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Modular Amps
Egnater / Randall Modular Amps
RM100 Tube failure light and randomly blowing tube fuses
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<blockquote data-quote="mThomasDutch" data-source="post: 147134" data-attributes="member: 2616"><p>Updates.</p><p>I measured all resistances and voltages around the tube sockets. All measure good according to the schematic I got from somewhere on this site. </p><p></p><p>I found that the reason the failure light was on was that the resistor R19A (1 ohm 1 watt) was open. I found that the voltage on screen 2 was about the same as plate (510 to 513), but other than that the heater voltages looked good, bias voltage was there and steady, etc.</p><p></p><p>So, I put a set of 6L6's in and biased them up. I biased one of them in a different socket, measured the bias voltage at the pin on the tube, and then put that tube in V3 and made the bias voltage the same until I can replace the blown resistor.</p><p></p><p>I plugged in and played a few minutes at low volume and all was well until the 4th of July happened.</p><p></p><p>Now this is weird. I saw light above and below thee board, so I made a thorough inspection. Here's what I now know:</p><p></p><p>1. The 6L6 that lit up came out of my RM100C. It now has a crack in the glass near the base and of course is bad. Unfortunately I don't know if it had the crack and lost vacuum before the event, or if the event caused the crack. </p><p>2. The resistors R9A and R10A on the A board both have holes blown in them. The schematic identifies them as R9G and R10G, but they are definitely on the A board and connect to the orange wires coming from the PT. I believe page 1 of the schematic identifies this as the 6.3 Volt filament supply. </p><p>3. The orange wires coming from the PT have 70+ volts AC on them, as does pin . That seems like a lot more than 6.3.</p><p></p><p>Am I misreading this schematic, or is my PT all kinds of jacked up?</p></blockquote><p></p>
[QUOTE="mThomasDutch, post: 147134, member: 2616"] Updates. I measured all resistances and voltages around the tube sockets. All measure good according to the schematic I got from somewhere on this site. I found that the reason the failure light was on was that the resistor R19A (1 ohm 1 watt) was open. I found that the voltage on screen 2 was about the same as plate (510 to 513), but other than that the heater voltages looked good, bias voltage was there and steady, etc. So, I put a set of 6L6's in and biased them up. I biased one of them in a different socket, measured the bias voltage at the pin on the tube, and then put that tube in V3 and made the bias voltage the same until I can replace the blown resistor. I plugged in and played a few minutes at low volume and all was well until the 4th of July happened. Now this is weird. I saw light above and below thee board, so I made a thorough inspection. Here's what I now know: 1. The 6L6 that lit up came out of my RM100C. It now has a crack in the glass near the base and of course is bad. Unfortunately I don't know if it had the crack and lost vacuum before the event, or if the event caused the crack. 2. The resistors R9A and R10A on the A board both have holes blown in them. The schematic identifies them as R9G and R10G, but they are definitely on the A board and connect to the orange wires coming from the PT. I believe page 1 of the schematic identifies this as the 6.3 Volt filament supply. 3. The orange wires coming from the PT have 70+ volts AC on them, as does pin . That seems like a lot more than 6.3. Am I misreading this schematic, or is my PT all kinds of jacked up? [/QUOTE]
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Modular Amps
Egnater / Randall Modular Amps
RM100 Tube failure light and randomly blowing tube fuses
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