Pics of Pentode vs. Triode wiring?

[Brad737]

Hello all,

I recently stumbled on a good deal for a Mark III. It has Simulclass, reverb, and GEQ, and is in really nice shape for its age. The seller told me it was a green stripe, but the stripe looks sort of teal. The serial number really isn't much help either, because it's strange. The serial is A2289x. I know that a 22,000 number should be a blue stripe, but I've read that the A probably means there's another amp with the same serial, so Mesa would typically add a letter to differentiate between the two.

I've read that Triode models have a resistor connecting pins 3 and 4 on the outer power tubes, and the Pentodes don't have it. But all of the threads I've found that have photos have broken links. I'm no amp tech, and know not to touch anything inside the chassis for fear of frying myself. Do any of you have photos that show what I should look for?

Many thanks,
Brad

 

[psychodave]

It's gotta be this amp... Nice price. 8) I'm red/green color blind, so I can't tell the stripe. lol
http://pages.ebay.com/link/?nav=item.view&alt=web&id=161701523429

 

[Brad737]

That's the one. Here's the mysterious stripe:

 

[Brad737]

Well, I have an update. My Mark III arrived, and I've finally had a chance to unpack it, and play it a bit. The tubes that came with it were crap, but after some quick swapping, it sounds REALLY frickin' awesome...sweet, chimy cleans and face-melting gain. Unfortunately, I only had spare 6L6s and no EL-34s, so I can't give the Simulclass a real audition yet. But I'm going to try and order some EL-34s, or maybe a set of JJ 6CA7s. I'll figure that out before long.

I'm pretty sure my amp is a Blue Stripe, even though the seller swore it was a Green. I bid on it thinking that based on the serial number, it must be Blue, but if it's Green, cool deal.

Anyway, like I said the serial number is A2289x. According to everything I've read, a 22,000 number should be Blue. Also, the inside of the chassis is dated 6/10/88 with initials LEK (?) in pink, but with a red check mark that looks to have been applied later. Also, the top of the chassis has Mike B's initials dated 10/88. There's also a small red R on the back under the power cord. I'm guessing this was sent back to Mesa for the Reverb mod? I've read online that Blue Stripes were built from 1988 to mid-1989, so this adds more credence to my opinion this is a Blue.

Now, onto the Pentode/ Triode question. As I said before, I'm no amp tech, and have no idea what I'm looking at. I just know not to touch ANY internals. But here's a pic of the outermost power tube socket. Does this look to be pentode or triode?

I'm going to contact Rich at Mesa tomorrow and see what he can tell me. But since the kids are in bed, I can't play through the Mk. III, so it's at least fun talking about it.

Any ideas which version I stumbled upon?

Thanks,
Brad

 

[kdorsey]

Unless I'm completely crazy, that looks like triode to me, making that a blue stripe. The big carbon resistor is the screen grid resistor, between pins 3 and 4, which tells the story. Hellova find, there Brad. Good power tubes - especially EL34s - and a preamp cocktail will give you years of experimentation and discovery. Now you only need about 4 different cabs and 5 different speakers to choose from... :wink:

Here's what my green stripe looks like (I have a bit of red/green color blindness but our stripes look pretty close to me...):