Phase Linear 400 issue help!

[enoyes12]

Now I'm stuck until I find those caps. I don't want to change anything else until I do that first. Planning on changing one thing at a time until I get it fixed so I can compare results and find the problem.

 

[enoyes12]

I bought 100pF/1000v ceramics because I was going off of memory and apparently my memory is failing. Getting older sucks

 

[Gepetto]

Well the 400v part is good because they didn't have them in 1000v. I don't know if they have the poly self healing either, I only saw ceramics, mylar and electrolytic. Typical all the good component suppliers by me are gone. People need to start fixing their $hit instead of buying new all the time! Where can I get them, Mouser?

Mylar is good, that is polyester and good for that application, self healing.

 

[enoyes12]

Oh duh, I guess so now that I think about it. I don't know if they had that size in mylar. I didn't look that close at the mylars though so I'll have to check tomorrow. I was just looking for the first one in that size. Thanks

 

[Gepetto]

Oh duh, I guess so now that I think about it. I don't know if they had that size in mylar. I didn't look that close at the mylars though so I'll have to check tomorrow. I was just looking for the first one in that size. Thanks

You have to withstand the voltage stored on the bulk caps plus 1.414*120VAC equals 82 + (120*1.414) = 251 minimum so 400V is just fine.

 

[enoyes12]

I thought 1000v sounded unnecessary. I can't wait to install them. cool thanks. I noticed on another thread from MJ, sounds like he is having the same issue as I am.

 

[Gepetto]

I thought 1000v sounded unnecessary. I can't wait to install them. cool thanks. I noticed on another thread from MJ, sounds like he is having the same issue as I am.

Perhaps the same, similar at least.

 

[enoyes12]

I installed the caps on the rectifier and it removed about 50% of the hum. I bought another rectifier but haven't changed it yet. I'm wondering if the transformer is causing the issue being so close the the left transistors. Does the transformer have to be grounded to the case? I was thinking of removing it and moving it away from the left output transistors to see if it helps. I can extend the wires and ground it to the case if necessary.

 

[laatsch55]

Leave the transformer where it is, we have built some world class residual noise amps right where it's at. Did you tighten up the x-former mounting bolts? Take a 7/16 wrench and ratchet and socket and tighten anyway. I do that as standard procedure. Some hum can come from Q1-Q4 aging and drifting in value, that's where I would go next.

 

[enoyes12]

yup tightened everything up already. I thought that might be an issue. I'll replace Q1 & Q4. What values are they?

 

[enoyes12]

Make that Q1-Q4

 

[laatsch55]

They are the front differential transistors. Q1, Q2 can be TIS-97's, MPSA 18's, or BC 550's. Q3 can be a TIS-93, MPSA 93, or MPSA 92. Q4 should be a MPSA 92 ONLY.

 

[laatsch55]

WATCH the pinout, print out the datasheets and keep them handy..

 

[laatsch55]

Could you post a pic of the backwall as it looks now?

 

[NavLinear]

Could you post a pic of the backwall as it looks now?

Lee - post #8 shows some of the back wall.

 

[enoyes12]

laatsch your a genius!!!!!!!!!!!!!! I had tightened the xformer down when I first started this process. After reading you post about getting a ratchet and wrench and really tightening them down. I did and tightened the hell out of them and if I jamb my ear against the left speaker I think I can hear something but it's so faint it's hard to tell. I may go ahead and replace the Q1-Q4 anyway but at least I can try it in my system now. Your my hero.

 

[enoyes12]

Nav now thats a back wall if I've ever seen one!

 

[laatsch55]

laatsch your a genius!!!!!!!!!!!!!! I had tightened the xformer down when I first started this process. After reading you post about getting a ratchet and wrench and really tightening them down. I did and tightened the hell out of them and if I jamb my ear against the left speaker I think I can hear something but it's so faint it's hard to tell. I may go ahead and replace the Q1-Q4 anyway but at least I can try it in my system now. Your my hero.

No, not a genius E, jist done a hundred or so of these things and ya learn a few things along the way, glad that cured it. They have to be embarrassingly tight.

 

[enoyes12]

I guess so. I had tightened them before with a nut driver but when you said use a ratchet I knew they weren't that tight. My thought was they're tight it can't be that. Then said what the hell and got the tools and really tightened them and its gone. Unbelievable!!!!! I can't thank you enough. Next time your in Phoenix I'm taking you out for a beer. I posted my results on the Cerwin Vega D9 hum thread as well

 

[laatsch55]

E, I'm gonna hold ya to that beer. You can buy it over the dinner we have at that little Mexican joint we ate at on the east side of 17. Man that was good stuff....