JCM -800. only one tube running. still worked?

[MRscratch]

ill try this again. i have a 100w 2203. its a CSA , and only has a 4/8 ohm tap.
so i pull two tubes, run it at 8 ohms into my 16 ohm cab.
the other day i discovered that only one tube was working. the other was stone cold.
the amp was still working, mind you i had it real low.
is this bad? i though you HAD to have at least two?

[SatelliteAmps]

It's not great, but you might be lucky. This usually means one tube is dead and the amp is running in single ended Class A. The amp can handle it, but you should put a new tube in the other socket.

[MRscratch]

Originally Posted by SatelliteAmps

It's not great, but you might be lucky. This usually means one tube is dead and the amp is running in single ended Class A. The amp can handle it, but you should put a new tube in the other socket.

i did. i put in a new set of NOS svetlana.
they say made in USSR on them! i though that it was strange, because i didnt see the heater light up, and it was cold! the amp sounded great though!
does this cause any unnecesary strain on the tranny or circuit?

[SatelliteAmps]

So one tube is still dead? If so, you need to have a tech pop it open and take a look.

A lot of whether there is strain or not, depends on what else is going on. If it happens with more than one set of tubes, then it needs to be looked at to determine what is going on. Could be something easy, could be something painfully expensive.

[GearHeadFred]

Hard to imagine a "painfully expensive" problem from lack of heater voltage on 1 tube.
Swap the tubes and see if the other one lights up in that socket.
No need to take the amp out of standby for this test,

[SatelliteAmps]

Originally Posted by GearHeadFred

Hard to imagine a "painfully expensive" problem from lack of heater voltage on 1 tube.
Swap the tubes and see if the other one lights up in that socket.
No need to take the amp out of standby for this test,

Painfully expensive can be a burnt board, a potentially bad OT, arc'd socket, Broken filament lead (which usually stops the other filaments down the line) bad tube, or some combination thereof. Might just be a bad connection on the filaments. Might just be a bad tube, which is why I asked about whether it does it with both sets of tubes. Without seeing the inside of the amp, it will be difficult to say exactly why this is happening.

[MRscratch]

Originally Posted by SatelliteAmps

So one tube is still dead? If so, you need to have a tech pop it open and take a look.

A lot of whether there is strain or not, depends on what else is going on. If it happens with more than one set of tubes, then it needs to be looked at to determine what is going on. Could be something easy, could be something painfully expensive.

oh no! it works fine now with the svets. both tubes light up.

[GT100]

Originally Posted by SatelliteAmps

It's not great, but you might be lucky. This usually means one tube is dead and the amp is running in single ended Class A. The amp can handle it, but you should put a new tube in the other socket.

Yeah, its running Class A -but the bias is WAY OFF.



Lloyd

[SatelliteAmps]

Originally Posted by MRscratch

oh no! it works fine now with the svets. both tubes light up.

Most likely, just a dead tube then. I wouldn't worry about it any more.

[MRscratch]

cool! good to know. I never thought that it would still work with only one tube!
half the tone?

[rockon1]

Originally Posted by MRscratch

cool! good to know. I never thought that it would still work with only one tube!
half the tone?

I was futzing around with power tube swaps one night. Fired up the amp and started playing. Noticed it sounded a bit weak. Looked down at me feet and one of the amps two 6L6's was on the floor. lol! Bob

[GearHeadFred]

Originally Posted by MRscratch

I never thought that it would still work with only one tube! half the tone?

Really quick explanation: The output circuit is called "push/pull", so one tube pushes the signal, and the other pulls it. So you'd think you would get very weird looking (and sounding) "hump-like" waveforms with only 1 tube, but because of the dynamic interactions of the OT and speakers, they look and sound fairly close to normal.

[SatelliteAmps]

Originally Posted by GearHeadFred

Really quick explanation: The output circuit is called "push/pull", so one tube pushes the signal, and the other pulls it. So you'd think you would get very weird looking (and sounding) "hump-like" waveforms with only 1 tube, but because of the dynamic interactions of the OT and speakers, they look and sound fairly close to normal.

Sound wise it is not close to normal, but it is a much lessened output, much early breakup, much more compressed, and with a lessened fidelity.