Bias for Jolida 502 P Amplifier

Just got my new Jolida 502 P yesterday and I'm enjoying it a lot - great sound! (Thanks Wolf and Jedinite for your posts re the Jolida amps) I'm surprised at the amount of bass and slam I'm getting with my Magneplanar 1.7's In fact I'm thinking that for a lot of music I probably won't even turn on my HSU sub.

On setting the bias - how important are small variations? When I got the amp I checked with my multimeter and the amp was set at about 560 mv for all tubes. Moved the bias back to 500 mv per the manual but I'm not sure if it really matters all that much for these small changes? How critical is this?
043365f5 77b4 4635 bcae 8db4d3f6384eejman

Showing 4 responses by jedinite24

Hi Ejman

I'm glad you are enjoying the Jolida 502P. Regarding the bias I keep it around 535MV to 560MV. I do that for a couple of reasons. Around where I live the voltage from the socket fluctuates quite a bit. I think it has gone from 126 volts down to 118 volts depending on the time of day and what else is going on in my house. I don't have dedicated lines and I plug the Jolida right into the wall socket. Initially I tried to keep the bias exactly at 500MV and there were times it dipped below and the red lights on the 502P would go out or flicker. If the voltage in your home is stable I'd just keep it a bit above 500MV.

Also it may be my meter but whenever I tried to bias the Jolida to exactly 500MV I would fail. So if I was biasing it and I got it somewhat over 500MV I was happy.

Hi Ejman

Please don't start with rolling tubes until you have spent A LOT of time with the 502P first.Definitely let it settle in.

For me I believe the red LED lights should be on all the time indicating that the amp is properly biased. Normally I turn on my system along with the 502P and I don't listen to music until all the LEDs are illuminated and steady.

Regarding tube rolling I say follow what Wolf did and not what I did. Wolf has the discipline to keep his tube set-up pretty constant while I kept swapping tubes. I've got a box of all sorts of power tubes and preamp tubes in my closet ready to swap out for the 502P. I had to write down all the combinations I could do I have that many tubes.

I found a non edgy sound with Tung Sol KT-120s, Tung Sol 12AT7 and Mullard 12AX7 re-issue. It was a bit mellow for me though.

Keep enjoying your Jolida.
Man all this talk about the KT-120s makes me want to put them back in my Jolida 502P. That or check out the PSVane KT-120s. They are pretty looking. Anyway I've been enjoying the music in a nearfield set-up for the past couple of months with JJ KT88 Blue Glass tubes, JJ 5751 tubes and Mullard CV4024s.

I have to look through my notes. One tube enthusiast by me strongly preferred the solid plate Penta Labs KT88SC vs the Gold Lion KT88s. I think he liked them better all around and the Penta Labs KT88s had better reliability in his experience.
Hi Ejman

I have the tube cover/cage for the Jolida JD-502P and it is an interesting one. If I could post a picture here I would. I didn't see it on the net when I did a quick image search right now. Sometimes I equate the cage/cover to the Darth Vader helmet. It covers a lot but does allow for ventilation from the top. I don't think the tube cover would fit with the Tung Sol KT-150s in place. It barely covers the amp when the Tung Sol KT-120s are installed. There are actually 4 screw holes. 2 on each side.