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The 287W T5 mystery.
The 287W T5 mystery.
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Old 13th September 2018, 06:26 AM   #1
ArcheusLedoux is offline ArcheusLedoux  United States
diyAudio Member
Join Date: May 2015
Location: lexington KY
The 287W T5 mystery.
Default The 287W T5 mystery.

So over the years Ive had a few of these boat anchors, all along one questioned persisted.
287W was a Booster amp. It was usually paired with an 127B 15 watt booster amp.
Now here is where things get sideways, the schematic shows a T5 on the 287W. This never happened that I could find. Instead T5 was mounted on the 127B preamp. T5 primary was lo voice coil ratings up to say 500 ohms.
The secondary was ct Hi Z. Now keep in mind that this was the 127B output transformer. So the Hi Z side would be attached to the 6L6 outputs.
So does this mean there needed to be a second T5 ? The part number for this was T16, Remember you need a Hi Z out put to drive the 805 grids,
So in my mind it goes 6L6 to T5 hi Z to Lo z, next second t5 goes from first T5 to second T5 Lo Z to Hi Z then on to 805 grids.
I'll try to dig up some schematics for this. I'm probably making it harder than it is.
My point is these amps came with a 500 ohm tap. But in order to run a booster amp you need another transformer to go from 500 ohms to grid resistance and center tapped for phase inverter. This would be the second T5
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