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

[MBD115]

I've tried to keep up with this thread and I'm glad you got if figured out. There has been a lot of good info going on here for sure. I'm trying to learn something

[Wayne]

Well, now you have one possible solution to the problem! That is good news! Now you've got a opportunity to "play" a bit more. You can play around with grounds, elevated heaters, phasing of the heater supply, and any of the other good suggestions mentioned in this thread. After you're sick of all that, you can run DC heaters and have a quiet amp.

Oh, yeah. Since by then you'll be an expert on hum reduction, you can counsel all of us with our noisy builds!

Enjoy!

W

[Phil_S]

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.

Ha! The main reason I didn't think it was the tube is that I just built a thing with two 6SL7 preamps and two 6SN7 (four sections) power amp. It's quiet as a mouse. Tubes are all old stock, probably NOS, but, as you know, there is no way to be sure about that. I didn't do anything special, either, just typical twisted pair heater string up in the air.

[dehughes]

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.

Nice. What did you find worked best for you? I'm considering both elevating the entire heater string, or using DC for the preamp tubes...

[Phil_S]

Dehughes: Of course, what you do is entirely up to you. If this were my amp, I would fix it by the simplest and most expedient means possible. That means finding the simplest way to deliver 6.3VDC to that one tube. Since everything else is good, you should consider whether you have now reached the stage where you are going to fix it until it's broken. Fooling with heater elevation, going all DC, etc, are now just ways to introduce another problem that isn't there now. Good luck.

Here are a couple of eBay auctions that have what will probably do a very nice job for you without having to build anything fancy. You drill a small hole near the tube for a receptacle and you can just plug in the heater separately. With the transformer off the amp and at the wall socket, you really should be good to go. You might look around for an unused cell phone charger, as these are generally in the right voltage and mA range.
http://tinyurl.com/ddyqeb
http://tinyurl.com/cohgav

[dehughes]

Thanks Phil. I don't want to go all DC...just for the first preamp tube on each channel. I'll look into those wall warts.....

[doctord02]

Nice. What did you find worked best for you? I'm considering both elevating the entire heater string, or using DC for the preamp tubes...

Well, to be honest, it's still a noisy amp. I plan on rebuilding it without the octal phase inverter tube. As I recall, making sure the heater string alternated phase helped, as did giving it a DC elevation. I didnt actually have the real estate nor patience to wire in a separate transformer for the heaters, I just decided to live with it at that point.

[billyz]

I have found those octal preamp tubes to be prone to heater noise. I had an old B15N and went thru a dozen or so tubes before finding a set that was quiet. They were all RCA's. Also, Ampeg elevated the heater string and put in a hum balance control. They can be very quiet after all that.

[Cygnus X1]

I'm working on a 5C3 amp with 6SC7 preamp and 6SC7 pi.
I have other issues to deal with, but it is as quiet as a church mouse as far as hum goes.

Didn't do anything special with the heaters at all-running 22gauge solid core wires in the standard twisted fashion.

I have also built a couple single ended amps using 6SN7's as a power tube-again-no unusual noise from the heaters.

HTH.

[jjman]

I also spent alot of time trying to reduce hum on an old amp that uses octal preamp tubes 6SL7. I had 60 and 180hz going on. DC elevating, hum balance control, and even the DC heater wall wart test didn't work.

The solution was to toss the sovtek 6SL7s and use NOS.

[Phil_S]

JJman makes a good point here. Dehughes: are you using Sovteks? If you are willing to roll the dice on fleebay, you can buy a couple of good pulls for about $10-15 shipped and they will be a lot better than those Sovteks. I just bought about a half-dozen or so for my recent project, and want to say I"m averaging under $5/tube and all turned out to be winners. No noise, and I've got them in the power stage, where I think you'd really hear it.

[dehughes]

JJman makes a good point here. Dehughes: are you using Sovteks? If you are willing to roll the dice on fleebay, you can buy a couple of good pulls for about $10-15 shipped and they will be a lot better than those Sovteks. I just bought about a half-dozen or so for my recent project, and want to say I"m averaging under $5/tube and all turned out to be winners. No noise, and I've got them in the power stage, where I think you'd really hear it.

I have a new Tung Sol....so basically Sovtek. I think it's a solid tube, though, in that it was perfectly quiet when hooked up to the lantern battery, so I'm wagering a good DC supply will do well for me.

[dehughes]

So...bringing this back up from the grave.

Here's the latest:

I think the PT is bad (one end of the B+ lead shorted to ground...see other thread), so I'm going to install a different one. Hopefully this will kill the rest of the hum.....getting close to silence....

OH, and I ran a old 50's 6SN7 (Phillips? Tung Sol? Can't remember...have to check...I think it was Sylvania...yeah, that's it...) for a few minutes, and it was cool (much more even and smooth, tonally), but the amp was none the quieter for it. Again...think the remaining hum is a PT issue...will find out for sure once the new one is installed.

Thanks so much for your help...it's really turning out to be a sweet amp (even better once the PT gets working.

[dehughes]

So, after a failed attempt to remove mounting bolts, I finally have the new PT installed (see attached pic)....it sounds great! One thing I noticed is though the B+ from the new PT (Allen Amps TP40D) is lower than the previous PT (Mercury Magnetics clone of the 125P17A Fender Brown Deuxe PT), the actual plate voltage on my 6V6s is MUCH higher than with my last PT. The Mercury Magnetics PT kicked out about 339-ish volts to the 5AR4 plates, but only landed about 356vDC on the 6V6 plates (no changes were made in the circuit when the PTs were swapped). This Allen TP40D PT kickes out about 329vAC to the recto plates, but lands about 413vDC on the 6V6 plates.

Now, this isn't necessarily a bad thing, as my amp sounds friggin fantastic now (noticeably better than with the other PT...must like that extra juice), but I am a bit concerned about the plate voltages on the 6V6s. They are cathode biased with a 300ohm resistor and a 25/25 cap, and I'm measuring about 26v across the cathode resistor. Screens are getting 401vDC after a 1k resistor. The tubes aren't red-plating, and the amp isn't humming loudly, etc....so I think I'm safe.

So, how is it that my old PT had a higher B+ rating but a lower voltage to the tubes, whereas theTP40D PT has a lower B+ rating but I'm getting much higher plate voltages? To be fair, my old PT ended up being returned as the B+ line shorted (something came apart in the windings....), so perhaps this explains it? Dunno...

I tried to calculate the power consumed by the 6V6s and came to about 11w each...but then each time I try to do those calculations I have to re-learn how to do it...so perhaps I'm wrong. If 11w is correct, then might I be okay leaving things as they are, even with the high plate voltage? Please correct me if I'm wrong...

THANKS!

[paulster]

Glad it all came good for you, after a bit of a labour of love!

Did you stick with AC preamp heaters in the end? I couldn't see any heater or mains wiring going to the filament transformer.