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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."

_________________________________________
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
edoll OP
12 posts
 
Thanks Johnsonwu, can you confirm if the bias is Bias Settings: 50 millivolts + 5 mV ?
xti16
1,525 posts
 
Before you swap power tubes on the Jolida you ought to set bias to the LOWEST and turn up accordingly.
I agree 100% but would add when I swap tubes I turn the bias to minimum - volume down to minimum and let them warm up for about 20 min. At that point I start to bias them up BUT not all the way. That's when I start playing music but not too loud for about another 10 - 20 min and look to see if the bias changed. I have found as I turn the volume up the tube starts to really work and heat up which influences bias. After a minimum of an hour but 2 hrs is better is when I make the final adjustment. Also keep an eye on the bias for several days after that. What I have seen is the tubes could take several to completely settle down. I have also found new tubes typically take 200-300 hrs to sound what there are going to sound like from that point on.

That being said I have an Octave V70SE that uses the same tubes. I have found changing the input tube (12ax7) will make the biggest difference in sound. My favorite now is not a 12ax7 but the Rca 5751 which has a slightly lower gain but sounds so right. After all the input tube is the first stage in amplification. Garbage in garbage out.

The drivers (12at7) controls the output tubes. For the normal *transconductance tubes (pretty much any *current production tube) I really like the Brimar 6060 yellow T or Amperex bugle boy ecc81's. For high transconductance you really want the Gec A2900/CV6091. They have the highest gain in the 12at7 family which will completely support high transconductance tubes.

* normal transconductance have a gain around 7000 where high transconductance tubes are over 10,000. Examples of high transconductance tubes are Shuguang Psvane - Eat kt88 diamonds - Ei Kt90 - vintage Gec/Gold lion/Gold Monarch KT88's. Note the Eat KT88 retails for $1800USD/Quad where the Shuguang Psvane is under $500USD/Quad for grade 'A' matching.

Good Luck
ghosthouse's avatar
ghosthouse
4,312 posts
 
Edoll- I own a Jolida 502B. You are correct. Bias should be set to 50mV +/-5mV. Also note that biasing should be done w/all input cables to the amp disconnected (as per the JoLida manual). I prefer KT88s to 6550s. I ran the stock Sovtek 6550s but switched those out to JJ KT88s (great sound & bass but in my experience unreliable). Ran Penta Lab Shuguang KT88s. Good detail and upper frequency extension, but the tube that worked best for me was the Winged C KT88. Nice bass heft. Had previously upgraded small signal tubes to Mullard 12AT7s and Ei Elite 12AX7s. Replaced the fuse w/a HiFi Tuning fuse. Lastly, sent the amp to JoLida Annapolis, MD for the factory upgrade (a bargain at the price they charged back in 2009; hope you might be able to do the same). Nice improvement to bass extension and overall resolution without harshness. I really like this amp. The only reason I'm not running it day to day now is that it doesn't have quite the "oomph" I like to drive my Totem Forests. Now using Consonance Cyber 800SEs for that. The JoLida is my backup. Eventually, I'd like to get some higher efficiency floor standers (Tecton Lores?) and put the JoLida back in service as a 2nd system. Hope this is of some use to you.
edoll OP
12 posts
 
Thanks Xti16... that Octave V70SE...OMG! It's a treasure!! Germany power!

@Ghosthouse: I really appreciate your advice, I already read your post "Tube upgrades for Jolida 502B?" Thumbs Up!!!!

I need to tell you that your advice is very important, as a Jolida 502B owner...don't let it many time in the bench!

About the tubes, I was looking at the web info about the Winged SED reviews and each one said the same: very reliable tube with tight bass.

As a retired bass player, I really understand what means bass heft...so that is a very good direction to me.

I think maybe it will be interesting attach the Winged C with the Mullard's AT and Ax's... as this could represent around $350 at USA but certainly $600 after customs here in Costa Rica. Think that Winged C get me that money back for sure...

I'm trying all this days to do my homework, learning about tubes. And the Bias issue it is a big issue to me, I never hear about it until reading the topic at this forum.

So, sorry but I need to bother you Ghosthouse! and any other guy of course if has this knowledge and experience.

FYI... I don't have the manual, just a scan page that I found at polkaudio forum...weird certainly!

As I try to understand, this is the basic procedure to manual Bias a Jolida 502b:

1- Unplug the AC power cord from the Wall and replace the tubes / replace the AC power once got replaced the tubes, with God help and if Danica Patrick keep quiet without crashes...

2- Remove all the audio inputs (??) what for ? not necessary to know ? :)

3- Depress the AC power switch to OFF

4- Adjust the bias levels to the lowest setting = counter clockwise until cannot turn any further (v3, v4, v7, v8)

5- Make certain the left and right speakers cables are attached

6- Volume control at lowest setting

7- Turn On the Amp

8- Let the amp warm around 30 minutes ??

9- Get the multimeter set to D.C.V. / milivolt range setting

10- Get the 5 female jack terminal behind the Power Tubes / Black or Negative probe goes into the center terminal = #0

11- Red or Positive probe goes in the hole numbered according to the tube I want to bias (v3 correspond to hole #3, etc)

12- Starting the bias procedure by turn the relative screw via the small recessed pot closest, clockwise until 45-55 millivolts or .045 to .055 appear at the multimeter -It is true that is better set 45-46 to extend the tubes life ?

13- ?? What else ?

Sorry if my post is too confuse to read fellas...it will be my very first time as electrician and learning this stuff from english language, I'm not very good with both themes!

Thanks again!
newbee
4,767 posts
 
Edoll, Re SED tubes, are you talking about the 6550's or the KT88's. FWIW, I find the 6550's linear and fairly uncolored. An excellent tube. The KT88 isn't nearly as linear - I find the mid/upper bass a bit on the full side and the upper mid range on the forward side, but in the right amp they can be really exciting. I'm using them in a Cayin A100T as I type. Both are rugged and reliable.

However, it appears that SED may no longer be shipping (or making?) tubes. The KT88's are very expensive when you find them, but the other SED's are still in the major retailers catalog.

Re question about bias setting. 45ma may extend life substantially but it will probably produce a cooler tone. Increasing setting to 55ma should produce a warmer tone. I've never measured the life expectancy at the two extremes, but years ago a major manufacturer, in their manual, recommended 50ma as optimum and maximum effective bias and said the tube life could be doubled by dropping the bias to 40ma. To get the tone I wanted I ended up at 45ma. I have another set of tube mono's and it was interesting to find that the manufacturer recommended 50ma per tube, but in a blog said he preferred a setting for tone which was about 40ma. It seems that the setting in the manual was more to obtain published results than it was to obtain an enjoyable tone.

Lots to consider..............
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