How to re-tube a 1980 Mark IIb

[Dude2Dude]

Hi all,

First post, nice to be here.

Original owner of a 60/100 Watt 1980 Mk IIb....that has never been re-tubed. javascript:emoticon('') (Feel free to laugh! But seriously, it still sounds great -- at least to my ears.) I was wondering a couple of things:

1. Should I replace the pre-amp tubes and the power tubes at the same time?

2. Do I have to remove the entire chassis to change the tubes? And if so, how do I do that? By removing the four screws on the top of the amp?

3. I've only used the 100 watt option a couple of times in the entire time I've owned the amp, so the two "inside" tubes (I think they're the ones) have never really been used. Coud I simply swap them for the two outside ones? The tubes are original Sylvania 6L6GC STR387. (FYI, Mesa also included an extra power tube and four extra 12AX7s that I still have.)

Thanks in advance for any help!

Cheers

 

[Elpelotero]

Wow....27 years without a retube? Do you play it often? the tubes should have blown 26.5 years ago! lol

-You don't need to pull the chassis. Just wiggle the tubes out one at a time.
-Since it's been so long, you should replace both preamp abd power amp. Generally, preamps last 1-2 years and power last 6months-1 yr....if you are an avg to heavy user.
-I would recommend you have a tech replace the filter capacitors as well...they are 27 years old and generally only last 10 years or so. To check if this is really necessary, unscrew the 4 screws, pull out the chassis, and take a look at the orange and blue caps. If they are bulging anywhere, especially on the sides of the blue one's, it's time to change pronto! DO NOT TOUCH 'EM OR YO MAY GET ELECTROCUTED!

 

[Dude2Dude]

Thanks for the input, Elpeotero! I'll retube the whole thing, and definitely check the filter caps, too.

But one more thing: Because it's a 60/100 W amp, can I swap out the two (basically unused) inner power tubes for the outer ones? Or would the simple fact that the inner 6L6s have had at least some juice passing through them mean that I should toss the bunch and replace with a new matched quad?

Thanks!

 

[recto-robbie]

hey dude2dude,,, I would order a full set of matched power tubes and keep the 2 slightly used tubes for backup...toss the other 2. Those 4 preamp tubes should be just fine. you can go ahead and install them whenever you want,,,no need to wait for your power tubes if you dont want to. I dont know how many preamp tubes your amp has but if its more than 4 I would make sure I bought another 1 or 2 to fill it up..
You said the amp still sounds great,,,then keep your old preamp tubes for spares,,,they do go bad once in a while if you play the amp.

 

[Dutchman]

First replace only the tubes that need to be replaced. Sounds like you've got very good tubes from the factory. Have them all tested.

The caps will make a big difference also.

If the Tech tells you your tubes are bad, have him show you on the tester.
There are are many Techs that will keep your old tubes and sell them for a premium on Evil Bay. And stick you with some crappy Groove tubes in, for a fee.

Test the tubes......echo.......echo.......