Hohner Contessa CA-100 Output

[CJ]

EL84 push pull job with a weird 18 K : 8 ohm ratio on the chopping block,

both coil and core are wax dipped together as opposed to the usual varnished lams which makes life easy and we can use the old lams because they ain't all bent up and stuff,

 

[CJ]

were gonna pull out the ol Billy Baroo heat gun which has nichrome wire spliced in many places due to multiple tear downs, oh Billy, just one more time Billy,

 

[CJ]

sweat those lams like a hog and they pop right out, wax is used on lams in small signal audio like the Peerless K-241-D etc,

 

[CJ]

there is our lead orientation,

 

[CJ]

10 KP wrapper of 1 turn gone and we see a secondary wind

 

[CJ]

margins are usually offset to allow for the bend in the wire at breakout,

 

[CJ]

looks like we gots a split secondary,

 

[CJ]

so one inner and one outer in parallel, which defines our structure as sec-pri-sec which corresponds to the DCR readings on the primary

 

[CJ]

little extra insl for the bigger sec wire, protects against sharp edges from solder connection,

 

[CJ]

first of two layers peeled off at 34 and 1/2 turns, it is common to start a new layer on the opposite side of the lead breakout to keep insl seams from building up,

 

[CJ]

sec-pri insl 1 L 5 KP, 1 L 3 Poly,

 

[CJ]

you see this a lot, corner stripes, holds the layer from slipping off the side of the bobbin while adding insl,

 

[CJ]

anchor on the pri wire, weak tape, i use mylar here,

 

[CJ]

wire looks like it ran a bit hot but not much, you can figure out I^2R loss, we gots 63 ma idle current (bias across 150 ohm resistor gives current) thru 480 ohms, 0.063^ x 480
= 0.003969 x 480 = 1.9 watts of pri heat

 

[CJ]

and down to the last section, inner sec, same margins,

 

[CJ]

former has 0.030 walls, semi un-square, they leave a bit of room for a wood shim to keep the coil tight. and to keep the former from collapsing from the accumulated tension. to see how the tension builds, wrap your thumb with 3600 turns of #37 and watch it turn blue.

if the core tube buckles, then the wire is now loose to vibrate and break.

 

[CJ]

got some leftovers,

 

[CJ]

KP and cheap tape was pretty crispy, kind of like Pringles, pizza flavor,

 

[CJ]

ok then... has anybody seen a tan Sierra? Or do i need to do a lot count?
(man, that wax is gettin to me)

 

[CJ]

build chart , if you roll your own, this helps to keep you from exceeding the overall dimensions of the coil, thus making sure that the coil will fit on the core.