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Krell KRS-100 caprevision

Dear All,

Just acquired a pair of Krell KRS-100 Class A fixed bias monaural amplifiers,
The blue large can Sprague Series 36DE filter-capacitors (6 of them per chassis) have a date-code of 8826 what means they're manufactured in week 26 in the year 1988. The other small caps are German Roedersteins 24 of them orange axial ones per channel. These are of the same age and most techs will state that the should be replaced.
I choose Vishay AML 138 series with a 105 degree Celcius rating. The smaller darkish red radial Roedersteins have all been changed by Vishay 105 degree Celcius types already.
Question: apart from the smaller caps I do not think that the big blue Spragues need replacement when they measure okay , I mean ESR and capacitance or am I wrong.

The drivers on top of each of the six coolingtowers are Hitachi K176/J56's followed by three MJE15024/25 outputtransitors.

There's also a opposite pair of MJE15030/31 TO220's in the middle of the blue coolingfins and these are used as temperature sensing devices I've been told and they should be attached to the two middle cooling towers of the six.

Any other advice regarding these amps? I like them very much and do intend to keep them.
As Krell wants I drive them with a solid state pre-amp (Threshold FET ten/e series) and it sounds gret to my ears.

Reactions are really welcomed because these amps are not very well documented like for instance the Levinson ML-2's

Thanks in advance
brian_eno
erik_squires
16,049 posts
 
Electrolytic caps made today are just so much better than in the 1980's  with better ESR, lower inductance and better lifespans.  Change them now and you won't have to think about it for 40 years.

I'd really leave it up to you more along the lines of:  Are you ever going to swap these amps out?  If yes, leave them alone and let the next buyer deal with it.  If no, swap the caps.

Best,

Erik

oldhvymec
5,101 posts
 
YUP That is old.. Time to change some caps and do a some resistor checks.. I re did a 5.1 Krell it was a class A preamp amp with a great DAC and stereo.  I love Krell remotes, man are they nice.. I used all factory caps, really wasn't that hard or expensive. Krell is Krell.. Good stuff.. They had all the parts in stock..

A guy on YouTube did the one like mine. Talked about the parts and where to get them.. Sure made it easy for me..

Those big filter caps.. There are better ones out there, not gonna be cheap though.. 105 at least ay? Class A, few bucks..

Regards
brian_eno OP
25 posts
 
Strange thing is though - I didn't want to mention it to not influence any responses - that all the Sprague's CDE's and Mallory's I swapped before from Thresholds, Levinson's and Conrad Johnson's measure great on capacity and ESR and I have at least 20 of them. Even the Sprague's from my Class A ML-2's from 1977 still measure okay. I have a dedicated ESR meter and capacity meter.
The only 105 degrees Celcius big cans are those KEMET (RIFA) PEH169 series, but these are hard to find and very expensive and do not have a rating of 40,000 uF in the same case as what is installed now.
bobbydd
97 posts
 
You doing the work yourself or did you send the amps to Krell?

Reason I ask is I also have an old Krell needing restoration.

Thanks.
brian_eno OP
25 posts
 
I would like to do it myself.

Just bought 50 Vishay 138AML Series axial (470uF, 100V 105 *c).
All radials have been done.
Big blue Spragues (40,000 uF, 90V and 95 *C) always measure good. Just measured 8 of them in a pair of KMA-100 Mk2's and their capacitance rating was more l than specified and the ESR's were all lower as 0.1 Ohm.

I've received much warnings but no real help as usual.
Bit dissapointed
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