class A

[z28lt16]

From what I understand its ok to run just 2 tubes in class A. I had 1 tube go bad so I put 2 tubes on the ends . The 1 that went bad was on the left end. This should work till I get my new tubes. Which will be in about a week or so. And they are the same numbered tubes too.

Another question would be did the wattage drop using this method..

 

[Shep]

if you are going to do this only run it in A class.. if you turn it to full power you can kill something..

 

[z28lt16]

I will just be leaving it in A class until I get my new tubes. This is in a Mark IV by the way.

 

[Shep]

i would just run it as low as it can go.. tweed,Aclass triode

 

[phaboo]

if you are going to do this only run it in A class.. if you turn it to full power you can kill something..

What can you kill? You're running LESS power through your output transformer.

 

[HipKitty]

From what I understand its ok to run just 2 tubes in class A. I had 1 tube go bad so I put 2 tubes on the ends . The 1 that went bad was on the left end. This should work till I get my new tubes. Which will be in about a week or so. And they are the same numbered tubes too.

Another question would be did the wattage drop using this method..

z28lt16, I apologize for possibly misunderstanding what your current tube situation is...from what I understand here, one of the end (far right or left) output tubes blew. It's still in there and you are still using the amp.

With that being the case, you want to run the Mark IV in Simul-class in tweed mode. Running the amp in Class A, you are essentially running the outside tubes at Class A voltages...thus disengaging the inside power tubes. This amp design falls into the Push-Pull category of amps. If you are using just the outside two, and one of them is blown or bad, you will stress the amp to a point of component failure. This is a costly mistake to allow to happen...that is unless you like your local Mesa tech an awful lot :shock: Seriously, you can damage the amp running the amp this way. If you must use the amp until new tubes arrive, do so in Simul-class. This will relieve some of the amp's stress...just not all.

Regarding the lower output, that's because you don't have the complete circuit of the "push-pull" happening...it's just doing one side of that in that section of the amp.

Running in "Tweed" mode will also drop certain voltages within the amp. This will also provide some relief to an improperly operating amp.

 

[z28lt16]

The tube on the far left went bad. So I put the tube next to it in that position. Then I took the second tube and put that in the right side spot. I really never ran the amp but maybe a couple days , and at very low volumes with that bad tube. Which I didnt know was bad. But it sounded kinda chessy which made me want to check the tubes.

I then called boogie tech support and this is what he told me to do also. I was also told to run it in A class with just 2 tubes on both ends.

All is good because my new tubes are on the way...

Hipkitty would this be the correct thing to do.

 

[HipKitty]

z28lt16, I think I got it now. I was under a different impression. In your case, you had only 1 confirmed "good" pair or tubes with 1 bad one and 1 good tube remaining out of the initial quad.

With that being the case, Boogie is correct by running the good pair in the outside sockets and run it in Class A, thus disabling the inside pair by not using Simul-Class.

It all is clear to me now says the blind man

Glad to hear that you got the new tubes in now!

Rock on my friend

 

[z28lt16]

I hope to get them in the mail on saturday... Hipkitty thanks for the info anyhow..