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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- [3These 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
Follow Ups:
Look into Singlepower headamps and preamps. Just 3 tubes, but types of tubes that can be used in their high-end amps in various positions (with adaptors to fit 6SN7 sockets) include: 6sn7(gt, wgt, gta & gta, etc), VT-231, 5692, 7n7, 7af7,CV1988, 5692, B65, 33s30, ECC32 / CV181, ECC33 / CV2821, 6cg7, 6gu7, 6fq7, 12au7, 12av7, 12ay7, 12bh7, 5965, 5814a, 6085, 6189, 6414, 6829, 7062, 7119, E180cc / 7062, 5751, 12at7, 12ax7, 12az7, 5687, 7044, 7119, 6900, 6bl7 (gt, gta, gtb), 6bx7, 6su7gty, 6N1P, 6BZ7, 6DJ8,.....This is a short list. Go to Headfi and look for the thread on "SDS, Supra, MPX tuberolling, the new global, improved thread"
anyone modified any XM/ Sirius gear for usage of tubes.???This is crazy, but of course I haven't searched first, but unfortunately I can't listen to FM anymore: too many commercials, except of course for the occasional good FM classical station.
However XM has so much good stuff.
Peace, aned I will search other forums now.
Peace,
Peace,
Peace,
-3db
The 6AU6's job is to amplify like crazy. The last tube in the IF strip's job, the limiter, is to drive the signal into hard clipping. In FM, clipping is a good thing! The linearity of this tube matters little in FM RF work--just amplify like crazy. I would be surprised if there is a sonic difference between 6AU6s in FM RF work. I would use the cheapest available for that application.
When I worked on my MR67 the biggest improvement in sound came by replacing the lytic caps under the chassis with film/foil or metallized types. Whatever I had on hand. If I remember correctly there's a couple of caps hidden under one of the front panel controls.
Just a thought rather than going the tube rolling route in a tuner.
DaveV,I believe I'll be doing the capacitors as well as the tubes. My MR67 has a problem in which I think the two tubes on the MPX decoder- 12AU7 and 6U8, are being driven too hard. These tubes appreared to be new when I bought it and soon developed burn spots in the flashing. Resistor, capacitor- RF emspitzeratoriser- who knows?
As the signal meter is sticky, no alignment for no one knows how many decades, mostly original tubes, the hot running MPX tubes, I'm planning a whole going through with caps, resistors, alignment, and all new tubes. This all may make this close to a $900 tuner, but after 20 years use with the inflation in McIntosh tube tuners, I anticipate the value around $901 and I'll have used the thing for free!
I find the sound of the MR67 to be just fantastic- nearly unbeatable FM- if reception is solid enough. I'm convinced the MR67 bests the MR71 sonically- I don't know why. With luck, this tuner will last the rest of my life- or at least until the end of analogue broadcasts in 2009.
BTW, What do/did you use for the 6U8 in your MR67? Modaferri suggests to use the ("higher gain") 6GH8A and I've also read that the 6BL8 is the thing. If the 6BL8 is best, I have an odd-out Amperex PQ 7643 (E80CF or 6BL8). I'm curious as to the relationship of the 6BL8 to 6U8- interchangeable? Also, I bought some Amperex (Philips, France) 6GH8As and these appear to be identical to the original "McIntosh by Amperex ECF80's- 6BL8s which are also Philips, France. For 6U8, I have these attractive Sylvania Gold Brand "GB-1252"/6U8As plus a couple of 6678s. So, 6U8 or 6GH8A or 6BL8 ?
Thanks!
Cheers,
Bambi B
To be honest I haven't used my MR67 in years because I found it difficult to find broadcasts that sounded good enough for me to want to sit down and listen to. Had I roof mounted my NOS Finco FM-4G antenna maybe it would have been different? Now that I'm out of the NY Metro area there's even less reason to listen to FM because the station choices in my area of SC are grim in my opinion. My FM experience now is with a Pioneer Receiver that serves only as background music when I'm puttering around the house. I stuck with the tube numbers marked on the MR67 chassis and never tried alternates. The MR67 is a good tuner but I thought my Citation lllX sounded better. My MR sounds too full for my taste, like too much bass overlay where the lllX has a brighter more open sound. Could be the different de-emphasis circuits in play but because FM broadcasts have gone downhill so much over what they were 30 years ago I gave up on trying to have FM sound I can really enjoy and all my efforts go to the enjoyment of LP's. I was never fully up on the interchangeability of 6U8, 6BL8, 6EA8 and 6GH8. I went thru that with a couple of Scott integrateds I have and I never reached a conclusion.
Seems that Scott was good at changing the tube numbers in different production runs of the same model. Maybe it was a price and availablity thing with them?
Bambi,The 6AU6 is the CLASSIC IF amplifier in VHF receivers. It was made in the billions. Not only did tube FM tuners use them in their IF strips. The 6AU6 could be found in the IF strip of virtually every TV made until the 1970s.
