DIY Audio Projects Forum

Hi forks this is what happens when you have a lot of left over parts and too much time on your hands. The 832 tubes were left over from a project that was not really all that great. Almost every part in the Funkywatt was recycled from earlier projects. It uses the old style Edcor 10 watt guitar output transformers and a stock (used) Edcor power transformer. The chassis was an orphan pre-production Poddwatt. Anyhow, it was fun. The circuit uses an alternative balancing method as the cathodes in the 832s are internally connected. It is also runs in push-pull pentode mode as the screens are also tied together internally. BTW the 832 is a dual RF pentode in a large acorn shaped bottle. Really an odd tube.

Power output is right on 5 watts RMS at 4 ohms and the response is unreal (see the 1 watt Bode plot). 20HZ to 50K within 0.5dbv. The -3dbv points are at 14HZ and 75K. Imagine what it could do with the better trannies. Sound is clean, and I need to look into the B+ filtering as the basic S/N wide-band is in the -85dbv range, but I have a spike at 120HZ that hits about -60dbv. Clearly a B+ filter issue.


Good listening
Bruce

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Some of my DIY Tube Amplifier Projects:

• PoddWatt: 5751 / EL84 Push-Pull DIY Tube Amplifier Project
• OddBlocks: KT88 Push-Pull DIY Tube Amplifiers (Mono Blocks)
• ForeWatt: ECC802S (12AU7 / ECC82) DIY Tube Preamplifier Project
• GrooveWatt: Tube (Valve) RIAA Phono Preamplifier Project

Right on!

A friend of mine took an 807 project and modded them for 832's (I still have the 832's in 807 bases) and it sounded great!

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-= Gregg =-
* Ratings are for transistors - tubes have guidelines*
Home: GeeK ZonE
Work: Classic Valve Design

Funky indeed! Thanks for sharing Bruce.

Cheers

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[ DIY Mains AC Power Cable Cord ] - [ Gobo LM1875 Amp Kit ] - [ Tang Band D4-1 Horn Speaker Kit ] - [ Monoblock Push-Pull KT88 Tube Amp Kit ]

I love the look looks of those tubes, "So ugly they're Beautiful" maybe.

I have a few questions
Do you use any sort of Inrush current limiting on your amplifiers? I have seen a lot people suggest using a CL90 in series between the power switch and the fuse is, is there any downside to doing this. I finished my K-502 kit recently and I love it but when I turn it on 3 tubes flash super hot and one is not nearly as bright. I swiched the tubes around and it is tied to the tube not the socket.

The "line filter and fuse" you list on your schematics. Is this just a typical filtered IEC socket of something homebrewed of your own?

I have been looking at a lot of your projects and it looks like you always start with these power and output transformers. Is there something special about that setup or do you just have those parts lying around

That´s funky enough!

Will you consider a guitar amplifier with some tone controls in another future project?

Thank you Bruce!

Hi, It seems like I'm not getting notifications of things I have subscribed to....anyhow.

I don't use inrush protection, but most of my amps (not this one though) use a B+ delay. I really have not found that the inrush is a problem. You do have to make sure that all components can handle the full B+ voltage though.

I hate noise regardless of the source so all my projects use IEC input filters. They are inexpensive. I believe this batch came from Jameco for under $2 each. They include a fuse as well. Search for Delta Electronics 04BEEG3S. They are good for both 120 and 240 mains. I also like to have the detachable cord feature.

I use a lot of the same transformers as they do what I want. Some of them were designed to my specs and fit what I want to accomplish better than generic ones.

"Will you consider a guitar amplifier with some tone controls in another future project?"

I already have it is posted somewhere on the forums as the GT-20. I attached a schematic. BTW this with a few small changes (like the deletion of the ability to use 6V6GT tubes) is in the works right now as a commercial product. PM me if interested as I don't like to mix diy and commercial on forums.

Good listening
Bruce

EDIT: ignore the red stuff as it was to try to correct something that didn't end up needing correcting. With the proper power transformer and output transformer (I used a CXPP60-MS 4K) you can use KT88s, KT90s, 6550, and KT120s as well as the 6L6 and EL34s). Available B+ needs to be about 450 volts and if you go to the biggest tubes at least 350ma. The amp is quite excellent for jazz and blues, but if you use the controls you can overdrive the preamp or the power amp or even both and get some really neat sounds. The preamp and power amp both have level controls and can be used independently. You can also put a reverb or other effect in between them. Power output depends on the tubes, but an easy 50 watts is available. If I can find the existing thread I'll link it to here (or if someone else can find it first please do the same).

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Some of my DIY Tube Amplifier Projects:

• PoddWatt: 5751 / EL84 Push-Pull DIY Tube Amplifier Project
• OddBlocks: KT88 Push-Pull DIY Tube Amplifiers (Mono Blocks)
• ForeWatt: ECC802S (12AU7 / ECC82) DIY Tube Preamplifier Project
• GrooveWatt: Tube (Valve) RIAA Phono Preamplifier Project

How did I miss this one?

Thank you so much for sharing Bruce!

By the way, what should be the recomended voltage for 6V6 tubes and how much power can I expect from them?

I have a pair of 6V6 in the shack...


Cheers,

Miguel

Hi Miguel, For new production 6V6GT you can run up to 325 Volts. For long life I would stay at 300 or even a little less. You can get about 12-15 watts at about 10% distortion. I would use the CXPP25-MS-6.5K or 8K with them. My preference is the 8K as it gives a really clean sound and the loss of output is minimal. That trannie is one of my favorites. Good for lots of things and very robust for a 25 watt rating. If you don't care too much what happens below sat 40-50 HZ the GXPP version is cheaper and will work fine. I don't think it has all the 4-8-16 ohm output taps though.

My apologizes for kind of hijacking the thread.

Good listening
Bruce

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Some of my DIY Tube Amplifier Projects:

• PoddWatt: 5751 / EL84 Push-Pull DIY Tube Amplifier Project
• OddBlocks: KT88 Push-Pull DIY Tube Amplifiers (Mono Blocks)
• ForeWatt: ECC802S (12AU7 / ECC82) DIY Tube Preamplifier Project
• GrooveWatt: Tube (Valve) RIAA Phono Preamplifier Project

Its your thread, how can you hijack it?

Thanks for the replies to my questions, I appreciate it. I just got into tube amplifiers and I love how simple they are, yet there is not really one best way to make them. I am very tempted to make an amplifier with at least a dozen extra tubes that have nothing hooked to them but the heaters. It would look as impressive as hell but not really do anything "FraudWatt" is what I would call it

Yeah, I suppose that's true.

Good listening
Bruce

_________________
Some of my DIY Tube Amplifier Projects:

• PoddWatt: 5751 / EL84 Push-Pull DIY Tube Amplifier Project
• OddBlocks: KT88 Push-Pull DIY Tube Amplifiers (Mono Blocks)
• ForeWatt: ECC802S (12AU7 / ECC82) DIY Tube Preamplifier Project
• GrooveWatt: Tube (Valve) RIAA Phono Preamplifier Project