Tube upgrades for Jolida 502B?

I realize this is something that has come up before, though in searching the archives I didn't come away with a clear path forward. My amp is completely stock and came equipped with Sovtek 6550s. Using it to drive Totem Forest speakers. I contacted Jolida. They recommend KT88s. Their reply is a bit unclear but they might be suggesting Electro Harmonix. They also indicate reliability issues with Chinese KT88s. Response Audio (Jolida dealer and modder) recommends Shuguang KT88s (Chinese). The Tube Store recommended JJ Tesla KT88s on the strength of their great imaging and deep bass (more bass being something I was looking for). I was initially leaning towards SED Winged "C" 6550s. Now I am a bit more confused. I'm curious about KT88 vs 6550 sonics and reliability differences. Thanks in advance to any one willing to take the time to share their experience and preferences.
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Replaced stock Shuguang KT88's with Tung-sol 6550 reissues on my Cayin amp used with Totem's also...right away there was a noticeable improvement.

Tung-sol's have all the bass of the Shuguang's but, slightly better imaging & resolution, tighter bass, but most of all, sweet, sweet midrange that makes voices, instruments more realistic sounding.

Without using so many audiophile terms, Tungsol's just "holds a note better".
Go with the JJ KT-88's..excellent tube in the 502. Balsy bass and superb imagaing. The recommendation is spot on IMO.I also tried the Penta solid plate KT-88 and they are excellent as well. a bit more open over the JJ's, But the JJ's are never bright and may be concidered a bit dark sounding.A very non-fatiguing sound.

I used a NOS GE 6201(12AT7's equivent) and the new issue Tung Sol ECC803S gold pins avail from The whole combo with a good PC and isolation base under the amp was realy good sounding.
I once owned an upgraded JD-502B and played around with various NOS GE, RCA, and Sylvania input tubes and SED KT88, Sovtek 6550, and Shuguang KT88 power tubes. My favorite combination of those I tried:

GE long plate 12ax7
Sylvania Gold Brand 6201
Shuguang KT88
I currently am running the EH KT-88's in my 502, to good result. I tend to think that the driver and pre tubes affect things a little more than the power tubes. Running a set of Mullard 4024's in the 12at7 positions, and tung-sol reissue 12ax7's in the pre positions have supplied really nice sound. The bass is not soft in any way-hits a little like solid state. I'm an electric bass player sensitive to that frequency region and I simply couldn't live with flabby bass. Hope this helps a little. -Fish
Thanks to all. Interesting that no one advocated 6550s. I'll follow up once I make a decision and actually do something. Thanks again.
By the way...
A follow up from Michael Allen at JoLida indicates the 502B now comes stock with EH6550s. EH was chosen for "excellent reliability". He said "If you wish to be perfect...look at the KT88s." He also suggested talking to the Tube Store for input on sound qualities.

The full 502B tube upgrade recommendation from the Tube Store was: JJ Tesla KT88, Ei Elite 12AX7E, NOS Mullard 12AT7WA. Any thoughts about this combination? The Tube Store review of the JJ KT88s using Quicksilver amp and Vandersteen speakers is very positive and appealing. Am just a bit antsy about reliability. The Sovteks ain't necessarily the "best sounding" but they are tough. Would prefer to compromise a bit on sonics to avoid blowing a tube or frying an amp circuit component. Thanks for your input. It sounds like KT88 is the way to go and I expect there are a number of options that will deliver very good results as your various systems show. May have to just close my eyes and "jump" as it were.
just fyi if you are interested in my little saga...I went with the full Tube Store recommendation as described above. Just installed them last night. Was only able to listen 1 1/2 hours. I assume the sound will improve further with time. My immediate impression listening to Peter Gabriel's "So" is that I'm hearing some bass notes that appear an octave lower than what I could hear before. Sub-sonic...almost felt more than heard. Greater clarity and more detail than previously. Highs at this point might not be as smoothe as before (I'm actually not quite certain about this) but the original tube complement was 5 1/2 years old. Also the Forests have <150 hours on them. Have to believe more time for tubes and speakers will make a difference. If anyone has thoughts about time for tube "break in"...or whether there is such a thing for tubes as for other components - I'd be interested to know what you think.
12at7 - brimar yellow "t" label 6060s circa 1954
12ax7 - mullards d "getter" circa 1957
6550 - tung sol black plate triple top getter circa 1957

HUGE difference
i like it better now tham my friends mac
How do you like the sound of the Tube Store set of tubes? Are they reliable? How many hours do you have on them?

