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

[Phil_S]

OK, my bad, you posted good closeups of the tube sockets way back and I've enlarged and printed them in color.

Here's easy lead dress stuff that you can do in 10 minutes, no soldering required!

On V1, 6SN7, bend some pins on the socket outwards, taking care not to break them. Do this to pin 1 with the 33K on it, and get it as close to the chassis floor as you can without actually touching the chassis. Put a scrap of cardboard in there, so you can press it down and not go too far. This will move the grid input away from the heater wire, which, IMO is way too close. Bend the 33K so that it crosses the other wires at a right angle or bend it up in the air to get it away from the wires going to pins 2, 3, & 4. Then, gently bend pin 8, heater, outwards a bit, maybe to 45 deg angle to further separate pins 1 and 8.

Next on V1, I suggest you move the wires for cathode 1 (pin 3) and grid 2 (pin 4) further apart. Do this by bending pin 4 outwards as far as you can go, and bend pin 3 inwards a bit. Re-kink the black wire on pin 3. Where the black wire makes the right angle bend in at the fold in the chassis, see if you can separate black, red, and white wires, even a little bit. Do this with the chassis live on the bench, speaker attached of course, with a chopstick or other non-conductive (no pencils) tool. Your ears will give you the answer here.

I can't see where the white wire goes from V1 pin 4. Where is the other end? I'm wondering if it can be relocated. Post this if chopsticking doesn't help.

On V2, the 12AX7, you've done this one a bit better than V1, but IMO, it can be tweaked. I can't see the cathode wire on pin 8. Bend that pin down towards the chassis floor to get it away from the heater wires. Bend the string of heater wires up a bit, away from the chassis floor, and away from the grid input on pin 2. Do something to separate the white grid wire on pin 7 from the black cathode wire on pin 8; bending pin 8 outwards should give you a bit of space there to work with and you might try a slight re-kinking of the second right angle bend on the white wire to help separate them. This might also lead you to re-kink the red plate wire on pin 1 if the white wire gets too close.

OK, I lied about no soldering...if the above doesn't help, rework the lead dress on the grid input for V2. Unsolder or bend the 33K and route the wire as follows: place the 33K (use a new one if needed) so it is parallel to the fold in the chassis and nearly on the chassis floor (not touching). Sleeve if needed and right angle bend the 33K lead to bring it to pin 2. Push the heater wires up a bit away from the chassis floor. This should give you clearance between the heater wires and the grid input (a vulnerable spot for hum to get in). Another right angle bend at the other end of the 33K to bring it up the side wall (find a place between the two red wires from V1 & V2) and then tuck the input wire along the lip of the chassis, to the corner by V1, and down to the floor. I can draw you a picture if this isn't clear. Right now, it looks like that 33K is practically resting on the heater wires. In fact, you just might be able to chopstick into a good place without all that work.

Finally, if there is still hum, change where the ground buss is making contact with the chassis. You have it soldered to the chassis near the input jacks. Cut that connection and find a way to stabilize and insulate that end. Run a jumper from the other end of the buss bar to the bolt where you are grounding the high potential stuff.

Do these things one socket or even sometimes one wire at a time and test. No sense doing more than is necessary and doing them all at once runs the risk that you might make something worse and you won't know what.

BTW, IMO, Rich G is also making a worthy observation that sometimes caps are just bad out of the box. Your fiddling with the power filters hints at this possibility. My inclination, though, is to work the lead dress first. There is no saying that I'm going to be right, as I don't have the amp in front of me and this remote work can be tedious.

Keep going. Patience will get you the reward you seek. On this one, slow and steady will win the race. I know this from experience.

[dehughes]

Dude, Phil...thank you. What a lot of time and effort you took in that reply.

So, first, the heaters are nowhere near as close to the grid resistors as the pictures make them look, but even then I have them much farther away than in those pictures (had to rewire the grid stuff after I took those pictures). There is still hum, but almost only coming from the 6SN7. I messed with the wires/lead-dress a bit per your recommendations and that changed nothing.....though I wager I could tame a bit of hiss by moving that all around once I get the hum under control. Really, if it weren't for this 6SN7 channel, the noise in general would be nearly okay.

My inclination is to try your suggestion about grounding the buss bar on the other side of things...away from the input jack. Being as I cut the hum out of nearly all but the 6SN7 channel just by re-grounding the power section electrolytics, I wager the rest of this can be solved by some ground movement. We'll see.... I'll post back after I tinker a bit tonight and tomorrow.

