sunn 200s amp help

[Jacobo]

hey everyone I'm new to the forum.
got some problems with my sunn 200s
after closer looks it seems like it was incorrectly repaired or it wasn't finished.

problem 1

urged caps
I have two caps rated at 20mfd at 600v they were wired in series
after I checked the schematic it says there are three 20uf caps at 525v in there place with a fourth at 40uf
so my first question is
did the circuit change between years of production or did someone just solder random caps

Problem 2

this amps fuse has been taken out and im not sure where to put a new one
i'm not great at schematic and at this point I need to make sure that im reading the correct schematic for the year if that is possible.

any help is awesome. I have discharged the caps
please don't tell me to take it to a tech to fix because there is no fun in that and I am not rich. I would rather learn to fish and risk getting wet than be dependent on a fisherman to feed me.
I know i'm working with high voltages that could injure or kill me
thanks in advance.

[soundmasterg]

hey everyone I'm new to the forum.
got some problems with my sunn 200s
after closer looks it seems like it was incorrectly repaired or it wasn't finished.

problem 1

urged caps
I have two caps rated at 20mfd at 600v they were wired in series
after I checked the schematic it says there are three 20uf caps at 525v in there place with a fourth at 40uf
so my first question is
did the circuit change between years of production or did someone just solder random caps

Problem 2

this amps fuse has been taken out and im not sure where to put a new one
i'm not great at schematic and at this point I need to make sure that im reading the correct schematic for the year if that is possible.

any help is awesome. I have discharged the caps
please don't tell me to take it to a tech to fix because there is no fun in that and I am not rich. I would rather learn to fish and risk getting wet than be dependent on a fisherman to feed me.
I know i'm working with high voltages that could injure or kill me
thanks in advance.

The original cap setup for all Sunn 200S models was a single can cap with 30uF, 20uF, 20uF, 20uF cap sections @ 525v. Sunn amps were very closely based on Dynaco hi-fi amps, and in fact the earliest smiley face ones were actual Dynaco kits in a Sunn box for the most part. Caps were expensive back then so the engineers would calculate the minimum cap value needed to achieve the specs they wanted, which meant that many benefits can be had in some cases by using larger cap values than stock. Another concern today is that with the higher AC wall voltages, the DC voltages inside the amps are higher than they used to be when these amps were made. So a voltage rating, in this case 525V that might have been ok back then doesn't cut it today, where my old Sunn 200S that I used to have had around 560V. CE Distribution/Antique Electronics Supply makes a replacement can cap for these amps, but it is rated at the same 525V as the old ones, and the same cap values as the old ones....the cap will last awhile but eventually will fail because of the higher than stock voltages these days.

For Sunn bass amps (or guitar amps used for bass), I recommend to use higher value caps connected in series, with parallel resistors to each cap for the first two filter sections. Bass amps benefit from the quicker bass response and the series connection allows two 350V caps to become one 700V cap at half the capacitance. So for example, two 220uF 350V caps connected in series give the same thing as one 110uF 700V cap. This is the value I recommend for a bass amp for the first section. For the second section, use a pair of 100uF 350V caps. Each one of these caps needs to have a 220k 1 watt resistor connected in parallel with the cap to share the load between the caps, or one cap will try to hog all the voltage and blow itself out. For the third stage, you need a cap rated to at least 500V, but I recommend to stay with the same 20UF value for this section and the other sections as you go towards what supplies the preamp. These sections are RC coupled and changing the value of the cap here changes the frequency response of the stage the cap supplies, whereas in the first two stages supplying the power tube plates and screens that is not the case and while the feel will change in that it will have quicker and tighter bass, the frequency response stays the same.

For Sunn guitar amps (or bass amps used for guitar), I still recommend the series connected caps for the first two stages, and a cap rated for at least 500V for the third stage, but whether you want to use the larger value caps is up to you. I personally think its a good idea and like the response change, but some people like stock values better. I personally don't like Sunn tube amps for guitar so I don't really think about this application too much. With either application, using discrete caps instead of one can cap is cheaper and will give better performance. One important thing to consider however is that any grounding points for the cap sections should ground in the same locations as the stock amp. You also have to get creative about how and where to drill holes for terminal strips to properly mount the parts.

Do not operate the amp without a line fuse in place. It is unsafe. Also the amp should be changed over to a 3 wire power cord setup instead of the 2 wire setup that some came with. Keep in mind however that in order to keep the light working on the power switch, you must wire the amp in the same way as far as the wiring going to the power switch. The proper approach is for the fuse and the switch to be on the hot side of the line supply, in the US usually the black wire. The other side, the neutral or white wire usually should go direct to the power transformer lead, but the light won't work on the switch if you do that, so wire it just like Sunn did, but put in the chassis ground connection too. It should go on it's own lug about an inch to an inch and a half from where the wires come into the chassis, and you should leave some slack on that wire so that if the power cord is pulled out of the amp, that wire will be the last one that stays connected. This is for safety reasons. Another important thing to this conversion is that the cap to ground from the ground switch, commonly known as the death cap, should be removed from the amp and the ground switch should be completely disconnected. If the amp already has the 3 wire power cord, then you can check to make sure the conversion was done right. On the stock setup, the fuse should go between one of the wires and the transformer primary wire just like shown on the schematic. If you don't know how to read the schematic well, now is the time to learn, before you get heavily involved in working on the amp. The schematic gives you all the info you need for the most part. It shows that the fuse should be a 3 amp slo blo fuse. If there is no fuse holder in the amp then you should get one of the Fender replacement ones from one of the many suppliers and install it, and put the proper fuse in before attempting to do anything with the amp. Also, make sure you are not just shorting the caps with a screwdriver to ground or something like that to discharge them. For old caps that you will replace it doesn't matter, but for new caps, it can damage them, and the spark can be scary too! Use insulated clip leads with a 10k 2 watt resistor clipped from ground to the main B+ cap when the amp is off and the caps will drain in less than 30 seconds.

