Sadowsky SA 200, is it THAT good?

[Wasnex]

You better adjust the bias, and not it doesnt pump up the amp, at least not as much and not in a way as you would expect, unfortunately. Mods are not really possible with that supply.
The thing is, it works sort of, the KT88 runs in this amp outside of specs, so does the 6L6.

My concerns with running 6L6s in the SA200 are the same with running 6550s, I assume the screen voltage is a bit high. I haven't measured the plate or screen voltage and they are not listed on the schematic, but the AC posted on the power transformer's HT taps and bias specs suggest the plate voltage is in the range of 530V, and the amp is biased pretty cold per factory spec (around 60% dissipation at 530V).


How is the KT88 being run out of spec? If anything, it's being run well under its voltage limits and also way under its max dissipation rating. I understand these parameters have ramifications on impedance matching between the tubes and speakers...but dealing with load lines is beyond me. The ramification though is using KT88s could possibly reduce power, because the amp is assumed to be optimized for EL34s. Have you measured the amp with other tube types?

My earlier inquiry about rescaling the bias supply is not what I would generally consider a mod (I consider it more a matter of maintenance). Basically rescaling the bias supply typically involves replacing one resistor so the bias falls in the proper range...this would be easy to accomplish in the SA200...apparently it's not necessary though, so I guess it doesn't matter whether it's a mod or not.

 

[Lemon]

Both of my amps are running Koch labeled tubes. I believe they are the same model as TAD EL34B-STR and Shuguang EL34B

The TAD EL34BSTR has higher voltage ratings on G2. The sSA200 has very high voltage on G2 its just below the Anode Voltage. Best is to ask in Germany, they know if you tell them what tube you have, they can tell you if it is a higher voltage G2. The original tubes came from TAD. I just didnt like the TAD preamp tubes.
In general I dont like TAD to much, to expensive for what it is, but they make the tubes for the amp and I got good matched sets, so the couple of bucks difference cant matter.

If the tubes are still original I would first change the Phase inverter tube 6N1P, that one doesent last, its kind a weak. Then i would try different 12ax7 in stage 1. I liked the 70ties phillips, yellow package.
the find a good one for stage 2.
The power tubes run really close to borderline, that means also the power tubes might not last that long.
Probably the tubes are also cheaper made, less material on the plates.
Chinese are masters at making something which looks good, is basically good but doesent last.
The famous Winged Russian lasted for ever if not overly abused. But in this case it could be that you burn up tubes and Screengrid resistors.

If you played it a lot its worth a shot and change the tubes. If the tubes are still good, you got replacements and a test set to see how good the old ones are.
They re not that expensive, good matching is really important. Bias should be as close as possible to get the most out of it.
If you get distortion, it should not at all, at most a little compression, scope it and check bias after a hour of playing it. It took me a while to really find the center and align it correctly. The pot is flimsy to begin with.

I haven't scoped my amp to see where it is distorting. The schematic shows the Master Volume feeds a 12AX7 triode. The signal is taken off the plate and is fed to a phase inverter (PI) built from two triodes of a 6N1P. The output tubes are driven off the plates of the 6N1P.

Since the louder amp is the one that can be pushed to (post master) distortion, I suspect the issue is not the PI balance. I agree the difference could be the amp has one or more stronger small signal tubes though.

If the inverter is not aligned you lose power and increase distortion. if the inverter is shot you also get distortion. If you look at the socpe its clear.
If the break up is rough, its either the inverter or the power tubes probably both, if it is very fine distortion more like getting unpleasant loud in the migh mids its probably the pre tubes over driven.

 

[Lemon]

My concerns with running 6L6s in the SA200 are the same with running 6550s, I assume the screen voltage is a bit high. I haven't measured the plate or screen voltage and they are not listed on the schematic, but the AC posted on the power transformer's HT taps and bias specs suggest the plate voltage is in the range of 530V, and the amp is biased pretty cold per factory spec (around 60% dissipation at 530V).

Yep in mine its 525 G2 and 550 Plate.
It better is cold biased, other wise it will kill em really fast.

How is the KT88 being run out of spec? If anything, it's being run well under its voltage limits and also way under its max dissipation rating. I understand these parameters have ramifications on impedance matching between the tubes and speakers...but dealing with load lines is beyond me. The ramification though is using KT88s could possibly reduce power, because the amp is assumed to be optimized for EL34s. Have you measured the amp with other tube types?

yes way under run, and also out of spec, its not going to sound like you would expect.
at least that what I meant by out of spec.
I think G2 would be in spec.
There where 6550 in there when I got it, didnt sound good a all.
I never tried 6L6. never measured with other tubes.
The powersupply cant deliver for a KT88, it wont really put out more power, mostly just sound different.
Certainly its not going to be what 6 KT88 can put out, basically a expensive waste.

