Archon 25 5881 tube question

[Dennyz]

Apparently (per tech recommendation) i need to replace the worn out 5881 Tungsols on my Archon 25 combo.

I know that these amps come biased between 25/30mV from factory.

I can choose between two sets of 5881s. Which one is "better"?

The 30mV one seems stronger with higher headroom. The 27mV is softer and lower headroom.

My stock Tungsols are set at 28mA from factory (they might drifted a bit).

 

[KentuckyBoiledChiccan]

It doesn't work that way. You need to do some math knowing what your plate voltage is, and aim for percentage of plate dissipation. The mA alone means nothing

 

[Dennyz]

It doesn't work that way. You need to do some math knowing what your plate voltage is, and aim for percentage of plate dissipation. The mA alone means nothing

344v for the plate voltage on Archon 25.

 

[KentuckyBoiledChiccan]

344v for the plate voltage on Archon 25.

Archon is a high gain so I would aim for colder bias. 55-60%.

Your readings would bias it as very cold; 40% to 45%. Safe bias, but I would bump it to 40mA which would give you just over 60% of plate dissipation: more lows, and volume. Shorter tube life.

If you happy with whichever set, put it in and leave it.

 

[KentuckyBoiledChiccan]

Bias is like an age; it's just the number. But like with age, if the number is to high, things can get fucked