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Jolida 502A Popping Noise in Left Channel

Send the following text to Michael Allen of Jolida this morning, and figured I would post it here to get some suggestions, thoughts and solutions from y'all while waiting for Michael's reply. Btw, I"ve "XXXXX" out the name of company doing the work, as there may be solution to this problem they can correct, and wouldn't want to hurt a company's reputation unnecessarly.

"Got a question on a "noise problem" I'm having with my Jolida 502A amp. First of all, thanks for sending me the "fuseholder". It was different than the orginal one (actually it was of "better quaility" - and I certainly appreciated that it had a screw top), so I called XXXXX and inquired how much it would cost to have the fuseholder installed. Their cost was $75 because of a one hour labor rate. Well, I figured if they were going to be "under the hood", so to speak and that the amp itself is ten years old that it would be a good time to check the amp out and replaces some caps and resistors and basically give the amp a "tune up". Anyway, got the amp back and placed it back into my system and turned it on to let the tubes warm up. I would say at approximately 30 seconds to 1 minute after turning the amp on, I hear a "squealing" sound out of my left speaker, followed by "humming" sound in the left speaker. After hearing that, I disconnected and returned it to XXXXX, to find out what was causing the problem. Anyway, the first thing they did was check all the tubes where it discoverd that three of my pre-amp tubes were shot, and at this time they also checked work done on the amp itself, and didn't find any problems there. At that point, the pre-amp tubes were replaced with some Jolida tubes (for testing purposes), and the amp was played to see if the "hum" problem was solved. And for awhile, during this test, it seem to be so, until the bottom cover of the amp was put back into place and the "hum" re-appeared in the left channel. At this point, the Power tubes (Tung-Sol 6550) were checked to see if one of them might be causing the problem and sure enough, it appeared that the tube in the V-8 position couldn't/wouldn't hold it's bias, so that tube was replaced and the amp was re-biased and the "hum" problem disappeared. Took the amp home, re-installed it in my system, and placed some older pre-amp tubes (Sylvania 12AT7, Sovtex 12AX7) into the amp (did this as I wanted to make sure that the amp was working properly before installing the RCA 12AT7, Tung-Sol 12AX7 that I had just purchased), turned the amp on, and after the tubes had warmed up, proceed to play music, and everything was sounding fine. Indeed it stayed this was throughout the weekend where I put probably 10 - 12 hours playing music through the amp. Well Monday, I figured the amp was indeed working well, and there didn't seem to be any problems, so I figured I would go ahead and replace the Sylvania/Sovtex pre-amp tubes with the RCA/Tung-Sol tubes (as I prefer the sound of this combination). Imagine my surprise, when shortly after turning the amp on that I hear some intermittment "popping" noise through the left speaker. Now these noise subsided after about 5 minutes and the amp was quiet (no "humming', ect) and when I played some music throught the amp, once again everything sounded fine. I did noticed that when I turned the amp off, there was a "thump" sound in the left speakers, which I had never heard before. Yesterday, I figured I turn the amp on, and see if the things that happened on Monday, happen again. And things went pretty much the same as they did on Monday. The one thing I did notice yesterday that when I first turn the amp on and was letting the tubes warm up, was that at one point the power tube in the V-8 position, light seem to "flutter" for a couple of seconds, and then stablized. btw, this was the tube that was re-placed at XXXXX. Anyway, I know I've gone on and on, in my description, but figured the more information you have the better able you'll be able to tell me what's going on, and what would might be the solution to solve the problem with the "popping" sound I hear in the left channel when turning the amp on and off. Other than that I'm happy with work done on the amp, as I feel that replacing the caps and resistors certainly upgraded the performance of the amp, in all area."
cleaneduphippy
7 responses Add your response
cleaneduphippy OP
323 posts
 
Williewonka,

It turns out one of Tung-Sol 12AX7 is faulty. Switch places and it followed. Think I may either go to the Sovek 12AXY-LPS7, EH 12AX7 or the JAN-Phillips 5751. Liked the Tung-Sol sound, especially with the "Gold Pins" but I do wonder if there is a reliabity issue with these tubes, as it's the second one I've had to replace. And yes I'm very aware that JAN stands for Joint Army-Navy. Anyway, Williewonka, caps and resistors have been replaced, so don't think that's an issue, but I do think you're giving me some good suggestions on the path I should follow as far as tubes and I do appreciate that.

Anyway, you and yours take care and I'm sure "down the road" I may be "picking your brain" about educating myself on various tubes.

Take care, my friend, and you and yours have a very Merry Holiday Season.
williewonka
3,075 posts
 
Cleaneduphippy - my apologies - the quote was from an email that Jon (of The Tube Store) had sent me in reply to my request for some recommendations - I had originally selected the Tungsol and he responded with that quote - so I bought the Ei and JAN Phillips.

Your plan of swapping the tubes is just what I would do to determine the preamp or power tubes as a cause for the popping.

One thing to watch for: the movement of the faulty tube sometimes causes the popping to go away, but it will probably come back in a couple of days (mine did).

Another Clue: Does the popping get louder if you increase the volume?
YES - then it's probably the pre-amp tube
No - then its probably the Power Tube

Dependent on the age of the amp and how hot it gets - you could have a faulty resistor or Capacitor, but I think the tube is generally the culptit - anything else generally causes a more catastrophic failure - that would be: POOF!

