200s amp, help!

[ian]

I just bought a 200s amp 60 watt at 4 ohm?  I'm running a 1970s 2X15 fender bassman cab @ 16ohm in the 16 ohm jack.  I believe its a 50 watt cab? It sounds good, really good.  The bass is on 5 the treble on 2 and volume on 5.  It tends to break up easliy. I really can't play the bass strings very hard at all.  Is it my bassman cab fuzzin out?
Ive tried other cabs but maybe i'm only hearing what this 60 watt head can do?

I guess, I expected this 60 watt tube amp to play loader/better than my 200 watt workingman swr played the same cab.
Is it time for new tubes! How do i know?
Can this amp be moded up to 90watts?  

I really would like to rap with someone who know this amp...and would like to share some knowledge.....  Please feel free to email me at ianheinsohn@yahoo.com , thank you for your time and considerations.

[EdBass]

I just bought a 200s amp 60 watt at 4 ohm?

60 watts is the rated output at any ohm load, the power output is not regulated by the load like a solid state amp is. The transformer has taps for 4, 8, and 16 ohms.

It sounds good, really good. The bass is on 5 the treble on 2 and volume on 5. It tends to break up easliy. I really can't play the bass strings very hard at all. Is it my bassman cab fuzzin out?
Ive tried other cabs but maybe i'm only hearing what this 60 watt head can do?

It could be a number of things, but all of my old Sunn 60 watters start to break up around 5-6, but don't get real nasty until 7-8 or so. Also, the higher you have the tone cotrols set (particularly the bass) the quicker the amp will distort. The bassman cab might have something to do with it, but I bet you are mostly hearing the amp breaking up.

I guess, I expected this 60 watt tube amp to play loader/better than my 200 watt workingman swr played the same cab.

A watt is a watt. I'm not sure why you expected 60 watts to be louder than 200 watts. Richer, warmer, smoother - yes; louder - nope. The old Sunns are very powerful for their rated 60 watts, but they ain't 200!

Is it time for new tubes! How do i know?

You could test them or have them tested to see how much life they have left. To be able to tell by the way the amp sounds, you would have to know what it is supposed to sound like with strong tubes. Also your amp is 30 to 40 years old, it could be other weak components as well. For example, if the filter caps are original you can almost guarantee they need to be replaced.

Can this amp be moded up to 90watts?

Sure, any thing can be done if you spend enough money. I'm not a tech, but I don't know of any magical "trick" to get a 50% gain in output. You should probably have the amp tested and brought back to spec by someone who knows what they are doing before you try to hot rod the 200S. If it isn't enough oomph then, you'll have to get youself a 120 watt 2000S!

[JoeArthur]

Are you sure about the impedance of your bassman cab?  Stock, the two 8 ohm speakers were wired in parallel for a total of 4 ohms.  It could have been rewired to 16 ohms... but if you don't know that for sure, it would be worth checking out.

A bassman cab would be nowhere near as efficient as a real 200s cab with JBL's.  The original cab was a significant part of the acoustic output of these amps, not just the wattage output.

You didn't mention what bass you are using.  If it's active or has modern hot style pickups you could be overloading the preamp prematurely.

Other than that... tubes, caps... what EdBass mentioned.

[ian]

this website is the shit! Yup my cab is 16ohm, two eights in series.  Yup 60 watts is sixty watts.  I guess im gonna look for the 4 ohm tap and put my cab back to 4 soz i can use it with the rest of my stuff too.  I'm playing a fender p bass with no pedals and no active pick up but i do play with the volume maxed, tone all the way, too.  
As i understand it, I can change the 6550's to jj kt88's, the tube rectifier to the weber solid state, up the filter caps to 100-110 mf, change my pre tube to a 12az7 or 12at7, get it properly bias and maybe get it to start to break up at volume 6,7, or hopefully 8 with bass dialied down.  The last thing to try (to use this amp and  keep up with my guitarist) is to ditch the bassman cts' and/or cabniet and go for a more efficient pair of fifteen's.  
Any suggestions on a more efficent new pair?  Jbl's? d130$$ d140$ Newer models? Emenice Delta's?

[ian]

i'm running the smaller bassman fifty cab that has the speakers kinda of on an angle, not the older bassman cab that has em stack evenly.

