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Ideas for a low power amp that is bigger than a flea amp. 5-10W out?
Ideas for a low power amp that is bigger than a flea amp. 5-10W out?
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Old 27th June 2019, 04:02 PM   #11
Guerilla is offline Guerilla  Denmark
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I would search posts by a member called eli something. Never heard his designs but he is so convincing when helping others that I would like to make one of his builds. Seems also that he is trying to make stuff cost-effective
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Old 27th June 2019, 04:12 PM   #12
huggygood is offline huggygood  France
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el cheapo
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Old 27th June 2019, 04:27 PM   #13
Lingwendil is offline Lingwendil  United States
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Quote:
Originally Posted by kodabmx View Post
I considered using 6P1P which is 6V6 in a 9 pin bottle with a bastard pinout but for another 3 watts of heater, I can use 6P43P and get twice the power.

A transformer PI is a good idea, but I don't have any. I have small toroid power transformers, but I'm read that they have fairly high capacitance and need to be "driven".

So right now, I'm thinking 6F12P VA/PI driving 6P43P in triode. 3K RLa-a. 280V or so. Biased at 20mA to start and see how it performs biased that cold.
I'll be using SS rectification for sure on the power stage, and a CLC filter.
The heaters will be AC from a 30VA transformer (which co-incidentally just happens to be how much heater power the tubes need, and an SMPS for a DC converter for the 380V I use for the VA/PI. Might use another for bias voltage, might use a transformer. Not sure yet
Sounds like a solid plan. That reminds me I need to get back to that driver board PCB for you. Last time I was messing with it I wasn't very happy with how I placed and routed everything, so I might spend some time with a pencil and paper before going back to it.

Do you have any UL transformers? With such nice triode curves I wonder how the 6p43p-e would handle it.
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Old 27th June 2019, 05:42 PM   #14
kodabmx is offline kodabmx  Canada
Affordable triode connected sweep tube amps.
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Ideas for a low power amp that is bigger than a flea amp. 5-10W out?
I do, but they are in use...

Here's the build so far... The goal is also zero cost. I'm not spending anything to build this hence the reused chassis. There's no wiring yet but it looks the part anyway
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Old 27th June 2019, 06:41 PM   #15
kodabmx is offline kodabmx  Canada
Affordable triode connected sweep tube amps.
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Ideas for a low power amp that is bigger than a flea amp. 5-10W out?
And here's the schematic I'm building:
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Last edited by kodabmx; 27th June 2019 at 06:51 PM.
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Old 5th July 2019, 08:46 PM   #16
kodabmx is offline kodabmx  Canada
Affordable triode connected sweep tube amps.
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Ideas for a low power amp that is bigger than a flea amp. 5-10W out?
Ok so I'm finished building and testing it.

I made some tweaks to the design and attached is the new schematic.

It draws 103W from the wall which is close enough to 100W for me.

B+ is 320V, biased at 35mA/tube. For that current, the bias is about -50V

1V in for 2.8V out into a 6R load.
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Last edited by kodabmx; 5th July 2019 at 08:49 PM.
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Old 5th July 2019, 10:50 PM   #17
wiseoldtech is offline wiseoldtech  United States
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Quote:
Originally Posted by kodabmx View Post
Ok so I'm finished building and testing it.

I made some tweaks to the design and attached is the new schematic.

It draws 103W from the wall which is close enough to 100W for me.

B+ is 320V, biased at 35mA/tube. For that current, the bias is about -50V

1V in for 2.8V out into a 6R load.

WOW! - 103 watts AC draw?


I've got an RCA Victor stereo console with 18 tubes (AM/FM tuner/Preamp and stereo PP power amp with 5AS4A rectifier) that only draws 180 watts idling.
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Old 5th July 2019, 11:45 PM   #18
kodabmx is offline kodabmx  Canada
Affordable triode connected sweep tube amps.
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Ideas for a low power amp that is bigger than a flea amp. 5-10W out?
This one has three power transformers, three SMPS, two DC boost converters, 6 heaters, VA/PI. This takes 48W. The power stage plate circuit takes the rest and will use more at full volume. Plus, it's almost 15WPC RMS sine in triode mode, and about 5WPC within class A. :P

FWIW my monoblocs both idle around 230W each. 6 tubes in there as well, but just the output stage uses 60W of heaters and 140W of plate. The rest is VA/PI, the SMPS and boost converter that drives it, and the driver stage. They put out 110WPC, 22W class a limit. My preamp uses 65W now, and has 8 tubes including line stage, two buffers, a dac, bluetooth, and electronic relay volume and input control. It runs from a 12V SMPS feeding several boost converters.

On the bright side, it only draws 0.3W on standby. It has feather touch power control, too.

Last edited by kodabmx; 5th July 2019 at 11:57 PM.
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Old 6th July 2019, 05:25 PM   #19
Lingwendil is offline Lingwendil  United States
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Cool, those suckers sure do need a lot of grid drive for what they are at that operating point. How's it sound? What's the power output?
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Old 6th July 2019, 05:37 PM   #20
kodabmx is offline kodabmx  Canada
Affordable triode connected sweep tube amps.
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Ideas for a low power amp that is bigger than a flea amp. 5-10W out?
Sounds really good actually. It's even still clean when turned out loud enough to drown out the A/C

As for power output, I didn't really test it, but it was still looking good with 5V drive. 5*2.8=14V into 6R. This implies 30W or so but I find that hard to believe. They usually put that kind of power out as pentodes, not triodes LOL Although it also could be my disregard for datasheet maximums... The 3k Ra-a load line goes well into the point of exceeding max Pd
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