Switch to el34 on single recto

should I just flip the switch on the back, and all will be fine!??? No "fine-tuning" of bias, or anything else to worry about!??
B.R. andershoeg

Thats it! What brand of tubes do you have going in?

Hi. Don''t know which brand i'm putting in it, haven't got a clue of what's best of powertubes! Maybe just some mesa el34.....?? Any ideas? I'm living in Denmark, so there isn't many to choose from. Think the choises are: Elektro harmonix, sovtek, ruby and groovetubes. Any idea of what's best!??(currently i'm having the stock mesa tubes).
B.R. andershoeg

Stock mesa's are 6l6's make sure the switch is set properly to the kind of tubes your running it is not a switch to change the sound to that type of tube it is to auto bias them instead of having it done by a pro (or learning how to do it yourself).

I am under the impression that having the switch set to the wrong setting can damage the amp ?

The tubes should say what type they are on them

mrdylan: I know that it's 6l6 that comes with the amp. I'm asking because I think it could be fun to listen to some el34's, just to hear the difference of the two kinds of powertubes. I just wanted to know if there shouldn't be any fine-tuning of the bias (done by some tech.), or I can go with "the flick of a switch"!?
B.R. andershoeg

I just didn't want you to mess up your amp.

That is exactly what the switch does put EL34's in it and flick the switch and vise versa.

OK, i'll try that 8) Thanks!

You might just like those EL34's, I do! I run the stock Mesa variety in my Dual Rec!

The switch on the back of the amplifier basically allows another 47K resistor to be placed in parallel in the Recto's bias circuit. This will basically give the EL34's the extra grid(bias) voltage it needs to operate at the same level as the 6L6GC's. 6L6GC's draw more natural plate current than EL34's, so they don't need as much. The Bias/Grid Voltage is a negative figure, so the more resistance you have on the circuit, the hotter the Cathode Current (Bias) will be.

If you placed EL34's in the amp, while it was still in the 6L6GC bias mode, you won't damage the amplifier or the tubes. The EL34's will just run way too cold, as there is not enough Grid Voltage being supplied to the tubes.

Mesa sets their amps up to run between 23 and 28 mA in the Bold/Silicon Diode power setting. I don't know what options you have with the Single Rectifier, but I'm sure it's in the same area with tubes that draw the same amount of natural plate current as the middle tier, "Mesa spec" tubes.

You can save yourself about $30 and get some tubes from a tube vendor who can supply you with tubes that draw the same amount of natural plate current that the Mesa tubes draw. I checked out Mesa's new prices last night and thought they were ridiculous. $60 for a matched pair of SED EL34's or 6L6GC's? You can get those for half that price from a good tube vendor who is more than capable of supplying you with what you need.

Your Single Recto doesn't have a bias pot, so all you have to do is flip a switch. It is a fixed bias amplifier that has it's bias set with a "fixed" resistor. Other Class A/B amplifiers that have bias pots are fixed bias amplifiers that have a "variable" resistor to adjust the bias.

Dale

I bought a pair of MESA EL34's(red) for $42 from Guitar Center. It's a nice change!! I would def. recommend it if you have the $$.

I've just ordered a retube kit from Bob at:

http://www.eurotubes.com/index.htm

Click on "policy info and online ordering" link and then click on "shop online now" then click on "6. full retube kits for MESA" you can choose what you'd like.

He has decent prices and supposedly they are very good tubes.

I ordered the high gain pre-amp tubes as well as the 6L6's and E34L's.

I'll let you know how they work out!


JA

I switched the bias switch from 6l6 to el34s pretty much not knowing what I was doing it played fine for a few minutes the the on light went out and now I'm powerless did I blow a tube or is there another problem

I would start by checking the fuse first. Make sure the switch is in the correct position for the tubes you are using.