200S recap

[george]

I have an older 200S with a solid state rectifier (no hole in chassis for the tube rectifier). What capacitors do you recommend replacing and what working voltages (I believe these amplifiers were built when mains were rated at 110 Vac). THX

[Isaac]

I used the SDS Labs Mk3/Mk2 Capacitor Board from Triode Electronics. The power section for the 200S is essentially identical to the Dynaco MkIII.
http://www.triodeel.com/dynaco.html

[Soundmasterg]

Do a search and you can find my recommendations from a couple years ago. Isaac did much the same by going with the SDS board, though instead of individual parts it is all on one board which is nice for a better orgainizational look. It really depends on what you want to do. You can go with stock replacement electrolytic caps and have the same sound. You can go with larger value electrolytic caps in the first two stages and get a tighter bass response and less hum. Its up to you....

Greg

[george]

Thanks for the info on the SDS Labs solution. I think I will try and stay with a more original solution and look into replacing the multi-section filter can. What about any direction on replacing bypass caps, bias resistors, etc? I uess I need to pull out my test gear 

[Soundmasterg]

The problem with the original can as I noted in my previous post from a couple years ago was that with today's wall voltages, it is over it's 525 volt max specs, and that is with the tube rectifier. With a solid state rectifier it is even farther over it's specs. It may work for awhile that way, but will have a greatly reduced lifespan as a result. In addition to that, can caps are yesterday's technology and are becoming more and more rare and expensive as time goes on. If you use discrete caps wired in series, you get a high enough voltage rating and cheaper parts too. You can choose to use larger value caps for better bass response and reduced hum, or you can stick with stock values. It can be wired up in a way so that it doesn't drill any holes and reduce the value of the amp exorbitingly too. If you are concerned about being original, then you should leave all the parts in there and not replace anything, right?

The bypass caps are electrolytic and should be replaced with modern quality electrolytics also. The bias caps are the same. The bias resistors and dropping resistors should be replaced with metal film but then that isn't original so if you're concerned about that, hunt down some carbon comps and replace with them. Plate resistors should be replaced with new ones also as they tend to get crackly and drift with age. Carbon comps here are a good idea as they do influence the sound in this position. The signal caps can be replaced with modern types and the sound will improve as those brown caps were not very good to begin with, but they probably don't leak DC so its up to you. With all the resistors and signal caps, testing first to see if they have drifted in value (resistors and caps) or are leaking DC (caps) is a good idea. With the electrolytics, replacing them with new ones is the best option.

Have fun.

Greg

[george]

Greg,

  Thanks for the summary. I'm very interested in using a PCB based filter cap solution if it can be do without drilling holes in the chassis. Sounds like this is possible and I'll look into it. I'm wondering if anyone has pictures of a an amplifier with this modification?

  My goal is to keep this amplifier in the family since I have owned it since the mid seventies - not going to do a museum quality restoration though . I managed to snag a Sonaro bottom which now houses a 15" Gauss driver. Really great for small clubs since its fairly portable.

gbonosurf@yahoo.com

[mckinnon audio]

  Hi there,Greg is 100% correct.I've re-capped both ways,with replacement cans and with single axial lead caps and the axial's are way cheaper.My cost was $40-50 CDN.plus shipping for each can as opposed to $10-15 per axial,and I could get the axial's locally.I leave the orig.cans on the chassis so the look is still there.Sorry I don't have any pics. available for you.Good luck Mel.

[djc]

I did that with my 200s.  replaced them with an SDS board hiden under the chasis, no new holes drilled, and left the original can in place.  I use a tube rectifier and the thing sings with 215's.  I love it and doesn't matter what I plug in it sounds good.  have fun.

[johnk]

why bother with a "cap board" when you can buy the stock multicap (20/20/20/30uf @525V) from antique electronics (and others) that is made on the original Mallory tooling and is rated at 525 volts? I've used them in 7 of my  Sorados, Sonaros, 200S and 2000S and they work perfect with no problems whatsoever. I also used two new Sprague 20uf 600V caps in the first stage of filtering. All of these caps look and sound just like the originals.

