Sunn 200s running on 6L6 tubes?!

[Pacafeliz]

Hey folks, nice to be back after many years of absence!
I'm back here in Mexico and happened to pick up an old 200s, and it's working. But i did realize it has a pair of 6L6 tubes instead of KT88s - that can't be right, right? The rectifier is a 5U4.
Original owner says he's been running it like that for the last 20-30 years!
The outputs on the back are not marked what impedance they take, so i guess it's 8 and 4, right?
So my brother has a big Fender Dual Showman cab here, which should be 4 ohms, so I connected that one.
No nasty noises, good sound, but one of the power tubes was massively redplating,  so i shut it off.
Will take it back to Germany with me and get some KT88 first,  then have my tech guy check it out.

Any thoughts?

Cheers,
Pat.

[Pacafeliz]

Here it is:







subir imagen gratis

[loudthud]

Those tubes are OK if that's all you can get, but output power is probably only 45 to 50 Watts. Probably needs to be checked out by a good tech.

Note: A 4 Ohm cabinet should be plugged into the "External Speaker" jack. The internal wiring should be checked to see if the amp is wired for 4 or 8 Ohm cabinets or 8 and 16 Ohm cabinets. There are pictures on this web site to check.

Link: https://forum.sunnstillshines.online/index.php?topic=4844.msg18880#msg18880

[Pacafeliz]

Those tubes are OK if that's all you can get, but output power is probably only 45 to 50 Watts. Probably needs to be checked out by a good tech.

Note: A 4 Ohm cabinet should be plugged into the "External Speaker" jack. The internal wiring should be checked to see if the amp is wired for 4 or 8 Ohm cabinets or 8 and 16 Ohm cabinets. There are pictures on this web site to check.

Link: https://forum.sunnstillshines.online/index.php?topic=4844.msg18880#msg18880

Oh wow, thanks man, that's great info!
I'll open the amp up and check (take pics) next weekend.
In the meantime I've ordered some KT88s.
I'll also try to get the correct rectifier tube, since this one's wrong, too.

Stay tuned!

PS: any idea on its age/year, by looking at the pics?

[loudthud]

For an amp this old, there might be other issues that pop up. Read through this thread over on the MEF board.

Link: https://music-electronics-forum.com/forum/amplification/guitar-amps/sunn/994060-200s-sunn

[Pacafeliz]

For an amp this old, there might be other issues that pop up. Read through this thread over on the MEF board.

Link: https://music-electronics-forum.com/forum/amplification/guitar-amps/sunn/994060-200s-sunn

Thanks, will check it out.

[Soundmasterg]

That's in the earlier range of the completely self contained in one chassis 200S. The grille cloth is the early style. Dynaco transformers most likely, with slightly lower voltages than the later Schumacher transformers. I personally like the Dynaco transformer amps better. That is probably from around 1967.

The 5U4 rectifier lowers the voltages in the amp below stock, which is probably why the 6L6's haven't blown out yet. 6L6GC are robust tubes, but getting above 500V and unless top notch vintage quality they will struggle to survive, especially in a UL circuit like the Sunn, and will certainly give less power than the 6550 or KT88 with the proper 5AR4/GZ34 rectifier.

It looks like a decent amp though. I'd replace all electrolytic caps in the amp, and in the first two filter stages, you should use series connected caps with parallel resistors to give it 700V capability for each stage. Something like two 60uF and 350V connected in series with 220k resistors in parallel with each cap to share voltage load will give the equivalent of 30uF and 700V. Then the second stage set up the same way could be two 47uF caps at 350V for the equivalent of 23.5uF and 700V. Mouser sells some in those values. You may be tempted to use the CE Distribution can cap that is like the originals, but it is overvoltaged with today's wall voltages, and doesn't have the best reliablity as a result, and it will also be more expensive than the solution I mentioned. Drill a couple holes in the chassis and mount some terminal strips and secure the series connected caps and parallel resistors to those. Ground in the same place as stock. Replace any 2 wire power cords with a 3 wire setup and get rid of the 'death' cap. Replace the tubes and set the bias properly, and you should be good for many years.

Greg

[Pacafeliz]

Thanks people!
Well i and the amp made it back to Germany safely. Got some KT88s and plugged it into my 110v step down converter.
There is sound, but a loud hum over it, that wasn't there before.

Opening it up it all looks original and pretty solid...











...but this here has broken, might have happened on the rough plane ride.
EDIT: resoldered it and now it's workig nice and quiet again!
Only the Lo and Hi switches don't change a thing?

My amp guy is currently on vacation,  dammit.



So looking at the pics, is this an 8 - 4 Ohm output?
BTW yes all the pots are dated 1967.

Any other thing that jumps in your eye?
Thnx,

Pat.

[Pacafeliz]

Ok so i sprayed the pot and switches with Deoxit,  now the latter ones work intermittently - they'll have to go, eventually.
But for now I'm a happy cat!   



Thanks for your help!

[loudthud]

Thanks people!
Well i and the amp made it back to Germany safely. Got some KT88s and plugged it into my 110v step down converter.
There is sound, but a loud hum over it, that wasn't there before.

Opening it up it all looks original and pretty solid...

( Pictures not duplicated )

...but this here has broken, might have happened on the rough plane ride.
EDIT: resoldered it and now it's workig nice and quiet again!
Only the Lo and Hi switches don't change a thing?

My amp guy is currently on vacation,  dammit.

So looking at the pics, is this an 8 - 4 Ohm output?
BTW yes all the pots are dated 1967.

Any other thing that jumps in your eye?
Thnx,

Pat.

It looks like your amp has been modified to have the 4 Ohm tap hooked to both output jacks with no switching involved. You can use either jack for a 4 Ohm speaker cabinet or use two 8 Ohm cabinets.

Other mods seem to have been done. There are two large resistors connected to the power tubes, not sure what the story is there. The three axial caps clustered around the original main chassis mount cap aren't stock. One of them says 150V so not sure what's going on with that. Then there is the black electrical tape, another mystery.

[Isaac]

If you're playing guitar through it, as you appear to be, you likely wouldn't notice any effect from the LO BOOST. What it does is to change the low end cutoff from 80Hz to 40Hz. That extra octave is below anything a guitar typically produces or a guitar speaker reproduces.

I'd have to review the schematic to see how the HI BOOST functions.

[Soundmasterg]

Black electrical tape is a no-no with high voltage DC. They modified something in there with the extra electrolytic caps too, as Loudthud noted. Personally if it was my amp, I would go back to stock with the whole circuit arrangement, but change all the electrolytic caps in the amp, and for the first two filter stages, use series connected caps with parallel resistors as I noted to get a good voltage rating that is sufficient for today's wall voltages. Even if you are running it at 110 VAC, the stock 525V caps were right on the ragged edge of OK. In the 200S I used to have, I used series connected caps to get to a 700V rating on the first two stages so it would be safe even with turn on surge.

Greg