Jolida 502 KT120 tube swapping

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?

Wolf,

I have a Jolida 801. I like it well enough but having to turn the amp over to bias the tubes is a pain in the arse. Thinking about maybe going with the 502. I lose 10 watts (70wpc in the 801 vs. 60wpc) but my speakers are efficient enough that I probably won't see too much difference. I gain a Remote, which purists may condemn, but hey, I am getting older, and HT pass-thru.

Will you describe what mods Jolida MD actually performed? I was looking at Underwood Wally but would like to have some options. Thanks.

I was advised (and my manual recommends) to bias any sort of tube to the stock 500mv and it seems to work fine. There is 50mv wiggle room built in.

Oops...missed the mod query. Here's what Jerrod sent to me:

2 - clarity esa caps .47uf/630v
4 - jolida custom caps .22uf/630v
4 - hexfred diodes
4 - ohmite little demon ceramic resistors 10k/2w
array of resistor changes within the signal path

An inexpensive installation of some seemingly worthwhile items, and, after almost a year and a half of tube rolling, this little amp has yet to sound anything but wonderful.