Hammertone Enterprises 2014

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Hammertone Enterprises 2014

Postby dhuebert » Fri May 23, 2014 8:51 am

It's been a long time since I posted anything here, I had gone over to the dark side and was building solid state devices for the past year or so. A few months ago a friend brought me a Pignose guitar amp to fix; it was a cute little solid state combo with a little plastic pig's nose for a volume control. It did not turn out to be worth fixing but it gave me an idea: how small a tube guitar amp could I build? After several months of mulling it over I came up with an idea. Here is the final product:

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The box ends up 12 inches wide, 7 inches deep and 16 inches tall. Once it was all built, I thought of several ways to make it smaller, maybe MarkII.

So here is the chassis:

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I took a Hammond 6 x 10 x 2 and cut it down to 6 x 6. A number of years ago I started a contest here to see who could build the smallest stereo amp, I won but I was never satisfied with the result so I scavenged the transformers and tubes from that amp to build this one.

Here is the schematic:

Image

What you see is the result of many hours on the bench solving problems; it had 2 nasty oscillations and the tone controls did not work as expected. I got it all worked out and mounted it in the box. One of the most challenging problems was that with a resistor on the output, it worked beautifully, but when I hooked up a speaker it would oscillate around 15 KHz, very nasty!
I put an 8 inch speaker in from Warehouse speakers http://wgs4.com/g8c and took it to a guitar player I know who has a recording studio http://www.bedsidestudios.com/photos.html . He put it thru its paces and we discovered some things about it: There is no clean mode, it is all THD all the time. At first we were not happy with the sound with the volume at 11 (10 with pull gain to make 11) the amp kind of folded in on itself. Yuck. I was pretty discouraged at this point but he suggested plugging in a different speaker so what the hell, we plugged it into a Marshal 4 x 12. Holy shit! The little amp came alive, Lenny liked it so much he bought the chassis from me and will build a little box for it and use it as a studio amp. It is perfect for that as it makes a unique sound and is only 6 watts so it is not too loud. I will build a second one but this time buy an even smaller power transformer and see if I can get it down to 3 watts, maybe that will make the small speaker sound better.

I think for my next trick I will build an amp with 2 6BM8 in push pull. I have a couple of transformers and a 10 inch Celestion that might do the trick.

Don
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Re: Hammertone Enterprises 2014

Postby Geek » Fri May 23, 2014 11:43 am

Dang that's cute :))

A lot going on in that little chassis. Congrats! (y)
-= Gregg =-
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Re: Hammertone Enterprises 2014

Postby EWBrown » Fri May 23, 2014 4:23 pm

I've posted this schemo in the past, Univox 45 6BM8 PP guitar amp:

Image
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Re: Hammertone Enterprises 2014

Postby dhuebert » Mon May 26, 2014 2:59 pm

Looks familiar I think I have it in my collection somewhere.

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Re: Hammertone Enterprises 2014

Postby Gingertube » Mon May 26, 2014 5:03 pm

There are actually quite a lot of DIY 6BM8 Push Pull Guitar Amp Schematics around the web.
Music Electronics Forum has several threads dedicated to 6BM8, some very "mature" designs are featured ("mature" as in 2nd or 3rd generation of a design which has been built by a number of guys).
Also some stuff on EL34 World.
Really worth doing some searches.
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Re: Hammertone Enterprises 2014

Postby Shannon Parks » Wed May 28, 2014 5:36 am

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Re: Hammertone Enterprises 2014

Postby TomMcNally » Wed May 28, 2014 4:56 pm

Here's a satellite shot of the mural they talk about in the article Shannon references.

Image
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Re: Hammertone Enterprises 2014

Postby dhuebert » Tue Jun 03, 2014 7:58 am

I feel so lucky and honoured to have known Gar, it was like having Leo Fender living down the street!

I was thinking of doing a push pull 6BM8 amp to match a 10" Celestion speaker I have.

In this case it didn't occur to me to look around at schematics since I had an idea of what I wanted to build. These things are like Lego, you just pick the colour of the block and plug it in. For this one I wanted a conventional front end with what I call 11 boost, that is a pull volume control to switch in a bypass cap for the first stage cathode resistor. I wanted to use a Fender style tone stack because I had never used one before and they do a lot of tone shaping no matter what you set them at. To make the amp as simple as possible I used a 6BM8 for tone stack recovery and output tube making it a 2 tube amp. The transformers I had as well as the chassis and smaller parts, it just needed a box and speaker. For push pull I might look at some schematics to see what other people have done but I already have a pretty good idea of what I want. The same as this except 2 6BM8 for tone stack recovery and split load PI. The idea is to make these things as small and simple as possible, so no reverb or tremolo, pedals can do that.

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Re: Hammertone Enterprises 2014

Postby Gingertube » Tue Jun 17, 2014 12:12 am

56T reverb.jpg
56T reverb.jpg (98.38 KiB) Viewed 3850 times
I chased up that popular DIY 6BM8 schematic.

It is the HoSo 56, with power scaling (well VVR or whatever you want to call it). Delete the Reverb and it becomes a 4 tube layout - but a lot more versatile.
The effects loop as shown is a bit of a "dud" and I would leave it out too.
I would ABSOLUTELY leave out the standby switch, it is just adding too much stress to the 5Y3 when hot switching.

The PAB (Pre-Amp Boost) switch is a Dumble inspired thing - it basically just takes the tone stack out of the circuit.
Feeedback is also switchable.

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