[dehughes]

Sooo, though it included shocking myself (don't ask....), I re-wired the preamp ground buss bar. What I did was disconnect the ground connection it had up by the input jack, and instead connected it to the main star ground on the PT bolt....where the center taps for the heaters and 5v go, as well as all the electrolytics. Here's what I found:

Before, the amp hummed (fairly loudly) the same amount regardless of the volume pots' settings, and mostly through the 6SN7 channel. Now, the amp is much less hummy, until you turn the volumes up....and then the hum presents itself as bad or worse than before, but now on BOTH channels. Again, with the volumes down it is nearly hum-free, and if that was all it hummed I'd be thrilled.

Interesting. I'm not sure what this indicates (feel free to spell it out for me...), but I'm going to continue tinkering with the ground spots and see if I can find one that solves my problem. I'll try other ground spots for the preamp buss....maybe the power tube cathode point, or somewhere between the input jack and that.

[dehughes]

Soooooo, I moved the ground point for the preamp buss bar to the same point that the power tube cathode and grid resistors are grounded, and guess what? It hums about the same with the volumes off, but when I turn them up, it is noticeably less hummy than when the preamp was grounded to the main lug. SO, progress! The 6SN7 channel is still injecting far more hum than the 12AX7 side, but less than before.

BTW, the amp sounds better now...which is amazing. The ground scheme really does help with tone. Super cool.

So, now what? Keep searching for the perfect ground scheme, eh? I'd rather not have to go with DC heaters...would rather solve this with a good ground scheme. I'm soooo freaking close...

[Phil_S]

Dehughes: I don't mind writing that stuff. There were people who did that for me when I started out. I don't always have the required time on my hands, but that day was OK.

I am thinking a few things here, and probably not in any particular order.

The easiest thing to do at this point is to fire it up and chopstick various wires. You might find what makes hum worse or better. I'd be looking real hard at that 6SN7.

You have two input jacks and I can't really see them in the pictures. You did link the grounds together and run only one wire from the inputs to the buss bar, didn't you?

You are using Switchcraft type jacks. You might unbolt them from the chassis and hang them in the air. The idea is to break a possible ground loop. If that fixes the problem, you will need to change to Cliffs type jacks or insulate the Switchcraft type with a nylon bushing. This sort of bushing can be found in a your local hardware store, but you need a big one that has the little drawers full of small parts. Home Depot and its ilk generally don't have this stuff. It looks like a washer with a lip that goes through the hole. You will need to enlarge the mounting hole.

You might be able to fashion an insulation workaround with some silicon goo and a pair of simple nylon or rubber plumbing washers, but it will be messy and I don't know if you can achieve what's needed and you'll still need a bigger hole. If you want to experiment, find a bit of scrap metal, drill the hole and use a spare jack to see if you can make it work. I'd say this is too much work, but you know about necessity and invention.

With the amp as it is now, with the buss bar grounded at the high potential end, pull the 6SN7 and tell me if that helps things. If it does, here's what I'm thinking and, I'll tell you, I don't have much foundation for what I'm about to offer. The 12AX7 is a higher gain tube than the 6SN7, considerably higher. I am wondering if you need to re-organize the order in which the grounds connect to the buss. Everything from the 6SN7 goes on the buss first and the stuff from the 12AX7 goes second. Because of the amount of work here, I'd save this one for last.

[rfgordon]

One more trick to try, (I looked for this in the thread, forgive me if I missed it.) is to connect the ground reference for the heaters to the top of the power tube cathode resistor. This is an easy way to put a DC reference voltage on the heater line, which can help reject 60Hz hum.

[dehughes]

Nice. Thanks guys. I'll try that stuff out and see what's up.

As it is now, I don't have the other input jack connected....it's just filling the 2nd input hole for aesthetic purposes. I didn't want to run them parallel, as I wanted one input for two channels....but this chassis was drilled for two inputs so I left it as-is. Right now, the active jack is just grounded to the chassis at that point...not to the buss bar. I'll try pulling it out of the chassis first and hanging it in the air, then I'll try grounding it to the buss bar, then I'll try putting the heater CT on top of the cathode resistor for the power tubes, then I'll try the lantern battery thing. After that...who knows.

And yes, pulling that 6SN7 out of the socket removes most of the hum.

THANKS. I'll post back with an update...

