Recent Posts

91

DIY / Re: Sunn Solos II - Turns on though no sound

« Last post by loudthud on June 05, 2024, 01:44:47 am »

There are schematics and layout diagrams in this thread:

https://forum.sunnstillshines.online/index.php?topic=4781.msg18696#msg18696

It looks similar to the Concert series amps. You can check Voltages on the schematic but beware, there is a floating power supply in the power amp. Check for DC at the speaker output, that's usually an issue with the output transistors or a short in the Driver Transformer.

92

DIY / Sunn Solos II - Turns on though no sound

« Last post by Babyshins on May 30, 2024, 08:33:40 pm »

Hello all

I have acquired a Sunn Solos II that turns out but sends out no output through any of its jacks. I've tried the preamp output as well as the power amp input and there is nothing. I haven't been able to find much material online on repairing solid state amps, and would love to be able to do this type of repairs myself. Do you all have any resources or advice you could point me towards to help teach me how to bring this beauty back to life?

Thanks 

93

Bands Using SUNN / Sunn Rigs 2024

« Last post by Janisdooms on May 05, 2024, 03:51:24 pm »

Send your Sunn rigs! Here's mine . Some non Sunn stuff too, 1979 Beta Lead 212 combo, 1984 Enforcer 212 combo, Crate Powerblock, and Carvin RL410T (for bass).

94

Q & A / Re: Sunn 200s running on 6L6 tubes?!

« Last post by Soundmasterg on April 19, 2024, 12:05:31 am »

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

95

Q & A / Re: Sunn 200s running on 6L6 tubes?!

« Last post by Isaac on April 18, 2024, 09:07:41 am »

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.

96

Q & A / Re: Sunn 200s running on 6L6 tubes?!

« Last post by loudthud on April 16, 2024, 09:30:26 am »

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.

97

Q & A / Re: Sunn 200s running on 6L6 tubes?!

« Last post by Pacafeliz on April 16, 2024, 07:38:09 am »

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!

98

Q & A / Re: Sunn 200s running on 6L6 tubes?!

« Last post by Pacafeliz on April 16, 2024, 06:06:51 am »

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.

99

Q & A / Re: Sunn 200s running on 6L6 tubes?!

« Last post by Soundmasterg on April 10, 2024, 11:39:19 pm »

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

100

Q & A / Re: Sunn 200s running on 6L6 tubes?!

« Last post by Pacafeliz on April 09, 2024, 10:02:41 am »

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.