EL34s in a MkIII

[keithus77]

Hi guys,

Just wondering what mod you need to run EL34s in a MkIII? My MkIII is the 60 watter with only 2 power tubes.

I ran EL34s for a while but I now have 6L6s running in it. The 6L6s arn't bad overall, but I think I prefered the sound of the EL34s - which was a little more aggressive and raw.

Thanks

 

[tim6string]

This may be an obious statement, but you would either need a tech to put in a variable bias so the amp can be biased to run the 34s, or change the fixed bias to one that is right for the 34s.

Sorry I can not help with actual parts and changes, but I think anyone who knows tube amps (and you trust) could make the change.

 

[Bullen]

The 60w version should only be used with 6L6 tubes unless it´s been modded for EL 34 tubes.

 

[Boogiebabies]

Old Mesa's ran 470 ohm screen grid resistors on the outer EL34 sockets.
If you want to run EL34's then go ahead. You dont need to install a bias pot, you just need to make sure that your tubes are not running hot or too cool. The input impedence on the OT is where you really need to know what type of load the EL34's will be seeing. I have run a lot of EL34's in 6L6 amps, including the SLO 100 with no modifications.

 

[keithus77]

Boogiebabies,

Are you saying that I can pretty much run EL34s (as long as they don't appear to be running hot or cold) without any mods?

 

[dancullinane]

My 60 watt Mk III came with 2 EL34s in it when I bought it. One of them was bad so I ditched them in favor of a pair of 6L6s. I call Mesa about whether the EL-34s could have damage the amp. The tech told me they would not hurt the amp,but might sound a little "thin". I would like to hear sound clips of each before I buy a pair of EL-34s
DC

 

[keithus77]

dancullinane

Thanks for the comments.

EL34s - to my ears - sound better in my MkIII than 6L6s, but that's just my preference.

I think they sound a bit more full on, more gain, and more responsive.

I think I'll put EL34s back into it.

The MkIII manual also stated that EL34s would not hurt the amp, but just wanted to check with you guys first.

 

[Boogiebabies]

Use the EL 34's and the pull deep. It you have a graphic they will be brutal.

 

[RussB]

Some MKIII's (well, at least mine) had flyback diodes on the outer sockets...these are there to help protect the screens from excessive flyback voltage. In other words, they protect the EL34's

I would add 1k screen resistors, and bias accordingly if I wanted to run EL34's in a 60 watter.

 

[keithus77]

So just throwing in EL34s would not be a good idea without modding the amp?

I was under the impression - from the Mesa manual - that EL34s wouldn't hurt the amp.

 

[RussB]

If Boogiebabies says it's OK, then it's OK. Ed knows his stuff 8)

 

[Boogiebabies]

A 1K 5 watt screen resistor would not hurt, but mesa has been running 470 ohm on the simul sockets and 6L6 sockets at 483V+ for years. I would just make sure that your tubes do not draw a lot of bias. A bias meter would help, but it probably running -57 V which would be fine on almost any mid range natural current draw EL 34.

 

[psychodave]

Old Mesa's ran 470 ohm screen grid resistors on the outer EL34 sockets.
If you want to run EL34's then go ahead. You dont need to install a bias pot, you just need to make sure that your tubes are not running hot or too cool. The input impedence on the OT is where you really need to know what type of load the EL34's will be seeing. I have run a lot of EL34's in 6L6 amps, including the SLO 100 with no modifications.

Would I would be able to run 4 EL-34's in my simulclass Mark III blue stripe (provided the inner tubes are not drawing too much current)?

 

[Boogiebabies]

I dont see why you would not.

 

[psychodave]

Well I tried 4 EL34's and it sounds KILLER!!! It has more mid range (expected) and I had to lower the presence a little bit, but the tone was a lot smoother and really tight.