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In Reply to: On the new CJ amps, posted by unclestu52 on April 28, 2007 at 16:48:15:
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 .
Follow Ups:
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 !!
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