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Conference napalm::guitar

Title:	GUITARnotes - Where Every Note has Emotion
Notice:	Discussion of the finer stringed instruments
Moderator:	KDX200::COOPER

Created:	Thu Aug 14 1986
Last Modified:	Fri Jun 06 1997
Last Successful Update:	Fri Jun 06 1997
Number of topics:	3280
Total number of notes:	61432

989.0. "PC boards for tube amp circuits?" by ROLL::BEFUMO (I chase the winds of a prism ship) Tue Nov 22 1988 09:13

        I'm in the process of building an (app) 60W tube amp, using 2 6CA7s
        for the output stage, and 3 12AX7s + and a 12AT7 comprising a 6-stage
        preamp and phase inverter respectively.  I'm using the chassis,
        transformers, etc from a Fender amp, and making my own circuit board.
        The original board was built on some kind of black fibre board,
        using lots of point-to-point wiring.  My question is, is there any
        reason I shouldn't use a PC-board for the new circuit, providing
        I take precautions to keep the high-voltage traces far enough from
        anything else to prevent arcing?   I really don't know a whole lot
        about how new tube amps are being built, and am just concerned
        whether the resistance of the traces might be a significant factor.
            Also, the schematics I'm using switch two of the six preamp
        stages in and out using opto isolators.  According to my catalogs,
        there are several types of isolators available - anybody know
        which type might be applicable to this kind of application?  Thanks.
        
                                            joe

T.R	Title	User	Personal Name	Date	Lines
989.1	wishful thinking	MARKER::BUCKLEY	Take me down to the Paradise City	`Tue Nov 22 1988 09:51`	2
	The 6 stage preamp sounds cool! You gonna include a variac in there as well?
989.2	VARIAC?	ROLL::BEFUMO	I chase the winds of a prism ship	`Tue Nov 22 1988 11:14`	6
	Variac? where would that go and what would it do? As for the 6-stage, I'm working from MESA MK-III schematics, so tow of those stages kick in under footswitch control to form a lead/overdrive configuration. Normally, it's just 4 stages. joe
989.3		MIST::CARSTENSEN		`Wed Nov 23 1988 16:23`	19
	I've not worked with tubes before, but I think a PC board would work, as long as you did it properly. Like you said, keep high-voltage traces as isolated as possible. I don't think the currents in the input stage will be very high, so resistive heating and voltage losses should be low. The traces to the output stage and power supplies should be as wide and short as possible. You may want to use double sided 2 ounce copper boards to reduce losses. If you can find 3 ounce boards, use those. If, after construction, a specific trace or two seems to have too much losses, you can connect the node with a wire to supplement the trace. Be sure to isolate the feedback and other sensitive traces from the power traces. Good luck, this sounds like a fun project. Frank Carstensen
989.4	Boards burn	ELESYS::JASNIEWSKI	Ah, the road within without	`Mon Nov 28 1988 11:13`	6
	I'd have to say keep the power tubes off the PC material - I've seen lots of "burned boards" from the heat. Joe Jas
989.5	Too, too hot.....	MIST::CARSTENSEN		`Mon Nov 28 1988 15:46`	6
	Good point. Will the tube sockets provide enough thermal insulation to keep the boards from discoloring or actually burning? Frank
989.6	Tubes will remain just where they are	ROLL::BEFUMO	I chase the winds of a prism ship	`Tue Nov 29 1988 16:04`	4
	re [.4] - As a matter of fact, the board is going to replace a fender bassman's guts, so all the tube sockets, as well as the transformers, will remain. It'll just be a matter of popping out the bassman board & connecting my new one to the outboard components.