Classic 50 212

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Steve JA
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Posts: 2
Joined: Sun Dec 04, 2022 8:25 am

Classic 50 212

Post by Steve JA » Tue Dec 06, 2022 2:36 pm

20221206_100416.jpg
20221206_100416.jpg (2.59 MiB) Viewed 973 times
I swapped in a new speaker into my classic 50. Because I wanted to here the new speaker alone I disconnected the B Marvel and plugged the new speaker into the 8 ohm jack. Played about 20 minutes and liked what I heard.
Next time I played there was no output, only a loud hum, which got louder . Switched off , turned amp around, when I switched on again saw smoke near the #2 EL84 power tube on the left. Also spark/smoke from a resistor behind the tube socket. The adjacent tube pin has intermittent spark, and signs of excessive heat. The pencil point in the photo shows the area.
20221206_100416.jpg
20221206_100416.jpg (2.59 MiB) Viewed 973 times

Did I damage amp by playing thru the 8 ohm jack ONLY ? Never got a manual w/ amp, research shows the 8 ohm jack is to be used w/ an external cab. Resistor in question is a large ceramic resistor on power tube board. All tubes light up, as amp warms up hum gets extra loud. Any help , suggestions appreciated. Thank you, Steve JA

Steve JA
New Member
Posts: 2
Joined: Sun Dec 04, 2022 8:25 am

Classic 50 212

Post by Steve JA » Tue Dec 06, 2022 2:40 pm

20221206_100416.jpg
I swapped in a new speaker into my classic 50. Because I wanted to here the new speaker alone I disconnected the B Marvel and plugged the new speaker into the 8 ohm jack. Played about 20 minutes and liked what I heard.
Next time I played there was no output, only a loud hum, which got louder . Switched off , turned amp around, when I switched on again saw smoke near the #2 EL84 power tube on the left. Also spark/smoke from a resistor behind the tube socket. The adjacent tube pin has intermittent spark, and signs of excessive heat. The pencil point in the photo shows the area.
20221206_101026.jpg

Did I damage amp by playing thru the 8 ohm jack ONLY ? Never got a manual w/ amp, research shows the 8 ohm jack is to be used w/ an external cab. Resistor in question is a large ceramic resistor on power tube board. All tubes light up, as amp warms up hum gets extra loud. Any help , suggestions appreciated. Thank you, Steve JA

Lester H
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Posts: 18
Joined: Sat Sep 12, 2020 12:06 pm

Re: Classic 50 212

Post by Lester H » Tue Dec 06, 2022 10:40 pm

Luckily I have no first hand experience in this but I was always under the impression running a significant ohm mismatch or turning on a tube amp with no load (no speakers) usually took out the output transformer but I don't know what other damage if any occurs when that happens.

How old are your power tubes? My thoughts are you coincidentally had a tube short out and it took the cement resistor out with it. I have had tubes short out before and it took out a cement resistor on the power tube board, so this sounds very reminiscent of my experiences when that has happened (more than once unfortunately). One time it was obvious the tube shorted out by looking at it and another time it looked normal with no obvious signs it was bad.

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