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Tuner fix tricks- 6AU6 picks for kicks?

Posted by Bambi B (A) on November 30, 2006 at 16:37:15

Mates,

In my tube collecting quest- I use 132 tubes of 31 types, I feel I'm winding down the tube collection - now about 500 - I realised that the 6AU6 is actually one of the tubes I use most of:

12AX7= 2, 2, 3, 3, 4, 8, 6, 1, 3 = 32
6922= 2, 4 low noise, 8, 3 = 17
6AU6 /6136/ EF94 = 1, 3, 4, 3 = 11
6550 = 8, 1 = 9
12AT7 = 1, 1, 1, 2, 2, 1 = 8
12AU7 = 1, 2, 2 ,1 = 6
6U8 / ECF82 = 3, 1, 1 = 5

-and so on,.. down to the types occupying 4, 3, 2 and 1 spots.

-11- 6AU6s in 4 pieces of equipment: McIntosh MX110 (1) and MR67 (3), Scott 330D tuner (4) , and Fisher 800D (3).

Eleven tubes of a kind seems like a lot- and I should be taking this type seriously. However, I feel I know really nothing about the 6AU6 and yet in five years of general ignorance I bought quite a few of this type- almost 60:

3- RCA- black plate-US- NOS
3- Tung Sol- black plate- NOS
1- Mullard 10M EF94- gold pin- UK- NOS
5- GE-grey plate- US- NOS
1- Telefunken square gtr- USED
2- Harmon Kardon/ Amperex sq gtr-USED
1- Eico/ Mullard- USED
1- GE 6136-USED
1- NEC 6136-USED
1- Valvo EF94- Holland -NOS
8- Telefunken EF94 by RCA- Brazil- NOS
5- GE 6136- 5 Star- blk pl- halo- US- NOS [$4
5- Sylvania 6136- “Gold Brand”- gold pin- US- NOS [5
12- Sylvania 6136- “Gold Brand”- steel pins- US- NOS [3
8- RCA 6136 - Command- US- NOS- [3

These purchases were based on scant comments, brand loyalty- and trying to use the premium, military version- whenever possible which for the 6AU6 is the "6136". It's a bit arbitrary, but when I saw a very few gold pinned versions, I assumed these were at some higher standard and bought those to try. I have Sylvania Gold Brand with both gold and steel pins, plus there's the single gold pinned Mullard 10M EF94.

The 6AU6 is a 7-pin "sharp cutoff pentode"- sounds a bit like a grounchy Pentagon spokesman- and beyond the fact that 1: they are tubes filled with a mysterious metal cylinder, 2: if you have about any kind of tube tuner or tube receiver- plus some ham and table radios, you'll be seeinga lot of these, 3: They must last forever- I've never actually had one go bad, even the 40+ year-old ones, and 4: the lasting forever means the very best ones are still very inexpensive- notice in my list, the last 4 listed cost $3 to $5 each. The average cost has actually been under $3 each and even though the 6AU6 started being made again since I started buying- the best NOS are still cheaper than the new ones.

So, I use a lot of this type, but have the vaguest notions:

What does the ubiquitous 6AU6 do for a living? Is for example "IF Limiter" respectable work?

What makes a good 6AU6 ? Are there sonic properties at work?

Have a favourite 6AU6- and why?

TA!

Cheers,

Bambi B

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