Can I bias adjust the 5150 III combo?

[crwnedblasphemy]

Before taking the chassis out, was wondering if there is an adjustable internal bias point, or if it's fixed? Wasn't quite sure. I have the 2x12 combo.

 

[Code001]

Adjustable fixed bias https://carlscustomamps.com/cathode-vs-fixed-bias

I believe only the "stealth" version of the heads have a pot to adjust externally. Other variants are internal (assuming they're fixed bias and not cathode biased like those lunchbox variants). Could be wrong, going by memory. Easy enough to figure out by opening 'er up though.

 

[7704A]

The 5153 EL34 50W head I did some work on had an internal bias pot and sense resistor if I recall.

 

[crwnedblasphemy]

Cool...I have the Eurotubes Bias Probe, so as long as I see the r171 blue bias adjustment I can just plug in the 6L6 probe and adjust to milliamps with a plastic or wood flathead.

 

[napalmdeath]

Cool...I have the Eurotubes Bias Probe, so as long as I see the r171 blue bias adjustment I can just plug in the 6L6 probe and adjust to milliamps with a plastic or wood flathead.

Easy as that.

 

[Geo]

I bought one when they came out and was set to 23mv per tube.

 

[crwnedblasphemy]

I bought one when they came out and was set to 23mv per tube.

What's the range it should be? 28-32ma per tube?

 

[BABMusic]

According to Dave Friedman, anywhere from 15 to 40 is okay. I think 32-38 is the best range. It depends on the amp, but anywhere you like the tone between 32 and 38 is fine. If you play loud, maybe do a colder bias at 32. If you play quiet in the bedroom, 38 might sound better.

 

[Geo]

What's the range it should be? 28-32ma per tube?

Technically yes, but it sounded better at 23.