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Author Topic: Sunn Sorado Coupling Caps  (Read 286 times)

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eddiemac

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Sunn Sorado Coupling Caps
« on: April 29, 2018, 09:27:00 am »

I have a May '68 Sunn Sorado with tag that shows KT88's.  Almost everything inside matches the Sorado (and 200S) schematic, except it has .1uF caps before the power tubes instead of the .25uF coupling caps the schematic shows.  I've seen pictures of other 200S, Sorado chassis with .1uF Black Cats in this same position (mine are obvious replacements  -  Mallory 150's).  Can anyone give me some insight on this situation, or offer a guess?  Am I better off with the .1uF?  I'm using JJ KT88's after a new, improved filter cap job.
     http://www.prowessamplifiers.com/schematics/sunn/Sorado.html
« Last Edit: April 30, 2018, 08:09:07 am by eddiemac »

Soundmasterg

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Re: Sunn Sorado Coupling Caps
« Reply #1 on: April 30, 2018, 12:15:22 pm »

The earlier ones often came with the 0.25uF Black Cats instead of 0.1uF, but either is fine. The bass response is a little tighter with the 0.1uF. The difference is because the early Sunns were a direct copy of the Dynaco mk.3 HiFi amp, which used the 0.25uF value. Later an engineer hired by Conrad tweaked the amps to be a little better for musical instrument use, and that is when the 0.1uF came in. The early amps also had Dynaco transformers instead of Schumacher, and slightly lower voltages. They seem to work better with the larger value cap than if you sub it into a later amp with the Schumacher transformers....likely because with higher voltages you get a wider frequency response and its a bit much with the higher voltages and higher value cap. Regardless, it is easy to swap the caps and see if you like it yourself or not. These days the 0.25uF value isn't as easy to find as a 0.22uF value. The 6PS series (polyester) of the CDE Orange Drops series comes in a 0.25uF value the last time I looked but I don't believe the M150's do, though I could be wrong. With the improved cap job (I'm assuming larger power supply caps?) the smaller coupling cap in that spot is likely a better choice, but YMMV.

Greg

eddiemac

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Re: Sunn Sorado Coupling Caps
« Reply #2 on: April 30, 2018, 06:42:32 pm »

Neither of my Sorado transformers says "Dynaco," although the ones in the Sonic that I had in the late 60's did (on second thought, it was probably the can cap that said Dynaco).  When did the Schumacher trannies come in?  What do you mean by "tighter"  -   does that mean less low bass?  I picked up a couple of .25uF 6PS caps on ebay and may try them.  My filter cap job brought me to 110/50/22/22 if I remember right, thanks to your recommendations.  Inrush voltage with a Weber Copper Cap was tested at: 601V; A: 545V; B: 469V; C: 354Volts.  With the 5ARU tube, it was 576, 545, 463, 353.  Thanks so much for your help.  I've learned so much from this forum.

By the way, will I need to re-bias after changing coupling caps?
« Last Edit: May 02, 2018, 01:25:29 pm by eddiemac »

Soundmasterg

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Re: Sunn Sorado Coupling Caps
« Reply #3 on: April 30, 2018, 08:08:31 pm »

Neither of my Sorado transformers says "Dynaco," although the ones in the Sonic that I had in the late 60's did.  When did the Schumacher trannies come in?  What do you mean by "tighter"  -   does that mean less low bass?  I picked up a couple of .25uF 6PS caps on ebay and may try them.  My filter cap job brought me to 110/50/22/22 if I remember right, thanks to your recommendations.  Inrush voltage with a Weber Copper Cap was tested at: 601V; A: 545V; B: 469V; C: 354Volts.  With the 5ARU tube, it was 576, 545, 463, 353.  Thanks so much for your help.  I've learned so much from this forum.

By the way, will I need to re-bias after changing coupling caps?

There should be an EIA code stamped into the transformer end bells.

http://www.triodeel.com/eiacode.htm

http://users.eastlink.ca/~mitchlane/EIA_Codes.html

I forget right now what the code is for Dynaco but Schumacher is 606.

Tighter would mean that the bass note will hold together a bit better than with the larger cap and be less mushy sounding. It is a subtle thing, and really just try it and see. Change both caps at the same time, then go back to the 0.1uF ones. Your ears will lose the memory of the sound during the time it takes you to switch between each, but if you play around a bit then you should be able to hear the differences.

The changeover likely happened by 1969 but some late 1968 models could have the Schumacher transformers also. No need to rebias when changing coupling caps...just make sure your work is good and the soldering is done well. All the usual safety rules apply for working with high voltage devices so if you don't know what you are doing fully, then please have others more qualified to do the work. The 6PS Orange Drops are radial caps so they will mount differently than the axial caps that were in there. Be careful about bending the leads and use needle nose pliers to bend the leads after the bend that they already have in them...do not bend right at the body of the cap, or you risk damaging the cap.

With the other changes you made to the amp, you have a stronger and tighter bass than it had stock, so the cap change will be slightly more of the same. Also, I will reiterate what I stated in those posts that you worked from for the cap job.....do not use the 5AR4 anymore in that amp unless you change the first cap to a size smaller than 60uF. The Weber Copper Cap or some other solid state rectifier must be used with the large first cap value or damage will occur to the rectifier tube, and possibly other things in the circuit. If you stick with the solid state rectifier/Weber Copper Cap then it will function fine.

Happy to help...keep learning and pass on what you have learned. Thats all I'm doing. :)

Greg

eddiemac

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Re: Sunn Sorado Coupling Caps
« Reply #4 on: May 19, 2018, 10:54:22 am »

Well, I've got to agree that the .1uF caps yield a slightly tighter bass sound (more punch, clarity?).  I tried the .25uF original value at a gig and, two weeks later at the same venue, the .1uF. 

Soundmasterg

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Re: Sunn Sorado Coupling Caps
« Reply #5 on: May 20, 2018, 12:35:32 pm »

Its a subtle thing, but the effect is clearly there. Its up to taste...use whichever one you like better.

Greg