Hoffman Amplifiers Tube Amplifier Forum
Amp Stuff => Tube Amp Building - Tweaks - Repairs => Topic started by: 12AX7 on March 22, 2012, 09:36:55 am
-
Of the wires from the OT, PT and choke, which if any should be twisted assuming they are long enough to matter?
-
Twisting is neat, but keeping transformer wires away from sensitive circuits is more important. I try to plan a layout such that all PT wires are kept far away from the signal carrying circuits.
I generally separate and twist PT wires according to winding, ie, primary, filament, HT, etc. I usually don't bother twisting choke wires unless they are both going to the same general location. I usually don't twist OT primary wires unless it's a U/L circuit, in which case I'll twist the plate/screen wires for each tube. Layout is a big factor on twisting OT secondary wires. Really, layout is a big factor in twisting any transformer wires for me. Sometimes I twist, sometimes I samba. Here are a few samples to give you an idea...
http://home.comcast.net/~seluckey/amps/vox/v_12.jpg (http://home.comcast.net/~seluckey/amps/vox/v_12.jpg)
http://home.comcast.net/~seluckey/amps/tdr/tdr_11.jpg (http://home.comcast.net/~seluckey/amps/tdr/tdr_11.jpg)
http://home.comcast.net/~seluckey/amps/5e3/5e3_rear.jpg (http://home.comcast.net/~seluckey/amps/5e3/5e3_rear.jpg)
http://home.comcast.net/~seluckey/amps/lightning/l1.jpg (http://home.comcast.net/~seluckey/amps/lightning/l1.jpg)
http://home.comcast.net/~seluckey/amps/warbler/w_06.jpg (http://home.comcast.net/~seluckey/amps/warbler/w_06.jpg)
-
thanks. What i was actually trying to understand was whether it's ok to twist or if there are any cases where it could be detrimental. I take it any twisting within the same part of the transformers is ok such as the primary or secondaries etc.
-
Twisting is an attempt to reduce the apparent field around a current-carrying wire. The idea is if you have two phases of the same a.c. current on twisted wires, the opposite fields emanted by each tend to cancel/minimize the field.
So, twist pairs that carry a lot of a.c., like heater wiring (6.3v and 5v) and the PT secondary. D.C. wiring/chokes/small-signal (small current) wiring benefits less from twisting.
But Sluckey's right that the biggest issue is, twisted or not, keep low-level or high-impedance circuits away from high current wiring.
-
This may be obvious to everybody else, but it took me a while to "get" that you run wires in 3 dimensions.
For example if you always run plate leads "down" from the board and run them flat on the chassis, it's easier to keep sensitive grid leads up and away from the higher current plate leads. On one Blackface Reverb build, I finally got the tremolo wobble out of the signal to the PI by running the lead from the Intensity pot as high above the board as possible and then dropping vertically down to its connection point.
Also, I haven't experienced any ill effects from twisting multiple signal wires such as going between the board and the tone stack. Sometimes that makes things a bit neater - but NOT neater than sluckey's builds!
HTH
Chip