My earlier inquiry about rescaling the bias supply is not what I would generally consider a mod (I consider it more a matter of maintenance). Basically rescaling the bias supply typically involves replacing one resistor so the bias falls in the proper range...this would be easy to accomplish in the SA200...apparently it's not necessary though, so I guess it doesn't matter whether it's a mod or not.

There is a pot to change the bias and the range works fine.

 

[Lemon]

The bias procedure specifies measuring for 25-30mV across the cathode resistors regardless of tube type. I would not bias the amp too much hotter than this without consulting Koch Amps or getting guidance from Sadowsky, because the transformers and power supply may not be able to handle the extra load.

With 6550 the bias was around 45mA if i remember right.
According to Koch it handels KT88 fine.

 

[Lemon]

One other thing; I also noticed that you were asking about cabs. I'm pretty sure that at least some of the Bergantino NV series would be great matches; and if I were rigging up an SA-200, I'd go straight for an NV610T. FWIW.

tried that didnt work.... wrote that already...

 

[Wasnex]

The TAD EL34BSTR has higher voltage ratings on G2. The sSA200 has very high voltage on G2 its just below the Anode Voltage. Best is to ask in Germany, they know if you tell them what tube you have, they can tell you if it is a higher voltage G2. The original tubes came from TAD. I just didnt like the TAD preamp tubes.
In general I dont like TAD to much, to expensive for what it is, but they make the tubes for the amp and I got good matched sets, so the couple of bucks difference cant matter.

If the tubes are still original I would first change the Phase inverter tube 6N1P, that one doesent last, its kind a weak. Then i would try different 12ax7 in stage 1. I liked the 70ties phillips, yellow package.
the find a good one for stage 2.
The power tubes run really close to borderline, that means also the power tubes might not last that long.
Probably the tubes are also cheaper made, less material on the plates.
Chinese are masters at making something which looks good, is basically good but doesent last.
The famous Winged Russian lasted for ever if not overly abused. But in this case it could be that you burn up tubes and Screengrid resistors.

If you played it a lot its worth a shot and change the tubes. If the tubes are still good, you got replacements and a test set to see how good the old ones are.
They re not that expensive, good matching is really important. Bias should be as close as possible to get the most out of it.
If you get distortion, it should not at all, at most a little compression, scope it and check bias after a hour of playing it. It took me a while to really find the center and align it correctly. The pot is flimsy to begin with.



If the inverter is not aligned you lose power and increase distortion. if the inverter is shot you also get distortion. If you look at the socpe its clear.
If the break up is rough, its either the inverter or the power tubes probably both, if it is very fine distortion more like getting unpleasant loud in the migh mids its probably the pre tubes over driven.

I assumed the screen voltage would run pretty close to the plate voltage based on the schematic. The TAD EL34B-STR shows 500V is the limit for G2. I believe the normal G2 limit for EL34s is 450V. Many amps run EL34s above 500V (correction above 450V). I have only run one set of TAD EL34B-STR and they had exceptional matching. Everything I have read says the Shuguang EL34B is the exact same tube and the datasheets I have found show 500V limits on G2. Unfortunately the last set of Shuguangs I bought were not matched nearly as well as the previous TAD tubes.

I checked bias recently on both SA200s. The output tubes are well matched and stable in one amp, and not so well matched and a bit drifty in the other amp. I alway let the amp warm up and stabilize before making the adjustment.

I have a spare set of Koch EL34Bs, but I was thinking about throwing in a set of JJ KT88s and keeping the Koch tubes in reserve.

I also have a full set of spare Koch preamp tubes and also bought some extra Voskhod 6N1P-EBs...they are identical to the Koch tube.

I have plenty of current production and NOS small signal tubes, but the amps sound great so I leave them alone. I don't really care that the one amp is down on power a little and compresses...it sounds awesome and if I need more power I just use the other amp...or choose something else from my collection.

Unfortunately I do not own an oscilloscope, so the PI alignment is done as best as possible by ear. I have not attempted to balance the PI on my SA200s.

 

[Wasnex]

With 6550 the bias was around 45mA if i remember right.
According to Koch it handels KT88 fine.

FYI Roger Sadowsky's amp guru suggests setting KT88s to 30mV (30mA)...same as EL34s.

