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?
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.

The higher you set the bias the shorter the tube life will be.I would leave them at 500mv for 50-100 hrs until it's settled into your system,then feel free to experiment.Some folks feel the sound is sweeter with a higher bias setting.Glad you are enjoying your new amp!
Seriously great amp. I keep mine biased at 500mv just because it seems the amp was built around that point...with KT120s (which I've been using daily for almost 2 years and they refuse to burn out) you can supposedly bias higher, but it sounds fine at 500 so there it stays. The Jolida guys told me there's at least 50mv in each direction that is still conservatively within spec (I think the manual says that also), so there's that. I check it every couple of weeks and there is rarely much drift...10 mv maybe here and there, but my house AC is nothing special and all over the map (I do a load of wash and the LEDs on the 502 blink a little) and the amp doesn't seem to care.
Thanks all. I haven't been paying much attention to the bias red lights assuming that my meter would be more accurate. But now that you mention it, the LED's are either dark or barely flicking with no music playing and once the music gets going they kind of flicker on and off in tune with the music beat. Should the red lights be on all the time?

I've been having a lot of fun with the amp and the breaking in period. It's interesting how changes seem to be taking place over time.

For a couple of hours last night the amp got kind of bright sounding to where I thought maybe I needed to consider different tubes? (I like a warm musical non edgy sound) and then all of a sudden it settled down again to a much more mellow musical sound. Maybe the caps or tubes just settling in. Did anybody else experience this?
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.
The "break in" period of my Jolida was hard to quantify since it was so subtle and sounded great right out of the box. I noticed more from tube rolling, my most recent being the amazing Psvane 12AX7T-II input tubes...highly recommended. I look at the LEDs when I adjust the bias and it seems that if you turn the bias up to the point where an LED is steady and then back it off until it's almost out, this corresponds to my amp anyway. After that, the house current fluctuations are evident and I ignore that, although the LED blinking indicates a sign of life.
another important thing to remember is that the bias of a tube amp takes 30-45 minutes to settle down after switching it on. During that initial period the tube bias voltage is all over the map so you shouldn't even bother measuring it until it settles down. Hopefully you already knew this & you were measuring after atleast 45 mins....

I used to own a Jolida 502A some time back but I have forgotten what the bias voltages for the output tubes were supposed to be.
Thanks guys. I've doing the adjustments after waiting about 10 minutes for the amp to warm up. (The manual says wait 5 minutes) but I think Bombaywalla's suggestion of waiting 30-45 minutes makes sense as the amp continues to warm up quite a bit over that time frame. But right now it's sounding wonderful so I think I'll just listen and smile...
FYI-upgraded tubes will yield significant improvements. I went to KT88's with great results.
Thanks for the info Tbromgard. Which brand KT88's did you prefer and what improvements did you notice?
I went with a KT88 Gold Lion tube package specific for the 502 by Upscale Audio in CA. Cant rec it highly enuff Check out the website - they ship. Improvements across every aspect of performance.
Do Gold Lion KT88s sound better than KT120s in a 502? I think they LOOK better for sure, but I've been putting off buying a set.
In my opinion the kt120's sound much better in the 502p.The 120's are more extended top to bottom with with better separation and a fun energetic presentation .The Gold Lions have less extension top to bottom and seem just ever so slightly congested when compared to the 120's the GL just seem more laidback and relaxed. FYI I had the gold lions in for the last 6 months and the 120's for about a month now.
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.
I called Jolida the other day wondering about why my 502P has 3 screw holes on the sides with no screws. The guy I talked to (not Jarred forgot to ask the name) said those are for the tube cover (didn't know one was available) anyway while talking I asked him about using KT 120's and he said he didn't care for the sound because he found them a bit bright but that the KT150's were really sounding nice (if one could afford them...)

My amp came with the Tungsol 6550 and it's sounding just wonderful as it settles in. Really liking the 3d solid soundstage and great bass. Lush but detailed at the same time. The proverbial discovering all sorts of new things in well known recordings taking place frequently . Paired with my Mapletree preamp it seems an exceptional synergistic combination.

You all don't know how much I worried about going from a very powerful SS amp (CJ MF2300A) to a tube amp a quarter of the power, particularly with my Magneplanar 1.7's. I worried for nothing.
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.

When I talked to the people at Jolida about the 120s a while back (almost 2 years), they hadn't tried them, but assured me 120s wouldn't melt the amp. That, plus the good reviews, made me try them. I also liked the 6550s that came stock, and a set of Sovtek kt88s I bought (cheap), so I have all those for backup or whimsy. Psvane 120s do look cool, but since I've seen 150s for about 300 bucks (Ebay) and I assume they also won't melt the amp, maybe I'll try those when my 120s finally croak. Maybe we can start a tube exchange me some 150s...somebody...
Instead of a stock tube cage, I'm thinking of making a small prison fence replica someday...little guard towers with tiny barbed wire around my tubes. Impractical but cute...I might be able to score something from a prison doll house company.
I see where you are going Wolf - with a cute little sign - "You are now entering Stalag JD 502 P..."
The issue is deciding which prison doll house company to use?