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It's been a while since I've posted on the Asylum and I am looking for some input. I am finally getting around to rebuilding my Scott 209 amps and I was wondering if any inmates had any insights they could share. They are great sounding amps but I want to do a complete rebuild replacing all of the caps and all of the resistors. The selenium rectifiers will also go even though they are still working properly. Am I likely to devalue their "collectable value" in the name of better sound quality or should I "damn the torpedoes" and go for it?
"Nothing quite like high voltage DC to sharpen the mind and body!"
Follow Ups:
Notice how the parts are put in with goop and it looks nice and neat and you can always reverse it..The four unilytic polys are used for added decoupling on each of four sections.I used k40 pio caps and Panasonic film and foil couplers and solen film and foil on the inputs..The gentleman is using the amp on Magnepan 1.7s but just using a good mix of caps,resistors,and Schottky diodes really make these vintage amps dance.
"
Rebuild the amps. I have yet to not improve the sonics when rebuilding amps. M. Sanmra also improves the sonics of vintage amps with replacement parts. The 'right' parts makes the difference.
SG
Upgrading amplifiers never devalues them unless you physically alter them to where you can't reverse them back to original should you want to sell them..I'm talking cutting up the metal chassis or drilling holes in it...This is why I glue in all the filter caps with goop or some type of RTV because it's very easy to undo the that.
What I would do if they were mine is put in a 50uf panasonic poly film cap in place of C1a which is a 30uf in the schematic.For C1b and C2a are a 20uf and 30uf in parallel and I would just put another single 50uf panasonic film cap in their place..Both of these 50uf caps can fit underneath the chassis with some goop.
For C2b which is a 20uf and C3a which is a 10uf I would use a dual 100uf at 500v JJ or F&T electrolytic there.You then have another 10uf and you can use a single axial lead 47uf electrolytic.
For the 75v caps you want to use 220uf at 100v Muse kZ caps.You can use a dual 100uf electrolytic if you don't want to use the 50uf poly film caps but I prefer the polys there,
The rest is coupling capacitors that should be paper in oil on the EL34 outputs and polys on the preamp..
"
Thanks Michael,
I was thinking on a similar line other than using the 50uf poly caps (didn't think of that). I was thinking about using the 4 x 20uf @475 CE multi-section cans and paralleling the sections similar to what you were suggesting and using smaller (1uf or so) bypass caps. Also will possibly use in addition the 100uf @500v U36D United Chemicon electrolytics I have left over. Already have the UKZ Muse 100uf caps which I have also used before. For the C3 25uf I was going to use 100uf Black Gates that I had left over from another project. For the pre-amp coupling caps I will probably end up using Multicap PPMFX as my budget won't allow me to use the RTX Polystyrene tin-foil caps that I used in my Mac MC60's. The ceramic discs will make way for polystyrenes. I am not sure about the paper/oil caps for the outputs though. Why do you choose them for that application? Resistors will mainly be Vishay RNC60E and RN65E metal films that I have along with some CPF3 metal films for the 1W ones. Thanks again for your input as it seems that there aren't many people who are familiar the 209.
SG
"Nothing quite like high voltage DC to sharpen the mind and body!"
I would not use film coupling caps in a mac60s except for the input and maybe in the cathode follower..You definitely don't want to use anything but a paper in oil for the .047s because it will be bright and brittle sounding and dry. Metal films from grid ground in the preamp and in the phono stage but in the amp you want to stick to more of the carbon films because of the sake of of bandwidth and a CC on the control grids are best because they are non inductive..I used to put metal films everywhere along with polypros everywhere and I could never figure out why I lost so much body and openness until I put them in my Acoustat servo amps..When I had gone back to the original carbon films,it all came back.
The paper in oil on the outputs are great as are Teflons if you can fit them in because there is enough B+ on the driver side which will break in the cap. I have done enough Scotts,Sherwoods,and Macs to know where to get the best sound and how just from proper parts selection..Anywhere you have a 100vdc is more across the cap is a good place to put a paper in oil or teflon cap.
The Solen film and tin foil are very good as well.These are the white colored ones and I like them better than the multicaps and they are less money..
