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Old 9th March 2004, 05:38 PM   #1
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Default 6SL7 or 12AX7 in Kimmel OTL

How do you guys rate the 6SL7 as opposed to a 12AX7?

Im thinking of using the 6SL7 inplace of the AX, in the Kimmel OTL, as the differential amp prior to the driver stages.

The drivers in the original were 5687, and in the text Ive read it mentions the use of the 6SN7 as drivers, so we should be OK here.

I would like to use the above tubes just because they look nice! More impressive than the B9A mini glass ones, but I have no idea what they sound like, although the 6SN7 appears to have a good name in this respect!

Thanks!!
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Old 9th March 2004, 07:38 PM   #2
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6SL7 is one of the all time best tubes in audio. They are used in many Cary and other well known tube amplifiers for good reason. It has mu 70, rp of 44K and will typically use a 120K plate load with B+ of around 320V. Typically this tube will give a wide, grand sound stage with a lush, beautiful harmonic spectrum. Lovely tube.

The 12AX7 is a washout by comparison. Mu is higher at 100, rp is 62.5K, but sound is only average by comparison.

Cheers,

Hugh
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Old 9th March 2004, 07:48 PM   #3
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Default 6SL7

And it looks much more impressive than the sometimes exceptionally overpriced 12AX7

Thanks for the much appreciated advice--Ill get hold of a couple, or four!-- Ive seen some for sale by KW Tubes on Ebay, at a very reasonable price! They are Russian, by the Reflector company, these should be OK shouldnt they?

I remember working on many P.A. amps, that were fitted with AX, and it was unusual to find one that wasnt microphonic!

Why then, does this tube have such a following?

guess fashon is fickle!
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Old 9th March 2004, 10:13 PM   #4
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Hi,

Quote:
I would like to use the above tubes just because they look nice! More impressive than the B9A mini glass ones, but I have no idea what they sound like, although the 6SN7 appears to have a good name in this respect!
As much as I prefer a 6SN7/6SL7 over any 12AU7A/12AX7A you're still stuck with the ECF82 and driver valves which are all noval...

Another point worth considering is that although the Russian equivalents of both the SN and SL are readily available, people still spend silly money on the NOS US ones...Why?
Do they really sound all that better?

I have never compared one to the other but I've heard various NOS 6SL7s and they seem to vary quite alot from batch to batch as well.
Just thought I'd let you know.

While I am a negative note (kidding) , of all the OTLs I've seen the Kimmel is certainly among the more complex ones.
If you're confident, go for it...
Me, I like the simple little gems.

Cheers,
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Old 10th March 2004, 04:05 AM   #5
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Are you talking about the Sweep Tube monoblocks? If so, I think these are far more complicated than necessary, could be simplified with nearly indentical results, and don't need the SS bootstrapping on the screens. MHO.
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Old 10th March 2004, 01:19 PM   #6
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Default Yes, Sweep/line o/p valve monoblock

I was thinking of using the 6SN7 as drivers after the 6SL7 diff-amps, but as you say, Im still stuck with the 6U8/ECF82 unless I could come up with some kind of replacement for the whole I/P stages, but Im not very confident of my tube designing to do this!!

As I have quite a few NOS ECF/PCF82/6U8/9U8, so these arnt a real prob. I was thinking of using a ECC91 for the first -I/P valve, I have some lovely Mullard NOS from the early sixties, in original "Master Valve" boxes--These are quite a good low noise common cathode double triode, and at this point in the circuit are not critical.
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Old 10th March 2004, 04:12 PM   #7
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Default Kimmel OTL

Forgot to mention, Ive simplified the design from construction standpoint, by making all the "bias cct" ( the main bulk of res and caps down the centre of the diagram) on a PCB, designed to run between the two sets of diff amp and dvr tubes, which are chassis mounted
This should simplify construction, and maybe a little time!
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