[JoeArthur]

Electrovoice Force 15s.

[Soundmasterg]

I'm the guy that posted most of those mod ideas last year or whenever it was, and yes, you can make some of those changes to the amp to get a little better tonal production for bass. Be aware that if you go over 60uf for the first cap stage that you CANNOT use the tube GZ34 anymore and have to use a solid state replacement or a weber copper cap. Also, you need to use series connected caps (with parallel 220k 1w resistors) to get a high enough voltage rating for the first two filter cap stages, and the third stage needs to be 500v rated. The fourth filter cap section is ok with a 450v rating. Hopefully you know enough about tube amps and working on them to not only understand what I said, but also to be safe so you don't kill yourself on the high voltages!

I prefer JJ KT88's in my Sunns as they are very reliable and sound very good too. They are also not bothered at all by the high screen voltage of the Sunn circuit, wheras the 6550A's ratings are mildly exceeded in the Sunns. I probably would stay with the 12ax7 for the first stage myself as it sounds and works fine there, and the amp can use the gain it provides in the circuit location.

Greg

[ian]

this guy is the shit!!

[Soundmasterg]

You're welcome.

[ian]

 UPDATE: just thought I'd stop on by again to brief anyone looking at this string of ?s.
The low down with my 200s amp was: one new cap, new tubes and replaced some of the carbon resistors and It's now very very clean and loud! Scary clean until 8, 9, or 10! It kills that 200 watts swr rig, which is since long gone! I've also gotten a music man hd150 ontop of a sunn 18, which sounds very good!  I use the sunn 200s with the bassman two 15 bass cab for a differnet band and I seem to like that god dam sunn better and better every time i play it!!   I'm glad a sunn was my first tube amp, the help online made me dig out my old electronic skills and do some of the work myself.  Thanks again to this website and to soundmasterg! And every body else who has helped, fuc$ing SUNN kicks a$$. One last question, what is a safe and or max bias range to be running a pair of jj kt88s or a pair of ruby6550's with ok tube life? -ian.

[MarkG]

You should still give some consisderation that your 200S and 16ohm cabinet MAY be a mismatch.This may vary depending on year of manufacture. The 200S I used to own had 2 output jacks.
1 was labled main the other labled extention. These were an auto tap configuration. If the main only
had a plug in it,was taped at 8 ohm. If while a main was plugged,and an extention was plugged it jumperd these parallell jacks to a 4ohm tap on the transformer for the collective output.  I believe mine was a late generation,maybe the early ones were 16/8 .   

[ian]

My amp is working fine, bias is fine, my cabniet is 4 ohm, my amp now has a 4 ohm tap.  I was simply saying thanks to all you sunn guys for help!!! I should have removed this string of blurbs, but a made a mistake by rekindling it... All the above blubs are old!!! Ancient... EXCEPT... the question about bias ranges for kt88 and gt 6550S Other than that, fellas, my amp kicks major butt, it is working fine, thanks for yer imput!  -ian.

[Soundmasterg]

Ian, the Sunn 200S is a fixed bias ultralinear amp. In most fixed bias amps, setting the bias for 60-70% of the max dissipation rating of the tubes you are using is a good bet. In a blues guitar amp, you can sometimes set the bias hotter to get a little more sag, but keep in mind that you reduce the tube life the hotter you bias. In a bass amp, setting closer to 60% works pretty well and extends tube life and gives you more clean headroom to a point. I set my 200S to about 65% of the max dissipation of the power tubes and it sounds and works great. If you are using 6550's then the max dissipation level for those is 35 watts. If you are using KT88's, then the max dissipation is 42 watts. So 60 % of 42 is  25.2 watts, and 70% of 42 is 29.4 watts. Since watts is voltage times current, you need to know the cathode current of the tubes while in circuit, and you need to know the plate voltage while the amp is running, and you need to re-measure each and re-calculate every time you adjust the bias pot. If you don't know what I'm talking about, then please learn how to be safe before you try this yourself. The JJ KT88 (or Winged C KT88, or EH KT88) is a better fit for this amp than any 6550 due to the higher screen voltage rating of the KT88 and the high screen voltages in this amp.

[ian]

sweet... I'll run my kt88s a little hotter, 65%.