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I am interested in Audible Ilussion 3 pre amp. How ever I would like to use 6SN7 tubes. Is there a convertor available that can do that? Will the pre amp be able to take advantage of the 6SN7 specs???
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Why?
If - as has been suggested elsewhere in this thread - you want the 'sound' of the 6SN7 - try the DeHaviland, or the MFA pre-amps - The MFA may be a bit more 'related' as the M = Bruce Moore, the orriginal designer behind the AI pre-amp.
some other bits to consider vis the AI modification that you are proposing:
the 3a has a double sided PCB, so the utilization of the traces from the 9 pin to the octal will present an additional challenge, especially if you cut through the PCB -
I am pretty sure that unless you mount the tubes horizontally they will not fit in the chassis - and that may only work for the Phono section - the stack-o-caps in the line stage is physically large...
The RIAA curve is an active circuit - calculated around the gain of the 6DJ8/6922, so you will need to re-design that portion also.
Be careful using the tape loops after your mod - they are rather unique with their own drivers - and again the different output from the 6SN7 may create some havoc.
While the Outboard PS could probably deliver more (current) you would want to look at the umbilical cord if you change the voltages or regulation.
just a few things to keep in mind -
"acid is like jet fuel for the mind, though some have volkswagen engines..." Jerry Garcia
correct-a-mundo!!!
What is your goal i.e. likes/dislikes of the 6922?
Perhaps some details from you and we could shed some light on said issues?
tz7 hi,
Aside from an overhaul of the circuit, the AI's heater supply would not support the 6SN7's heater current load. It's 2x that of a 6922.
The AI in stock form, only hits around 5.8V on the heaters w/four 6922s.
Cheers,
Wheeze
Besides other issues, the 6922 has way more gain than a 6SN7. Try old RCA label 6922 with gold pins. The tube is marked Made in Germany and should have black ink stamp Made in Germay on box too. These are Siemens 6922 and reported to have the .028" grid that is same as the Cca.
What you want to do really can't be done without totally re-working the circuit(s). You'd end up with a different preamp. Take a look at the deHavilland UV3. It uses a single 6SN7 input tube + 6AH4 cathode follower. The sonic character is most affected by the 6SN7 one uses, but in general a vintage 6SN7GT to your liking will give you the tone you want without sacrificing dynamics. Use a good 5U4GB to get good bass, like the Japanese tube (mine are branded Raytheon).
Observe, before you think
What tone are you after? Maybe, coupling cap and altering the plate voltages, idle bias, and feedback could get you close to what you want. Without going to another gain stage tube. And an octal, at that.
If you are set on the 6SN7 tone --- perhaps think of the 6CG7. At least you'll keep the same footprint on the chassis.
Wheezer and Chris O make a good point in regard to the heater current which a couple of us overlooked and it applies equally to 6CG7. Many manufacturers overate their heater supplies by 100% plus but I know Wheezer has extensive experience with AI and Chris probably does too so I'd heed their advice.
Naz
and are generally good sounding tubes. Often they can be a drop in replacement for 6922 although the operating point should be checked and tweaked as required.
Naz
The Elaborate DAC=Johnny's Balloon Meshplate 27 Balanced Preamp=Balanced Six Pacs=Newform Research 645
iRiver H140/MB Balanced dac/amp/Ultrasone Ed. 9/JH13 Pro IEM's
see images at: www.pbase.com/jamato8
optimum circuits for each after extensive listening. I would prefer, do prefer, the 6DJ8 family for transparency, imaging and detail.
The Elaborate DAC=Johnny's Balloon Meshplate 27 Balanced Preamp=Balanced Six Pacs=Newform Research 645
iRiver H140/MB Balanced dac/amp/Ultrasone Ed. 9/JH13 Pro IEM's
see images at: www.pbase.com/jamato8
The 6SN7 pulls twice the heater current and has different bias voltage requirements and will pull more plate current when operated properly.
Tubes are not just interchangeable.
:-)
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