low watt tube suggestions

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jckid66
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low watt tube suggestions

Postby jckid66 » Sat 01/01/11 7:35 pm

Hi All,
I am looking for low power tube ideas for a TMB I have heard of a 12au7 but I am curious about others like 6sn7 , I am open to any ideas


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NOGE
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Postby NOGE » Sun 01/02/11 3:35 am

I tried 12AU7, 12BH7 and 6SN7 in a Lite 2B style amp and was very disappointed. None sounded as good as my Lite 2B with VVR. I can get lower saturated volume with VVR as well. 12AU7 is still loud enough to get complaints from the neighbors.

12BH7 sounded marginally better than 12AU7. 6SN7 was a lot better but still not as nice as pentode distortion. Just my .02.

The Moonlight Amp by Simcha Delft uses a 6SL7 as a PI into a 6SN7. It's supposed to sound pretty good but I've never heard one. Maybe that's a better combination than a 12AX7 PI into a 6SN7.

I'm going to stick with VVR and EL84's
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Postby katopan » Sun 01/02/11 11:19 am

+1 To some people triodes in a push-pull output stage sound fine, but to me because the 18 Watt topology relies so much on output stage distortion (including the TMB) and the triodes made it sound harsh, not the smooth distorted tone I was used to from the full size version. I was using a 6SN7 in my 1.8W build. After that I changed tack and went with submini valves and got an amp I've been really happy with.
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Postby jckid66 » Tue 01/04/11 5:59 pm

I would be very interested in schematics
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katopan
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Postby katopan » Mon 01/10/11 4:45 pm

Sorry, took a while to get back to replying....

See the links in this thread for the 1.8W:
http://www.18watt.com/modules.php?name= ... ic&t=23753
The links ZP posted show the schematic and a sound clip. The thread Deric posted the link to used to have all the info you need but with past hacking of 18Watt.com all the attachments are lost. But the layout is the same as a Lite IIb except for the connections to the power valve and no screen supply. When I built mine I "corrected" all the component values back to a Lite IIb (all PI resistors back to standard, removed 1M master volume & put the power grid leak resistors to ground back to 470k). Found the PI overdrove the power stage too much (6SN7 or 12AU7 even more sensitive than EL84s). Changing the power grid leak resistors down to 100k fixed this, and I changed the PI to power stage coupling caps to 47nF to keep the frequency response the same. Alternatively you could use split plate resistors on the PI and keep the 10nF/470k standard as per the full size 18 Watt.

If you were building a low power version of an amp which used a clean power output stage then a 12AU7/6SN7 in push-pull would work really well. Of course we couldn't talk about that here, but would have to take it over to the Wattkins Forum.

The submini Superlite TMB is here:
http://www.18watt.com/modules.php?name= ... bminiature
Once again all the attachments are gone but I have the schematic, photos, etc here:
http://chosenaudio.comfypage.com/4.htm
As you can see in the thread thegman (Matt) tried building one but had troubles with hum that we didn't end up resolving. The submini's are more susceptible to heater hum and we didn't ever hear back whether a hum balance pot fixed his problem. I still use mine all the time and have had no problems. But it is one of a kind.
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