Yep in mine its 525 G2 and 550 Plate.
It better is cold biased, other wise it will kill em really fast.

yes way under run, and also out of spec, its not going to sound like you would expect.
at least that what I meant by out of spec.
I think G2 would be in spec.
There where 6550 in there when I got it, didnt sound good a all.
I never tried 6L6. never measured with other tubes.
The powersupply cant deliver for a KT88, it wont really put out more power, mostly just sound different.
Certainly its not going to be what 6 KT88 can put out, basically a expensive waste.


There is a pot to change the bias and the range works fine.

The idea with the KT88 is to improve reliability. So if the amp sounds decent and produces about the same power I won't consider it a waste. If the KT88s sound awful I will just throw in the new set of Koch EL34s. I have plenty of amps that are designed for KT88s. Hopefully Tom Bowlus will get around to trying out KT88s before I do . I am in no hurry to buy a new set of tubes.

 

[Lemon]

I assumed the screen voltage would run pretty close to the plate voltage based on the schematic. The TAD EL34B-STR shows 500V is the limit for G2. I believe the normal G2 limit for EL34s is 450V. Many amps run EL34s above 500V. I have only run one set of TAD EL34B-STR and they had exceptional matching. Everything I have read says the Shuguang EL34B is the exact same tube and the datasheets I have found show 500V limits on G2. Unfortunately the last set of Shuguangs I bought were not matched nearly as well as the previous TAD tubes.

Unfortunately I do not own an oscilloscope, so the PI alignment is done as best as possible by ear. I have not attempted to balance the PI on my SA200s.

Most EL 34 have between 425 and 450, I would say, 50 volts more is ok, but 175 is a bit much.
By ear is not possible its off for sure.
A old scope can be found for little money.

As for the KT 88 I cant say how it sounds but 6550 sounds bad.
Looks like in that other thread some one installed KT88 and it sound good,
KT 88 is basically a big EL 34. I just never tried, six matched KT88 it isnt exactly cheap, about double the EL 34.

 

[Wasnex]

Most EL 34 have between 425 and 450, I would say, 50 volts more is ok, but 175 is a bit much.
By ear is not possible its off for sure.
A old scope can be found for little money.

As for the KT 88 I cant say how it sounds but 6550 sounds bad.
Looks like in that other thread some one installed KT88 and it sound good,
KT 88 is basically a big EL 34. I just never tried, six matched KT88 it isnt exactly cheap, about double the EL 34.

I added a note to my last post...Marshall and Hiwatt 100W heads run the screens around 460V, rather than above 500V. My Matamp GT120 does push the screens to about 512V on US voltage. The schematic shows 500V for HT and pretty sure the voltage was in spec lower on German mains. It's running Shuguang EL34Bs and biased to about 55%...so I have tried to take reasonable precautions to extend tube life.

Is it possible the 6550s you had were trashed? The only time I ever compared 6550 to KT88, I could not tell the difference, but I only tried the tubes clean. I have read that the way they transition into distortion is where the difference becomes more noticeable. I believe KT88s are said to be more abrupt and more harsh.

 

[agedhorse]

Allright, and now ... ladies an gentlemen... Aged Horse a.k.a G....

Oups I better shut up

Hmm Overtones maybe ?
Or are you suggesting here frequencys below 5 or 15K dont have overtones ?
What if those amps cut way below 20k, actually Im pretty sure, it was.


I Agree Bandwith became better, that was what, 20(?) years ago. Probably more like 10
but still even the latest really expensive class D "high end" BASS HEADS didnt convince me.

Costs of developement is still there, meaning if it isnt necessary, its not done.
Anyone believing different should wake up, in times of shareholders value and mass consumption, everything is calulated down to the last penny if not fractions of a penny, dictated by the biggest in the game.

In other words, because of just one in a1000, its not worth the trouble (cost)

They just sound boring to me, kind a stiff, dead no life, not inspiring.
In a band context this, is most likey lost and for most people (anyway) not important. For me it is,
especially if i play a solo.

I still rather play a big mosfet or a tube.



I know that and I was not that accurate I know...
How .

As stated before a $500 piece of consumer junk, cant be compared to a 10 Grand FOH amp.
I want to see the FOH company buying 100 piece of a $10000 amp not making sure it is good.
And the company which would deliver $10000 pieces of consumer grade junk would not survive a day.



Believe it or not I do know that territory in and out, from all kinds of Horn flares over TL to BR, Ripol, Bandpass and and and.

Most of the cabs these days are desiged to be loud and very important looooow.
That impresses the consumer in the store.
If ever, he will find out later what the caveat is.

if you ask me, the Intention or design goal is usually mostly high sales numbers.
We cant even be p!$$€d, they are also sitting in the vice being squeezed.

