Single Rectifier rev 2 (raw on ch2), tubes safe bias range

[wiorys]

Hi,

I wonder what is safe bias range for:
- EL34
- 6L6
tubes in Single Rectifier.
Or - what's the plate voltage?

Maybe I used wrong words to search, I've only found one specific post with 432 v / 29mA values for 6l6.

Somebody mentioned:
https://www.eurotubes.com/store/pc/mesa%20boogie%20amps.htm
But unless I am wrong, 88ma for EL34 is ridiculous, even 50ma is a bit high.

I'm buying matched tubes so I can ask for specific "rating". I own couple of different quads so I know what rating I need to get to achieve some bias. I don't want Mesa tubes for simple reason: I can get same thing for much less money.

I could measure plate voltage, I have an multi-meter but I don't want to mess with amp internals unless I have to.

I have bias tester. My current Mesa 425 5881 tubes have 19mA. AFAIK low bias won't hurt amp so I could go for some low rated tubes, but I just want to know what's safe range.

PS, some weird experiences:
- I've borrowed Mesa 440 from my buddy and one had 5mA so I guess not as reliable as they say
- I own Splawn Nitro KT88, svetlana S tubes, _20mA_ mismatch... sound amazing(matter of taste, mids are fuller), compared to matched Sovteks/EHX.
- played year or so on Marshall 6100 Svetlana Winged C with three working tubes (I didn't know that one was not working, you could see it works, but after measuring it..it didn't). Never could achieve so good tone with any other tubes (and I've tested most of them). It doesn't mean that svetlanas are superb, just they've worked good with my amp/preamp tubes.
- I tend to like old tubes, sound warmer (probably because of reduced bass/treble or something), also the ones with low rating (so bias is low)

I mean, that in my case, theory doesn't work Anyway usually I'm trying to stick with "proper" values.

 

[vick1000]

You have to know thw plate voltage to calculate the proper tube bias.

http://www.webervst.com/tubes1/calcbias.htm

Get a bias probe to measure plate voltage and/or bias.

If you do not know what you are doing, leave it to a tech. The leads on the probe have enough current to stop your heart, even after powering down the amp.

 

[wiorys]

That's why I don't use bias meter which measures plate voltage and that's why I asked this question in the first place.

Plate voltage can change, but not that much so unless amp is broken it's some kind of fixed value.

 

[vick1000]

There are probes you connect to a meter to measure plate voltage....

http://www.ebay.com/itm/Bias-Tool-Plate-Voltage-Tester-for-tube-amp-amplifier-/360140563557

You don't have to open the chassis, but the leads must stay in the meter when the probe is in the socket at all times.

Tube bias on fixed bias amps is not that big of a deal anyway, as long as the amp is built well, the tubes are with in specs, and also built well, you should never have a problem. But "proper" values are determined by plate voltage measument with the mathmetical formula. Basically if you like the tone you are getting from the amp, and the tubes are not red plating, you are good to go. If you think you are in cross over distortion, they you need to addreess tube bias.