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Old 16th July 2012, 07:34 PM   #191
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Yes - a real sleeper tube. Listen to it and all those uber-expensive 12AX7s and 6SN7s and those Telefunken tubes with diamonds on the bottom start to look pretty silly.

Ale - yes there's a 126B. Twice the current and half the inductance. They're both single ended, and really good quality and value. Another sleeper.

What I've noticed with this 4P1L preamp is that it is absolutely the best ever for jazz. The double bass is solid and clear and the drum kit has to be heard to be believed - snare drum, brushes, floor toms, hi-hat, ride and crash cymbols. It's really, really lifelike.

Andy
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Old 16th July 2012, 07:40 PM   #192
mogliaa is offline mogliaa  United Kingdom
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I'm glad you like it. If I look back when I started the 4P1L preamp thread, there were a lot of discouraging comments about the microphony of it, but few comments about its sound. When I built it got very impressed with its sound. I listen to Jazz most of the time (e.g. Coltrane, Monk, Davis, Rollins, etc.) and is definitely a great one. With its low anode resistance (like the 71) and current capability it's great with a gyrator load.

Will buy a pair of IT and try them out as well!
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Old 16th July 2012, 08:56 PM   #193
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Are you thinking of getting the 126b or 126C? There may be arguments for either. Would be interesting to see how the 126B works. It would probably be good for a driver stage into outputs. Think about using filament bias though!

Andy
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Old 16th July 2012, 09:38 PM   #194
316a is offline 316a  England
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Originally Posted by mogliaa View Post
there were a lot of discouraging comments about the microphony of it,
I did a 4P1L---4P1L SE DC coupled amp which suffered quite bad microphony , if the chassis was tapped there would be a noticeable 'poing' that lasted a few seconds , sometimes when I hit pause there would be a bit of a poingy sound too . I find as output stages microphony is fine but as linestages microphony poor although I do use 98dB speakers so just about any hum/buzz/filament clanging comes through . Running the fils under 4v seemed to help a little to tame the microphony

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Old 17th July 2012, 07:55 AM   #195
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I thought you were still using this amp, maybe in a second system? I can't remember where you are with speakers - last I heard were treble horns and big bass units, so I can believe you need to take extra precautions with your amps. My system is quite benign - Mark Audio Alpair 10s. They're like Jordan JX92s but better, smoother and more musical when used full range. My chassis all have 4mm alu top plates so quite massive, and my room is carpeted, so I get away with quite a lot as regards microphonics. I even had a 1G4G preamp for a while, and that takes some doing. That rang like a bell in other people's systems.

So, depending on the system, 4P1L preamps are not impossible with starved filament. Did you find some of the tubes were more microphonic than others? Maybe selecting them helps?

Andy
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Old 17th July 2012, 08:52 AM   #196
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Hey Ale,
At what load did you get the sweet spot?
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Old 17th July 2012, 02:06 PM   #197
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Andy,
Sounds a very promising setup. Keen to see your results!
I'd rather run the 4P1L at above 20mA of anode current. That is where it performs the best.
Hi - I have been reading this thread with great interest. What would be the Rp at this operating point?

I am thinking of trying out the 4P1L as a driver for my SE 45 amp with an interstage transformer. I have a couple I can choose from. I may try it with these:-

Valve Transformer VT1399

Martin
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Old 17th July 2012, 05:46 PM   #198
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Originally Posted by Deco-Doctor View Post
Hi - I have been reading this thread with great interest. What would be the Rp at this operating point?

I am thinking of trying out the 4P1L as a driver for my SE 45 amp with an interstage transformer. I have a couple I can choose from. I may try it with these:-

Valve Transformer VT1399
If you can get 2W from 4P1L driver that means can get enough of voltage swing to drive 45 tube for 2W of output power.
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Old 17th July 2012, 06:48 PM   #199
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If you can get 2W from 4P1L driver that means can get enough of voltage swing to drive 45 tube for 2W of output power.
OK I take your point, but my question is what is the plate resistance of a single 4P1L at the chosen operating point?
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Old 17th July 2012, 07:02 PM   #200
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Deco-doctor

Have a look at the 126B and 126C at Bluebell Audio - look at Transformers > Interstages. They are exactly the same price as Danbury and probably at least twice as good. Also they are bifilar wound and have a known and stated inductance. Philip at Bluebell is very helpful and knows his tubes.

As for the current to run through the 4P1L, I was shocked to find that in my 4P1L preamp with filament bias I was running less than 2mA through them. I still haven't got to the bottom of why the current doesn't agree with the curves. Anyway, I actually like the sound at low currents - it has thinner mids and more apparent treble but it's very clear. 7N7 who is also working on this project prefers the sound at higher currents because it's fatter in the mids. I use the 126C and I want to set up some kind of rig where I can vary the current through the 4P1L as I listen to it. I'd like my ears to have a say in this, even though the results may be counter-intuitive.

Andy
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