Brown Deluxe/Constellation build...help please...

[dehughes]

Dude. Thanks Phil. That's great advice. I have a ton of suggestions to work through, so I'll add this to the list of "to-do". I'll post back after I've tried a bunch of things.

[M Fowler]

Good information Phil and hopes this helps out. I am including one picture of my Spitfire amp showing three ground spots: the IEC left lower corner; center taps left middle; and all the rest upper middle green wires.
This amp has no noise but then it isn't exactly high gain either being only 18 watts. But as you can see the AC is separate from the center taps and the gain stages are separate.

Mark

[dehughes]

So, what about some issue pertaining to the fact that the 6G3 12AX7 side has the cap on the B+ side of the 100k plate resistor, and is then mixed into the 6SN7 channel before the PI? Might that be a problem somehow?

[Phil_S]

So, what about some issue pertaining to the fact that the 6G3 12AX7 side has the cap on the B+ side of the 100k plate resistor, and is then mixed into the 6SN7 channel before the PI? Might that be a problem somehow?

I'm not sure I understand this, as I am not am amp designer.

Think about trying this: from the 2nd triode of the 6SN7, bypass the .002 cap and the 220K resistor. Simply run a jumper wire right to the .01 coupling cap before the PI and you can leave that other stuff in place. Then try just bypassing the .002 coupling cap. Then try running the jumper from the plate to the spot between the .01 and 22oK, both channels are sharing the 220K.

If this isn't clear, I'll draw some pictures and post them.

I can't say why. Something doesn't look right to me.

[dehughes]

Thanks Phil. I'll add that to my list to try. As well, something doesn't seem right to me on the schematic, but then I'm still too new at this to say exactly what that is. We'll see...just something in my gut says that the blending of the channels is the cause...probably wrong, though.

[dehughes]

So, I checked that 220k divider resistor between the 12AX7 stages, and it is making a ground connection. I tried swapping out a different tube for the PI, but it's still humming. Next, I'll try moving the PI electrolytic over to the preamp buss bar and see if that helps...

Well, that didn't help either. But I do notice that the hum changes a bit when I switch in that extra 16uf cap....don't know what that indicates. I'll keep trying stuff...

[Phil_S]

I can't help but feel you are stabbing in the dark. I suggest you take a step back and do something very basic here.

0) no tubes in the amp and it hums? Look at the iron and grounds. Something non-amplifying is passing signal to the speaker.

1) pull all tubes but the rectifier. Hums? Yes=change the rectifier, no=goto step 2.

2) with rectifier and power tubes in, hums? Yes=power tube/power section related; no=goto step 3.

3) add in the PI. Hums? yes=something to do with the tube or related components. Swap the tube, check the components. No=goto step 4.

4) add in 6SN7, leave 12AX7 out. Hums? yes=6SN7 problem, swap, check stuff around it; no=leave it in the amp.

5) add in 12AX7; same basic stuff as #4. Try only 12AX7 and only 6SN7, etc.

6) with all tubes in, pull the PI. Hum stops? it's the preamp sections, hum continues, it's the power section, see step 2. You might try this first.

The idea here is simple. working backwards from the rectifier, keep adding tubes until it hums. That will give a BIG hint about where in the amp the problem is coming from. Then you focus on that section rather than random poking around.

Post findings.

Good luck.

[dehughes]

Thanks Phil. It does feel like I'm stabbing in the dark. Here is what I've found:

DUDE....I re-wired the electrolytics in the power section so that each has its own path to the ground, and that the PI electrolytic hangs off the preamp buss. Check this out....

0) No tubes in the amp = just the audible hum from the PT itself....nothing out of the speaker. Perfectly quiet.

1) Rectifier in: A very little swell of hum, but then perfectly quiet, just like 0.

2) Rectifier and Power tubes in: Hum is present now, albeit at no more than HALF the volume as with all the tubes in. This is way less hummy than before. If this was all the hum I ever heard, I could live with it, no problem.

3) Recto and Power Tubes and PI in: Hum is identical to #2.

4) Recto and Power Tubes and PI and other 12AX7 in: Hum is the a bit more than #2 and #3, albeit with some slight hiss (normal....not bad at all). OKAY, now THIS is better! This used to be waaaay hummier, having only the 6SN7 missing. It didn't use to matter which preamp tubes were pulled, for as long as the PI was in it still was a hummy little brat.