Im waiting for my first tube amp to arrive- JD 502 brc. Cheers.
I own a jolida 502p and I have put the current tube store premium package recommendation of 4 Gold lion KT88 reissues, 2 Northern Electric 12AX7 and 2 NOS Mullard 12AT7WA / CV4024 in the amp.The combo is quite nice open sound stage, deep bass and clear highs. It is the best combo I have tried I have used the tungsol and the winged c 6550's, GE and rca 5751,JJ 12ax7,Ei 12ax7, mullard cv4004 sovteck and EH and the list goes on for small signal tubes. I do like the tubes stores combo and it has been in for the last year. One note I purchased all the tubes from other sources GL from a local store just because I heard kt88 can be kind of fragile and did not want the hassle of shipping them back if something was wrong and the others I found a better price elsewhere.The GL's have been operating just fine for the last two years.
Tbromgard - I hope you enjoy your Jolida 502 as much as I did mine. The tube complement recommended by the Tube Store sounded great. Unfortunately, the JJ KT88s just did not seem that reliable. I had a couple fail in well under 1000 hrs and on at least one occasion necessitate an amp repair. Ultimately, I went to Winged C SED KT88s purchased from Upscale Audio. That isn't anything against the Tube Store. I have subsequently purchased and will purchase again from them. The Mullard and Ei Elite small tubes they sold me were just fine. Because I changed all the tubes out at the same time, however, I can't give you any impressions about their individual contributions to the overall sound. Before you do any tube rolling, do take some time to get familiar with how the amp sounds in stock form. I think the Jolida represents good value and it does benefit from some relatively inexpensive tweaking. I heard improvement from the following: Herbie's Tenderfeet between amp and hardwood cutting board used as platform for it; HiFi Tuning Fuse; upgraded power cord. I went with a MAC Soundpipe but today would also consider a Pangea AC-9. Finally, after you have lived with the amp for a good while, get in touch with Jolida. Call them direct and find out about their factory upgrade. It was maybe $250 or a little less when I did it. Thought it was well worth the $. Noted greater clarity and a bit more detail as well as deeper tighter bass from it. Wished I had done it sooner. I don't use the Jolida day to day anymore but did keep it as a backup. While they sounded great with the Jolida, the Totem Forests I was running really needed more power so I eventually got some higher power tubed monoblocks. If WAF allowed, I would love to get a 2nd set of more efficient speakers (e.g., Tekton Lore's?) to use with the Jolida from time to time. Good luck with your 502B. Again, I hope it gives you many hours of listening enjoyment.
I stuck KT120s in my Jolida 502p after being assured (By the Jolida MD people) they would work. They do. Amazingly. The stock 6550s were fine, as are the Sovtek KT88s I tried, but the 120s just sound better in every way I can hear. Then, it was suggested by a dude at the to try their "preferred" 7025s in place of the 12AX7s...another brilliant idea that, combined with the 120s makes the amp just sing...more accurate seemingly, crisp but still tube rich...all good, and the 120s hold the bias settings really well. Now I'm thinking of trying Mullards in place of the EH 12AT7s and if that makes things even better, my head might explode from happiness.
Hi Tbromgard

Another Jolida JD-502P owner chiming in here. I too have Tung Sol KT-120 power tubes installed on the 502P and am very happy with them. Out of curiosity I did try the a matched quad of solid black plate Penta KT-88SC tubes. I found the bass to be less tight with the KT-88SC tubes vs the KT-120s. Mids and Highs were slightly better with the KT-120s to me. I may keep the Penta KT-88s since they don't come up for sale often or if I want a change of pace.

Now for preamp tubes here is what I've found in my system. All these notes were done with the Tung Sol KT-120 power tubes in place.

With a mellow source I found Penta Labs 12AT7 tubes and Groove Tubes 12AX7 Gold tubes make for better detail in the music without any listener fatigue.

With a source that is very forward I found The Preferred Series 7025 tubes along with Tung Sol 12AT7 tubes made the music more warm and mellow in my system with just the right amount of detail.

I also found the re-issue Mullard 12AX7s along with the EH 12AT7s made for a very mellow less detailed presentation to the music in my system. A lot of songs I was playing were really laid back. Maybe it could have been revealing the true mellowness of my source but that is what I found.

