36w redeaux: Squeal City

[v00d00blues79]

I just finished up redoing my 36w to match the latest layout available, and i am getting some horrible squeal when the volumes and master are turned up. I wired everything per the schematic, but for some reason the feedback switch only works when its in the off position. Can anyone shed any light on this for me?

Thanks,

Andy

[rjgtr]

This can happen with any transformer swap. You need to reverse the plate wires from the transformer on your output tube sockets. Your feedback is in phase (positive feedback). This will make the feedback negative again and your squeal will go away and your switch will work.

[v00d00blues79]

ahhh... ok. The transformers are the same, but i did rewire everything else. I'll do that today and see how it works. Thanks!

Andy

[NewGuitar]

I had a very similar issue with a previous build of the 36 watter based on the older layout. I read somewhere (Kevin O'Conner, Morgan Jones, Randell Aiken, etc, I can't remember) that swaping the leads on the plates of the phase inverter from pin 1 and 6 on V3 where they connect to the board would correct the issue. I tried this and it did correct the issue. However, I had many other problems and ended up completely rebuilding the amp using the latest layout.

The following is just my suggestion based on my hard-headed experience. I found most of my initial problems were related to poor solder joints. When rebuilding using the latest layout I used a new solder station that allows proper soldering techniques. I made certain that every solder joint was done right. This made trouble shooting and tweaking much easier. My build is not perfect. I still have an issue at higher volumes (see other posts of mine), but the amp is very, very good.

[v00d00blues79]

Ok... i tried switching the plate leads to the V3. Even worse, loud horn-like squeals coming from the speakers. This is with the left plate lead, as if you are looking at the board from the back, is run to V3 pin 1, and the right plate lead is being run to V3 pin 6. I had them reversed before and i at least got sound before the squeal, now i only get squealing. The transformer primaries have never been switched from the last wiring, but could something in the NFB switch be causing this? I have it wired like the layout, but it seems that it only allows sound in the off position, whereas before it was wired like the old layout and it worked fine. Could it be possible that the transformer primary leads would still need to be reversed? i have the brown lead going to the left set of el-84's and the blue lead going to the right set. again this is as if the back was closest to you.

Thanks,

Andy

[rjgtr]

Andy,

It obviously is not the transformer or PI wires. Just put them back. Then see if you can provide pictures of how the NFB switch is wired all the way back to where it connects to the PI.

[kd]

I haven't seen the 36 watt schematic but, do you have the output jacks grounded, if not ground them and see if that helps.

Ken

[v00d00blues79]

I'll try and get some pictures up on how i have the NFB switch wired, but i can say that its wired similar to the way the layout shows, except i'm using the ground point from the previous wiring and connecting the .1 and 1.5k ground points to the output jack common connection on the 8ohm tap. Could this be causing some problems? The output jacks are grounded, just not exactly like the layout.

Thanks,

Andy

[kd]

Ground the .1 and 1.5k somewhere other than the common on the output jack, then gound the common on the output jack. See if that helps.

Ken

[v00d00blues79]

Grounded the 1.5k and the .1 elsewhere and it took care of the whine, but that wasn't all that needed to be done. The ground connection for the off setting wasn't shown on the version of the layout that i was using, i added that and everything is great now! Thanks everybody!

Thanks,

Andy

[fightingzero]

Grounded the 1.5k and the .1 elsewhere and it took care of the whine, but that wasn't all that needed to be done. The ground connection for the off setting wasn't shown on the version of the layout that i was using, i added that and everything is great now! Thanks everybody!

Thanks,

Andy

Can you technically dime the volume(s) and there are no issues?

-Scott

[Plexi]

"""Can you technically dime the volume(s) and there are no issues? """

You should be able too without problems.

Richie

[v00d00blues79]

Well other than the fact that i would blow the speakers in my test cabinet, i am happy to report that other than a little hiss, i was able to dime the controls and not experience any whining or obnoxiously loud noises... besides my playing...

Thanks,

Andy