Bias precision?

[SoundMods]

Just a comment -- when firing up your amp. and you wish to check bias give it at least a half hour to "cook" before checking.

It takes a while before things stabilize. The game I play when installing new tubes is to let things get hot for about a half-hour or longer after an initial adjustment to protect the tubes -- then aftera half-hour or so set the bias where you want it -- then go back much later after playing music for a final check and adjustment. You should then be good to go for the long term.

[justinis]

Just a comment -- when firing up your amp. and you wish to check bias give it at least a half hour to "cook" before checking.

It takes a while before things stabilize. The game I play when installing new tubes is to let things get hot for about a half-hour or longer after an initial adjustment to protect the tubes -- then aftera half-hour or so set the bias where you want it -- then go back much later after playing music for a final check and adjustment. You should then be good to go for the long term.

Thank you! I have definitely not been doing this. I will change my ways!

[SoundMods]

You're welcome! The nice thing about cathode bias, as opposed to fixed bias, is that you can plug in a pair of matched tubes and play music -- no muss -- no fuss.

Then there are the mixed versions. G.E. of the long distant past and Jadis (more recent) used a mix. They used fixed bias to set a starting point together with cathode bias.

I had a Jadis Defy-7 that was set up that way and it did work quite well. Different strokes for different folks.

[Pelliott321]

Doug at Douglas Tubes suggests with new output tubes to run the new tubes at half bias for a few hours. Then 3/4 bias for a few hours, then full bias for a few hours checking for drift every so often.

[dberning]

I would assume that what he means by half bias is not half bias but half current which is more bias!

David

[Pelliott321]

correct, I misspoke
but you know what I meant

[justinis]

For what it's worth, I don't have new tubes; I have very old tubes I took out of a Heathkit AA-100...

[Pelliott321]

does not matter the need to be biased the same to sound the best.
if you can not bias them then something is wrong

[Roscoe Primrose]

I think he was referring to your 1/2->3/4->full progression recommendation not necessarily applying to old, well worn, tubes...

Roscoe