Best of luck with the search.
Thanks for the tips guys. Any other experiences tube rolling with the JD 502B?
You might want to confirm with Jolida but to me the only difference between the 502B and the 502P is that the 502B has volume, input controls and subwoofer output. Other than that the Amplifier section is the same.
I have to wonder what difference better 12at7s would make as I have been told that particular tube purpose (driver/phase inverter) is somehow less important. I welcome any opinions about that, as long as they aren't meant to intentionally upset me.
Based on an entertaining conversation with a really cool and tube savvy woman at thetubestore, I ordered a pair of matched section JAN Philips 12at7s...they may or may not be the best option but she was so much fun to talk to (maybe I need to get out more) it's worth the relatively small cost to find out.
Thanks for the responses. Now can anyone explain how to bias tubes in the 502brc? I dont have the owners manal
I am considering changing amplifier to cary SLI-80.
My amp is a 502A with some upgrades done at time of purchase.
Could also consider the KT 120.
Speakers are Merlin VSM, and I think they deserve better.
If it's like the 502p you turn the little bias screws down (a lot) before installing tubes, disconnect any signal to the amp, put the tubes in and turn the amp on and wait 10 minutes or so...then turn the bias up on each tube just until the LED all of 'em and check 'em in an hour or so and you're done. I bought a Radio Shack meter just to fine tune the bias (and out of curiosity) and found that the LEDs are surprisingly accurate. Note that due to house current fluxuation throughtout the day the LEDs change a little from time to time, but unless your tubes are failing this isn't a worry.
Wolf Garcia-
I would think the 502b is the same. But do I understand correctly that you turn the screw until the led light comes on? I heard the opposite-that you turn the screw to the left until the led light goes off. Im not sure what to do. I put the tubes in turned it on and seems to operate great. sounds fine. none of the led lights are on...
You turn the screw down initially, then turning it up adds bias current until the light just comes on (this merely keeps you from accidently frying new tubes with too much current). Then you're set...backing off from the light being on is fine as there is some wiggle room...50 milliamps or so at least. I've checked this with a meter and adding bias current does correlate with the LEDs coming on so it all works fine on my amp. The LEDs on my amp blink stay on or go off depending on the house current...but the KT120s still stay within a few milliamps of far anyway.
Put EH 6CA7s in that amp and it will put out more dynamics and tighter bass than with standard EL34s.
I don't think you can put EL34s (or equivalent) in a's a mostly 6550/KT88 based design.
Oops my bad, mistook this for a 302, apologies.
Too late...your comment lead to hapless 502 owners all over the world blowing up their amps during xmas...likely igniting trees and festive hifis festooned with decorations (I mean...doesn't everybody festoon their hifis?) leading to holiday audiophile depression. All your fault Stevecham, or shall we call you "the Man who ruined the Holidays for Jolida Owners?"
I decided to go with th following tubes:
Gold Lion KT88s. In the 12AT7 position, the Mullard CV4024. For the 12AX7s, Tungsram ECC83. All matched and designated "platnium." Get them this week. Cant wait to hear them. HOW LONG DO TUBES TAKE TO BREAK IN???
I've bought a majority of my tubes used or already burned in from the seller so it has been plug in, play and enjoy. From reading in other forums about 100 hours will do for your tubes to break-in. Enjoy. You've got quite a batch of tubes there for your Jolida. I have the Mullard CV4024 in my Jolida amp as well. The only tubes I've been swapping are the 12AX7s.
Or the audio grinch who incited incendiary hifi jinks and stole playback of Mannheim steamroller the world over. Hey legacies are hard to come by in this 5 milliseconds of fame world. Happy New Year everyone, at least the solid state folks will just say...wha?
Risking redundancy I offer the following: My Jolida 502p is currently sporting "matched" KT120s, "Preferred" tubestore 7025s (a Chinese version in the 12AX7 family that really sound great), and tubestore sourced NOS JAN Philips 12AT7s that I just installed...the JAN Philips seem to sound a little more refined than the stock EH 12AT7s, and they have the benefit of having more exposed glowing bits and that's always a wonderful thing regardless of sound quality. "We roll because we can", Wolf Garcia 2013.
question about kt120 tubes. i spoke to walter from underwoodwall the other day and asked if i can use 120 tubes in my 502p amp. he said no. i dident ask why but i see other folks here using them. so, whats the story?? is it safe to use kt 120 in this amp. and if yes, do you still bias so the led,s go on??. i understand they use more current or something so wondering if the 502p power supply stiff enough for them. thanks
It has to do with the current supplied from the transformer for the tube "heater" or "filament" elements in the 120s...100mA to 300mA more than KT88s. Walter is simply wrong about this, and based on all the discussion about it in this forum, I'm surprised about that. I bought a 502p a year or so ago and upon getting the approval of the guys at Jolida MD (they said the amp can easily handle the extra current), I took the bold and dangerous step of sticking KT120s in my amp. Yes, I'm clearly a courageous risk taker, but that's how I roll (tube roll anyway). In any case, myself and other courageous risk takers have been using 120s in these amps for a while (in my case almost a year) with zero issues. As part of my ever dilligent KT120 amp explosion death watch campaign, I have yet to hear of ANY amp melting down from using 120s...but I shall continue to my vigilence on behalf of my fellow 120 users, because, clearly, I'm a giver.
thanks wolf, i was hoping to hear from you about this. and what about biasing. just set it till the led light and thats it. couldent these tubes go for alittle more. i think these amps are set for 50 mg's what would happen if we crank it up alittle past the led setting til say the light goes off. would that be like going to 60 or 70.
Hi Tomtab

