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In Reply to: 0.15µF caps in a c-j sound like bypass caps for larger ones. Do you have a schematic? (NT) posted by jeffreybehr on April 25, 2007 at 00:11:23:
Yes, CJ uses 0.15uf Styrene caps as bypass caps in the power supply . I am actually referring to the 0.15uf Styrene coupling cap from 6FQ7 to 6550 tube in the Premier 11a amp.
Follow Ups:
...I'd use either SoniCap Platinums or, if I wanted a somewhat warmer sound, a combination of Jensen PIO/CFs and SCPs, about 2/3rds and 1/3.I added the 4 0.15µF 'styrenes to the output of the main PS, 2-each immediately AFTER the high-Voltage fuses.
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Tin-eared audiofool and obsessed landscape fotografer.
http://community.webshots.com/user/jeffreybehr
High voltage fuse? Hmmm are you refering to the BBS-1 connected to the output transfomer?Just curious, how did you install the caps . Did you disassemble the PCB or just cut the existing styrenes and solder the NEW caps?
...cutting old leads and soldering new parts to those leads...but I suppose that would be necessary in some cases.Here's a pic of the new couplers...
This was the later of the 2 Elevens I owned....and here are the old 'styrenes added to the PS fuse.
The green wire is circuit common/neutral/return/ground.I state again that I'm no GEA, so I can't tell you how (or even 'that') these 2 changes improved the sound. I'm more of a longer-term-changes guy, but I sold both Elevens soon after this.
I do recall having some problem getting a couple of the the new caps' leads soldered effectively, but I was using 5%-silver solder then and didn't want to overheat the board. I now use Cardas Quad Eutectic; it flows MUCH easier.
Also, you might change slightly the value of the caps depending on how you're using the amp. For instance, if I were biamping and the Eleven was driving the upper 8 or 7 octaves, I might choose a 0.1µF cap. If I were using it fullrange, I might choose 0.22µFs.
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Tin-eared audiofool and obsessed landscape fotografer.
http://community.webshots.com/user/jeffreybehr
Cool pictures !! That's excatly what i am thinking as some problem might occur after dismantling the PCB and desoldering other connections. I think i'll settle on the 0.1uf Mundorf Silver/Oil since it's where my budget can reach and maybe upgrade to V-Caps TFTF in the future : )
the tube ones at least, the top plates comeoff as well as the bottom plates. Replacing parts is considerably easier compared to older designs, as you then have easy access to both sides of the board.
Stu
unclestu52,Thanks for the tip !! I unscrewed the six 4mm screws and was able to access the other side of the PCB. Time to clean the flux again !! Atleast i can just desolder the coupling caps i plan to replace.
By the way, have you done any tweaks/upgrades on CJ amps ? Care to share your experience .
Cheers,
Jason
and void your warranty?.....One cheap tweak: on the ground leg of your bias pots, install a small electrolytic cap (or film if you can find the space) to ground. Usually the ground leg has a resistor to true ground. A 5 to 10uF cap is sufficient at say 50 volts to be really safe will buffer the bias to the tube tremendously, and give your amp a significantly greater control of the bass. Remember the positive leg goes to ground for the bias supply.
Stu
Fortunately my Prem 11 warranty had looong been expired so i don't need to worry abouy voiding the warranty. I just want to tweak or update/upgrade some parts . After removing the top cover, i've noticed that the tube sockets are also quite dirty ( oxidized a bit ) and also some tubes are a bit loose. Maybe due to the aged tube sockets. Any recommendation of good tube sockets? ( ceramic or teflon types )Anyway , i tried to lay-out your suggested capacitor tweak. Is the schematic below correct ? There is a 18.2K connected on the ground leg of the bias pot which is connected to ground. So i just put the electrolytic cap in PARALLEL to the 18.2K resistor. Am i correct ?
I don't have the schematic in front of me but yes parallel the cap (4 of them) with the resister, remember the correct orientation, positive to ground!I wouldn't change the sockets. Those fancy ceramic gold plated pins stuff made in China, look good, but have terrible metal work, and lose tension quite rapidly. You can get those dental brushed for bridge users and clean the sockets quite nicely. Use a bit of alcohol.
What I don't like about many ceramic sockets is that they have an uncoated bottom surface. Cleaning solutions seem to penetrate the porous surface and they seem to get stained permanently.Stu
While you're at it, I like to reheat the tube sockets for the 9 pin sockets with a junk tube inserted to align the pins. Had some problems with Mullard made tubes cracking from uneven socket tension. If you want more pristine highs and very fine detail you can use a solder sucker and replace the leaded solder with unleaded stuff. Try the output sockets first before doing the rest of the joints, as it is quite a tedious job.
Thanks for confirming the capacitor tweak. Will get some BGs to try.Have seen some ceramic tube sockets at tubestore and also some pricey teflon tube sockets at partsconnexion. I also noticed some of the socket tension are uneven ., but i did not experience cracking sounds though. This is the reason i plan to change them. I think your suggestion of cleaning and replacing the solders with WBT silver solder is a better route... thanks mate !!
CJ does not remove the flux?
I think the flux become more noticeable as the amp ages. I called CJ service to ask any advise . They told me " If not broke .. don't fix !! ", but i still went ahead and use IPA to clean them. I didn't hear any sonic difference :)
about the flux getting more moticeable as the amp ages. The flux being organic in nature, tends to carbonize with heat. The pins certainly get quite hot on the tube sockets. I notice that with age the flux deposits get considerably darker. I always clean off the flux deposits as you do with alcohol, and I just feel safer with less of a possibility of arcing.
I know with burnt resisters which can also burn the circuit boards, it is imperative to cut all the carbonized sections off or else the traces will most definitely arc again in the future. You know what they say: an ounce of prevention....Stu
Nope, at least not at that point. I have an MV75 and a PV5 that have just as "dirty" boards.
I guess I'm spoiled because ARC boards are super clean. Also I occasionaly used the flux removal system at work to clean my boards.
Some solvents will attack the film caps, but there are safe alternatives.
CJ probably did not want to deal with it.
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