Of course low loud small is nice, but because of that there is almost no other type drivers anymore, unless you can custom order as a company.
But even that is over, many companys slap off shelf stuff inside its cheaper =)
Probably because there is no more free samples.

The worst part about those low loud small drivers is, most have a terrible phase behavior, if thrown in a reflex cab tuned to low loud small.
If you tune the cab for least phase there is NO BASS anymore, ha, great...
There are some nice exeptions but now its really hard to get hold of.

Tell me, when did you see the last time a bunch of reflex cabs, by design damped, that it reproduces "acurate" and more on the dry side ?

Yeah ok some are, but for a tubeamp you need at least a 410 better a 610 or even better 810.
With those cute little toy amps you dont need that, a 12 does it, at most a 2x12, but its just not the same.
The Read/Lab combination is good and its usable with out ear pain, also that is still not the same.

Anyway, didnt i write about TUBES amps wich have a really low damping factor ?
Then I threw in the cabs.

Try to find a cab today, with the internal volume of the SA410.
Ohh right, there is your (over) damping.

Most cabs these days are twice the volume, probably because there is not to many tube amps on the market and unfortunately such shallow cab would sound pretty thin with a non tube amp.

Its very simple, something like this has not enough volume in the market and therefore nothing like that is being produced.

Dont get me wrong, I know you have always something to say which is more acurate.
Since ancient times it has always been easier to take things out of context and and say its not accurate.

I addressed your comments, you are making factual misrepresentations about the technology, AND since you were disrespectful to me quite a while back and I see the same tendency again, we are done.

 

[Lemon]

FYI Roger Sadowsky's amp guru suggests setting KT88s to 30mV (30mA)...same as EL34s.



The idea with the KT88 is to improve reliability. So if the amp sounds decent and produces about the same power I won't consider it a waste. If the KT88s sound awful I will just throw in the new set of Koch EL34s. I have plenty of amps that are designed for KT88s. Hopefully Tom Bowlus will get around to trying out KT88s before I do . I am in no hurry to buy a new set of tubes.

I meant that the 6550 draws 45 when you plug it in after you had a EL34 in and that the adjuster pot has enoug travel to adjust that to what it should be.

 

[Wasnex]

I meant that the 6550 draws 45 when you plug it in after you had a EL34 in and that the adjuster pot has enoug travel to adjust that to what it should be.

OK...before taking the old tubes out, I recommend maxing out the bias voltage so the tubes are pulling minimum current. This will minimize the possibility of an over current situation when the new tubes are powered up.

I usually bring my amps up on a variac when I install new tubes, so I can monitor for problems as I increase the line voltage.

 

[Lemon]

I addressed your comments, you are making factual misrepresentations about the technology, AND since you were disrespectful to me quite a while back and I see the same tendency again, we are done.

Thats fine with me.
Possibly you should think about, how you aproach people, you might get different and more friendly responses.
Its really questionable how was dispespectful.

 

[Rockbobmel]

Here we go again.........

 

[Lemon]

OK...before taking the old tubes out, I recommend maxing out the bias voltage so the tubes are pulling minimum current. This will minimize the possibility of an over current situation when the new tubes are powered up.

I usually bring my amps up on a variac when I install new tubes, so I can monitor for problems as I increase the line voltage.

A long time ago I asked Koch about all the possible Tubes.
5881, 6L6GC, 6AC7, EL34, KT66, KT77, KT88, KT90, KT100, 6550.
All of these tubes "work" in the SA 200.
The problem is, that except for 2 all of the run way off, its optimal loadline and most of the way over specs or under specs.
The KT120 also "works" BUT the heater current is borderline,
They wrote: "the rating of the PT is 10A, the PT probably can deliver 12A"
I would NOT try the KT120, to risky !
The EL34B is a Beam Tetrode so is the KT88.
The KT88 is quite a miss match to the OT.

 

[jsbarber]

Has anyone tried the KT88? If so it would be great to hear your findings. Tom B. indicated an interest but hasn't had time...

 

[Wasnex]

Has anyone tried the KT88? If so it would be great to hear your findings. Tom B. indicated an interest but hasn't had time...

Okay it took me awhile but I found the post where someone tried KT88s: The Un-Official Sadowsky SA200 Thread...

 

[baxter_x]

For those still following this thread, I'm the proud owner of that jewel.
Pictures soon.

 

[chadds]

If you're having difficulty taking pics of it here's my address. Ship it to me and I'll take pics.

 

[baxter_x]

If you're having difficulty taking pics of it here's my address. Ship it to me and I'll take pics.

Haha.
Once am back home, which means tomorrow, I'll make pictures.