[dehughes]

SO, I floated the input jack in the air (no change), grounded it to the buss bar for the 6SN7 channel (no change), separated the PI circuit and ran that ground group to the buss bar (no change), and then re-flowed the grid and heater pins on the 6SN7 and moved the pin 1 input off to the side and out of the way a bit more (slight change...the hum is the same volume, but when the volume controls are turned up, the amp is less hissy/hummy than before).

In short, the input jack and preamp grounds don't seem to be the problem. I'm going to go to the store and get a lantern battery for the 6SN7 heaters and see if that makes any difference...

[Phil_S]

...6SN7 and moved the pin 1 input off to the side and out of the way a bit more (slight change...the hum is the same volume, but when the volume controls are turned up, the amp is less hissy/hummy than before).

...get a lantern battery for the 6SN7 heaters and see if that makes any difference...

IMO, you do not have a problem with the heaters. Referencing the ground through the power tube cathodes is a good idea and easy to do if you like.

Do you have another 6SN7? What's it like without the 6SN7 and/or with a swap? When you turn up the volume, the hum goes down. There is something about the 6SN7 or the channel it's on. Re-check to see that every ground connection that should be made is actually made, and made to the buss bar.

What happens when you chopstick G2 (pin 4)? This goes to the Vol pot closer to the input jack? Fiddle with this wire a bit and see what happens.

Just to see, while we are at it, I think the bit of circuit from that volume pot to the 220K resistors needs some rethinking. You have no ground reference and I think one is needed. From the 2nd plate, you have the .002 cap and then a 220K. Insert a ground reference resistor between those two, maybe a 15K like on the 12AX7 channel. Just tack it in and see what it does. You don't need real tidy here until you know what it does.

Here's a longshot: try reversing the grid input wire by putting the 33K at the jack. I don't believe I have ever put the resistor on the tube, I always put it on the jack.

We've been concentrating on the preamps, but I looked at your output jacks. Do I see this right? You've got the green and black transformer wires going to the jacks? I'm not sure what you've got going on here or your intentions. (Aside: Assuming your schematic is correct, wiring two output jacks in parallel for a single 8 ohm tap means you've got to plug in two 16 ohm speakers to get the 8 ohm load.) I also see a black ground wire going from the jacks to I don't know where.

I don't implement this way. I'm not saying it's right or wrong. What I do: ground the black wire from the OT to the main chassis ground (power tube cathodes, filter caps, etc.) and then run the black wire between the output jack sleeve to the same main chassis ground. This might cure your power tube hum and might have an upstream impact. It is hard to know.

[dehughes]

FIXED IT!!!!!


It WAS the 6SN7 heaters! The lantern battery solved alllllllllll the hum, save for a teeny bit which is normal for a cloned Brown Deluxe PT. AWESOME! Thanks SOOOOO freaking much to all of you. I owe you all a beer or something....thanks.

One thing of note: I noticed a drastic change in tone/feel of both channels depending on how I grounded them. That is, when the preamp buss bar was grounded to the same point as the power tubes cathode, the amp sounded and felt wonderful. But, when I ground the 12AX7 and 6SN7 stages to the other end (up by the jack), it felt kinda lame....harsh, midrangey, flat, flappy....just kinda "yech". Interesting. So, I guess I'll be re-doing my grounds for the sake of tone/feel now, huh.

[greiswig]

Great thread...really useful info in here by a lot of good contributors, and good troubleshooting. Thanks all for contributing so much time.

[Phil_S]

FIXED IT!!!!!

Excellent news! IMO, the simplest thing to do here is find a 600mA DC wall wart, strap it to the chassis, and wire it in parallel to your power transformer. Anything that does 6 to 7 volts is good. Good luck. Good for you for sticking with it.

[Structo]

Good news, so apparently the 6SN7 does not have spiral wound (humbucking) filaments?

So what now, DC heaters? for all the preamp heaters or just the 6SN7?

[dehughes]

Good news, so apparently the 6SN7 does not have spiral wound (humbucking) filaments?

So what now, DC heaters? for all the preamp heaters or just the 6SN7?

I'm thinking of DC heaters for the 6SN7 and the first 12AX7.

[doctord02]

Funny... I was just about to mention, every 6SN7/6SL7 I've ever played with had noisy heaters... and required doing crazy stuff to clean up - like wiring the heaters out of phase, elevated or powered by a different source.

Congrats on finding the problem.