Class A Mode: Do the 6L6's need to be plugged in?

[Heady Jam Fan]

The manual says you can pull the center 6L6's in Class-A Mode and just run the EL34's, but does the transformer still expect an 8ohm speaker load, or a 16ohm load with the 6L6's pulled?

I busted a 6L6 in an amp I'm selling so I put the 6L6's from my MKIII into that amp and I guess I don't have any extras, except an old set of EL34's.

 

[megavoice]

This subject had been discussed here a few months ago and I added that I'm playing my first Mark III now for nearly three decades without the inner pair of tubes and he's still running great ! The second that I have now 1 1/2year as well.
Can't tell about the the tranny and the speaker load, but the manual says also you can vary between the different speaker outputs without any doubts. (????)

 

[Heady Jam Fan]

This subject had been discussed here a few months ago and I added that I'm playing my first Mark III now for nearly three decades without the inner pair of tubes and he's still running great ! The second that I have now 1 1/2year as well.
Can't tell about the the tranny and the speaker load, but the manual says also you can vary between the different speaker outputs without any doubts. (????)

When you run 6L6's without EL34's, your supposed to use, for example, the 4ohm tap for an 8ohm speaker (or 8ohm tap for 16ohm speaker). Running the wrong load can distress your transformer (and even tubes), although Mesa does say theirs can handle it to a degree (as you mention above), yet there will be tonal differences of the expected (at the amp) and actual (speaker load) impedances are not matched.

Also, when pulling tubes, the remaining tubes sometimes run hotter.

 

[megavoice]

This subject had been discussed here a few months ago and I added that I'm playing my first Mark III now for nearly three decades without the inner pair of tubes and he's still running great ! The second that I have now 1 1/2year as well.
Can't tell about the the tranny and the speaker load, but the manual says also you can vary between the different speaker outputs without any doubts. (????)

When you run 6L6's without EL34's, your supposed to use, for example, the 4ohm tap for an 8ohm speaker (or 8ohm tap for 16ohm speaker). Running the wrong load can distress your transformer (and even tubes), although Mesa does say theirs can handle it to a degree (as you mention above), yet there will be tonal differences of the expected (at the amp) and actual (speaker load) impedances are not matched.

Also, when pulling tubes, the remaining tubes sometimes run hotter.

NO !!!!! I NEVER run the 6L6 in the middle without the outer EL34 ! Iknow, this not allowed and as I know it even doesn't work !

 

[Heady Jam Fan]

This subject had been discussed here a few months ago and I added that I'm playing my first Mark III now for nearly three decades without the inner pair of tubes and he's still running great ! The second that I have now 1 1/2year as well.
Can't tell about the the tranny and the speaker load, but the manual says also you can vary between the different speaker outputs without any doubts. (????)

When you run 6L6's without EL34's, your supposed to use, for example, the 4ohm tap for an 8ohm speaker (or 8ohm tap for 16ohm speaker). Running the wrong load can distress your transformer (and even tubes), although Mesa does say theirs can handle it to a degree (as you mention above), yet there will be tonal differences of the expected (at the amp) and actual (speaker load) impedances are not matched.

Also, when pulling tubes, the remaining tubes sometimes run hotter.

NO !!!!! I NEVER run the 6L6 in the middle without the outer EL34 ! Iknow, this not allowed and as I know it even doesn't work !

It works, your just supposed to use the 4ohm tap for an 8ohm load (or 8ohm tap for 16ohm load). IIRC there is an article about this published from Mesa, other threads discussing it, and I've talked to local amp techs as well. Unless you know something else about it? But the 6L6's just run a bit hotter - they are biased cold anyway.

 

[megavoice]

Ah ! Interresting...............

 

[Heady Jam Fan]

Ah ! Interresting...............

Yeah - I could be wrong, but that was my understanding. When I was using Celestion speakers (mostly V30's but also Golds and Gold Clones), I preferred the 6L6's alone over the added midrange of the EL34's. Now that I switched back to an EVM12L, I love the creamy mids of the EL34's. I just don't want to buy a set of 6L6's just to hold the center power tube spots (and wear the tubes out heating them for no reason) if I don't need to. I emailed Mesa just to make sure - I'll post their response when I get it, but I appreciate all the help!

 

[Heady Jam Fan]

From the manual:

In an amp with four power tubes, the shorted tube will cause the one next to it to also turn red hot even though that tube is fine. You
can determine which tube is actually bad by using the 60/100 or Class A switch to turn off two of the four tubes (it turns off the center
two tubes). And you can safely run the Boogie with only two of the four tubes plugged in. In this manner you can at least determine
which pair ("outer" or "inner") contains the defective tube, and then you can isolate the defective by substituting a replacement for each
of the two "suspects", one at a time. In the 100-watt (non-Simul) mode, the same tube (6L6) is used in all four sockets, so a good tube
from the inner pair could be used to replace a defective in the outer pair if necessary; but in the Simul-Class model, the inner tubes
must be 6L6's while the outer tubes must be EL-34's.

But a Mesa rep said he wouldn't suggest doing this - the manual only suggests it for troubleshooting.
I guess I ought to get another set of 6L6's to put in there...

 

[Authorized Boogie]

As I said by email - the sentence you highlighted is for determining a defective tube. We do not recommend running the amp with the tubes pulled for anything other than troubleshooting. Thanks

 

[Heady Jam Fan]

As I said by email - the sentence you highlighted is for determining a defective tube. We do not recommend running the amp with the tubes pulled for anything other than troubleshooting. Thanks

Thanks!

Now to try to see if I had the foresight (or hoarding) to save my old 6L6's!