.. I used the left over parts to make something else. I couldn't get the single ECL82 to make enough volume - so I put the project on the back shelf for a while. Then last month I decided to add a second valve and aim at a four ohm output design to see if I could get the thing to be a bit louder.
That means it would have to be a twin speaker design to use my leftover drive units - and I bought a 70 year old beaten up toolbox off eBay and routed holes for a pair of 8 inch speakers.
I bent a basic chassis out of brass and made a two valve amp using a pair of ECL82s. There's a single 9 turret strip in there, the rest of the components are point to point.
The pentodes are run in parallel class A to give about 4 watts into 4 ohms, the triodes are used as a gain stage then a cathode follower. The OPT is from a 1950s radio and I guess 4 watts is about as much as it can handle anyway.
That arrangement still requires a proper front end, so I have my usual FET preamp built in to the design, which can be used to add some nice front end crunch.
I quite like the rat look. I tried to re-use rusty old screws where I could and sourced some vintage looking radio speaker cloth.
So there you go: The Toolbox Twin.
Pete
That means it would have to be a twin speaker design to use my leftover drive units - and I bought a 70 year old beaten up toolbox off eBay and routed holes for a pair of 8 inch speakers.
I bent a basic chassis out of brass and made a two valve amp using a pair of ECL82s. There's a single 9 turret strip in there, the rest of the components are point to point.
The pentodes are run in parallel class A to give about 4 watts into 4 ohms, the triodes are used as a gain stage then a cathode follower. The OPT is from a 1950s radio and I guess 4 watts is about as much as it can handle anyway.
That arrangement still requires a proper front end, so I have my usual FET preamp built in to the design, which can be used to add some nice front end crunch.
I quite like the rat look. I tried to re-use rusty old screws where I could and sourced some vintage looking radio speaker cloth.
So there you go: The Toolbox Twin.
Pete
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Looking good Pete!
Real retro man!
Thanks
I do like using brass for the chassis - its easy to work with and it gives the control panel a bit of class.
I know it will probably tarnish, but hey - that just makes it sound better.
How about adding brass (effect) chicken head knobs? Chicken Head Knob - Premium Metallic (Choose Colour) - Canada
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Modern fabric covered cable is readily available. Round or twisted.
Or just re-purpose it from an old clothes iron.
https://www.lampspares.co.uk/braided-flex-cables/
Or just re-purpose it from an old clothes iron.
https://www.lampspares.co.uk/braided-flex-cables/
Here's another example of a brand new, fabric covered, 3-core power cable from the UK.
Large section electric cable 3x1,50 round - covered by Natural Brown Linen RN04
Large section electric cable 3x1,50 round - covered by Natural Brown Linen RN04
That's neat! I've been messing around making little amps the last couple of months, none for guitar yet, but in the fullness of time...
The hard but for me if finding a case I like, or for want of a better words, suits the concept. I have a small 10W Kustom practice amp chassis I hope to use, but I'll probably struggle getting it all to fit!
And this does look the part!
I would only change the power cord, those knobs look vintage enough (I have loads of those types, some 50 years old or more, and some brand new- some styles dont change!)
The hard but for me if finding a case I like, or for want of a better words, suits the concept. I have a small 10W Kustom practice amp chassis I hope to use, but I'll probably struggle getting it all to fit!
And this does look the part!
I would only change the power cord, those knobs look vintage enough (I have loads of those types, some 50 years old or more, and some brand new- some styles dont change!)
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Like the idea of fabric power cord - that would be neat.
(When I was a nipper, our electric iron had a fabric power cord, and you could fit an adapter so it would plug in a light fitting, just over the ironing board. Ah, those were the days. If you set fire to your house, well it was your own fault. You didn't sue anybody)
I did consider chicken head knobs but the controls are too close together, so I bought a set of compact circular knobs.
I also thought of vintage brown bakelite radio knobs - they would look great. But getting a set of 5+ is tricky, and I bet they fall apart easily.
This amp should look ratty, but sound excellent. Well the look is pretty neat.
The sound? I have killed most of the hum. There's very little hiss and the tone controls work well. Strictly - it isn't loud enough and I blame the leftover speakers. If I were going to spend more money on it, I would buy a pair of Celestion 8-15s. I have used them before and they sound OK, for an 8 inch. However this is just supposed to be an amp that uses up leftovers, as far as possible
Pete
(When I was a nipper, our electric iron had a fabric power cord, and you could fit an adapter so it would plug in a light fitting, just over the ironing board. Ah, those were the days. If you set fire to your house, well it was your own fault. You didn't sue anybody)
I did consider chicken head knobs but the controls are too close together, so I bought a set of compact circular knobs.
I also thought of vintage brown bakelite radio knobs - they would look great. But getting a set of 5+ is tricky, and I bet they fall apart easily.
This amp should look ratty, but sound excellent. Well the look is pretty neat.
The sound? I have killed most of the hum. There's very little hiss and the tone controls work well. Strictly - it isn't loud enough and I blame the leftover speakers. If I were going to spend more money on it, I would buy a pair of Celestion 8-15s. I have used them before and they sound OK, for an 8 inch. However this is just supposed to be an amp that uses up leftovers, as far as possible
Pete
You might be inerested in this Pete:
TV's etc run off light fittings. - UK Vintage Radio Repair and Restoration Discussion Forum
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
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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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?
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?
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...
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
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
Toolbox Twin Amp Demo by Pete Hanson | Free Listening on SoundCloud
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