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Question about filament voltage for 5687 tube as output tube in an SP MPX3 Slam model

post #1 of 5
3/31/11 at 11:54pm
Thread Starter 

Does the 5687 take a 12.6 or 6.3V filament supply when it is used with an adapter in an Single Power MPX3 Slam model?  I am trying to replace an adapter for the 5687 tube?

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post #2 of 5
4/1/11 at 8:22am

Whether the 5687 adapter takes a 6.3V or 12.7V heater supply depends how they & the amp are wired. The vast majority were wired for 6.3V operation, but some were set up for 12.6V. The safest bet is to measure the adapter you still have and see how its wired. 

 

Be super extra careful about this in general. The 5687 adapters had a resistor IN the adapter that non-singlepower adapters may not have. More checking what you have now. Be sure to get this resistor in the new adapter or bad things may happen (the tube will probably overheat, melt together, and cause the catastrophic failure of the rest of the amp) at the very least it will never run right.

 

 

 

PLEASE! 

Filaments are on directly heated tubes, which are totally badass. Heaters on indirectly heated tubes which pretty much wish they were directly heated tubes. OK the 5687 is a pretty awesome tube, but still. 

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post #3 of 5
4/1/11 at 9:33am
Thread Starter 
Thanks for the headsup. I see the resistor. What does it do?
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post #4 of 5
4/1/11 at 9:57am

Its in series with the cathode resistor in the amp. The cathode resistor in the amp is sized for the 6sn7 or tubes with similar operating points, but the 5687 does not have similar operating points.

 

Without the resistor in the adapter Vgk with the 5687 would be too low, which allows current to go very high, which results in too much power dissipation by the tube and then the tube overheats. 

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post #5 of 5
4/2/11 at 2:32am
Thread Starter 
Thanks. simple.
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