Questions about Mark I

[jonathanccwong]

Hi, I recently just got a 1977 Mark I and i am super excited about it
I own a Mark V and really like the versatility but the Mark i's simplicity and tone is something else.


Currently I have a set of International ServiceMaster tubes in the amp and the consensus is that these are crap.
It looks like its about time to replace the power tubes anyway

so is it ok to use 5881 or KT66 in the Mark I?
Or would you all recommend just getting a pair of 6L6GCs

Also would anyone know the tube layout for this amp (it doesn't look the same as the Mark 1 reissue)
(that stubby thing is a TS12at7 Fetron)

more pictures
http://imgur.com/a/5zL1V
Thanks

 

[user 21540]

I think you'll need to stick to 6L6GCs unless you want to do some mods under the hood. Someone will correct me if I'm wrong.

 

[Don]

Switching from 6L6GCs to 5881s in my Vibrolux Reverb required a bigger bias setting change than just switching to another pair of 6L6GCs would have so I wouldn't do it unless a bias adjustment pot has been installed in the amp.

 

[RR]

Nice score! Tone if quite Fenderish with a fat midrange.

Remember this Boogie uses cascading gain where the "rhythm" preamp setting effects the "lead" preamp setting.

As for power stage tubes, the best tubes are Sylvania's 6L6s (MESA STR-415s). The Mark I, II were build around this power tube. If you use some other brand 6L6s, it's fine but I suggested you have an amp tech to bias your Mark I for optumium performance.

 

[igfraso]

If I recall properly, Mike Bendinelli discourages the use of 5881s on the Mark I and the II-A and he recommends the 6L6s. He said that these two are dark amps (the IIA, in the lead channel) and 5881s will make that more apparent.

 

[jonathanccwong]

Thanks for all the advice. Yeah the amp is definitely dark so if 5881 will make it too dark then I'll throw in a set of sylvania in there and see.

I'm still trying to find out the preamp tube layout and see whether the Fetron position is v1 or PI

 

[MrMarkIII]

If the Fetron is in the position closest to the input jack, it's V1.

 

[igfraso]

https://reverb.com/item/164857-all-original-mesa-boogie-mark-i-1975-blonde-with-original-extension-cab

We are all familiar with the 1976 letter that Randall and Rayven Smith were sending to new owners of Mark I Boogies.

As you can see in the attachment, back in 1975 Randall and Rayven were sending General Info, Maintenance Guide, and Schematic to the original purchaser along with the amp.

Does anybody have a similar copy of these documents?
Thanks in advance.

 

[jonathanccwong]

so pertaining to the original question of whether 5881s can be used in a mark I. here is the response from Mesa Boogie:

The tube layout is the same as the MKI RI, but will also vary depending on if you have reverb, etc.
I've also attached the original owners "manual" which gives some information on changing out the fetron for a 12AX7

You can use 5881's, they will be more round sounding and have less output, better for jazz, etc.

 

[igfraso]

Can you upload the original owners "manual" you got from Mesa?
Thank you.

 

[jonathanccwong]

This was what was shared with me from Mesa

http://www.mesaboogie.com/manuals/Mark%20I%20Maint-Repair.pdf

 

[soundguruman]

Hi, I recently just got a 1977 Mark I and i am super excited about it
I own a Mark V and really like the versatility but the Mark i's simplicity and tone is something else.


Currently I have a set of International ServiceMaster tubes in the amp and the consensus is that these are crap.
It looks like its about time to replace the power tubes anyway

so is it ok to use 5881 or KT66 in the Mark I?
Or would you all recommend just getting a pair of 6L6GCs

Also would anyone know the tube layout for this amp (it doesn't look the same as the Mark 1 reissue)
(that stubby thing is a TS12at7 Fetron)

more pictures
http://imgur.com/a/5zL1V
Thanks

5881 is a wimp version of 6L6. Not as heavy duty. I would not recommend 5881 at all.
The bias adjustment is a real problem, since it's non-adjustable.

No matter what tubes you install, the bias "should" be adjusted. But you can't do that.