I was advised (and my manual recommends) to bias any sort of tube to the stock 500mv and it seems to work fine. There is 50mv wiggle room built in. |
Don't be sorry. I appreciate the feedback and respect your technical tweak choices, although you assume I have the ability to install, match, and adjust this stuff when I rarely venture past soldering something that looks unsoldered. That said, I'll look into your suggestions and see if I trust myself to do the surgery. I have spoken to everybody but the janitor at Jolida at length about the KT120 having enough current available to not melt my amp, and they assure me it's overbuilt to easily handle the 120s. If it blows up they'll fix it (at least for the next 2 years). Along with the KT120 appealing to me as an amusing tweak, I'll certainly be trying whatever KT88s seem interesting also. I do plan to mess with the input tubes (I roll tubes in my guitar amps from time to time and do notice obvious differences)...I mean really...this is the entire point of this amp for me...I can mess with it! In any case, thanks again for the feedback...nice to know there's a braintrust out there. |
I think that's a done deal as all the important (seemingly) resisters in the signal path were replaced when Jolida MD did an "upgrade" mod before shipping the amp to me. The tube "rolling" is simply for my own amusement as every review I've seen of the KT120s (which are fairly inexpensive as these things go) has mentioned there is a significant audible difference between those and other types, and if your transformer can take the "heat" you can drop 'em in...I am merely fishing for owners who've tried them in a Jolida. I have no issue with the current Tung Sol 6550s as the amp sounds absolutely great with the supplied "stock" tubes (Tung Sol 12AX7s, EH 12AT7s). |
SO...I put the KT120s in the 502P..and they work swimmingly. It is a LARGE tube in every way. Just more of everything...power (hard to say how much, but it's there), better, sweeter treble...more overall tonal range across the board. They do run hotter of course, but highly recommended at least until my amp blows up! (Talked to Jolida again and Mister Allen says no worries...and he's the warranty man!). |
Other than the "upgrades" they did on the amp before shipping there are no mods...I just dropped the 120s in and I bias them to the 502P specs and check it with my trusty Radio Shack meter just for the hell of it (a compulsion, but I'm getting better at not burning my fingers while poking the probes into the test port), even though the "ez bias" works well...In fact, now that the KT120s have settled in it sounds better than I noted in my last post, just fuller and brighter. Highly recommended! I bought the 4 "matched" tubes from "Ctech" on Ebay mostly because of their price, and they're on the East Coast so they shipped really fast. I don't think there's anything to risk buying one of these amps as they seem to be an insane bargain for something that sounds this good. |
There are a LOT of "small tube" suggestions around...I'm using "preferrd" 7025s (12ax7) from thetubestore, and recently added a pair of Mullard 12at7/4024s. Jolida's Jerred likes GEs, Michael Allen likes Phillips Mini Watt tubes...I like whatever sounds good and doesn't cost a fortune. |
I should have said "ordered" the Mullards...they don't get here until Monday or something. The only tube Jedinite24 seemingly doesn't have (and I do have) are the el cheapo Sovtek KT88s I bought a while back...and damn if they don't also sound great in the Jolida, although the KT120s are in there currently. I nominate Jedinite as the official 502p tube information and testing source...I might send him my KT88s for a review! Somebody should make a little LED lighted tube holder so you could enjoy extra tubes as visual art, instead of sticking them in a drawer like I do. |
HA...yeah...the Sovteks were an impulse purchase from an electronics/hobby shop so I was clueless about them...really bought because they were so inexpensive (about $100 for all four), but they look cool when glowing. I had to return the JAN Phillips 12at7s since one failed in the amp...weirdly...no harm to the amp ...and they suggested the Mullards so I bit. Warranty! Since KT120s have no "vintage" relative to re-issue, we can assume they're safe in the current "matched or cryoed or shaken and not stirred" world...I do wonder how many of these are being made relative to other tubes as they show up everywhere now. |
Follow up: The Mullard 12at7s sound great. And the frightening glow explosion flash when the amp powers up is a beautiful thing. |
Yeah...I had heard about Mullard Flashing and also was calmed when I looked up specific information about it. It adds a dramatic moment to amp start-up that otherwise would be a non-dramatic event. Maybe my threshold of entertainment is too low. |
Oops...missed the mod query. Here's what Jerrod sent to me:
2 - clarity esa caps .47uf/630v
4 - jolida custom caps .22uf/630v
4 - hexfred diodes
4 - ohmite little demon ceramic resistors 10k/2w
array of resistor changes within the signal path
An inexpensive installation of some seemingly worthwhile items, and, after almost a year and a half of tube rolling, this little amp has yet to sound anything but wonderful. |
