2. amps-preamps
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Bass tones and low cost tubes for a Jolida 502B

Hi everybody.

I asked in another thread looking for advice with the Jolida tubes but I decided open a new topic focus on it.

I have the Jolida 502B with Paradigm Monitor 11 speakers, with Xindaq DAC and reader, waiting to upgrade this periferials.

I really like to hear jazz as Joshua Reed, Herbie Hancock, Spyro Gyra, Chick Corea, Yellow Jackets... rock as Everything But The Girl, Depeche Mode, even Metalica or Rammstein... and electronic DJ"S as Armin Van Buuren, Oakenfold, Chicane, Enigma...

At this moment I have a Electro Harmonix salad in the Jolida, last owner legacy.

The sound that I have is very "shinny" or in excess sharp...with a feel of "we need a subwoffer", despite the Paradigme Monitor 11 and the 502B punch. I'm conscious about some room reflection yet but I can't improve it more...family matters :)

In my country Costa Rica, a $45 individual tube will cost around $110 with the custom taxes and shipping costs. So I have to be low profile about it.

I REALLY APPRECCIATE YOUR ADVICE ABOUT IT! I know is difficult but a good tube is a good tube and a poor brand too.

Reading the reviews on tube depot and tubestore on this tubes:

AX7
large plate AX7's ?? I read that this get more medium bass and tight bass presence:

- BLACK SABLE Sovtek 12AX7LPS
- SOVTEK 12AX7LPS Preamp Vacuum Tube
- JJ ECC803s / Hi-Performance 12AX7 / tubedepot.com

- Mullard 12AX7 / ECC83 / thetubestore.com
""Microphonics is not an issue despite the larger that average plate structure. The transconductance on my sample was the same as two NOS samples I measured. Not really high gain at all, but a real good noise floor and a nice smooth tone that doesn’t encourage ear fatigue the way some preamps can be."

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AT7's:

- 12AT7 / ECC81 Mullard / tubedepot.com

or

- Mullard 12AT7WA / CV4024 / thetubestore.com
"The NOS Mullard 12AT7WA / CV4024 tube is low noise and long lasting. This 12AT7 tube is a very good choice for hifi preamps, driver stages, and guitar amp reverb circuits. The Mullard 12AT7 is original production from Great Britain."
_________________________________________
For the KT88;s

- Sovtek 6550WE / tubedepot.com
"The Sovtek 6550WE has higher gain / output than most others and really has a ballsy sound. Recommended for any bass application and most Hi-Fi amps. This tube has a slight bump in the midrange making it a great choice for lead guitar."

- Sovtek KT88 / thetubestore.com
""The Sovtek KT88 tube has smooth, warm and clear with excellent imaging. The bass (except for the very bottom end) is tight and the high end is crystal clear. The separation of parts and balance is better than any of the 6550 tube types."

- JJ KT88 / thetubestore.com
"The JJ KT88 tube has the best imaging of all the tubes in this category. The bass is unique in that it compresses the very bottom end. This provides incredible bass response without ever losing control. Overall a great KT88 tube for orchestral, opera, and jazz music."
edoll
wolf_garcia
6,695 posts
 
I recently found out (from the "horses mouth" as it were) that you can use KT120s in the Jolida 502p...not sure what will happen (haven't tried it yet, as my 502P is new and not past the 12,416 hours and 8 minutes break-in period) but hey...there it is.
ghosthouse's avatar
ghosthouse
4,306 posts
 
Edoll - that procedure looks good to me. The only thing I'd change is to make turning off the amp THE FIRST STEP. Then discconect AC cord, input cables, replace tubes etc. Turn bias pots and volume to lowest setting (full counter clockwise) before turning on amp. I don't know why they recommend disconnecting the input cables but I do it that way anyway. Leave only the speakers connected and allow time for the tubes to warm up. I'm not sure what effect being over or under the 50mV setting has on tube life. I did think being a little low (e.g., 48mV) was better than being above 50mV but I really don't know if that is how it works. Mostly I just try to get as close to 50mV as I can though things will drift a little. Not sure there's a significant effect so long as you are in the +/-5mV range. By the way, usually I'd get in the neighborhood of 50mV when the pots had been rotated to somewhere in the 12-2 o'clock position. Do the adjustment on each gradually. For me oit seems like there is a little lag before the change registers and settles on the mulitmeter. Also, when I got to the 4th pot, I'd go back and check the others again and make any adjustments for what little drift occurred. Even so, don't expect to get an exact, rock steady 50 mV on each tube. It's really not a difficult procedure just keep your multimeter cords and fingers away from the tubes!
edoll OP
12 posts
 
Thanks guys!!! U rocks!

Update coming soon.
edoll OP
12 posts
 
Newbee, i'm consider the KT's , your conclusions are exactly as happened with my 6550 EH's vs the Sovtek Kt88's (the few hour that the KT's works before the blow they was with more bass delivery but maybe eith some "enclosure" or "inside the box" sound.

But i'm sure that after two swaps at 4 years the amp has been never biased.

Si, if I get new KT's, and with the Mullards AT's and AX's and doing the Bias procedure, hope to share you and enjoy a new sound as I never have it before.
edoll OP
12 posts
 
Well, after compare your recommendations and research in another sites and forums, finally I bought new tubes at Upscale Audio tonight.

I found very good references of this store, especially very good references from Kevin Deal everywhere.

I think I'm very lucky to find with Kevin four matched SED Winged C KT88"s, and a matched pair of Mullard CV's 4024 and another Mullard's 12AX7 (this one the most popular)

I really was in love of the Mullard AT7 CV 4004, but this tube is very expensive, around $90 and this price rise to ¢195 each tube after customs here in my country...insane! That exceeds my budget and compromise have the KT's winged C...

The Jolida at this moment has never been biased, at least the last 4 years...and operate with the basics 6550 EH's and THREE!! 12AT7 EH's and just one 12AX7...

I hope that doing Bias Procedure, swap the EH's with the Winged C SED KT88's and get the new pair of 12AT7/ 12AX7 Mullards, results in a sound experience as I never have it before with the actual status.

Thanks a lot guys for your advice.

I learn a lot from each one of your posts.
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