5) Recto, Power Tubes, PI, 12AX7, AND 6SN7 in (all tubes): Hum is ABOUT as bad as it was, though I think it is a bit less overall. INTERESTING....

I'm going to have to get my brain around all of this....I think I'm making progress (thanks nearly entirely to you all...) so I'm excited but still wanting to nail down the last hum problem. Maybe time for DC heaters? More ground tinkering? Very cool...I'll get to this more tomorrow or Thursday.

Please feel free to post more suggestions before then...they're greatly appreciated. It's getting close!

[sdp1234]

WOW... that build is just way to neat and tidy. I thought I was getting better. Your build may either motivate me or make me quit.

[sdp1234]

I'm going to post some pictures of this amp above my work area for motivation.

[MBD115]

I'm sorry dehughes that my post was incorrect. After looking at your drawing more I seen I made a mistake. The 220k resistor I mentioned was on the plate B+. Again I'm sorry for any confusion on my part.

Best of luck

[rfgordon]

I suggest you build the aggie-engineered signal injector, so you can put a signal on it, starting at the PI and moving toward the front of the amp.

Here's what you need:

1. Choptsitck
2. guitar cable to sacrifice
3. clip lead
4. 630 V capacitor, almost any mF value will do
5. Shrink & tape.

1. Chop off the plug from one end of the cable, and prepare the ends of the signal and shield conductors.
2. Solder the cap to the signal conductor with the leads straightened out.
3. Solder the free end of the clip lead to the shield.
4. Attach what you just made to the chopstick, with the end of the cap sticking about 1/2" beyond the end of the chopstick.
5. Cover the exposed parts with shrink/tape.

Connect the amp to a speaker and power the sucker up.

To use, plug the cable into the headphone out of a stereo, clip the gator end of the clip lead to the amp chassis, and touch the exposed cap lead to where you want to inject the signal. (The cap prevents you from frying the stereo with HT from the amp, should you touch the wrong side of a coupling cap.)

If you hear sound while touching the PI entrance, then move on to the previous gain stage. Lather, rinse, repeat until you find the non-amplifying stage.

[Phil_S]

1) Rectifier in: A very little swell of hum, but then perfectly quiet, just like 0.

Once the caps charge, they do their job.

2) Rectifier and Power tubes in: Hum is present now, albeit at no more than HALF the volume as with all the tubes in. This is way less hummy than before. If this was all the hum I ever heard, I could live with it, no problem.

Whatever you did probably made some difference, but I think the grounds are not all as they should be. You've got hum in the output stage.

3) Recto and Power Tubes and PI in: Hum is identical to #2.

Good, PI doesn't appear to be problematic.

4) Recto and Power Tubes and PI and other 12AX7 in: Hum is the a bit more than #2 and #3, albeit with some slight hiss (normal....not bad at all). OKAY, now THIS is better! This used to be waaaay hummier, having only the 6SN7 missing. It didn't use to matter which preamp tubes were pulled, for as long as the PI was in it still was a hummy little brat.

Take a good look at where your heaters are in relation to your signal wires. You want heaters as far from signal wires as possible. I can't see it real well in your pictures...more below.

5) Recto, Power Tubes, PI, 12AX7, AND 6SN7 in (all tubes): Hum is ABOUT as bad as it was, though I think it is a bit less overall. INTERESTING....

Though I can't see it well, I think your heater wires need to be more up in the air and away from all signal wires. I think you are doing a very neat, but not functional job near that 6SN7. Do you have another 6SN7 to swap? A close up of the preamp tube sockets is in order. Same for the power tube sockets.

Also, Rich Gordon is giving you a very good poor man's diagnostic tool. Try it.

Keep going. You'll lick the hum. Hiss is another animal all together. I suggest we take that up later.

[dehughes]

Right on. THANKS. I'll post pictures of the preamp sockets ASAP, and will get to the other suggestions as well.

Also, the power stage hum is super minimal....way less than I'm making it out to be. I wager the grounds still could improve, but the problem is significantly greater with the preamp stage(s) for sure.

[rfgordon]

I will offer this, related to the filter caps: just because they're new doesn't mean they're good.

A couple of years ago I built a 5E3 for a guy, and its noise made me nuts! Turns out the new F&T twin cell cap was bad. I only found it by disconnecting and clipping in a new one for each filter.