You have some collection. It's no secrect I like RCA tubes. So, I'd keep them. I also like TungSol. There are 2 sets of T/S 6AU6s in my stash, destined to go into a McIntosh MR71.
JMO, sell the Sylvanias and sell that Mullard for all that the traffic will bear.
IIRC, you are not keen on DIY. However, with some tweaking, the 6AU6 can be a pretty good audio pentode. The 6AU6 also serves well as an active load for a cathode follower.
Eli D.
Eli Duttman,Good to hear from you.
The collection: Yes, I never intended to end up with so many 6AU6's- it's a case of realising I used quite a few, but also that they're so inexpensive- the Tung-Sols cost I think less than $1 each. The "Telefunken" EF94s are relabelled RCA, Brazil- and $2 each. The boxes, by the way, are old and several still had a cellophane wrapping, so I wonder if Telefunken bought and boxed RCA, Brazil output. Seems unlikely, but a $2 each I felt I couldn't go wrong- as a curiosity. Plus, Telefunken did relabel and box late GE 6201s as Telefunken.
I'm interested in your comment vis a vis RCA vs. Sylvania. All this 6AU6 interest is related to my complete retubing of the MR67 tuner. I was sort f set on using the Sylvania Gold Brand gold pin 6136. Did I simply fall for the cheap glamour of gold pins? -I am certainly a fan of RCA as well- I have new respect for the Command 5814A for example and I like a lot of there other tuner tubes- 6AV6, 6CS6, and am open to the possibility of using RCA "Command" 6136. I thought the Sylvania Gold Brand 6136s were just interesting- again a gold pin premium and steel pin military version seems as though it should be a high performance machine. This was interesting too in light of the Sylvania Gold Brand "GB-1252" that appear to be a premium, gold pin consumer 6678 or military grade 6U8A.
What makes a 6AU6 a good one- a high performer? What do you like about the RCA?
DIY: When I was poking around trying to learn something about the 6AU6, I came across someone who had designed a 1.5W integrated SET amplifier using the 6AU6 as a triode gain device- wiring across sections I think- and I forget the output tubes- -or were those the drivers- 12BA4 or some such. I'm always interested in this sort of project- giving new exciting work to ubiquitous tubes!
May I ask what tubes you're using or planning for your McIntosh MR71?
My MR67 choices:
McIntosh MR67
3- 6AU6> 1st, 2nd IF / 1st limiter :Sylvania Gold Brand 6136- gold pin -NOS
GE 6136 “Five Star”- grey pl halo- NOS > The original “McIntosh” 6AU6s are GE
RCA "Command" 6136-NOS2- 6BL8 > L&R audio amplifiers:
Valvo E80CF / 7643- Philips/Hamburg- red label, military label- pinched waist- gold pin- NOS
12AU7 > MPX oscillator :
Siemens 5814A triple mica- test NOS
CBS 5814A, black plate- square gtr- test NOS,
RCA ‘Command’ 5814A blk pl- halo gtr- NOS
Valvo 6189- RTC- France- dbl getter sup- NOS12AT7 > 2nd RF amplifier, mixer:
Sylvania Gold Brand, gold pin 6201- NOS
Siemens triple mica E81CC-NOS6DS4 > Nuvistor 1st RF amplifier:
Amperex- NOS
6AB4 / EC92 > Oscillator
Telefunken EC92- Germany- NOS
6CS6 /EH90 > 4th IF, 2nd limiter:
Telefunken EH90- NOS
6U8 / ECF82 > MPX amplifier:
Sylvania “GB-1252"/ 6U8A - Gold Brand- -grey pl- halo- gold pin- NOS > I’ve never seen this version before
Sylvania 6678- “Communications Quality”-grey pl- halo- NOS > These appear to have identical construction to the “GB-1252", only without the gold pins
RCA - 6U8A- black plate- stirrup getter- NOS6GHA [for 6U8] > MPX amplifier:
Amperex 6GHA- orange globe label- France- NOS > Modaferri recommends the higher gain 6GH8A in place of the 6U8 in MR67 .
6BL8 [for 6U8] > MPX amplifier:
Amperex PQ 7643- Hamburg- gold pin- NOS > I’ve also heard of people using the 6BL8/ECF80/E80CF for the 6U8. What do you think?6AV6/EBC91 > Muting amplifier:
Telefunken EBC91
Cheers,
Bambi B
RCA and GE are the only 6AU6A tubes I've compared but I found rhe RCA samples to be much less microphonic. As Eli says, this tube in pentode mode makes a good CCS in the tail of an LTP phase splitter - that's what I mainly use it for. I've also found that it's a good linear audio amplifier when strapped in triode-mode. I believe it's also a good AF amplifier in pentode mode but I've never tried that.
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