Author Topic: New low voltage tube amp project. Runs on 12v walwart 62v inside. not to scary.  (Read 39593 times)

sajy_ho

Thanks alot Greg.
Life is too short for being regretful about it.

Shoeman

I found the correct Hammond OT in my stash today.  I have a bunch of terminal lug strips too.  All I need is the tube sockets, the LT1054 and a few of the caps and I'll be building one of these next.  Gooneybird.....  Hmmmm.... not very elegant ;D
Geoff
Cheap guitars, homemade amps and garage rock technique.  But I have fun.

solderburn

I'm very new to this but this is still possibly stupid question,

What OT is that? and what diodes are the ones in the power supply?

I'm planing on building a project soon, currently a tube cricket /w bridged LM368s, active 3 band EQ and a lot of small mods. But if this is in the same price range I'll build this instead.
Thanks in advance ;D
Dan

psychedelicfish

What OT is that? and what diodes are the ones in the power supply?
The OT is any transformer that with its secondary connected to an 8 ohm load will have a primary impedance of roughly 20K. A fender reverb transformer will work well, and I suspect this is what Greg used. A 240:5V mains transformer will work as well. You can also use any of the hammond 125*SE transformers if you connect an 8 ohm speaker across the black and orange leads. The power rating of the transformer shouldn't matter too much, this amp probably puts out less than 500mW (0.5W).

As for the diodes, 1N400X would be good, I'd go for 1N4004. They all cost the same, though, so it doesn't matter too much.
If at first you don't succeed... use bigger transistors!

solderburn

The OT is any transformer that with its secondary connected to an 8 ohm load will have a primary impedance of roughly 20K. A fender reverb transformer will work well, and I suspect this is what Greg used. A 240:5V mains transformer will work as well. You can also use any of the hammond 125*SE transformers if you connect an 8 ohm speaker across the black and orange leads. The power rating of the transformer shouldn't matter too much, this amp probably puts out less than 500mW (0.5W).

As for the diodes, 1N400X would be good, I'd go for 1N4004. They all cost the same, though, so it doesn't matter too much.
Will a Hammond 1750A work?
Datasheet link:
http://www.hammondmfg.com/pdf/EDB1750A.pdf
Dan

Shoeman

Sure will.  22K primary and 8ohm secondary is perfect.  I have the same tranny I'll be using for my build. 
Geoff
Cheap guitars, homemade amps and garage rock technique.  But I have fun.

solderburn

Awesome! Hopefully I'll get the parts in the next couple of weeks.
Dan

zambo

lol!! Ive made these with a 1k/8 ohm audio trans from radio shack quite a few times and never melted anything. The correct one is the 22k  reverb or line trans, but it only has 60-70 volts going through it. I used the reverb trans in the kits because I know  it wont melt. the 3 dollar rat shack pp trans does work though.
I wonder what happens if I .......

zambo

keep in mind though, i just came home from work after drilling a 1/4 inch hole in my hand......Not to be trusted... :icon_sad:
I wonder what happens if I .......

Shoeman

Ouch!
Geoff
Cheap guitars, homemade amps and garage rock technique.  But I have fun.

solderburn

Two more quick questions, Can i use 1/2w resistors? And will 24v caps work for every thing other than the power supply caps?
Dan

zambo

you can use 1/2 watt resistors. i use a heavier watt cathode r though. 2 watts that i have around. use caps at least 100v. safety margins are good. cathode bypass caps are 25 volt electrolytic. all others should be 100 or up. the diodes i used are 1n4148 btw.  i revised the board to be a bit better and added a fe reservoir caps to cure some of the sag. just a bit. will post new pics asap.
I wonder what happens if I .......

solderburn

Thanks! now i have all the info that in need, Btw your guitar playing in the video is fantastic!
Dan

zambo

Hey thanks! I havent been doing enough of it latley so thats good to hear  ;D
I wonder what happens if I .......

sajy_ho

I can't wait to see new schematic, Btw how about biasing second preamp stage with a 47K Ra as merlin suggested in his book?
Life is too short for being regretful about it.

zambo

I will leave the schematic the same except for the reservoir caps being added.  Changing the plate resistor to 47k would be a simple thing though. I am actually going to take this kit I am starting so I can film and photo the build and modify it afterwards to have a treble and bass only eq with bright switch. I may also modify it to have an el84 or 6v6 ( will have to swap ot out) but still run it at low voltage. I think it will still work.
I wonder what happens if I .......

sajy_ho

I will leave the schematic the same except for the reservoir caps being added.  Changing the plate resistor to 47k would be a simple thing though. I am actually going to take this kit I am starting so I can film and photo the build and modify it afterwards to have a treble and bass only eq with bright switch. I may also modify it to have an el84 or 6v6 ( will have to swap ot out) but still run it at low voltage. I think it will still work.
That's a good idea. Can this supply handle PA section powered by el84?
And one other rookie question: Can I use this type of supply for getting more voltage? I'm trying to build a 4 stage 12AX7 overdrive pedal and cannot find a good PS, I've tried 555 smps but I got only oscillations and fried MOSFETs! I just want about 150V @ 6mA. Please help me through it.
Thanks
 
Life is too short for being regretful about it.

zambo

you can make this supply do it, you just need to make sure the supply caps are of the right voltage. So at the end of the power supply you will be using 175 to 200 volt caps. You could use a 1363/4 smps from taylor electronics and get 150 up to 200 volts pretty easily. you just have to load it down enough to not whine. Oscillations usualy mean you need to use sheilded wire for the signal path. there are a lot of reasons but thats a big one. the 555 should work but i have always used the 1363. 12ax7 will run fine at 100 volts. you could built this supply using 19 or 21 caps and get 100 volts. it would just be biig.
I wonder what happens if I .......

sajy_ho

Thanks for the quick reply, unfortunately I don't access to Tylor Electronics, so I guess I need to buy lots of 10Us and 4148s...
Thanks again Greg.
Life is too short for being regretful about it.

zambo

if you have access to step down transformer they work to. a 120 to 12v coupled to a 12v to 120 for b+ works well from what i hear. i havent tried it yet but should.
I wonder what happens if I .......