On May 17, 7:24*am, "Phil Allison" wrote:
"William Sommerwerck"

** Bill - *how do we get you to go away and stop *****ING *trolling ??

Do we have to track you down to the stinking rock you hide under and get
someone to bullet you between the ears ?

Would breaking every bone in your body do the trick ?

How about sticking a pike up your arse an out your chest ?

Would that stop you ?

.... *PhiI

As I said previously the 100 watt Technics mono amplifier has just one
output which I believe to be 8.0 ohms. The model number of the amp,
for purposes of this discussion is irrelevant. One of the other
"junker" amps I have here is also operational and is actually a
control amplifier from an old school PA system. Among other circuits
present in this unit, microphone etc, there are two paging circuits.
One is a 3.0 watt amp which was used for paging to an individual
classroom, and the other is a 60.0 watt amp which was used for "all
call" or emergency paging throughout the building.

The 60.0 watt amp is essentially built around an STK hybrid. It was
powered by a + and - 60 volt DC supply. For this application the
output of this amp is fed through a1000 uf cap in series with a small
coil directly to the primary of the output transformer. The secondary
has taps for 8.0, ohms, 25V and 70 volts. The spec sheet for the chip
shows a typical connection diagram for test and evaluation purposes.
The output load was a speaker load. I don't recall what the speaker
impedance was, but it was either 8.0 or 16.0 ohms. Except for using
the output transformer primary in place of the speaker load, the test
circuit almost exactly mimics the school PA amplifier portion of the
intercom system.

That's where I got the idea of using a transformer (of this type) in
my proposed application. I reasoned that if the primary was anything
close to a typical speaker impedance and the 70.0 volt output side was
properly loaded then how could this damage the Technics?

I had another thought. First let me say that I'm well aware of how DC
resistance is related to, but not equal to speaker impedance. Lets say
for argument sake I was to measure the DC resistance of the 8.0 ohm
tap on the transformer secondary. And lets assume that it happens to
measure 2.0 ohms. We know that this tap has an impedance when
operating in its normal environment of 8.0 ohms. Now knowing that, if
I were to measure the transformer primary and it also measured
something close to 2.0, can I assume an impedance close to 8.0 ohms
for that primary as well? If not then how would one go about
determining this?

One other note I thought would be interesting to mention. Not every
amplifier manufacturer does this but Bogen seems to on many of their
PA amplifiers. They include what seems to be the equivalent impedance
in parenthesis next to the voltage output. For instance, the four
output terminals of the CHS 60 amplifiers I have here in the shop are
marked as follows:
1. 8.0 ohms
2. 25 volt (10.4 ohms)
3. 16.0 ohms
4. 70.0 volt (82.0 ohms).

And one final question. Phil, why did you deem it necessary to change
the title of this thread? (I'm asking nicely). Lenny