- centrre shield- and the RCA 6CG7- top getter "chrometop" black plate, D getter, centr shd. There is also a TungSol camp, but the heavy favourites are the RCA's. I bought more of the "cleartop" version, but the sonic champ is supposed to be the black plate, D-getter "chrometop". I say "supposed to" as I can't say I've really evaluated this type. I only tried the cleartop in the D115 very briefly- too briefly really to comment. However, from that experience and reading a lot of opinions, I'm convinced one of the RCA's will do very well in the D115 and I believe that either should be quite nice in the D70.

The CAT SL1 at the time (1987) happened to be the only serious competitor to my beloved ARC SP10- the SL-1 is really outstanding. Bob Hovland thought the SP10 and the SL-1 were the two best preamps then as well. It is just brilliantly refined. I haven't actually heard of tube survivability issues with the SL-1 in the way the ARC SP10 and AI Modulus have become known. And, like your SL-1 experience, in 23 years of the SP10, I've never had a tube life problem except with briefly tried, experimental Amperex ECC88's.

You have very good taste in gear!

Cheers,

Bambi B



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