Jolida 502 KT120 tube swapping

Hey Wolf

In order to get the KT120 into the Jolida 502P did any special modifications have to be done to it so that KT120s could be used in place of the 6550s? Was it just drop 'em in run the EZ-Bias? Also where did you get the KT120 tubes? The more I look at the Jolida 502P and reading about it I keep thinking about getting one.

Thanks

Hi Rattosecond

Welcome to the club. Like Wolf said there will be LOTS of preamp tube suggestions from owners to tube sellers.

Here are some combos that others have recommended to me and some that I have tried.

Tungsram 12AX7 tubes platinum or gold matched paired with Mullard CV4024 12AT7 type tubes.

I too also liked the Preferred 7025 from the tubestore paired with the Mullard CV4024 tubes.

If your source is a bit laid back or mellow to get more detail out of your music I liked the combination of Penta Labs 12AT7 tubes paired with Groove Tubes Gold Series GT-12AX7-C.

If your source is forward or has a high gain I liked pairing reissue Tung Sol 12AT7 and Mullard reissue 12AX7 tubes together.

Again this is all system dependent and in the systems I had these last 3 combinations is what I found after weeks of listening. I had Tung Sol KT-120 tubes in my Jolida at the time.

Best of luck on your search. I hope I have not confused you further.

Morning Wolf

I'll pass on being a testing source. Doing the swapping I did and keeping notes of findings and combinations was getting annoying. That and like everything else findings are subjective and system dependent. I'll definitely keep compiling info from others though about different tubes used in the Jolida 502P as I get them. I'll definitely share although most of the tubes I got were based off of your recommendations. You get lots of better information than what I got when I called Jolida or the Tube Store. I'm even trying JAN 12AT7 type tubes but from GE now but am finding them to be the same as the Mullard CV4024 tubes. Will give it more time though.

I bought way too many 12AT7 and 12AX7 tubes when I saw deals on various sites. I did try to get the Sovtek KT-88 tubes based on your thoughts about them but my local pro audio shop couldn't get them for me. Speaking of Sovtek from talking to Jim McShane he was suggesting a real quiet Sovtek is the 12AX7LPS. I was tempted on that one too but decided to pass.

I'm going to cry if Tung Sol makes the Gold Pin uber rugged version of the KT-120s. Another set of tubs to get. I think I need to be put in a straight jacket.

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.

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?