"
Edits: 10/15/14
Hi Michael,
Thanks again for the input. I should mention that I am still not sold on the use of the paper in oil capacitors due to their high dielectric absorption and leakage characteristics. My experience with them is they can be great in guitar amps for tailoring their tonal qualities, but not so great in higher end audio equipment for tonal accuracy. I am not really looking for the "classic warm tube sound" in my audio equipment as much as I am looking for tonal accuracy. I do like using Teflon caps as you mentioned but their relatively large size (and expense) can make them difficult to use. I will have to look into the Solen tin foil caps that you mention as I have not used them before so I have no common point of reference. Metal film resistors do exhibit a bit more inductance (still very little) as opposed to carbon film resistors but are much less noisy and much more temperature stable. The real advantage of Carbon films is in their failure mode as they will fail safe (similar to carbon comps) whereas a metal film can possibly short. I really do appreciate your responding to my inquiry and all of the friendly advice you have provided. You are most certainly a valuable resource to this forum. I should have mentioned that I am not a novice to rebuilding tube (or solid state) equipment as I have been doing it for about 30 years now. Thanks again for all your input!
Best Regards,
Sidegetter
"Nothing quite like high voltage DC to sharpen the mind and body!"
This is a stock Mac Mc225 and notice it has all film and foil caps other than the four bumblebee paper caps which run from the phase inverter to voltage amp and on the input which you can use a film cap there as well..They did this for a reason and the voltage is 330vdc or more across those caps and a paper in oil there is much more stable with frequency change in that position..
"
Here is a picture of my 209's
"Nothing quite like high voltage DC to sharpen the mind and body!"
Nice amps
I have a pair of 99D and a 272 and a 296 and a pair of 299s and an LK72 and an LK48..All these amps I rebuild with the same philosophy of a mixture of electrolytics and film caps in the power supply as well as paper in oil and film and foil couplers in signal coupling..They kind of remind me of my 272 as mono versions without the added gimmicks.Those are really nice amps and can really sing if you use good selection of components in the rebuild/
That quad 20 cap will not be sufficient for these amps..I would use dual 100s which are cheaper and better caps..Once you remove the quad 75v cap in these amps,you can put a second dual 100@500v and then a 3rd and 4th...The 75v caps you put underneath on a terminal strip and you can drill a small hole in the chassis to hold the strip or just goop it on..All the cap you put in with Goop like I did on that Mc240 and you will be fine..
"
The 209's really are sort of like your 272 but without the gimmicks. That was what attracted me to these amps. I like their straight forward approach and tube compliment(no triode/pentode for phase inverter, no "Dynauaral") which I agree should sing when updated/modified. I do like your idea of using the (2)100x500V caps but my only concern is the physical size of them. I was trying to keep my amps as stock looking as possible. My approach to rebuilding/modifying has always been to keep the amp stock looking from the top of the chassis. Also I do have both metal and wood cabinets for the amps that would not allow the added height of the (2) 100x500V caps. My original though was to use multiple quad section cans with the same physical size of the originals and augment them under the chassis as it does have room. I would like to use the 50uf poly film cap as you have suggested. One question is where to source them from? Thanks again for your assistance.
SG
"Nothing quite like high voltage DC to sharpen the mind and body!"
Hi Sidegetter, Mike and Sony are right When I watch American Restoration,the guy Rick with the sleeveless jacket always shows the final project,what ever it is and always proves(but does it work?).It wouldn't be worth a lot unless it was firin on all 8 cylnders if you know what I mean.Make that Scott sing......I wonder if Mike Samra just knew all those mods and such off the top of his head without looking at the schematic...wow!...Mark Korda
I was definitely going to rebuild my amps (they're mono by the way), but I guess my question was really how much? I remember when I got heat from members when I mentioned about my rebuilding of my (4) Mac MC60's in which the only remaining stock components are the chassis, transformers, choke, and tube sockets. All the rest including the wiring has been replaced (not to mention an overkill power supply). I may have damaged their collectable value, but they sure sound good. I'm hoping that the 209's will turn out as equally nice. Thanks for the input, I will have to post some pictures of them when I'm done with them.
SG
"Nothing quite like high voltage DC to sharpen the mind and body!"
Unless you are selling them, the heck with the collector value. Sure you wouldn't hack the chassis up, but put good parts in. Consider using carbon resistors on the output tube grids and carbon films on the small tube grids and cathodes. Other than that use the metal films. Rewire also. Of course it will sound far better than it did when it left the factory. The parts are better and the power supply is much better.
If people want to collect old amps with old and failing parts that is fine. If you want to listen to a piece then rebuild it....
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