Advantages of PTP wiring?

[teemuk]

here Is a nice way to use different construction methods Tone King Amplifier

Looks nice but I would hate to repair that.

[xk49w]

here Is a nice way to use different construction methods Tone King Amplifier

Looks nice but I would hate to repair that.

Comment on the FB link say it sits on top of the tube socket but I can't see how it connects to the socket from the picture.

[Ken Moon]

When designing a typical layout using turret boards or eyelet boards, with the tubes at the back of the amp and the control knobs at the front, you always end up with some long leads that have to go all the way from the front to the back of the amp.

A point to point layout that is well thought out, like this one, gets rid of that problem:

[img750]http://tinymaninside.net/Audio_Designs/ ... 0_17_1.png[/img]

A similar layout can be done by making turret/eyelet boards with big holes going right down the middle of the board, so the tubes are in the center of the board (sorry, I don't have a pic of that style).

I've built some amps with the preamp tubes up front, which helps keep the tube-to-knob wires nice and short, and that seems to worlk well too, without going all the way to PTP (the front of this amp is at the bottom of the drawing):

[img749]http://i514.photobucket.com/albums/t346 ... layout.jpg[/img]

[rp]

Comment on the FB link say it sits on top of the tube socket but I can't see how it connects to the socket from the picture.

Looking more closely you can see the standoffs and light from around the socket knockout. So they are using something like this, though custom. Call me a stuck in the mud curmudgeon but I still think tube sockets should be mounted to the chassis, even if it's just preamp tubes and they are extra tick epoxy boards.

http://www.partsconnexion.com/product3160.html

[Firestorm]

Every amp has to be designed with insight into how the various subcircuits might interact. If you guess wrong in PTP, you can move stuff. If you guess wrong with PCBs, well, you're sort of screwed. Remember some of the Acoustic tube amps? They ordered a ton of PCBs and then found they had problems. Factory-original examples have cut traces and last-minute fixes. With PCBs, you have to be abso-f***ing right.

My only complaint with PTP is their tendency to be "layered." They're built from the bottom up, so when you need to service the power supply section, years later, it's usually underneath all the signal leads, which are fine.

I guess that's an old radio complaint. A modern designer could avoid it.

[Prairie Dawg]

One thing that may have been touched on here is the genius behind Leo Fender's eyelet board construction. I didn't tumble to this until I started building amps with boards I made myself.

Once you've got a board built and tested with its flying leads attached, the process of installing it and wiring it up is rather simple and requires no specialized knowledge. It's no more complicated than stitching a pocket onto the seat of a pair of jeans.

So, by a simple division of labor you have upped your throughput because the amps are easier to assemble and you've reduced production defects significantly.

In true point to point wiring on a production basis, for each project you build, you expose yourself to the entire range of manufacturing defects as components are layered by individual operators.

For serviceability, nothing beats eyelet boards or turret boards. True PTP is a service man's nightmare.

[teemuk]

A similar layout can be done by making turret/eyelet boards with big holes going right down the middle of the board, so the tubes are in the center of the board...

And a similar layout can be done with PC board with holes in the center of the board for "flyby" wiring of tube sockets.

[img:750:592]http://www.chambonino.com/work/miscguitar/misc8e.jpg[/img]

By the way, this is actually a somewhat heinous design to fix because there is very little slack in the wiring and it ties the board down to chassis from many sides. You have to unsolder all those wires to gain access to solder side. The seemingly "best" practices are not always that although they might look impressive.

Speaking of holes in boards... those can be used for other purposes too: They can isolate high-voltage risk-to-arc traces from another or one can place them to positions where hot components would rest: Now they won't scorch up the board if they go up in flames or just overheat in normal operation (Marshall and Ampeg take note ).

There are lot of neat tricks one can do with PC boards that are seldomly employed in things like ordinary guitar amps.

Anyway, usually if you can make a good layout on a 2D plane (like most of these tag/eyelet boards) then you can also make an equivalent printed circuit board. Furthermore, you can shorten the wiring even more by mounting tube sockets and all the interface controls (jacks, potentiometers, switches...) to the board itself.


...And yes, this can be done reliably and with easy serviceability in mind with just some proper planning. For example, one could employ metal bars that would both reinforce the PC board (to prevent flexing) as well as serve as mounting planes for tube sockets, potentiometers, etc. Chassis would have holes in right places to allow tube sockets, pot shafts and other imaginable things to portude out but the mechanical mounting of said components would rely on the "reinforcement bar" only. The PC board itself would be fixed to chassis with standoffs connecting to the reinforcement bar and removing few screws would allow to lift the entire assembly off. (Well... almost, usually you have to deal with few external connections that can be hooked to easy-to-remove connectors). The reinforcement bar could also serve as heatsink or heat spreader, electrical conductor / ground plane or any other imaginable purpose.

Yes I know, it -costs- much more than a way simpler assembly. That's usually what it's all about, though.

[Phil_S]

I understand there may be reasons why I've not seen it done, but is it reasonable to think you might be able to use push on connectors on tube sockets? I'm looking at the board cut outs and the comment on no slack and need to unsolder for service. OK, have at it, I have the flame suit on.

[Ken Moon]

That's the first thing that crossed my mind too.

There is a wide variety of push-on wire connectors that are designed for PCBs. If you use different colored wires, it would be simple to service. The same could be done for wires going to/from the front and rear panel jacks, switches and pots and the PCB.

[teemuk]

There are, it's not uncommon to see solutions like this...

[img:300:375]http://sussexvcs.files.wordpress.com/20 ... hiclet.jpg[/img]

...but you have to choose the connectors wisely or you'll end up with a catastrophy - like Ampeg and Behringer did when they found out that the molex connectors they used couldn't handle filament current draw. Intermittettency and corrosion are always a risk too. ...and it's not always the best practice to break the signal paths with connectors in a high-impedance, high-gain circuit like modern tube amp. Basically a solid solder connection with proper stress relieve is usually more reliable (both mechanically and electrically) than a connector but the latter provides faster assembly, easier serviceability, modularity, etc. so using connectors and sockets is usually a compromise between two different design goals.