I decided to tube roll one of my pre-amps today, which uses 12au7/ECC82 tubes, and unfortunately, one of the triodes was damaged in shipping.
The amp only uses two tubes, but it only uses one triode per tube, but these tubes have 2 triodes.
Looking at the datasheet, it seems like if I pull the faulty tube, bend out pin 5, and install the tube backwards, the other triode will line up perfectly.
I wanted to ask if this is OK before I tried. I already checked to make sure it only uses one of the two triodes in each tube.
The amp only uses two tubes, but it only uses one triode per tube, but these tubes have 2 triodes.
Looking at the datasheet, it seems like if I pull the faulty tube, bend out pin 5, and install the tube backwards, the other triode will line up perfectly.
I wanted to ask if this is OK before I tried. I already checked to make sure it only uses one of the two triodes in each tube.
Pin 9 becomes pin 4 and pin 4 becomes pin 9. I don't understand why they won't be connected installed backwards. The amp doesn't use pin 5 at all.
Why is that? The positions are just reversed when installed backwards. This amp doesn't even use pin 5, as it center taps.
Well, I decided to give it a shot, fingers crossed and on the power switch in case anything went wrong... and it didn't.
Amp fired up, and the faulty tube came to life. Seems you can install the tubes backwards in this amp. No issues yet anyway, but the audio is clean and nice sounding, so I foresee no problems.
Amp fired up, and the faulty tube came to life. Seems you can install the tubes backwards in this amp. No issues yet anyway, but the audio is clean and nice sounding, so I foresee no problems.
Pin 5 must be connected to pin 4 for 6.3v (parallel heater) for this to work, either on the PCB, or at the socket. Obviously, this is how your amp is configured, so you are able to use the other triode section.
jeff
rich1051414
Can I ask a couple of simple questions?
On the amplifier side that has the valve / tube in the 'correct' way round, do you see the heater (orange glow) on both or just one half of the 12AU7?
Now on the 'turned' valve again, do you see the heater glow on both or just one half and is it as bright as or dimmer than the 'correct' located tube?
A perplexed, Alan
Can I ask a couple of simple questions?
On the amplifier side that has the valve / tube in the 'correct' way round, do you see the heater (orange glow) on both or just one half of the 12AU7?
Now on the 'turned' valve again, do you see the heater glow on both or just one half and is it as bright as or dimmer than the 'correct' located tube?
A perplexed, Alan
Sorry for being slow here, but the amp has 2 x double triodes and uses just half of each one? Bizarre or what?
So another problem, if it uses 4 and 9 for heaters normally, that heats the pin 1, 2 and 3 triode half. Then if you turn it round, you are still heating the pins 1,2 and 3 half, via 9 and 4 correct?
But now the 'unheated' half (pins 5 to 9) are in the pins 1,2 and 3 location - so how does it work???
Really more perplexed now than before.
Alan
PS. Unless you have joined pins 4 and 5 together when you bent 5 'out of the way'?
PPS. Or both halves are strapped together (1 to 6, 2 to 7 and 3 to 8) and then normally only use the 1,2,3 half??? Bonkers.
So another problem, if it uses 4 and 9 for heaters normally, that heats the pin 1, 2 and 3 triode half. Then if you turn it round, you are still heating the pins 1,2 and 3 half, via 9 and 4 correct?
But now the 'unheated' half (pins 5 to 9) are in the pins 1,2 and 3 location - so how does it work???
Really more perplexed now than before.
Alan
PS. Unless you have joined pins 4 and 5 together when you bent 5 'out of the way'?
PPS. Or both halves are strapped together (1 to 6, 2 to 7 and 3 to 8) and then normally only use the 1,2,3 half??? Bonkers.
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Both sides on the one the correct way around. Only the active triode on the one backwards.
It's not that bonkers. It's actually fairly typical. I think they use 2 tubes for aesthetics, but perhaps there's an actual reason. Many tube amps that use 2 physical tubes only use one triode in each of them.
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Thanks Rich,
That makes it a lot clearer. There has to be a heater connection to pin 5 to the socket that heats the pins 6,7 and 8 half. Or only the one half would glow.
Understand that, but I think that the only way your 'fix' can work is if both halves are in parallel by design, i.e. pins 1 - 6, 2 - 7, 3 - 8 are joined as will be 4 and 5. Then two valves makes sense.
A quick look at the socket wiring would confirm that.
Alan.
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