I bought my Jolida 502P from Underwood Wally some time after Garcia got his and Walter didn't comment when I inquired about using the Tung Sol KT-120 tubes in the Jolida. I guess he is playing it safe since Jolida sends the amp with 6550 Tung Sols or KT88s. I've been using the amp for months with the KT-120s and have had no issues.

Also biasing is the same. Just put in the KT-120s and turn the screw until the LEDs light-up. I would still get the meter though to make sure you are at 500 millivolts for the KT-120s. One time I had RCA 6550 tubes in the Jolida took them out and put in the KT-120s. Turned on the 502P and after the amp was fully warmed up I checked the bias with meter and the tubes were at 723 to 865 millivolts. The LEDs were all red but I would never have known without the meter I was so way over the recommended 500 millivolts of the KT-120s.
Fear not TomTab. Not only do I have KT120s on my 502B I even have ECC99s replacing the wimpy 12AT7s (of course the driver stage is completely rebiased for ECC99 operating point). I am running a lot more heater current on this thing and the power supply tranny is still holding up AOK after almost a year.
According to the 502P manual (or I would never have known) you're supposed to turn the bias screw all the way down when changing power tubes...I wondered what would happen if I didn't, but thanks to Jeninite24 I now know! I also bias the 120s to the 500mv spec and they tend to stay there...the LEDs are pretty accurate and you have 50mv in either direction as adjustment "headroom" anyway...when I check the bias drift from time to time (or really the neighborhood juice drift) its never moved more than .05 to .010 mv with any of the various output tubes I've used, and seems VERY stable with 120s. The LEDs seem to track the available voltage or something (without preamp signal) since they blink, stay on, all go off...whatever, all the time.
thanks guys for the info. 120's will be going in. just one step closer to the promised audio land.
I have the 502Crc (the integrated version of this amp) and verified w/ Mike Allen at Jolida that it is okay to run 120s in it (& they sound great in mine).

I have Kt120's on my Jolida 502B for over a month now. So far no issues and I love the sound better than the stock 6550s.
I do wonder how long the 120s are supposed to last as I've been driving mine hard for about a year and they've stayed absolutely stable, unlike myself.
the 120's are not working as hard as 88's or 90's would be. and who said that this amp can be run in mono?? there is nothing in the manual about this. and if they can be run in mono, what is the speaker hookup. + to +, - to + ??
The 502p supposedly generates 120 watts in mono, and I suggest a call to Jolida to find out how to make that work.
i did call jolida about it. heres what they said. you need a y cable to plug into both inputs. then short wires to tie the negative taps together and short wire to connect the 4 or 8 ohm taps together (just the ones you are using,not both or boom) then run speaker to one set of taps. basically running the left and right speaker outs in parallel conection. also said will not get 120 watts,more like 100 this is from michael allen of jolida
There has to be an easier way...I assume a qualified tech could put a switch in there to join the input signals, and "Underwood Wally" has been claiming the 120 watt mono spec for a while so that could make for an interesting call.
yes a mono switch on the back would be nice. then something similar to car amps for speaker connection. left channel negative and right channel positive. done!! i dont get the only 100 watt rating also. did you or anybody notice a power increase using the kt120 tubes. if you read the spec's for the 120's everybody has you believing they can make 120-150 watts a pair. im guessing thats if the amp was designed around the 120 tube to get the maximun out of them. im betting a 60 watt amp will maybe put out 70 with the 120's
I have no way of measuring the output of my 502p, but I will say the amp with 120s seems to have a bit more headroom, and can play plenty loud in its designated space seemingly effortlessly...I never feel like I "need" more juice. New amps utilizing the extra power available with 120s seem to be coming along all the time...a Rogue Atlas Magnum now does 100 watts pc with 2 120s per side, with what I assume are redesigned trannys and such (at around twice what a Jolida costs). It is nice to have only 4 output tubes to deal with as a money (and heat) saver, and 120s are still a relative bargain.