Any idea of the temp that opens this Pepi thermal fuse? Seems like the glue would soften up and release pepi prior to tripping
80-100c?
80-100c?
Dang. With the big ole fat heat sink and monster fins the unit must run cool at max attenuation. And or its a good way to keep the user honest .
Thanks for the spec.
Polarized plug adapter installed. Verified original working left channel with it. Dim bulb 💡 charged mains up, then dimmed . 🎉
Measured 70mv of idle voltage and 9mV of dc offset. 👍 No load applied for these measurements.
Rebuilt right channel goes in tomorrow.
It was DOA. Multiple blown
Pieces of silicon and passives🤞……
Measured 70mv of idle voltage and 9mV of dc offset. 👍 No load applied for these measurements.
Rebuilt right channel goes in tomorrow.
It was DOA. Multiple blown
Pieces of silicon and passives🤞……
It appears the Left channel is using a different version driver board than the Right channel. pc CFE379. I happened to also notice a device placed on the output board between the Base snd Collector on the NPN side.
CFG378 version Driver board.
Outputs of left channel w/ component placed across BC.
CFG378 version Driver board.
Outputs of left channel w/ component placed across BC.
Hello, fellow DIYers. Right channel board placed and connected. At first i was only interested in in dialing in the idle current. When poweted up idle was at around 40mV. I dialed it up to 75mV. No abnormally high current detected on dim bulb. .
I then checked DC offset. Its going to 31V!
I then checked DC offset. Its going to 31V!
Your 31VDC offset voltage is roughly half of the DC rail voltage (60VDC or so). That indicates to me that there is still a faulty transistor in the cascade output. You effectively have 2 transistors in series across the +/- DC rail to the output - each sharing the voltage. This is allowing that voltage to appear at the output. I would check all output transistors again in that channel - especially the older original types connected to the output .
Hi. So disconnect all the output wires and apply +/- rail to driver board and ground accordingly .
Do you leave the +/- mid rails floating?
Any particular ECB voltages to highlight?
Note all outputs were replaced with mj15023/24. Tested and matched. Seeing half the rail voltage at out was an unfortunate surprise.
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Yes, all the outputs were replaced along with new mica and lube. Thats what bothers me. I kept unit on dim bulb to avoid any blow ups. 8 x 15023s and 8 x 15024’s.
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This might be a stupid comment/question, but do TO-3s require insulated shoulder washers to keep the screws from shorting the case (collector) to the heatsink?
Did you check with a DMM on resistance range that there are no shorts between each TO3 transistor case and the heatsink? Yes each mounting screw needs an insulating bush where they pass through the heatsink - these should all have been fitted on the original build.
The micas insulated it. Nuts and screws tie into midrails. I need to check for the bushings.
I did, but I'm second guessing everything now. I’ll take another look. Post pics in case i am missing something.
The screws go thru the heatsink. If any of these touches the heatsink, it will tie the TO-3 collector to it. I would verify every single one of these. Normal TO-3 mounting kits, such as the Aavid 4804G, include insulated shoulder washers.