As far as the performance ratings you mentioned - once again it really depends on the design of the amp - from the ratings, the two tubes are so close that you would think there was very little difference between them

I have now tried three makes of pre-amp tube, 2 sets of 12AX7 and 1 set of 5751's and they all sounded completely different
- Ei Elite - very bright and extremely detailed and lively
- JAN Hpillips 5751's - very detailed and lively but extremely smooth with a silky top end - strings sound great!
- Shanguan - not very dynamic in comparison to the others - would not recommend them

The "JAN" stands for Joint Army & Navy - so they are apparantly a very high military grade product and very robust.

Hope you find your problem

Regards...
cleaneduphippy OP
323 posts
 
Willywonka,

Exactly where on the "Tube Store" site did you find the quote on the Tung-Sol? I've gone over there and the only stuff I found that talked about the Tung-Sol was in a review of the the Tung-Sol 12AX7 which stated.

"There are only so many ways to describe tube tone and most have become cliché's. The Tung-Sol 12AX7 has the gain and drive of a Chinese 12AX7 and the pure tone of a Mullard or Brimar from the U.K. I've had two people come to me recently with amps they thought were in need of complete overhauls. In both cases, careful examination revealed no serious problems and all the tubes "tested" as good. At the end of the day, I replaced the NOS Mullard and RCA pre-amps (one in each amp) with a reissue Tung-Sol 12AX7. In both cases the owners were very impressed and thought that their amps had been restored to full health. Believe it or Not."

and

a comparison chart which rated various 12AX7s for Microphonics, Noise, and Musical Detail and Dynamics. The Tung-Sol 12AX7 were rated 5, 4, and 5 where "0 is Unacceptable and 5 is Excellent". The JAN-Philips 5751 rated 5, 5 and 4.

In any case, plan on putting the Tung-Sol 12AX7 back into the amp, but this time with the left tube on the right side, and visa versa and see if the "popping sound" follows. If not, then I'm going to assume it must be in one of the "power tubes" (probably the one in the V-8 postition) on the left side. Of course, I just replaced that tube last week, as the old tube wouldn't/couldn't hold it's bias. Of course, I wondering when the amp was worked on if the tech might have done something internally to the amp that's causing problems with the tubes in the left channel?

Any suggestions?
williewonka
3,075 posts
 
I have experience similar popping sounds with my amp - it turned out to be the power tubes

For the pre-amp tubes I got great result using the JAN Phillips 5751's - really low noise with a nice warm sound

Here's a quote from The Tube Store...
" For the 12AX7 I would not suggest the Tungsol. We find the Ei Elite 12AX7E to be much better in hifi equipment. Another nice one is the JAN-Philips 5751 (12AX7 variant)."

Here's the link:
The Tube Store

I also tried the Ei Elite, but found them to be too bright - they made my amp sound like a Solid State.

Hope this helps
cleaneduphippy OP
323 posts
 
Oops, sorry for the similar but double post. I was going to edit the first, but hit the wrong button. Anyway, the second one was what I meant to say.
cleaneduphippy OP
323 posts
 
I have lot's of friends who are guitar players and they name their guitars and amps after various women they have known. I'm thinking about naming my amp, as no doubt a woman's spirt inhabits her. Today I after I sent this post out, I decided to see what would happen if I pulled the Tung-Sol 12AX7s out and replaced them with the Sovtex 12AX7s. Want to guess what happen? The long and short of it is, my amps seems to like the Sovtex much better than the Tung-Sols, (Oh, btw, the Tung-Sols were tested before I bought them, so I don't think I had a "bad tube"). Why do I say this? Well, I put the Sovtex back in and fired up the amp, heard absolutely no "popping sounds" in the left channel, matter of fact everything was as quiet as a "church mouse". Played a couple of CDs, everything sounded fine, turned off the amp, no "thumping" noise. It's a enough to make it one "pull his hair out". Anyway, the problem is I like the sound of the Tung-Sol 12AX7 better than the Sovtex 12AX7. But if my amp is going to be contrary (Just like a woman) then I need to find a 12AX7 tube, that is as "sweet" as the Tung-Sol, but one that my amp will like as well as a Sovtex (suggestions appreciated). Anyway, since this is older Jolida 502A and the casing is black, think I'll name the amp, Natasha (after Boris and Natasha from the old Bullwinkle cartoons).
cleaneduphippy OP
323 posts
 
I have lot's of friends who are guitar players and they name their guitars and amps. I'm thinking about naming my amp, as no doubt a woman's spirt inhabits her. Today I after I sent this post out, I decided to see what would happen if I pulled the Tung-Sol 12AX7s out and replaced them with the Sovtex 12AX7s. Want to guess what happen? The long and short of it is, my amps seems to like the Sovtex much better than the Tung-Sols, (Oh, btw, the Tung-Sols were tested before I bought them, so I don't I had a "bad tube"). Why do I say this? Well, I put the Sovtex back in and fired up the amp, heard absolutely no "popping sounds" in the left channel, matter of fact everything was as quiet as a "church mouse". Played a couple of CDs, everything sounded fine, turned off the amp, no "thumping" noise. It's a enough to make it one "pull his hair out". Anyway, the problem is I like the sound of the Tung-Sol 12AX7 better than the Sovtex 12AX7. But if my amp is going to be contrary (Just like a woman) then I need to find a 12AX7 tube, that is as "sweet" as Tung-Sol, but one that my amp will like as well as a Sovtex (suggestions appreciated). Anyway, since this is older Jolida 502A and is the casing is black, think I'll name the amp, Natasha.
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