Hey Gringo! Q For You On The Radio-Head

[Paul Marossy]

I built the Radio-Head today and finally used my 12AT6 and 12BA6 tubes after at least a year after they were given to me. It sounds good, tons of gain, but also has a pretty loud hum/buzz.  

I tried the usual 100 ohm resistor to ground trick on the heater supply, but it only has a minimal effect. Did you power the tube heaters with an AC or DC supply? I'm thinking that I'm going to need a DC heater scheme...

Here's a few pictures. It's in a recycled computer switching box of some sort. The box is actually a bone color, not yellowish like in the pictures.

[guitarhacknoise]

Hey paul,
Not to interject, but that looks SWEET!
"lay over" tubes and all!
what's the basis of this project?
sopht-amp?
-matthias

[Paul Marossy]

That's OK. This circuit of Gringo's popped up in this thread that I started last March: http://www.diystompboxes.com/sboxforum/viewtopic.php?t=20178&highlight=12ba6

I built the Real Mctube II first, and this followed a similar layout and design approach. Here is my McTube project: http://www.diyguitarist.com/DIYStompboxes/RealMcTube.htm
The case now has a folding carrying handle on the right side. The McTube is a very quiet build, and it uses a DC heater supply.

I'm wondering if there is something else that I was supposed to do that the Radio-Head schematic doesn't indicate... Gringo?

[Gringo]

Paul, my build uses dc heater voltage (filtered and regulated, 7812). There was hum, but nothing overwhelming, and i attributed it to my awful wiring (first tube project ).

IIRC, i was using a 220vac-110vac stepdown transformer (commonly used for printers around here), which after rectifying, gave a 160vdc B+. I also recall that i used some huge caps for B+ filtering (2200uF/400v or so) i got from blown computer PS's.

Right know it's wired with three 12ba6 pentode stages, waiting for me to stop messing with my hotrodded, ultra modded jcm800 pre, and give it some rewiring/tweaking.

Good luck, and keep us posted

[Paul Marossy]

Gringo-

Thanks for the info. It has a real healthy hum/buzz without a DC heater supply. I'll have to convert it to DC when I get back from my little outta town vacation.

Otherwise, it sounds good. Thanks for sharing that circuit with us.  

[Prive]

Pablo, no te enloquezas que te podes electricitar!!!!!!!!

Jajajaja, saludos en estas fiestas y muy feliz año nuevo, o mejor seria un año vintage?? jejejeje con valvulas y todo.

Saludos, Marcelo.

[Gringo]

I forgot to mention that i had/have both transformers out of the "box" (open back baquelite radio chassis), while you have both in. That might be another thing to have in mind with hum issues.

Beautiful build, by the way

[Paul Marossy]

Thanks Gringo. I pushed wires around in there, no effect on the hum at all. I think it is the heater supply. I also have the transformers inside on my RealMcTube build, and they are in even more cramped quarters, but no hum - at all. I think that is due to the DC heater supply.  

[Paul Marossy]

Well, I converted it to a DC heater supply. Much, nuch better. I could have maybe used a little more filtering than a single 3300uf filter cap, but I think it works OK as is. Here is a little page I whipped up on it: http://www.diyguitarist.com/DIYStompboxes/RadioHead.htm

Thanks for the help Gringo.  

[RDV]

Paul:

You might need to re-up the schem PDF, when I try it says "File damaged & could not be repaired".

RDV

[Paul Marossy]

Yeah, I got that error message, too. I re-uploaded it and it works now.  

[Fret Wire]

Nice looking build Paul. Very rugged and "industrial" looking.

[Paul Marossy]

Very rugged and "industrial" looking.

Yeah, I guess it kinda looks like a piece of laboratory equipment, doesn't it?  :lol: