Sunn 200S Missing a power tube, is it still safe to play??

2719 · #1 02-24-2011, 08:03 PM

Hello everyone,

First post on TalkBass though I have lurked here frequently in the past for some very helpful advice and information. I couldn't find a current thread pertaining to my most recent issue so I figured I'd start an account and ask a question that I should probably know the answer to already.

So, about a month ago I had a gig at a local bar that doesn't have a closed room to store your gear in while you aren't on stage. Turns out, while I was off stage and enjoying some of the other bands of the night, some jerk took the liberty of plucking out one of the 6550EH's from the rear of my Sunn 200S.

It actually took me a couple of weeks and rehearsals after the fact to even notice that it was missing,

so yes, I have jammed with only one 6550 a few times since and it seems to have been working out pretty decent. Of course, I don't want to continue this in the slightest if it means I could go ahead and damage any other part of my precious amp before getting the tube replaced and the amp re-biased. My questions: Is it safe to temporarily play with only one power tube? When I do have the tube replaced, do I have to have both 6550's replaced so the bias is matched properly or will that not make a difference (the remaining tube still looks and sounds fantastic)?

Thanks so much in advance to whoever can answer my ignorant question!

christw · #2 02-24-2011, 08:27 PM

Stop using it as is. You can just pop in a different 6550 as a temporary solution, but yeah, you wanna run a matched (and biased) set in it.

T-Bird · #3 02-24-2011, 11:32 PM

Hi.

Welcome to TalkBass 2719.

Someone stole an output tube from Your amp at a gig? That's a new one to me.
I've seen that happen on rehearsal spaces, but on a gig, that sucks.

Anyway, stop using the amp. Depending of the circuit, the possibility of damage ranges from non-existant to severe. I have no experience about Sunn amps, so I can't obviously give any exact info. If there's a chance of damage, it's to the OT, so I wouldn't take any risks.

With only a pair (?) of tubes in a A/B PP amp, the matching is not as critical as in the amps with multiple parallell tubes, but a tech should still do the swap and biasing if a non matched set is used.

As I have no idea about the sound You're using, I won't question your comment about not noticing the missing tube

.

Regards
Sam

blastjv · #4 02-25-2011, 07:25 AM

1 - Not for nuthin, but if it took you several weeks to notice, can you be sure of where it happened? Doesn't matter to me, but you might want to think about who has access to your rehearsal space, etc...

2 - When you noticed the tube was gone, was that because you were hearing some problem or difference with your amp, or you just happened to look back there and see it missing? Just currious.

Regardless, tubes are cheaper than repairs. Don't run it until you at least get a tube in there. A shop may be able to throw a used tube in there that matches what you already have...

-JV

2719 · #5 03-17-2011, 10:00 AM

Quote:

Originally Posted by christw

Stop using it as is. You can just pop in a different 6550 as a temporary solution, but yeah, you wanna run a matched (and biased) set in it.

I'm going to try this out today, a tech from a nearby shop said that if I pop a 6550 in and it sounds right then the problem should be solved, at least temporarily. Though I'm still a little skeptical, I'll let you know how it goes.

Is it safe to match two different brands of 6550?

Quote:

As I have no idea about the sound You're using, I won't question your comment about not noticing the missing tube .

Well, it's a very tube overdriven sound, and I still didn't have to turn my amp up much louder than before the tube was missing so I'm kind of in the dark as to where exactly it did happen.

Quote:

2 - When you noticed the tube was gone, was that because you were hearing some problem or difference with your amp, or you just happened to look back there and see it missing? Just currious.

Believe me, I couldn't believe I didn't notice it any sooner. The difference in sound just really wasn't that noticeable.

Thanks for the responses on this everyone.

JimmyM · #6 03-17-2011, 10:47 AM

you can use two different brands of power tubes no sweat. ultimately, you're going to want them to match on a technical level so it can be biased properly. but as long as they're matched, it doesn't matter if you mix brands or not.

Calaverasgrande · #7 03-17-2011, 11:49 AM

I have stupider stuff get stolen at gigs. Who steals a kick drum mic stand? who steals a $10 guitar stand? Or just a compression driver?
Sheesh.
Seriously, get another 6550 or a pair even better. Since you were running it without that tube maybe get it looked at by an amp tech as well. Might need a few minor components replaced.

coreyfyfe · #8 03-17-2011, 11:54 AM

Quote:

Originally Posted by Calaverasgrande

I have stupider stuff get stolen at gigs. Who steals a kick drum mic stand? who steals a $10 guitar stand? Or just a compression driver?
Sheesh.

