Metropoulos Forum

Hey all,

I just got my hands on a quad of NOS Mullard xf2's! Yes I'm excited.

But I have a question: Will I have to have these tubes "biased"?

If I do I won't be doing it myself as I don't want to risk damaging these tubes one bit. Does anyone know of any places in the Los Angeles area where I can have these biased?

Thanks!

Brandon wrote: But I have a question: Will I have to have these tubes "biased"?

Absolutely YES! Especially if you didn't have similar spec tubes in before. Do not risk these tubes!

It's not difficult though, with a set of probes and a reasonable multimeter...

search for el34 biasing guide for an idiot

Thanks for the answers!

Another question.

I have reissue mullards (russian) in there right now. When I get the amp biased to the nos mullards will I still be able to us the tubes I have in there now?

No, you'll still need to bias every time.

Unless!

Bias the set that is already installed, notate that bias reading, then install the other set and check bias. If they bias similarly you can just pop the newer set in as a backup if you have problems, on the fly.

Example: I have a 100 watt Marshall with Mullards that bias 37.8, RFT set that swaps in and reads 37.2, and a new set of 6ca7s that read high 36 range. All safe, and they all sound good at that one setting.

Similarly means different things to different people. When I buy tubes, I mark the boxes for which amps I biased them in, which slot each tube was installed, and what the bias reading/voltage was on that amp. I normally have at least one extra set I can swap in to any given amp with peace of mind.

Congrats on the new tubes. I hope you put them in and couldn't care less... lest you starve yourself affording tubes for the rest of your life. HAH!