Can I use 6L6 tubes in my marshall 2555?

[marshall2555]

I know that some marshalls came with 6L6 or 5881 tubes. Some say they can be used with the proper bias. Others say that the output transformer is not compatible and that I would need to change it to an OT that was used in a marshall 6L6 5881 application. So what is the truth and/or where can I find out?

[Mars Amp Repair]

the 5881's & the 6l6's are pretty much interchangeable...what tubes did the amp take originally...I'm not immediately familiar with that one...glen

[marshall2555]

the amp came with el34's.

[whippin]

original kind of pre and final tubes on marshall 2555

Hi excuse me, surely you can help me ..
ive a marshall 2555 and i have a very quite sound very low, maybe could be the final tubes finished.. i've checked and foud a set of groove tubes (pre and final) but what are the original brand of tubes? i would like to replace wuth the exact original.. please write me at my e mail address
whippin@libero.it
any answer will be very helpful..thank you

[MWJB]

OT impedance shouldn't be an issue when subbing EL34 for 6L6/Sovtek5881 (NOS & some current 5881 style tubes are not rated for the higher voltages in some EL34 amps).

"Some say they can be used with the proper bias." It is advisable to check your bias when changing power tubes in a fixed bias amp, even if they are the SAME brand and type as supplied originally in that amp.

Typically 6L6/Sovtek5881 will work in a socket wired for EL34, but NOT the other way around. EL34 usually require a 1K5W screen grid resistor and for pins 1&8 to be tied together & grounded...many 6L6 amps are not wired like this. EL34 amps usually have larger value grid stopper resistors at pin 5.

Plate voltages (<520vdc at correct bias current for 6L6/Sovtek5881) and bias current should be checked to ensure that these perameters are not exceeded.

Whippin - The only "exact original" tubes that exist for your amp are the ones that were in it originally, which are probably worn out now. Even if you bought tubes of the same brand & type they would still most likely be somewhat different.

Preamp tubes do not require biasing, I'd suggest buying a selection and swapping them around to see which ones you like in various positions.

[paulh]

These amps I believe shipped with Marshall branded Chineese tubes. You can change them to 5881/6L6's but you will have to modify the bias circuit. from the schem it looks like you will need to change the values of R47 and R23 to get a higher bias voltage that will run a 6L6. If you just install 6L6, you will burn them up and possibly other compoinents in you amp. Changing the screen resistor to 470Ω 5 watts is not a bad idea either but not necessarry. The output transformer will run 6L6's.

[mac1amps]

I'm very curious as to what pre-conceived notions you have that make you want to convert your Marshall to 6L6's. Are you hoping to make it more Fender like? Or perhaps more like a "rectifier" series Mesa? FWIW, you should be aware that if you use the amp with low master volume settings, the different power tubes will have a very subtle effect on your overall sound (most any effect that they DO have will be because they are new/fresh tubes, moreso than because they are a different model tube). Then again, there's also what I call the "placebo" effect that you may perceive.........'just "food for thought".

[whippin]

i'm sorry i ve leave my post under a wrong title, i don't want to replace the tubes with 6l6.. but i only want to replace the tubes with the original ones, becouse my amp has a very low volume and i think could be due of the final tubes inside, my question was only to know what brand of pre and final tubes i have to buy it to replace the original..
sorry for the inconvenience,
and thenk you for your interest