Sunn 100S Weird Noise

[JMacSunn100S]

I have a Sunn 100S (modified AC power section), that makes a very high pitched noise once it is warmed up and I've played the guitar through it.  Just strumming a chord and muffling it causes the noise.  It eventually stops after 3-6 seconds.  I can lightly bang on the top of the amp that causes a low-volume noise also.  If there are any suggestions how I can fix this noise problem(s) please let me know... I can do any typical electronic repair.

[mckinnon audio]

  Hi there,sounds like it could be a combination of microphonic tubes and/or dirty tube sockets and tube pins.Clean the sockets and fire in some other tubes and see what happens.Good luck,Mel.

[JMacSunn100S]

Thanks McK.  I'll give that a try this evening.  I did inadvertently reseat one of the tubes (preamp section) but I didn't continue noise checks.  I'll clean tonight and post the results.

[JMacSunn100S]

Okay, seems to be pretty noise free.  I can still tap on the chassis and get noise out of it but it takes a pretty hard tap.  I think I'll R&R the sockets.

Question, Should I replace the pre-amp tubes (12AX7, 6AN8A, 5AR4)?
The 6550's are relatively new.

[EdBass]

  Hi there,sounds like it could be a combination of microphonic tubes and/or dirty tube sockets and tube pins.Clean the sockets and fire in some other tubes and see what happens.Good luck,Mel.

Very impressive remote diagnosis, Dr. Mel! You're like the "Web MD" of audio. 

JMacSunn100S, try tapping on the individual noval tubes instead of the chassis, I'll bet you find the culprit.

[mckinnon audio]

  MD,I wish I was,I'm more of a Parampmedic,emergency repairs.....Mel.

[JMacSunn100S]

In the meantime, ... Anybody know where I can find this multi-Cap?  (online, $$)?

[EdBass]

In the meantime, ... Anybody know where I can find this multi-Cap?  (online, $$)?

There is a general consensus that the original can cap in the old Sunn tube amps is rated a little light, that startup voltage exceed the cans rated voltage.
This will work, however the seller warns against using them in a MkIII based amp for the above mentioned reason;
http://store.triodestore.com/40ufat52twis.html
But lookie here;
http://www.die-wuestens.de/dindex.htm?/k8.htm
KTL13 will do it just dandy.
I've never ordered one, but it seems it would fit the bill. They are a German company; maybe forum member Oli can help you out with translation.

I've had excellent success with this;
http://store.triodestore.com/sdslabmk3cap1.html
I've got it in a 200S (I'm pretty sure Isaac does also), and because of the good result I just put one in a 2000S. I haven't played the 2000S yet, but I'm sure it will work just fine. It's a little tough finding real estate inside the chassis for the board, but it will fit. If I get a chance I'll post a picture of the recent 2000S installation when I get back to the shop.
The SDS board tightens up the bottom end a little, and seems to output some more power overall, but I've never actually scoped it to see for sure. IMO it's a noticeable improvement over stock for bass guitar, not sure if a guitar player would agree, I guess it depends on the player.
It also can be used with either a solid state or tube rectifier.

[JMacSunn100S]

What's the difference in a solid state rectifier as opposed to the tube (5AR4)?

Any pictures of the Cap Install on your 2000S yet?

[EdBass]

The SS rectifier is more efficient than a tube rectifier, and provides a more consistant and powerful power supply overall. When Sunn switched to SS rectifiers in the 60 watt amps they increased the power rating to 80 watts, and the four output tube amps from 120 to 150 watts. The stronger power supply also eliminates the natural "sag" inherent to a tube rectifier under high current demand situations.
This may or may not be a good thing, depending on your personal tastes.
Most bass players seem to prefer the quicker response of the SS rectifier, but for guitar a lot of players like the "browning" effect that the tube induced sag causes. IMO one is not better than the other, it's a matter of personal preference.
The tube rectifier is probably easier on the amp components also, because a tube won't conduct until it builds some heat, and the power comes on gradually as it warms, whereas the SS rec. that slams the circuit with full power at starup.

I'll try to get a pic of the SDS install on the 2000S up this week, I actually have the amp with me at home instead of in my shop with it's Sunn siblings.

[scotzoid]

The SS rectifier is more efficient than a tube rectifier, and provides a more consistant and powerful power supply overall. When Sunn switched to SS rectifiers in the 60 watt amps they increased the power rating to 80 watts, and the four output tube amps from 120 to 150 watts. The stronger power supply also eliminates the natural "sag" inherent to a tube rectifier under high current demand situations.
This may or may not be a good thing, depending on your personal tastes.
Most bass players seem to prefer the quicker response of the SS rectifier, but for guitar a lot of players like the "browning" effect that the tube induced sag causes. IMO one is not better than the other, it's a matter of personal preference.
The tube rectifier is probably easier on the amp components also, because a tube won't conduct until it builds some heat, and the power comes on gradually as it warms, whereas the SS rec. that slams the circuit with full power at starup.

Good to know, Ed. That's something I need to look into on my Sceptre, I think it's a tube rect, which would be what I want for guitar. And I think my Sorado, used for bass, has a SS rect, but that's just a guess, since I haven't seen my baby for a coupla years now...if my band's guitar player ever gets his life together, I'll be visiting her regularly again.

[EdBass]

Any pictures of the Cap Install on your 2000S yet?

Better late than never!
The first pic is a closeup of the SDS board, the second is a shot of it in the chassis. I also recapped everything that was questionable, installed a grounded AC cord, and made the polarity switch a ground lift instead. I may also post this in the correct forum. 

[djc]

I've had excellent success with this;
http://store.triodestore.com/sdslabmk3cap1.html

2 thumbs up on the SDS.  I have one in my 200s.  tube rectified, very satisfied.

[loudthud]

Ed, I noticed your amp has different octal tube sockets than mine. They look original because they are riveted in. Mine has the wavey washer type. What's with the extra blue Sprague cap near the old can cap? I like to use radial caps in the bias supply. I've found that you can usually rotate the exsisting clamp 90 degrees to hold the cap.