I don't know man, most of that stuff serves some purpose. A single tube out of someones amp? Unless someone else on the gig needed a 6550 for their head (or they're just dirtbags who wanted to mess with the guy) I really don't see a point to taking a single tube.

JimB52 · #9 03-17-2011, 03:14 PM

Quote:

Originally Posted by coreyfyfe

A single tube out of someones amp? Unless someone else on the gig needed a 6550 for their head (or they're just dirtbags who wanted to mess with the guy) I really don't see a point to taking a single tube.

A not so subtle way of saying the bass is too loud?
Seriously, criminals are stupid. That's why they're criminals.
Fun's over, I'd suggest tube replacement asap.

2719 · #10 03-23-2011, 05:05 PM

Temporarily replaced the single 6550 without a bias and it does sound pretty good.

It'll do for now. I'm planning on getting the amp looked into as soon as I get the cash.

Quote:

A not so subtle way of saying the bass is too loud?

**f64** · #11 03-23-2011, 05:24 PM

Here's a copy of the schematic:http://sunn.ampage.org/site/schematics/220s.gif
The KT88's and 6550's are interchangeable- but you must replace both with a matched pair. From the looks of things with one tube gone all you're doing is cutting your power section. The real problem is that you've probably changed the ohm output. I'd stop until you get a matcher pair so you don't damage the transformer. I'm making the assumption that you didn't cut your speaker load. It wasn't uncommon in Hiwatt, Fender and Sunn amps to remove tubes to cut power. Guitarists do it all the time to get the crunch they need. But they do adjust the speakers to match the new output load.

2719 · #12 03-24-2011, 05:32 PM

Quote:

Originally Posted by f64

Here's a copy of the schematic:http://sunn.ampage.org/site/schematics/220s.gif
The KT88's and 6550's are interchangeable- but you must replace both with a matched pair. From the looks of things with one tube gone all you're doing is cutting your power section. The real problem is that you've probably changed the ohm output. I'd stop until you get a matcher pair so you don't damage the transformer. I'm making the assumption that you didn't cut your speaker load. It wasn't uncommon in Hiwatt, Fender and Sunn amps to remove tubes to cut power. Guitarists do it all the time to get the crunch they need. But they do adjust the speakers to match the new output load.

That makes sense. The original output is 4ohms. So, does that cut to 2ohms with only one tube, or somehow change to 8 ohms? The cabinet load is 4ohms, the matching 2x15 that came with the 200S. Does this mean that I could have been risking damage to my cab?

will33 · #13 03-24-2011, 06:22 PM

Isn't the 200s an A/B push pull type of amp? If so, the tubes work in pairs, each amplifying half the soundwave and it can't be a good idea to run only one of them. If it's a true class A, it'd still work with one but still maybe not the best idea as the rest of the circuit isn't made to work that way although I'd leave it to someone who really knows what they're doing to tell you. A re-bias and/or having different ohms setting from the transformer taps would be a minimum change at least.

coreyfyfe · #14 03-24-2011, 06:31 PM

Quote:

Originally Posted by 2719

That makes sense. The original output is 4ohms. So, does that cut to 2ohms with only one tube, or somehow change to 8 ohms? The cabinet load is 4ohms, the matching 2x15 that came with the 200S. Does this mean that I could have been risking damage to my cab?

I'm not well versed on the technical details but when you pull a tube you're supposed to double the impedance (half as many tubes to distribute the impedance match while still using the same ratio on the transformer). I know you can do this with amps that use multiple pairs of tubes, not entirely sure if it's good to do in a single pair amp.

BluesBear · #15 03-24-2011, 06:45 PM

Quote:

Originally Posted by 2719

Does this mean that I could have been risking damage to my cab?

NO.
You CANNOT damage a speaker cabinet by supplying less power to it. And the cabinet doesn't give a tinkersdamn what impedence the amp likes best. Impedence only matters to the amp.

As for the amp... I once ran a Fender Dual Showman Reverb Amp with only three 6L6GC power tubes for three weeks straight, gigging six nights a week.
(It was a rental and I didn't have access to the lower chassis.)
There was a slight loss of power but otherwise nothing bad happened.