2 cents...

[Soundmasterg]

why bother with a "cap board" when you can buy the stock multicap (20/20/20/30uf @525V) from antique electronics (and others) that is made on the original Mallory tooling and is rated at 525 volts? I've used them in 7 of my  Sorados, Sonaros, 200S and 2000S and they work perfect with no problems whatsoever. I also used two new Sprague 20uf 600V caps in the first stage of filtering. All of these caps look and sound just like the originals.

2 cents...

The problem is that the B+ voltage in almost all of these old 2x6550/KT88 Sunns is up around 560v with today's wall voltages. Sure the can rated at 525v will work ok for awhile, but it will have a shortened life span due to working beyond it's ratings, and it is more expensive than the other options. The other advantage to using discrete caps is that you can use larger cap values in the first two stages to tighten up the bass and reduce hum. For a bass player these things are good, though a guitar player may not like it. The caveat to this mod is that you can no longer use the GZ34 rectifier tube and must use solid state rectifiers. Most bass players will like the tonal change however.

Sprague Atom caps are greatly overpriced, and are not made like the originals anymore. If you look at the internals of the caps, there is a very small cap inside the large housing, which can cause some heat dissipation problems and makes it more susceptible to vibration. Further, on their 600v caps, there are actually two caps inside the housing which is not how they used to be made. There were some dissection pictures posted at the Hoffman amps forum several moths ago.

Greg

[johnk]

i've never had a problem with the 525V multi's or the 600V spragues. and by the time the multicap sees the voltage that it is filtering it is no where near 560V (the highest being 500V) and all of my Sunns work perfect with them whether they're tube or SS rectified.

2 cents........

[EdBass]

I remember posting about the SDS board long ago, works great and I like the 50/50/50/50 @630V, but...

How about this can cap, Model #KTL13 30/20/20/20 @550V, 600V surge. direct fit, new manufacture German can?

http://www.die-wuestens.de/dindex.htm?/k8.htm

Much easier than the SDS board, and would get the job done but a little pricier. Maybe $70-$75 delivered.

I've got an SS rectified 2000S that's getting a little "soft", and I might try one out. I'll post the results if I ever get around to doing it.

[johnk]

 Alot of people like higher cap values (i.e. 50uf instead of 20uf), but i am not only a tradionalist but also somewhat of a purist when it comes to my amp restorations (so i always strive to use OEM and NOS  parts with stock sizes and values).  I also prefer the stock filtering's compression and low end (less stiff sounding to me) but YMMV. 

i also saw the german multi-cap that Ed mentions and think that it would be a great replacement. although i haven't tried one yet, i have heard nothing but good things about them (quality, reliability etc.).  As far as the price goes, i feel that they are still reasonable since you  won't have to replace them for another 20-30 years (yeah, i know all of the techs say that they only last 10-15 years, but i have seen them go more than 30 years without any ill effects). I have always felt that using the amp, or at least firing it up every 3-6 months during its lifetime makes the caps last much longer than if you let them sit for years on end without use. its kinda like letting a car sit in dry dock for years and watching the tires crack and battery go dead. caps need to be charged and discharged, otherwise they can dry out and are destined to fail.

[djc]

I put my 200s with an SDS board against my buddies Sonaro with a new can and I'd say(my opinion) mines softer, punchier, all -er.  I like it better.  I went wtih the SDS and a GZ34 to regain the original sag.  sounds great.  I have to admit, I went with the SDS because of suggestions from this site and the 600v ability.  I've heard 3 Sunns in total, my 200s, my concert lead and my buddies Sonaro, so not going on much but the sound is far better than any other amps I've used.  I went through a lot before my 200s.  it will be burried with me.  it's the only amp I like for bass.  I'd take it even with the non-original cap board.