General guidelines for types of wire used...

[ZBod]

What are some general rules of thumb when using
different wire types in an amp build/rebuild?

For example, which circuits should use solid core wire
versus shielded/braided/other types? Which gauges
are preferred?

If this has been discussed already, please send me a link to the thread. Thanks.

[bob p]

In general, there are two really important things to look out for: flame resistance and the voltage rating for the insulator. Everything else is pretty much a matter of personal preference. In general, any hook-up wire that's UL listed for the application will be fine.

At the bare minimum, you'd want a wire that can withstand 600 VDC. The garden variety inexpensive PVC coated hookup wire typically meets this specification. Some amps use voltages higher than 600V. for those I'd recommend wire with a 1000V insulator.

Most people will use something in the size range of 22ga hook-up wire, either solid or stranded. Stranded wire is flexible, which can be good or bad. Solid wire tends to hold its shape and stay where you put it. Either one is fine.

Some of us who are spoiled like to use more expensive wire with a teflon insulator. Its NOT necessary, and run of the mill PVC is fine. Similarly, some people like to use vintage type wire with a braided cloth covering. If you're not working on a restoration project then its not necessary and PVC is fine.

As far as shielding goes, shielded wire is only needed for the signal path, and its necessary from the input jack to the first tube grid. You probably won't need it after the first grid, but there's no real downside to using it. I buy Belden wire that's shielded/uncoated. Some people around here just cut up a dead audio interconnect cable, but bear in mind that it may not be rated for flame resistance.

[Enzo]

Good summary. On shielding, shielded cable does have a capacitance between shield and center conductor. A few pf here and a few pf there can add up. If you wired an amp completelty with shielded wire, I would expect it to have a duller sound - less bright. Like playing through a 50 foot guitar cord.

But the few inches from jack to first grid won't hurt you. The only other place in the amp I would consider it would be a relatively long run across other circuits. Like over to a panel control that has to be away from wher the rest of the circuit lies.

[bob p]

Enzo, +1 on the added capacitance. I should have thought of that.

Regarding wire specs, I took a look at a spool to look-up the UL numbers. UL Type 1015 is 600V PVC covered wire that's rated at 105 degrees C. You can find it in any of the catalogs under hook-up wire.

[ZBod]

Thanks for the info. I bought a bastardized
silverface Champ that had solid core wire running from
speaker out -> speaker. I changed it to braided, but was
that so necessary?

[bob p]

Most people will use something in the size range of 22ga hook-up wire, either solid or stranded. Stranded wire is flexible, which can be good or bad. Solid wire tends to hold its shape and stay where you put it. Either one is fine.

Thanks for the info. I bought a bastardized
silverface Champ that had solid core wire running from
speaker out -> speaker. I changed it to braided, but was
that so necessary?

in case this is still unclear, i'll try to clarify the point i made earlier: solid vs. stranded makes no real difference at audio frequencies. NONE. (more on that later).

what is FAR more important is the combination of the gauge of the wire and the length of the wire run. a suitable combination needs to be chosen for your application. for a champ output to the speaker, either type of 22 ga wire should be sufficient. generic 18 ga stranded lamp cord would be OK as well. the only reason to use stranded wire over solid wire in an OT to speaker application is durability. stranded wire can withstand flexing better than solid wire. this is important in a head to cabinet hookup (which gets a lot of flex) and is less important in a combo hookup (which is rarely if ever flexed after installation).

if you want to look-up the recommended gauge of wire that's needed for a run of a specific length, look at the table in Reference Data for Radio Engineers. In another post I've published a link to Technical Books On-Line, where you can download the book.

Back to the earlier subject of stranded vs. solid wire: At audio frequencies there is no audible difference between solid and stranded wire of the same gauge. "Skinning" is commonly endorsed by knowledge-impaired HiFi types who buy and sell large caliber stranded mojo-Hifi wire for the sonic improvements that its supposed to impart. In reality the skinning effect only occurs at radio frequencies. It doesn't occur at audio frequencies (and certainly not at bandwidth limited guitar frequencies), so you don't need to worry about it.

what is important for your speaker wire is the combination gauge of the wire, and the length of its run. Unless you're looking at a really LONG run (like a head into a remote cabinet), 16 or 18-ga stranded lamp cord is fine for everything.

hth