Postby Slashwannabe1 » 22 Jan 2012, 18:10
If the power tubes are not red plating you should be alright but make sure you keep a close eye on them and for hum that seems to get louder.
The bias on my 2466 Vintage Modern was 79mv which is factory spec and they red plated prior to biasing at 92mv. So in theory as long as your tubes don't red plate and the noise floor seems acceptable you should be ok. One sign of a tube red plating is when the noise floor rapidly gains noise in which case you should turn the amp off. Now the down side to this is that without biasing you won't get the full potential out of your tubes for tone, so comparing various types of EL-34s may be redundant.
I ran my Bandmaster for years without biasing just slapping new JJ's in every 3 years, I was lucky to have had cooler running tubes during that time, by the time your tubes shit the bed a tube running unbiased cold sounds better than a tube thats going out so it always improved the tone and I never thought much about biasing early in my playing because I figured there was a big mystery surrounding it (myth!). My first year playing guitar using that Bandmaster I used to hit the top of the amp with my fist when noise would come followed by the tube red plating and that actually helped those 30-40 year old tubes stop red plating a few times till one day they just got unplayable and I switched them out.
I now bias all of my amplifiers :)
Amplifiers: Marshall 2555x 100watt Silver Jubilee Full Stack with matching 2551AV & 2551BV 8x12 70 watt Vintage 30 speakers.
Marshall 2466 100watt Vintage Modern w/ Matching 425A cab
1966 Fender Bandmaster
Effects: MXR:M234 Analog Chorus, Phase90, Slash Octave Fuzz, Slash SC95 Wah. BOSS: RV-3 & DD3 Reverb & Delay, GE-7 EQ,NS-2 Noise Suppressor, CS-3 Compression Sustainer
Guitars: 6 Les Pauls with Seymour Duncan Alnico 2 Pro Pickups.