Also, you may be unaware, but there is a Sunn specific forum at Ampage...here is the link >> the sunn forum - Index

But don't limit yourself to just that area. The rest of Ampage, and many other forums such as Hoffman, AX84, 18watt, Weber, etc have lots of good info on all kinds of amps.

Hope that helps!

Greg

[loudthud]

There were changes to the 200S over it's production from about 1967 to 1970. Sadly, there is no archive of all the changes with dates and schematics. Basically the same amp was sold as 190B from about 1971 up until about 1974. One of the most obvious changes was removal the the rectifier tube, a GZ34, and substitution of solid state diodes. There are examples that have the hole in the chassis for the rectifier tube with an small cover over the hole and solid state diodes. Another change was that the fuse was replaced with a circuit breaker. Note that if your amp has a GZ34, you shouldn't increase the filter capacitance. It will damage the tube.

Sometime after the change to solid state rectification, which brought with it higher B+ voltage, a change was made to the filter caps, two 20uF 600V were installed. The picture below is a 190B, it has the 600V caps, a circuit breaker and no hole for the rectifier tube. A "Tested By" sticker dates the amp to 7/12/72. The power transformer has the 5V winding for a rectifier tube, the wires just go to a terminal strip.

The Sunn 60W guitar amps have a circuit board under the chassis that contains the reverb and tremolo circuitry. Bass and PA amps just have a blank space so a board could be constructed to contain the filter caps. There is also a board available here: Upgrade Power Supply Capacitor Boards for Dynaco & Fisher Amplifiers It's not designed to fit the Sunn chassis, but some people have used it and made it fit somehow.

[soundmasterg]

There were changes to the 200S over it's production from about 1967 to 1970. Sadly, there is no archive of all the changes with dates and schematics. Basically the same amp was sold as 190B from about 1971 up until about 1974. One of the most obvious changes was removal the the rectifier tube, a GZ34, and substitution of solid state diodes. There are examples that have the hole in the chassis for the rectifier tube with an small cover over the hole and solid state diodes. Another change was that the fuse was replaced with a circuit breaker. Note that if your amp has a GZ34, you shouldn't increase the filter capacitance. It will damage the tube.

Sometime after the change to solid state rectification, which brought with it higher B+ voltage, a change was made to the filter caps, two 20uF 600V were installed. The picture below is a 190B, it has the 600V caps, a circuit breaker and no hole for the rectifier tube. A "Tested By" sticker dates the amp to 7/12/72. The power transformer has the 5V winding for a rectifier tube, the wires just go to a terminal strip.

The Sunn 60W guitar amps have a circuit board under the chassis that contains the reverb and tremolo circuitry. Bass and PA amps just have a blank space so a board could be constructed to contain the filter caps. There is also a board available here: Upgrade Power Supply Capacitor Boards for Dynaco & Fisher Amplifiers It's not designed to fit the Sunn chassis, but some people have used it and made it fit somehow.

Thank you for the post loudthud. I did forget to mention that if you go with larger caps, you can no longer use the tube GZ34 rectifier. In the past on the amps I have modded as I recommended above, I've used a Weber Copper Cap WZ34 or WZ68 solid state tube rectifier emulator. They don't care about the larger cap sizes and they emulate the voltage drop and sag of the tube rectifier. You could also just use a regular solid state rectifier setup too for a bit higher voltage. The example I quoted above used the Weber Copper Cap so the voltage of the third filter stage in the amp with a solid state rectifier might be higher than 500V. I forgot about the circuit breaker amps too....so the OP's amp may have a circuit breaker instead of a fuse....

The Triode boards have worked well for some people and they certainly fit into the bass amps easier than in the guitar amps.

Greg

[Bruce / Mission Amps]

If it has the GZ34, and you want to use much bigger filter caps in that Brute Force PI filter, (not sure how much extra capacitance is even needed with a PI filter, if any)... I bet you can put a 5 to 10 watt 47 to 68 ohm resistor in series with the B+ from the cathode of the GZ34 tube to the standby switch and subsequently, first filter cap....
and it will work fine with just about any large capacitance value.

[soundmasterg]

If it has the GZ34, and you want to use much bigger filter caps in that Brute Force PI filter, (not sure how much extra capacitance is even needed with a PI filter, if any)... I bet you can put a 5 to 10 watt 47 to 68 ohm resistor in series with the B+ from the cathode of the GZ34 tube to the standby switch and subsequently, first filter cap....
and it will work fine with just about any large capacitance value.

Probably...I wonder if that would increase sag again though? You wouldn't think going from 30uF to 110uF on the first cap section would make such a big difference in these Sunns with the tightness of the bottom end, but it does make a big difference. I've got a 2000S that I'm going to go with the same basic idea as above, but using Solen polyprop caps instead of e-lytics. The chassis has a ton of room for the huge caps so it should be interesting if I can ever get around to it.

Greg