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Instruments and Amps Everything that makes music, Especially including instrument amps.

The one valve guitar amp is dead, so ....
The one valve guitar amp is dead, so ....
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Old 10th August 2019, 01:45 AM   #11
Gnobuddy is offline Gnobuddy  Canada
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Originally Posted by snaarman View Post
So there you go: The Toolbox Twin.
Very nice!


-Gnobuddy
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Old 11th August 2019, 09:23 PM   #12
Thomasha is offline Thomasha
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Nice looking little amplifier!

Is the cathode follower better than a normal gain stage? Is it in front of the tonestack?
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Old 11th August 2019, 10:09 PM   #13
snaarman is offline snaarman  United Kingdom
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Originally Posted by Thomasha View Post
Nice looking little amplifier!

Is the cathode follower better than a normal gain stage? Is it in front of the tonestack?
The circuit is like this:

FET preamp with adjustable non linearity to give an overdrive sound. Then there is a medium impedance tone stack based on the fender black face. Then volume control and first triode direct coupled to the cathode follower. That then drives both pentodes in parallel.

I decided I could not use both triodes for cascaded gain because I would have stability problems, so I used one as a cathode follower instead. It isn't a great design and two ECL82 valves make for a hot amp, but it sounds quite good..

Pete
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Old 12th August 2019, 08:20 AM   #14
snaarman is offline snaarman  United Kingdom
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Originally Posted by Thomasha View Post
Nice looking little amplifier!

Is the cathode follower better than a normal gain stage? Is it in front of the tonestack?
And here's the schematic. I think the only change I would make now it to fit better speakers, perhaps something with higher efficiency..
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File Type: jpg Twin ECL82.jpg (162.0 KB, 70 views)
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Old 12th August 2019, 08:39 AM   #15
Thomasha is offline Thomasha
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Thanks for the schematic! For some extra distortion the tonestack could probably be used after the cathode follower too. The fet would hit the first triode much harder.

I was thinking... with a 10k OT it should deliver roughly 3W, only a little lower than what you have now, and you would have another pentode to use elsewhere. I never tried to use the pentode of the ECL82 as a gain stage, but it could work. That would definetely produce enough gain for some extra distortion.

But I'm also tempted to use the cathode follower as a cathodyne and make it a PP output stage. Would give almost 10W. I think the Westminster did that with ECL86 tubes.

The box really looks nice, are those 8" speakers for guitar or are they also radio speakers?
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Old 12th August 2019, 08:46 AM   #16
snaarman is offline snaarman  United Kingdom
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Originally Posted by Thomasha View Post
The box really looks nice, are those 8" speakers for guitar or are they also radio speakers?
In the spirit of making the amp out of leftover parts, there's a speaker from a Fender 15w bass amp in there, and one from a Tanglewood acoustic amp :-)

The bass speaker sounds brighter, the acoustic speaker sounds less toppy. Weird. They are small magnet things so it could be much louder with a pair of Celestion 8-15s.

Having attempted the one valve amp and failed, I just used the leftovers to make this object.

My amp design of choice is ECC83 then a pair of EL90s in parallel, SE class A. That can give 4 to 5 watts, and I have built a couple of those. They sound great with the right speakers...
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Old 12th August 2019, 03:04 PM   #17
johnsurnamerobinson is offline johnsurnamerobinson
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I use epiphone valve junior for guitar totally retro 50s down to to the chicken head knobs.Looks great, Very well made! Five ear splitting watts from class A single ended EL84.Eminance speaker inside.cost 119

Made in CHINA !!!!
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Old 12th August 2019, 03:13 PM   #18
johnsurnamerobinson is offline johnsurnamerobinson
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I use epiphone valve junior for guitar totally retro 50s down to to the chicken head knobs.Looks great, Very well made! Five ear splitting watts from class A single ended EL84.Eminance speaker inside.cost 119

Made in CHINA !!!!
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Old 13th August 2019, 10:17 AM   #19
snaarman is offline snaarman  United Kingdom
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Originally Posted by Thomasha View Post
Thanks for the schematic! For some extra distortion the tonestack could probably be used after the cathode follower too. The fet would hit the first triode much harder.
Novel idea. I was wondering why you don't usually see the tone stack after the driver triode.. and I guess that's because it puts the tone stack inside the negative feedback loop if there is one. And that is probably not a good idea from the point of phase and gain margins perhaps..

As to Epiphone amps: Yes, it was listening to their Chinese 5 watt amp that got me back in to amp design.

Instead I bought a second hand Fender Champ 600. It had so much hum I had to get in there and rework it straight away. Then I gave it a tone control and mild over drive.

And the rest is history, I now have four or five home designed valve amps under my belt and - alas - no sign of stopping

Pete
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Old 13th August 2019, 07:42 PM   #20
snaarman is offline snaarman  United Kingdom
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Here's a sound cloud sample of this Toolbox Twin - recorded with a capacitor mic and using my Luthier modified 3 pickup Yamaha Telecaster..


Toolbox Twin Amp Demo by Pete Hanson | Free Listening on SoundCloud
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