PCB construction for valve amplifier

[Simon Wicks]

Hi guys, i found this site googling PCB etching and thought i'd ask a question as my first attempt at etching was unsuccsessful.

I am tring to make a new board for an old 70's guitar amplifier which is valve driven. I copied the circuit layout and transfered it by hand using a permanaent marker pen. However, when i etched it, many of the tracks show severe degradation, likely where i havent gone over the tracks well enough with the pen. Since this board has to carry ~ 500V dc/ac is there anything you can recommend? I read some tutorials from here, but i have no laser printer, just inkjet.

I think one problem was that i didnt prepare the board well enough. I just gave it a wipe with acetone. I'll try shining it up a bit with some fine abrasive, but i dont know whether it will give better results. I also have a DECON PC33 marker that i got from Maplin, would that be better to use?

 

[philba]

I've not had good luck with permanent markers. I would probably draw an outline of the traces and then make a photocopy to use for toner transfer. google "pcb toner transfer" for more detail.

 

[RadioRon]

The PC33 will definitely work better, but the key problem is that your board must be scrupulously cleaned, it has to be shiny copper. This can be done by rubbing with fine steel wool.

 

[Rolf]

I've not had good luck with permanent markers. I would probably draw an outline of the traces and then make a photocopy to use for toner transfer. google "pcb toner transfer" for more detail.

I think the problem with markers are that they are essentially ink based. Elmer's Painters are paint based and do a fantastic job on just about anything. Surprisingly the paint don't even dry on the marker tip but on anything else in just a few minutes. A box of five different colors at Walmart is about $8.00, the individual pen's about $3.00. Be sure to get the fine tip.
Have not had a chance to try them as resist yet, since my Print N Peel is doing such a fine job.

 

[philba]

I thought those were water based. I'll have to take a closer look.

 

[Rolf]

I thought those were water based. I'll have to take a closer look.

The box states that they are real acrylic paint, works on Wood, Glass, Metal etc. but heat set fabric before laundering.
I guess acrylic is water based but it is water fast after drying.

 

[Hero999]

https://en.wikipedia.org/wiki/Acrylic_paint
Acrylic is a water soluble paint which becomes insoluble when dry.

Haven't you got a laser printer?

The toner transfer method is possible one of the most cost effective methods around. You print your design onto Press 'n' Peel/Photo/magazine (the latter is the most cost effective in my oppinion) paper using a laser printer, iron it on to the board, soak it in cold water (this isn't needed for Press 'n' Peel) and peel the paper off leaving the toner on the board. Now you just etch the board in the normal fashion. If you don't have a laser printer then you can easilly go to the library and use the photo copy machine.

For higher quality PCBs the photo resist method is best but you need a UV exposure and photo reisit or pre-sensitised board.

 

[Nigel Goodwin]

Why use a PCB at all?, it was common to handwire valve amps, using tag strips or tag boards - PCB's were only introduced to make commercial manufacturing cheaper!.

Incidently, the old TV manufacturer KB, even used to produce handwired colour TV sets - no PCB's at all!.

 

[Simon Wicks]

Why use a PCB at all?, it was common to handwire valve amps, using tag strips or tag boards - PCB's were only introduced to make commercial manufacturing cheaper!.

Incidently, the old TV manufacturer KB, even used to produce handwired colour TV sets - no PCB's at all!.

Very true. The amps i have previously built have all been constructed using turret boards. They are easy to continually tweak and mod. However the particular amp i have uses PCBs as it is from the early to mid 70s when turret board manafacture became more expensive than PCB. Building it on a turret board only makes for a massive headache in layout and hum reduction.

There is also no schematic for this amp. I am building it from notes i took of another amp. I will therefore have to draw a schematic when i get it all together!

Thanks for all the replies though, i think the photocopy toner idea should work for me in lieu of a laserjet printer.

BTW, is there anyone here who still fiddles with old valve gear? I have a multitude of unanswered questions!

 

[Nigel Goodwin]

BTW, is there anyone here who still fiddles with old valve gear? I have a multitude of unanswered questions!

I work on when I see it, often younger people don't have a clue (even service agents who do PA and band gear!). Any of the older members here will have experience of valve amps, they are really pretty crude and easy to build and repair.

 

[Simon Wicks]

Thats what i like about them. I built a small single ended guitar amplifier without knowing anything about how vlaves worked. I know a little about basic electronics (well, i dont know how much the little i got taught in a level physics is of any use) and asembled it. It was a clone of a 5F1 Fender Tweed with a single preamp stage, one 6v6 power valve and a nice valve rectifier. Trouble with the american grounding system has kept it from working properly so far so a rebuild is in order.

 

[Nigel Goodwin]

What do you mean by "the American grounding system"?, there shouldn't be any difference (apart from the obvious voltage of the mains transformer primary).