Just for the fun of it - DIY tube amp

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Just for the fun of it - DIY tube amp

Postby Beate Ritzert » Fri Jan 18, 2019 5:27 pm

Ingedients:

- chassis and headshell and a few parts of a dead 1974 Dynacord HiFi Favorit.
- a spare transformer set made for EL84 in push pull.
- 2 6L6 GC, one ECC82/12AU7, one ECC83/12AT7

Result: 12 clean and powerful watts until onset of clipping. Sounds like a big one, a bit hiwattish (intended) but darker (not fully intended). This is fully my own design and i tried a few less common.

The headshell still needs to be restored, and a little bit of tweaking the tone will be done tonight.

Here on its first soundcheck:

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Re: Just for the fun of it - DIY tube amp

Postby John Clifford » Fri Jan 18, 2019 10:21 pm

Cool! Looks like you could have a lot of fun with that, if it doesn't kill you. You should post a sound clip somewhere.
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Re: Just for the fun of it - DIY tube amp

Postby Mario Proulx » Sat Jan 19, 2019 12:48 am

How are you only getting 12 watts from two 6L6? Do you have it biased low, or very little gain in the preamp section?
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Re: Just for the fun of it - DIY tube amp

Postby Beate Ritzert » Sat Jan 19, 2019 5:37 am

Well, the power the tubes can deliver must first all be delivered by the power transformer. It turned out that it couldn't.
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Re: Just for the fun of it - DIY tube amp

Postby Brian Evans » Sat Jan 19, 2019 9:13 am

12 watts from a pair of 6L6's is somewhat common for hi-fi-amps, I have a Gromes Little Jewel that is similar.
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Re: Just for the fun of it - DIY tube amp

Postby Mario Proulx » Sat Jan 19, 2019 2:51 pm

A typical 6L6 guitar amp runs 35 to 40 watts.

And yes, if the power transformer isn't strong enough, the wattage won't be there, and you'll soon kill the transformer. You'd be better off switch to a pair of 6V6
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Re: Just for the fun of it - DIY tube amp

Postby Beate Ritzert » Sat Jan 19, 2019 4:01 pm

Brian Evans wrote:12 watts from a pair of 6L6's is somewhat common for hi-fi-amps, I have a Gromes Little Jewel that is similar.


It is indeed pretty "HiFi" for a guitar amp. It actually sounds quite similar to my Hiwatt clone with 4 KT88 and 200 W. Just not quite as loud.

BTW: i have another 6L6 amp providing 22W and not far as clean sounding. The two are pretty complementary in character.
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Re: Just for the fun of it - DIY tube amp

Postby Halgeir Wold » Mon Jan 21, 2019 7:01 pm

A pair of EL84s usually gives 15-18W in HiFi-amps, 6V6 typically aorund 30, 6L6 35-50 depending on type, - the old metal jacket appx 30-35...
There are several designs out there...
I'm currently working on a 2x6L6 that's supposed to deliver aorund a 100, but I'm holding it back a bit and going for appx 80....
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Re: Just for the fun of it - DIY tube amp

Postby Daryl Kosinski » Tue Jan 22, 2019 3:09 pm

Many years ago when I was purging all my tube equipment I sold 2 100 watt Bogen Power amps they were never used. I got them surplus when GE moved out of Epcot. They were spares for low bass rumble in the sound system.

They had 4 6L6 power tubes. Pushing 2 6L6 power tubes to 100 watts would result in a very hot short life.
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Re: Just for the fun of it - DIY tube amp

Postby Beate Ritzert » Tue Jan 22, 2019 4:56 pm

Halgeir Wold wrote:A pair of EL84s usually gives 15-18W in HiFi-amps, 6V6 typically aorund 30, 6L6 35-50 depending on type, ...


... dependent on the properties and capabilities of the power transformer and the OT. Here i am using a transformer set for an EL84 and can actually not expect more. If i did i would become really famous because i would have invented a perpetuum mobile ;-)


BTW: the 7027-A is a variant of the 6L6GC which is specified for larger output demands. The data sheet - otherwise identical with that of a 6L6GC - documents a design with 70W. But a normal 6L6GC is already run out of specs doing so, especially regarding the anode voltage (and many of us might dream of a 6L6GC that could be run at 800V in "nearly B" mode... spitting out up to 120W from two tubes ...)
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Re: Just for the fun of it - DIY tube amp

Postby Halgeir Wold » Tue Jan 22, 2019 6:43 pm

Of course it depends on the transformers, - and several other parameters, but the numbers I referred to are a sort of average for several HiFi-amps, and to some extent moderately driven guitar amps.... things can always be pushed, but not without a cost..
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Re: Just for the fun of it - DIY tube amp

Postby Beate Ritzert » Tue Jan 22, 2019 7:47 pm

And it depends on how You measure the power. Here my 12W signal - You see it is just starting to clip (and upon close look You also see that the idle current is still a bit low). A pair of EL84 will do no better - and You need to drive it close to B for a larger output swing anyway because of its strong amplification. And a pair of 6V6 or 7591 will not even reach that in the given environment. At leas not if i model those tubes with LTSpice and adapt the circuitry to the peculiarities of those tubes.

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