Jolida 502B correct tube allocation


Greetings from Costa Rica.

I'm a really fan of hearing jazz and electronic music too (weird I know)

At this moment, I have a Jolida 502B with Paradigm Monitor 11 v6, Xindaq DAC and CD Player.

I'm trying to upgrade the Electro Harmonix original tubes and looking for this I asked at tubestore and they answered me:

"You require one 12AT7 and one 12AX7 per channel." (actually the 502B has a salad of 12AX7 brands)

So, I will need a matched pair of 12AX7 plus another mp of 12AT7, that's clear.

My question is: where is the correct location or side for to the AX7 and the AT7 ?

There are 4 sockets, guess left-right = two for channel, but I don't know where to put the AX and AT, outside or inside of each channel ?? Or there is another distribution possible ?

Thanks for your help.
From the far left. AT7 then AX7 another AX7 and then on the far right side AT7. Two center tubes are AX7's.

Thanks Detredwinds!!!

It's so amazing how useful is this forum.

Here in Costa RIca, there is an absolute limbo about it: we have Intel main processor plant here, Amazon, DHL, Hewlewt Packard, etc, maps customer service departments, the biggest NASA joint to development space rockets, a Peace Nobel Prize, No Army, the largest volcano crater in the world, the most beautiful beaches, but nobody knows a s...t about a vacuum tubes amplifier!

I'm very obsessive and compulsive with this kind of technical issues, if I don't bother too much, I want another a last advice:

At this moment I have Electro Harmonix and the sound that I have is very "shinny" with a feel of "we need a subwoffer", despite the Paradigme Monitor 11 and the 502B punch.

So, I'm thinking buy new tubes:

For the AX7: I'm thinking on large plate AX7's because I read get more medium bass and final bass presence:

- SOVTEK 12AX7LPS Preamp Vacuum Tube
- JJ ECC803s / Hi-Performance 12AX7 /

- Mullard 12AX7 / ECC83 /
""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."

And for the AT7's:

- 12AT7 / ECC81 Mullard /


- Mullard 12AT7WA / CV4024 /
"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 /
"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 /
""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 /
"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."


First Detredwings, I'm clear about this true that you said in another thread: "Tubes choices are a very personal thing. For someone to say what will be best for you is almost impossible."

And, a matched pair around $48 will be finally $110 in my door (taxes and shipping to Costa Rica)

So, I'cant at this moment go for very expensive tubes...

I'm not sure what tubes you are refering too? Anyway be careful getting on the NOS tube rolling wagon. Expensive and you may be dissapointed. You may be perfectly happy with some new tubes like JJ or EH and save a lot of money.

You may start a thread and ask for advice on new production tubes. Good luck!
I bet there's a tiny old electronics shop someplace in Costa Rica with a treasure trove of NOS tubes...maybe that's wishful thinking and not the case, but hey...look around...
If you don't like shiny or typical EH sound I suggest you go with all Mullard (NOS) for the small tubes or possibly the GL reissues (not cheap either). The output I am very enthusiastic about is the Gold Lion reissue KT-88s. They are well worth the extra money trust me on this one. The source I use is Jim McShane over on Audio Asylum.
Thanks guys!!

@Detredwings...yes, I have noticed some post about the NOS stuff, I think that I will remain on new tubes only.

@Wolf: hope the Gods made you prohet! Believe me: there is nothing here around vacuum tubes...just expert technicians on transistor amplifiers and similars, and only 4-5 five stores with a few of Nakamichi's, Denon, Bose, and very rare to see but sometimes you can find some McIntosh.

Mechans, do you find many difference between the NOS - New Mullard's ?
Don't get me wrong. I really like NOS tubes. I have a nice hoard to prove it. But you mentioned that shipping and customs duties where high in your country. It can get very expensive trying NOS. You should have some tube guys around. Don't give up!

I have never tried the Genalex tubes. I have tried the Full Music and Pasvane and like them both. But they are not cheap.
Now I got the idea Detredwings...thanks!

I will be shopping the tubes next week I think...

Costa Rica is a very small country, 53.000 km2 ( West Virginia similar size)

and San José and Escazú the main cities fits twice at District Columbia :)) believe me...we need a High End - or vacuum tube store for real!!
To answer your question , yes there are very significant differences between the NOS and the current Mullard branded tubes.
The current "reissues" are made in Russia and evidently come from the same manufacturers as do Sovtek, they are now called New Sensor. The good news is that the new Mullards and Tung Sols don't sound like Sovteks. They are much fuller,less dry, have much less glare or treble brittleness. They are indeed very very good and its nice to know they are around.
The old Mullards posess an incomparable and indescribable warmth and richness with a perhaps a small emphasis on the midbass (the opposite of a thin sounding tube). The old tubes still preserve detail and have treble extension but are very sweet, non fatuiging in the upper registers -mellow toned if you will. If you can afford some like the fairly common, later CV-4004s, I encourage you to try them. Don't forget the Gold Lion KT 88s you will be thanking me for that recommendation, you gotta believe me on this one.
Wow!! Clear as water Mechans!!

I'm very focus about the AT's and the AX's... I will try to get Mullards the CVs something :)

You make me think again about the KT's: at this moment I'm thinking at the SED WINGED C or the Gold Lions...