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A Very Compact Hybrid Amp - Page 102

post #1516 of 2213
Quote:
Originally Posted by rds View Post
I'm having an issue with a Amperex 6DJ8 tube in my CTH.
Has anyone else experienced this? Is the tube dying?
My guess is that the tube is dying... Esp if this does not happen w/your other tubes.

Both my "bad" tubes do exactly what you describe (in one channel). For both of them I've others of the exact same type that work perfectly.
post #1517 of 2213
Quote:
Originally Posted by cfcubed View Post
My guess is that the tube is dying... Esp if this does not happen w/your other tubes.

Both my "bad" tubes do exactly what you describe (in one channel). For both of them I've others of the exact same type that work perfectly.
That's been my experience as well. Don't know if yours was an NOS tube, but I had one that went about fifteen minutes, and then one channel slowly faded away. I think after sitting around for decades, if they are going to fail, it seems to happen in the first hour of use. Maybe the dealer you got it from will swap it out for you...
post #1518 of 2213
When you get a bad tube you probably dont want to leave it in the amp trying to figure out whats wrong. Trash it and move on.
post #1519 of 2213
This happens on the same channel of the 3 tubes I've tested so far (and regardless of headphones), so I'm thinking something in the left o/p stage is slightly fried. I did pull out the headphones without turning off them amp :/

I wonder if the servo is keeping a bad transistor in check until it has warmed up enough that the amount of current its dumping is too large for the op-amp? Does that sound reasonable?
post #1520 of 2213
Forunately fo me I've not yet ran into a bad tube (yet!).

oldblue, I really love the hungarian tungsram and it is as described -- thanks.
post #1521 of 2213
Quote:
Originally Posted by zkool448 View Post
Forunately fo me I've not yet ran into a bad tube (yet!).

oldblue, I really love the hungarian tungsram and it is as described -- thanks.
Great, I am glad you like it.
post #1522 of 2213
maybe q8 is toasted, but it's the warm up thing that throws me off. It takes between 2 and 10 minutes before the channel goes weird. Now there is a constant hiss from that channel and very low volume music very it goes bad.
post #1523 of 2213
after some playing around it appears that the left channel sonicap is bad. Has anyone experienced this?
If I push on the cap I can start the hissing (which then continues) and if I push it around a bit more I can stop the hissing. It seems like there's a bad connection between the lead and plate.

Surprising for a $4 capacitor
post #1524 of 2213
Quote:
Originally Posted by rds View Post
after some playing around it appears that the left channel sonicap is bad. Has anyone experienced this?
If I push on the cap I can start the hissing (which then continues) and if I push it around a bit more I can stop the hissing. It seems like there's a bad connection between the lead and plate.
Surprising for a $4 capacitor
When this has happened to me its been the contact between the caps leads & the PCB... In fact exactly what you described happened to me a couple times in the build I'm using to roll C4 caps.

Since I'm mounting the C4 under the PCB I could choose to go to a more secure connection spot (e.g. the tube socket pins themselves).

So before you give up on the cap(s) think about firming up their connections. Even if you have to run a jumper or something below board.
post #1525 of 2213
Thanks for the advice.

So you find that solder points for the coupling caps don't make a very secure connection?

I'm using tombstoned sonicaps, maybe I should try to reflow the solder joints and if that doesn't work then jumper from the leads under the board to the tube socket?
post #1526 of 2213
Quote:
Originally Posted by rds View Post
So you find that solder points for the coupling caps don't make a very secure connection?
Not generally. For my case, I consider pulling & changing C4s a bit abusive
It's probably not unusual that they do not stand for a lot of soldering & desoldering.

Quote:
Originally Posted by rds View Post
I'm using tombstoned sonicaps, maybe I should try to reflow the solder joints and if that doesn't work then jumper from the leads under the board to the tube socket?
Perhaps just the re-flow will remedy the problem. Only need jumpers if the traces / pads are gone or damaged.
post #1527 of 2213
About four rounds of careful desoldering is what the cap pads are good for (he says knowingly)
post #1528 of 2213
Yeah, with the cap removed the pads look and measure completely fine.

So that makes me worry about the Sonicap since I don't have a spare.
post #1529 of 2213
if the caps are at fault call Jeff at sonicap they will take glady take the cap back to find out why it isnt working right and probably get you another. I had issues with my sonicap during prototyping or any caps with long leads. I have my Mcap silver/oil leads shielded with small copper tubing.
post #1530 of 2213
*redacted
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