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Tubes / Valves All about our sweet vacuum tubes :) Threads about Musical Instrument Amps of all kinds should be in the Instruments & Amps forum

Need 3-5W tube amp
Need 3-5W tube amp
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Old 5th January 2019, 06:12 PM   #11
Diabolical Artificer is offline Diabolical Artificer  United Kingdom
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Have a look at the Mullard 3-3 - Mullard 3-3. Three Watt Amplifier which gives concise instructions, layout etc. The ampt has excellent performance and is simple to build. Local feedback ensures excellent bandwidth.

VVT transformers do transformer "kits" see - http://www.vvttransformers.co.uk/valve_tx_sets.htm which are reasonably priced and good quality.

Andy.
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Old 5th January 2019, 06:42 PM   #12
rpi is offline rpi  United States
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Thank you! Unfortunately the kits for Mullard 3-3 are not available on VVT site. The one which I found on e-bay:
Mullard 3-3 Magnetics kit | eBay
costs the same as the whole amp which I referenced.
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Old 5th January 2019, 06:50 PM   #13
pcan is offline pcan  Italy
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Need 3-5W tube amp
Nice project! Having a real tube amplifier instead of a fake one is surely a big advantage for the sound quality, if you use a high quality, high efficiency speaker. Tubes become hot, do not put any heat sensitive device near them. If you need to use plastic parts, use a sheet of metal as heat shield.

You are also looking for something that glows: I suggest a 6E5P "spud" amplifier. The cathode of this tube is exposed, so you will see it glow when the amplifier is turned on. The enclosed picture is my build of the schematic described here: Spud Amplifier with 6E5P Tube. It works and sounds really well, power output is lower than your requirements but it does not matter if you have a high efficiency speaker.

If you still want to buy the ready-made 6AD10 appj tube amp, be aware of the drawbacks. The output transformers are tiny and low frequency response is not good. I attach the picture of the inside of the transformer cover of the EL84 version of this amplifier, I believe it is the same on the 6AD10 version. As you easily see, the output transformer has the same size of those found in the kitchen radios from the '60 (but high frequency response is better on this modern part). For $200, you may get much better quality elsewere.

The 6AD10 tube is a standard one and therefore only the top and bottom part of the glowing cathode are visible. On most China sourced amplifiers there is a big red LED underneath the tube to light it up, but it looks fake to me.
Attached Images
File Type: jpg 6e5p_proto_front.JPG (118.0 KB, 636 views)
File Type: jpg 6e5p_night.JPG (60.9 KB, 643 views)
File Type: jpg appj tu.JPG (170.4 KB, 629 views)

Last edited by pcan; 5th January 2019 at 06:55 PM.
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Old 5th January 2019, 11:03 PM   #14
rpi is offline rpi  United States
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Thank you pcan! That's probably what I need. The wattage is lower then I expected but hopefully I can find small efficient speakers.

The size of transformers is a bit on a large side but I hope that at least the one for the power supply I could keep outside of the enclosure.

I'm not sure which current is flowing in that amp. Could you give me the wattage of the resistors used in the amp?

Is it better to buy a matched pair of the tubes or it doesn't matter for this amp?

How long the pair of tubes can serve if I will use the amp let's say about 2 hours a day? I'm just wondering how many pairs I have to buy.

There is the question in that thread about transformer which could be used in US for that amp: Spud Amplifier with 6E5P Tube

Is Edcor XPWR058 suitable or not? EDCOR - XPWR058

Thanks a lot!
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Old 5th January 2019, 11:46 PM   #15
6A3sUMMER is offline 6A3sUMMER  United States
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Caution,

There is a thread on this site regarding the Mullard 3-3 amplifier. It can have problems with various EF86 tubes. The DC voltages and currents of the input and output tubes can be "just about anywhere they want to be". Just my opinion, and something one of the recent builders observed. Also, be careful of using negative feedback with transformers that may not match the original transformers for gain / phase characteristics, unless you are prepared to adjust the feedback components, and have proper test equipment to do so properly.

Maybe the kit has transformers that are close enough. But you may need to select EF86 tubes, and they are expensive.

Last edited by 6A3sUMMER; 5th January 2019 at 11:53 PM.
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Old 5th January 2019, 11:48 PM   #16
Miles Prower is offline Miles Prower  United States
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Quote:
Originally Posted by Eli Duttman View Post
However, I dislike pentode voltage amplifier into pentode "final". I fear bludgeoning the setup with NFB will be needed to deal with highly irritating IM distortion.
.
SE pentode pretty much SUX. From the spec sheet, THD= 10%. YUCK!. Also, let us not forget that the 6AD10 small signal section really isn't a pentode: it's a quadrature FM demod tube as the type was intended for the audio strip of TV sets, and sonic performance wasn't a consideration. I wouldn't go that route.
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Old 6th January 2019, 12:19 AM   #17
rpi is offline rpi  United States
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The project from Lingwendil also looks attractive. I like the small form factor of the toroid transformers. Is it possible to use toroid output transformers with that Spud amp?

Thanks!
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Old 6th January 2019, 12:35 AM   #18
Eli Duttman is offline Eli Duttman  United States
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Quote:
Originally Posted by Miles Prower View Post
SE pentode pretty much SUX. From the spec sheet, THD= 10%. YUCK!. Also, let us not forget that the 6AD10 small signal section really isn't a pentode: it's a quadrature FM demod tube as the type was intended for the audio strip of TV sets, and sonic performance wasn't a consideration. I wouldn't go that route.
From the data sheet, I was thinking gated beam detector. Thanks for confirming my suspicion.

The OP stated a "steampunk" look is desired. That makes me repeat the 0A2 regulated g2 B+ suggestion. Gas discharge regulator tubes glow with pretty colors. Look here. The color of the suggested 0A2 is similar, but it is a physically small 7 pin mini type, which is well suited to a "boombox".
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Last edited by Eli Duttman; 6th January 2019 at 12:37 AM. Reason: punctuation
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Old 6th January 2019, 12:48 AM   #19
rpi is offline rpi  United States
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Thank you Eli Duttman. I'm all ears right now. Is there any real implementation of the amp which you described? I'm not afraid to make the one from scratch. I just don't have any experience in building tube amps though I completed many other audio projects.
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Old 6th January 2019, 01:31 AM   #20
Old Big is offline Old Big  United States
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Rip,
That is cool and will be real heavy with that galvanized pipe and transformers to boot!
Please post the finished product!
Doug
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