Specifications

Fig.5
In Fig.5, the interior of the power supply side of the amp is shown, with the power
transformer removed. The letter "E" points to the "step-start" fuses. The letter "B" shows K-
12, and "C" points to K-11. K-11 is the primary contactor, which engages when the "ON"
switch is pushed. K-12 is the "step-start" relay, which closes after a short time-delay, after K-
11 closes. K-12 shorts the step-start resistors out of the circuit, when closed.
The problem with my unit, was that K-12 had worn out contacts which would not allow the
resistors to be shorted out of the circuit, which in turn caused a large current flow through
and burn up the resistors. I replaced K-12, and the resistors. I also found that the time-delay
IC was not sending current properly to K-12, so instead of replacing the IC, I built a small
RC network using a resistor and capacitor that caused about a half second delay in K-12
closure after power "ON". The replacement relay I used for K-12 was not a 24Vdc coil like
the original, all I had was a 12Vdc coil relay, but the resistors in the RC time-delay network
allows it to operate at the 28Vdc that the LVPS provides. The resistor I used was 50 ohms
@ 20 watts, with 4400µF @ 50Vdc capacitor. The main difficulty of this installation was
finding a place to put the components I found a small space to place them just to the left of
K-12 along the bulkhead.
The "step-start" system works fine now.
Surge suppression
It was a surprise to me to find that the 86 does not have any form of AC line voltage surge
suppression system.