Jolida 502a (early 1994/6922 version) - worth fixing?

EC34343 · « **on:** 9 Dec 2013, 05:31 pm »

I bought a Jolida 502a in 1998. It appears to be one of the initial runs from 1994 that runs the 6922/E88CC tubes along with slightly different circuitry from the version listed on http://www.drtube.com/schematics/jolida/sj-502a.gif.

I have been unable to find a schematic and Jolida hasn't responded to my requests yet.

This amp has been out of commission for about 10 years and I thought I might as well try to rebuild it. There was a blown cap in the power supply, a few of the wires going from the power switch to the PCB were fried, a bias pot is broken and some of the resistors are way off stated values. I was originally planning on replacing all of the power supply caps, new tubes, sockets, volume control, remove balance, update the bad resistors to metal film or wirewound, replace coupling caps, etc...

Is it worth fixing this amp or buying a new one? I've read that this version should be avoided. Anyone have a schematic?

JakeJ · « **Reply #1 on:** 10 Dec 2013, 02:23 pm »

I hate to point it out but I think you've answered your own question.

Ericus Rex · « **Reply #2 on:** 10 Dec 2013, 04:23 pm »

If you can tinker yourself it might be a fun project...that you may have to do every 2 or 3 years, it sounds like. If you have to pay someone to do this than it certainly is not worth the dough. Maybe someone can modify this amp to be more stable but again, you'd probably be better off putting that money into a newer more reliable design.

...but send it to me before you toss it in the trash

orientalexpress · « **Reply #3 on:** 10 Dec 2013, 06:32 pm »

i'm not even trying to fix something with fry a pcb .the casing might be a good project for something else.

bladesmith · « **Reply #4 on:** 10 Dec 2013, 07:01 pm »

How much to replace the parts, you know are bad. ?

planet10 · « **Reply #5 on:** 10 Dec 2013, 09:04 pm »

I would look at this as a donor amp.

I'd recommend the DynaMutt front-end board from Classic Valve Design.

dave

EC34343 · « **Reply #6 on:** 11 Dec 2013, 02:57 am »

Thanks. Parts maybe $150 plus tubes to replace, but without the schematic any additional mods would be difficult. Already bought the PS caps, diodes and pot. The board is actually fine, just both blue wires going to from the PCB to the switch/LED are fried for some reason.

Saw a used JD707a on eBay, so I'm thinking I would transplant some of my caps if the values are close. There's not many reviews or mod info on the 707a.
Also considering a Yaqin mc-100b. Any thoughts on these two? Have Quad 11L bookshelves.

bladesmith · « **Reply #7 on:** 11 Dec 2013, 03:09 am »

If there is any delicate chips/parts on the brd, they might have been compromised with the voltage/current running high thru the wires to/from it.

The only way to tell, is start replacing parts, and it is a gamble.

Especially, with no schematic.

Snap a photo of the inside. Post it.

EC34343 · « **Reply #8 on:** 11 Dec 2013, 03:47 am »

The white wires are the ones coming off the 3.15(?)V tap from the transformer and are soldered to the same tube pins as the blue. The black wire on the switch is actually a heat shrinked wrapped resistor. Both blue wires are toast. There's an LED somewhere on my table. The main read power wires appear to be fine.

bladesmith · « **Reply #9 on:** 11 Dec 2013, 04:09 am »

That amp took a hard hit...

Might be a long project, to repair with out a proper schematic.

301.953.2014, they are in Maryland, call them.

(You might start there, not sure how they respond to enquiries. Or if they might have an old brd left over to sell you. )

planet10 · « **Reply #10 on:** 11 Dec 2013, 05:29 am »

Quote from: bladesmith on 11 Dec 2013, 03:09 am

Especially, with no schematic.

It is not hard to trace the schematic.

dave

Ericus Rex · « **Reply #11 on:** 11 Dec 2013, 01:37 pm »

Quote from: EC34343 on 11 Dec 2013, 03:47 am

. ..The black wire on the switch is actually a heat shrinked wrapped resistor....

That sounds like a terrible idea. Why?

vinylkid58 · « **Reply #12 on:** 11 Dec 2013, 07:38 pm »

Quote from: EC34343 on 11 Dec 2013, 03:47 am

The white wires are the ones coming off the 3.15(?)V tap from the transformer and are soldered to the same tube pins as the blue. The black wire on the switch is actually a heat shrinked wrapped resistor. Both blue wires are toast. There's an LED somewhere on my table. The main read power wires appear to be fine.

Holy cow, why would someone connect mains power right to the heater connection? Before going any further, I'd make certain that the power transformer is ok. If the PT is cooked, then the amp might as well be a parts donor. You've had this amp since 1998?

jeff

EC34343 · « **Reply #13 on:** 12 Dec 2013, 12:12 am »

Thanks for all the replies. Yes, I bought it in 98 or 99 for $700. It sounded very nice at the time with my North Creek Borealis (scanspeak kevlar woofer/9300 tweeter). Looks like I'll be parting this amp out as I don't feel like dealing with a bad design and wiring. Time to shop for a new integrated amp.

EC34343 · « **Reply #14 on:** 12 Dec 2013, 12:16 am »

Quote from: Ericus Rex on 11 Dec 2013, 01:37 pm

That sounds like a terrible idea. Why?

Ha. I almost thought it was just a wire until I noticed a small bulge in the middle. Goes to show how Jolida's very early models had some production issues.

rlee8394 · « **Reply #15 on:** 13 Dec 2013, 08:18 pm »

As Dave mentioned, it isn't hard to trace out a schematic. I can do it for you and probably repair it as well. I also just happen to work down the street from Jolida. I'd be happy to stop by and ask if there is a schematic available for that amp if you like.

Ron

jarcher · « **Reply #16 on:** 15 Dec 2013, 01:53 am »

If anyone does get a schematic, please let me know. I picked up one of these cheap some months back and have considered bypassing all the crumby volume / selector / balance boards and turning it into a straight amp. It's a surprisingly "modern" sounding tube amp but lacks that last 2/10th of refinement which I think could be more closely reached by eviscerating the previously mentioned junk parts. I liked the sound best with KT120s and still messing with different tubes for the other sections.

rlee8394 · « **Reply #17 on:** 15 Dec 2013, 02:55 am »

OK, I'll swing by Jolida on Monday and see if I can get a schematic.

Ron

rlee8394 · « **Reply #18 on:** 16 Dec 2013, 07:16 pm »

Jolida is no longer in business at that location. Checked with the Post Office for a forwarding address which was just a P.O. Box in Brookeville, MD. I'll see what else I can dig up.

Ron

rlee8394 · « **Reply #19 on:** 16 Dec 2013, 09:29 pm »

Called and spoke to Jared. He's going to try and dig one up for me.

Ron