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Jolida 502 KT120 tube swapping

Having been told by the nice people at Jolida that the 502 transformer can handle the KT120's "filament requirements", I wondered if any Jolida-philes out there have tried them in either the 502BRC integrated or 502P (what I have) power amp, as they're apparently similar circuits. I'm tired of reading about how groovy the KT120 is and plan to try 'em eventually just to stop the madness and have some extra tubes around.
wolf_garcia
wolf_garcia OP
4,650 posts
 
Follow up: The Mullard 12at7s sound great. And the frightening glow explosion flash when the amp powers up is a beautiful thing.
jedinite24's avatar
jedinite24
1,502 posts
 
When I first saw the Mullard CV4024s flash so much on the initial turn on I was a little alarmed but then read that flashing is normal for them. It is cool looking. They glow brighter than the Tung Sol 12AT7 re-issues. Very pretty.
wolf_garcia OP
4,650 posts
 
Yeah...I had heard about Mullard Flashing and also was calmed when I looked up specific information about it. It adds a dramatic moment to amp start-up that otherwise would be a non-dramatic event. Maybe my threshold of entertainment is too low.
rattosecond
12 posts
 
Thanks Jedinite24! Will try those combination if I get a chance.

Someone is recommended me to use Telefunkens. Dont know what to expect till I have it.

How did you do guys the biasing? My speakers sensitivity is 86 so I am thinking the Jolida is struggling. I am thinking of making it a little hotter at 60, would it cause some problems?
jedinite24's avatar
jedinite24
1,502 posts
 
Hello again Rattosecond

For my Jolida 502P with the KT120s or any of the KT88 or 6550 type tubes in place I would always bias the amp at least 515 to 525 millivolts. One time by accident when I was swapping out NOS 6550 tubes for newer KT88/KT120 I had forgotten to lower the bias settings and found when I checked with my meter some tubes were getting 625 to 712 millivolts. I didn't notice anything odd with the tubes or any additional heat coming from the Jolida but I also didn't have the 502P at these bias settings for long.

I think if you increase the bias you will be taxing the tubes more and the transformers. My speakers are mostly 88db sensitive. Only the Ohm Walsh 2s I have maybe are the most difficult load for the Jolida. I used the 4 ohm taps on the 502P with the Ohms but kept the bias at around 515 to 520 millivolts. The music was relaxed and not so forward. Really good for nearfield listening. When I swapped out the Jolida and put in a Class D Audio amp that put out just 120w/channel into 4 ohms it made the Ohm Walsh 2 go quite a bit louder, more forward but the treble became a bit harsh till I made adjustments.

What do you feel is lacking with the Jolida 502B and your 86db sensitive speakers?
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