Hoffman Amplifiers Tube Amplifier Forum
Amp Stuff => Tube Amp Building - Tweaks - Repairs => Topic started by: Heph333 on May 02, 2019, 01:02:29 pm
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I would like to build a bedroom volume power amp for my Bogner Ecstasy clone preamp. It's currently in front of a 6L6 LTP power section & is the greatest sounding amp I've ever played, but is ungodly loud. I want to keep the tone as true to the original 100B amp as possible, so that means LTP PI into pentodes with NFB. Plus I have an empty JCA custom5 headhsell that needs something in it asap.
I like Bancika's 3 watt 6ak6 design here: http://diy-fever.com/amps/3w-tube-power-amp/ I especially like the biasing design that should emulate fixed bias. I would convert to LTP.
My question: is this the best & lowest wattage design to accomplish my goals? (barring the use of obscure rare tubes). 3 watts is a bit loud, but 3 watts is a lot easier to attenuate than my current 50 watts.
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This might not meet your "no obscure tubes" criterion, but there are some 3 watt PP amps on the Dvnator web site, based on the Russian 6f4p tubes. I tracked down some 6F4P tubes and plan to try one of his designs.
http://chasingtone.com/dvnator/category/6f4pamps/ (http://chasingtone.com/dvnator/category/6f4pamps/)
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6F4P aka ECL84 - 6DX8 - 6DQ8
https://tubes-store.com/product_info.php?manufacturers_id=46&products_id=701 (https://tubes-store.com/product_info.php?manufacturers_id=46&products_id=701)
Franco
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Some threads on the SoLow Watt amp design using ECL84 for 3-4 watts:
http://el34world.com/Forum/index.php?topic=13438.msg127145#msg127145
http://el34world.com/Forum/index.php?topic=13151.0
With respect, Tubenit
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AND we have in the SCH Library of Information an entire thread on low watt push/pull amps. Special thanks to Pete (Dummy Load) for his contribution to that thread. You may find some pp power sections in that thread that would work.
http://el34world.com/Forum/index.php?topic=12526.0
With respect, Tubenit
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And on this thread on the AmpGarage a builder named passfan built a SoLow Watt using ECL86 6tubes and did a great job with it. Look at the 2nd page of that thread.
https://ampgarage.com/forum/viewtopic.php?f=6&t=17599&hilit=SoLow+Watt&start=15
With respect, Tubenit
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As far as common tubes I would say find a pair of nos rca 6K6. They sound crisp and clear, more like a 6L6 than a 6V6 but not as nice of bass resppnse as a 6L6 and half the wattage of a 6v6. The only thing is you may have to watch the voltage and drop it below what you are using on the 6L6s.
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3 watts is a bit loud,
from the original post
vs.
pair of nos rca 6K6
is going to be maybe 6 to 7 watts? ( I have a pair that I use occasionally)
With respect, Tubenit
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It looks like It really wouldn't cost much more to build for 6V6. With VVR & adjustable bias, I could run 6G6 but have the extra watts should I ever need it. The Hammond 125E looks like it has enough secondary taps to where I can have 22k, 11k and 5.5k primary impedance just by switching jacks. And it's only $3 more than the 5w OT.
I could build the VVR as a 3-way toggle to select for 6V6, 6K6, 6G6. I'll need it anyway to avoid starving the preamp when using 6G6. Then use PPIMV to get it to bedroom volumes.
And coke bottles are cool.
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Another way to reduce volume is reduce voltage. Instead of a 300-0-300 Or whatever look around I have gotten stuff out of old radios that are like 230 -0-230. Also you can use a isolation transformer with a bridge rectifier and get around 170 volts b+ and just use a 6.3v 2a filament transformer for your 6.3 and those can be found for pretty cheap. Then you get less power out for lower volume. If you have a variac you can use it to lower the power output. Occasionally I have done this and put 80 or 90 volts on my pt primary instead of 120v so that 30 to 40 volts less . It take a few seconds longer to warm up because instead of whatever you need for filaments it may be 5.7 volts I stead of close to 7 which is normal @120v . This makes a good 20% reduction of volume.
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If there's anyone else in your bedroom, then no wattage is low enough. In my experience, if my playing can be heard at all, it's too loud. If it can't be heard, then the sound of the pick on the strings is too loud. If I don't use a pick, then the sound of the fretted strings is too loud. If I don't play it at all, then it's visually too loud, as in: what's it doing taking up space in the bedroom?!?
Anyway a Champ @ 3 -5W is loud enough to annoy the neighbors.
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I just remembered about this ( two 5902 as power tubes)
https://jjs.at/electronic/class_ab_subminiature.html (https://jjs.at/electronic/class_ab_subminiature.html)
Franco