YellowJackets in a Mark IV

[radmo]

Someone out ther have info on what Yellowjackets go in the outer sockets, and inner sockets on a Mark-IV? Anyone using all el84s in their Mark-i\IV? If so, do you have your amp the way the manual says for 6V6 operation (Tweed/SimulClass/4-ohm jack) or have you been able to safely use EL84s in other settings?

Finally I believe someone mentioned using EL84s AND EL34s together..Can you elaborate on your settings? Was is full power, etc???

 

[Monsta-Tone]

The guys at Mesa Hollywood said that they didn't think it was a good idea.



Ed Degennaro from THD said that they have a model that works with Cathode Biased (this is really what the Class A setting is) tubes.

You can get their phone # from their website. They are very good guys to deal with. I had an older THD Plexi combo that was modded. I wanted to return it to original spec. They sent me all of the parts for FREE.

 

[Boogiebabies]

Too scary for me, but if you want to blow up your own amp feel free.

 

[JimAnsell]

i've been using the groove tubes el84 converters in my c+ for a few days now, and they sound great. not much difference tonally, just better tone at lower volume.

 

[mtnb1kr]

The guys at Mesa Hollywood said that they didn't think it was a good idea.



Ed Degennaro from THD said that they have a model that works with Cathode Biased (this is really what the Class A setting is) tubes.

You can get their phone # from their website. They are very good guys to deal with. I had an older THD Plexi combo that was modded. I wanted to return it to original spec. They sent me all of the parts for FREE.

Why is it a bad idea? Supposedly the yellow jackets are safe to use in any amp. At least that's the way they're advertised. I've never heard of an amp blowing up from their use but I'm also not a real expert.

 

[Monsta-Tone]

Since the Mark IV is Simul-Class, the outher pair of tubes is actually Cathode Biased.

This is what Randall Smith calls "Class A." Many others call it that too, while still others contest that it is not Class A at all.





All debating aside:


Ed DeGennaro from THD said that it is perfectly safe as long as you use the Yellow Jackets that are made for Cathode Bias in the proper sockets.

I am not positive on how they work, but basically, the Yellow Jackets take convert a Fixed Bias tube socket to Cathode Bias for their EL84's.

I am not sure what would happen if the wrong type were used in an already Cathode Biased tube socket, but I would follow Ed's advice.

THD are great guys, I have spoken with them numerous times over the phone. They are always very helpful and knowledgable.

I think Mesa just doesn't want them in there for fear of warranty repairs.

 

[jamme61]

The yellow jackets in my MKIV have solved all my volume issues. I put them in the outer sockets and 6l6's in the middle. At home I run the amp on class A and on gigs simulclass. The amp never sounded so good. I called THD on the phone and the rep said no problem running the YJ's in any mode on the MKIV. Still I'm a little concerned if Mesa said it's not a good idea. I've been running the YJ's for about a month with no problems.

 

[screengrid]

Hi, I don't think, that the "Class A Section" of the MK IV is cathode biased.
According to the schematic I have ( version 08/92 ), the cathodes of the outer power tubes V8 / V9 are connected directly to ground like the inner power tubes V6 / V7 running Class AB. Further they are fixed biased like the inner power tubes. Same neg. bias voltage source. But due to add. 220K resistors the negative bias voltage at the grids of V8 and V9 is more positive. Measuring the idle bias current of the powertubes shows the differrence between the inner and outer tubes. The outer tubes are running hotter. My measurements in the past with 4 x 6L6 tubes did give me readings with the outer tubes around 24mA in Tweed Power and 32mA in Full Power, which should be also quite normal for class AB. In comparison to that the idle bias current of the inner tubes are very low, readings around 10-11mA in Tweed and 13-14 mA in Full Power. The outlet voltage was 220 V~! IMO, the amp is biased on the cold side, may be too cold at least regarding the inner tubes.
So finally I also don't think, that the outer tube section is working real class A. But for me it doesn't matter at all, if it is real class A or somewere between Class A and AB1, because the sound is so good. BTW, as far as I know also the well know good old Vox AC 30 is not real class A, although most people think so, also me for a long time.

regards
Arno

 

[jamme61]

the yellow jackets sound awesome to me. instead of buying a attenuator, try a pair of yellow jackets IMHO.