New Here, With My Sunn 200S

[twocorgis]

Hi All!

For some time now, I've been trying to find a suitable replacement for the Sunn 200S bass amp that I foolishly sold some years back, and have found out that there's just not many of them out there. I've passed on a few of them that I thought were either in poor condition or overpriced, and then one surfaces on Craigslist last night, so I just had to go have a look at it.

I got there, and the amp was really in beautiful condition, and despite the seller saying it needs new tubes, it sounded GREAT. The 6550s that are in there actually aren't correct. I know from the fact that there's no "®" sign after the Sunn logo tells me it's earlier than 1969, and should have KT88s. My luthier has a friend that does tube amps, and I plan on taking it to him for evaluation. Pics soon, and I'll be getting rid of my GK and Hartke heads shortly!

Where's the best place to procure KT88 tubes? I see prices all over the map! For instance, are these any good? I'm afraid it's been a while since I mucked around with tube amps, and certainly don't want to do anything detrimental. Happily the caps on this amp seem fine, and it's nice and quiet. I still have a bin with 1x15" EV SRO speaker, and two more Hartke bins; a 4x10 and a 1x15. Need to play a bit and figure out which combo sounds best. back in the day, I played my '72 Fender P-Bass (still have) through the 200S with 2 15" EV SRO speakers in a Fender Bandmaster cabinet (that eventually fell apart under the weight of the SROs) and it was LOUD. Kept up with many a Marshall stack.

I'm looking forward to bringing those days back!

Sandy

[loudthud]

There should be a small piece of paper glued to the inside of the head box or on the chassis that shows the tube layout. But, there really isn't any difference between the amps that shipped with KT88s and the ones that shipped with 6550s. JJ KT88s seem to have the fewest complaints, but you need to adjust the bias. As with any 40 year old amp, the filter caps could fail suddenly at any time.

http://www.eurotubes.com/

[twocorgis]

There should be a small piece of paper glued to the inside of the head box or on the chassis that shows the tube layout. But, there really isn't any difference between the amps that shipped with KT88s and the ones that shipped with 6550s. JJ KT88s seem to have the fewest complaints, but you need to adjust the bias. As with any 40 year old amp, the filter caps could fail suddenly at any time.

Eurotubes

Thanks loudthud. Dumb question I know, but how do you adjust the bias?

Yikes! I see you just added a link to your site, and I already bout a pair of JJ KT88s here. Lemme see If I can cancel it, and thanks!

[soundmasterg]

The Eurotubes site is not Loudthud's site...it is the site for one of the US Importers of JJ tubes. They're a great vendor btw.

If you don't know how to adjust the bias, then you probably don't belong inside a tube amp until you learn how to be safe. There are high DC voltages in there that can kill you, and setting and adjusting the bias requires you to measure those voltages while the amp is live. There are also AC voltages in there that will shock you if you mistakenly touch them. The easiest way to set the bias is to purchase a Weber Bias Rite that measures the plate voltage as well as the cathode current. Using one of these eliminates the safety concern since you don't actually have to open up the chassis to test anything. You can get these at Weber Speakers - Making the world a bit louder each day.. Also, most of the Sunn activity here at ampage is at the subforum rather than here. Here is the site address>> The sunn Discussion Page - Index .

Greg

[Greg_M]

Eurotubes has a section on biasing here

euro-q

They have a gizmo for helping you bias that is $25. I think I will get one at the appropriate time.