Transformer and Wire Color Standards for Tube amps
From the ARRL handbook:
BLA - grounds, grounded
elements, returns
BRO - heaters/filaments,
off ground
RED - power supply B+
ORA - screen grids (and
base 2 of transistors)
YEL - cathodes (and
transistor emitters)
GRN - control grids,
diode plates (and base 1 of transistors)
BLU - plates (and
transistor collectors)
VIO - power supply, minus
leads
GRA - AC power line leads
WHI - bias supply, B or C
minus, AGC
Is there a standard scheme for power
transformer wire colors?
From Orr's Radio Handbook:
Primary leads
-------------- black
(if tapped)
Common
----------------- black
Tap
-------------------- black/yellow
End
-------------------- black/red
High voltage secondary
----- red
Center
tap ------------- red/yellow
Rectifier filament
winding - yellow
Center
tap ------------- yellow/blue
Filament winding No. 1
----- green
Center
tap ------------- green/yellow
Filament winding No. 2
----- brown
Center
tap ------------- brown/yellow
Filament winding No. 3
----- slate
Center
tap ------------- slate/yellow
I have seen primaries with other color schemes; if it includes black it
should be a primary lead of some sort. I've seen transformers with only
one filament winding that was brown. I've seen high voltage secondaries
with red/white centers. And on old transformers, the colors may have
faded to the point brown looks black or green looks black or brown, and
so forth. I'm not aware of any standard for filament winding numbering,
so if there is more than one, verify the voltages. The rectifier
winding will normally be 5 volts, but again, verify it. If you have an
old tranny with odd or indistinguishable colors on the leads, verify
them. In fact, it's a good idea to verify any PT before using, just to
be safe. Miswirings are, AFAIK, rare, but do occur, as do shorts.
Is there a standard scheme
for output transformer wire colors?
Derived from the ARRL Radio Amateur's Handbook:
Single-ended transformers:
Plate lead (pri.)
-------------- blue (or brown)
B+ (power supply) lead
--------- red
speaker (typ. +) (sec.)
-------- green (or yellow)
speaker return (sec.)
---------- black
Push-pull transformers:
Plate lead (pri.)
-------------- blue (start)
B+ (power supply) lead
--------- red (center tap)
Plate lead (pri.)
-------------- brown (finish)
speaker (typ. +) (sec.)
-------- green (or yellow)
speaker return (sec.)
---------- black
Ordinarily the black side should also be grounded, if the speaker is
grounded. Replacement transformers are not always identical, so if you
get squeals or other odd sounds when hooking up a new output
transformer, try reversing the output leads. "Start" and "finish" are
arbitrary terms with respect to this configuration.
Is there a standard scheme for
interstage coupling (such as phase inverter) transformer wire colors?
From the ARRL Radio Amateur's Handbook:
Plate finish lead (pri.)
------- blue
B+ (power supply) lead
--------- red (whether center tap or not)
Plate start lead (pri.)
-------- brown
Grid finish (sec.)
------------- green
speaker return (sec.)
---------- black (whether center tap or not)
Grid start (sec.)
-------------- yellow