Single Ended 6V6/EL34/KT66/6550/KT88 Amp

[priesty]

Finished my second "PriestyAMP" project, a single ended amp based on a Blackface Champ aa764. It has the following design features I incorporated:
- Adjustable Cathode Bias
- Fan Cooling
- Foot-switchable "Turbo Knob" feedback lift boost

Sounds:
- Sounds best for Rock and Blueswith American sounding 6V6 (JJ 6V6s operating on its limits) or British sounding EL34 (Groove Tubes)
- Preamp tube Groove tubes ECC83S (Great for Blues to Metal depending on volume setting) or 12AU7 for Jazz/Country (with 6V6).
- Brutally distorted with ECC83S/KT88 combination
- "Turbo Knob" gives noticable bite and mid-boost when engaged

I've probably made tons of errors, which will no doubt be pointed out forthwith by the experts, but I think the Amp plays good, so I'm putting this out there to help any other people looking to try a single ended amp with more than 5 watts.

[maxwedge]

That came out really nice, did you build and paint the chassis too?

[bob p]

It looks like you started with a hammond chassis and painted it and lettered it yourself. The paint and the lettering looks very good.

I have a few comments and questions for you.

1. I like your schematic. Its well drawn, clear to read, and the objects are well proportioned in size. Can you tell me what software you used to draw it?

2. I like the footswitchable NFB loop. Do you get any pops when you use the footswitch?

3. Since you're using such a wide variety of tubes, I was wondering if you've given any thought to using a selectable switch for the primary OT impedance.

4. The lettering looks nice. Am I correct in assuming taht its a peel and stick sheet that you put through a laser printer? I'm interested in hearing about it.

Looks like a nice build. Congrats!

[priesty]

It looks like you started with a hammond chassis and painted it and lettered it yourself. The paint and the lettering looks very good.

I have a few comments and questions for you.

1. I like your schematic. Its well drawn, clear to read, and the objects are well proportioned in size. Can you tell me what software you used to draw it?

2. I like the footswitchable NFB loop. Do you get any pops when you use the footswitch?

3. Since you're using such a wide variety of tubes, I was wondering if you've given any thought to using a selectable switch for the primary OT impedance.

4. The lettering looks nice. Am I correct in assuming taht its a peel and stick sheet that you put through a laser printer? I'm interested in hearing about it.

Looks like a nice build. Congrats!

Hi Bob in answer to your questions:

1. Schematic drawn at great length on MS Word. If you make a few standard components and copy and paste, you can make it look good, but it does take time!!

2. The foot-switchable NFB boost has no pops at all, I put this down to the fact the stock NFB resistor (2700ohm) is always in series with the switch. There is no "opening" of the NFB loop, just switching in the high value pot. The foot switch is actually closed for the non-boost option, shorting out the "Turbo knob". With no footswitch, the "Turbo knob" is active for use for say, practice or recording. Important to use a stereo insulated jack for this!

3. Impedance - the Hammond 125FSE has multiple tappings on the seondary, I use a 3 position marshall style impendnace selector to alter impedance as required.

4. As you noticed, used a Hammond blank chassis and cage, cut holes to suit. It was powder coated by a friend who does it professionally. Lettering was waterslide decals printed on laser printer, like old Airfix kits!

Thanks again for your comments!!!

[priesty]

That came out really nice, did you build and paint the chassis too?

Maxwedge, thanks for the comments! As mentioned above, the good people at Hammond made the chassis and cover (Hammond Aluminium 1444-22 12x8 chassis, steel cover of same 12x8 size). George at Shetland Powder Coating did the painting after I'd cut all the chassis holes. He used a flexible epoxy as it is a more forgiving finish, less brittle/flaky.

[Groover]

Great looking amp! Thanks for all the good ideas.

[overtone]

airfix

thanks for sharing that with us. I did not know that there are more elastic types of powder coating out there.

Having just given up using MS Word for texts and after twenty-five years of using CAD and I can tell you that I am totally amazed that you drew that schematic on MS Word. Hats off to you Sir!

"Airfix" decals = Lasertrans, am I right?

[priesty]

"Airfix" decals = Lasertrans, am I right?

Overtone - Airfix was/is a type of scale model plane company here in UK, the insignia were always on waterslide decals, hence why I mentioned Airfix! Here is the place I got the paper from: Inkjet Papers and Fabrics, Window Stickers and Other Arts and Craft Materials

Glad to share my "research", especially on this forum seeing I got lots of help from here with my first amp!

[jmaf]

priesty, very kind of you sharing all this with us. not to mention your build, superb.

the decal paper tip just gave one of those eureka moments...i've been using silk screening and it's such a cumbersome process.

do you or anyone else know if one can safely apply automotive polyurethane varnish on top of the decal to protect it? or will it destroy the decal?

[tubeswell]

Very cool looking amp there priesty 8-)

[overtone]

will it destroy the decal?

jmaf,
I have used "CLOU" nitro-cellulose, which is intended for joiners and cabinet makers in Germany, over "Lasertrans" decals on a guitar headstock with acceptable results ...well it was perfect for the low-tech, "warts and all" feel that I was going for!
It was before I had an air compressor, so I used a brush with some care. It did smudge a little in places where I became careless. It has been fine sitting on there a year now and has seen some temperature change abuse too.
The edges of these kind of decals will show up in certain light conditions, so the brush was really useful to build up a few layers around the decal first helping to feather-the-edge-in a little. You will still see the edge if you are looking for it.
Take a look at the images to see if the smudging is acceptable for you and bear in mind that an air gun should give a much better result.

[Hurricane]

¿ Output ?

Excerpt :

I've probably made tons of errors, which will no doubt be pointed out forthwith by the experts, but I think the Amp plays good, so I'm putting this out there to help any other people looking to try a single ended amp with more than 5 watts.

================


So - - What is the out put per tube choice ?

Thanks and wow what a nice job I'm inspired to make one now

Hurricane Ramon

[Alf]

That's a fantastic looking amp Priesty !! And does it sound like you hoped for as well ?

I'm getting very curious to hear what it actually sounds like. Could you do a clip ?
I'm planning to do a SE amp myself, I have already all the hardware including a Heyboer OT but haven't got the time right now.

[priesty]

That's a fantastic looking amp Priesty !! And does it sound like you hoped for as well ?

I'm getting very curious to hear what it actually sounds like. Could you do a clip ?
I'm planning to do a SE amp myself, I have already all the hardware including a Heyboer OT but haven't got the time right now.

Alf - Amp is with a friend who I built it for, I will get a clip next time I visit him.

Hurricane - I havn't been able to borrow a scope to check output, but it was so loud when trying it through a Marshall 4x10" cab that you couldn't be heard when shouting to the guitarist! Amp runs with B+ of 440V at anode load of 5K and withEL34, about 30mA idle current.

[Alf]

I will get a clip next time I visit him.

Looking forward to it .