Looking for build literature/articles/tips

[nsubulysses]

Yay I am going on vacation for a week!! That means I will actually have free time! When I get back I will be building an amp and I was hoping to research some information on builds while I have this time. You know, anything that is tips for order of assembly or which wires should be crossed with others at 90 degree angles, etc. I have seen heater wires flying up high in Fenders but in a lot of other amps they are kept close to the chassis. I have re-arranged heater wires on various old Fenders to reduce hum because they ran right next to the grid wires.

I guess just tips on things like this so my first build it goes as smooth as possible. The design is already been engineered and honed by someone else. I'm just getting hired to do some builds. I guess I shouldn't worry too much because the noise floor is extremely low already and I can just copy the prototype, but would be nice to check out some info too.

FWIW the amp will be turret board with 4 KT88s and an ultralinear OT like in the Model T style. I think the preamp is somewhat modeled after a JMP. It won't be hard to physically build, but I would like the layout to be the best it can be.

edit: also i know I could just google this but was hoping to have people chime in with material that was helpful to them.

[defaced]

I'd approach your goal from a more pragmatic standpoint. You can read theory forever and still get pegged when you go to realize your design.
Find projects similar to yours in architecture and look at their layouts. Analyze them and see trends and differences.
Pick apart the differences and choose what you feel is a best chose for your application based on whatever engineering reasons you have.
Then take your observations and build your amp. You will probably find that the layout style you chose is almost a copy of an existing layout style, so I'd probably just copy the existing layout.

For my purposes, I like to use a layout style like the SLOClone turret layouts you can find around. This works well for cascaded gain stage amps because the ground is logical and the tube wires are short and direct. And from a gain perspective (voltage gain, not distortion), the SLO is a very high gain amps so methods that work with that design are likely to work with other designs.

[Mick Bailey]

You say the amp has already been prototyped and has a low noise floor. My gut feeling would be to replicate what's already there so long as the design is safe. I've lost count of how many times I've breadboarded a design, or built a rough-and-ready prototype to test some ideas, only to find that the polished version doesn't perform as well.

Being hired to build the amps and then making layout changes suggests to me that those changes would need to go back to the customer for sign-off and a new prototype version created to prove and test the changes.

However, if you see something that looks incorrect, or maybe could have been done more effectively or better, it may be worthwhile raising the ponts with the designer to understand why it was done that way in the first place. Sometimes things that appear wrong work best.

Charlie Watkins said that the Copicat echo machine sounded the way it did due to a mistake in the prototype that got carried through to the final production. If it had been corrected it wouldn't have sounded as good. You wouldn't want to be the guy who 'fixed' the Copicat.

[Pdavis68]

Here's some stuff I've read:

Lead Dress in Tube Amps
How to Layout and Construct a Guitar Amp Chassis
Building Your Own Tube Amp
Amp Builder's Guide - Trinity Amps

[nsubulysses]

Hey thanks for the replies I haven't been able to check this thread for a few days but this is helpful.

I have been given 3 prototypes but all are slightly different

I think you are correct to say copying the existing layout is best. They have been honing the design for a couple years and there is not oscillation or extraneous noise. I just want to read up a bit before I assemble to avoid possible amateur mistakes. I have never built an amp, only fixed them.

I am not too keen on the screen and plate resistors for the power tubes being riveted to the back of the chassis. I think an additional turret board to mount these on would be better, somewhat in the style of the 90s Matamps. This is my only suggestion so far. A main goal of this amp is that one day when a tech opens it up for servicing they are pleasanty surprised at how easy it is to work on.

The prototype is the first pic, the Matamp is second

[Pdavis68]

I could be wrong, but those metal power resistors on the back are probably using the chassis as a heat sink.

[defaced]

Take a look at Tim Williams' book The Circuit Designer's Companion. The first chapter is on grounding, which for me was worth the price of the book. You can preview most of it through Amazon and Google book preview. The book covers topics that extend beyond theory (which is usually taught with ideal parts) and how those variances in real parts effect the circuit and what to do about them.

The reason I bring this up is because I can see several chassis ground points, which may or may not have some room for optimizing depending on what they're connected to. I know everyone has their views on grounding, but between his book and Merlin's (the valve wizard website) chapter on grounding (mainly the illustrations), I went from very foggy on the topic to reasonably comfortable.

[g1]

those metal power resistors on the back are probably using the chassis as a heat sink.

Yes, that is the whole idea of them and why they have holes for mounting screws. If they are rivets, I would suggest screws & nuts for easier servicing. I would also use heatsink grease between them & the chassis.

[Mick Bailey]

Screen resistors shouldn't dissipate enough to need a heatsink, though.

[g1]

Doh! I thought they would be supply voltage droppers or something? What good are plate resistors that aren't going to give fuse action?

[nsubulysses]

Starting to wade through some of this material and it has been helpful thanks

I ordered The Circuit Designer's Companion book and have yet to receive it, then came acrross this PDF version online -- http://diagramas.diagramasde.com/otr...0Companion.pdf

Seems like it will be a very nice reference indeed