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    Building, troubleshooting and testing of these amplifiers should only be
    performed by someone who is thoroughly familiar with
    the safety precautions around high voltages.

Pro's&con's of PCB's

Hi all!

I'd like to know severall opinions regarding the construction of tube amps with PCB's. I don't get along with hand wiring (the first tube amp i did last week - 3v only hifi - is a mess!).
I think my way of wiring will get more noise on the circuit than if it's done on a etched pcb.
I'm having the tracks layout with a spacing of 20mil.

What do you think?

Thanks!
 
Hi Petman,

Both methods have their pros and cons. For one thing, PCB is much neater. Depending on the quality of PCB, the thickness of the copper, and how wide you make the lands (traces), you can have every bit as good a product as point to point.

Of course, there are limitations of PCB that I have found. For example, I can improve the sound of a power amplifier made on PCB by hard wiring the power from the main filter right to the location that needs it with 18 gauge wire, and connecting the output right at the output to the speaker terminals with 16 gauge wire, even though they are wide tracked printed circuits.

With point to point one has the benefit of directly connecting components to sockets, as well as good quality wire. The negative there is the risk of shorting components if not careful.

Cosmetically, both can be very beautiful.

That is my story and I am sticking to it!

;-)

Gabe
 
Petman,

plus:
as Gabe said, PCB always looks neat.
PCB amps are reproducable to a higher degree.
PCB is cheaper, no soldering posts, (ceramic) terminal strips and the like are needed.
PCB is easier to solder, less artistics are reqired :) .
PCB: neat software available for documentation.

p2p wiring sounds better.
p2p wiring has way lesser stray capacitances causing oscillations, provided no shorts occur, it is way more newbie-safe.
p2p can have way less soldering joints and way shorter connections.
p2p is harder to foul up on the umteenth resoldering.

minus:
PCB layout can produce an instable circuit, particularly if the circuit has feedback. For the circuit desinger, PCB layout is as tricky as p2p looks concerning oscillations.

PCB: the dielectric (FP4) in inferior to air in any respect.

on a PCB, conductors/routes are closer together and prone to be parallel Hence stray capacitances are higher.

A properly done p2p wiring requires expensive mounting stuff. Particularly the ceramic terminal strips. And, better have a digital camera to document what you did. No neat software available for documentation.

a p2p wiring requires considerable spatial imagnination and thinking to arrive at a servicable structure with short leads and few solder joints. You should know what to do in detail before you start wiring. Figuring out the wiring during wiring creates a mess.

my personal conclusion : p2p is the way to go.
Hinthint:
get your hands on an old faultyTektronix tube oscilloscope and take your time to unsolder all parts in a meditative mood :), Zen style, and let slowly soak the Tektronix staff's mastership into your mind (if you cannot observe the master work, share the space of the master's work :) ).
After that mental barriers concerning p2p wiring are gone, promised. Been there, done that.

BTW, you'll find a lot of the stuff you slaughtered very usable for your own p2p wiring. Particularly the ceramic terminal strips.
 
Dice45,

While I agree with all of your points, I have questions about two. Maybe three.

1) Ceramic terminal strips????? Where can one get them? I have only seen bakelite terminal strips. And 5 for about $1.50 USD for that matter.

2) Oscillations. While I agree, most amplifiers are not that susceptible to stray capacitance oscillations due to the fact that open loop gain isn't that much to begin with (maybe the phono stage). With either topology, design forethought will avoid such difficulties. Radio on the other hand...

3) Sonic difference??? In a tube amp, I have noticed that even 24 gauge solid bell wire can sound as good p2p as 20 gauge stranded. I don't know why, because in my SS amps 20 gauge is the way to go for low level, and 18 to 16 gauge for output. So a trace on a PCB may not make that much of a difference. Also one can design a PCB where the parts layout makes for short connections between components.

BTW, Just about every tube tuner (HiFi, after the late 50's) I have seen uses PCBs for RF. Strange.

Just some thoughts.
Gabe
 
Gabe,
1) Ceramic terminal strips????? Where can one get them?
read my last post :)
get your hands on old and faulty Tek scopes. Then butcher them, but do so with respect and appreciation and proper Zen mood and the usage of the side cutter limited to count 10 or else the old scope's ghost will come and haunt you :)

I did so 5 times, now i have a bucket full of those strips. They are w/o sheet metal lugs, they only have metalized notches to keep the solder. So real p2p wiring is supported w/o having unwanted metalcrap in between.

BTW, i even salvaged the logos and serial numbers from those Tek scopes, the are meant to go into my preamps frontplate in a small milled square, the honour corner :)

Oscillation: me no genuine electronics person and no PCB design wiz. I managed to get a tube preamp prone to oscillation and also collect Radio Moscow, after rewiring p2p, it was gone and stable. Having said that, design forethough is always required and it is possible to design a PCB tube amp w/o technical shortcomings.

Sonic differences: p2p takes the stress out of the sonics and relaxedness in.
Solid wire is better than stranded, thin solid is better than thick solid. Hang a big IMO on that statement, however more than only one forum member will agree with me from own experience.

I currently use solid twisted telephone wire for almost every speaker and interconnect cable as at the moment, everything in my system changes. But that doesn't mean phone wire is bad. On the contrary, it is terrific!

Just about every tube tuner (HiFi, after the late 50's) I have seen uses PCBs for RF. Strange.
Yes and almost any $$$$$$ measuring equipment made in the 50ies, 60ies, 70ies by Rohde&Schwarz or Siemens or Wandel&Goltermann i have seen and/or butchered is p2p wired, no matter if used for AF or RF or UHF.

Methinks the PCB for brown ware RF is used due to manufacturing considerations and to reproducablitiy issues.