Hoffman Amplifiers Tube Amplifier Forum
Amp Stuff => Tube Amp Building - Tweaks - Repairs => Topic started by: Baguette on December 12, 2014, 08:19:17 am
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Hello,
I'm building a simple Champ style amp with 6SL7, 6V6 and 6X5.
I'm gonna wire the heater the old school way, i.e., 1 pin connected to the 6.3VAC supply and one pin connected to ground.
Since the amp has a 6SL7, notorious for its hum, I'm wondering if I could make things better if I connect the heaters this way instead:
1 pin goes to the 6.3VAC and the other pin goes to the 6V6 cathode (about 15VDC reference).
Is it doable?
Would it make things any better?
(I'm pretty sure I can't do it but who knows)
Thanks!
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google "6sl7 hum"; get, e.g.: http://www.ax84.com/bbs/dm.php?thread=404166 (http://www.ax84.com/bbs/dm.php?thread=404166)
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1 pin goes to the 6.3VAC and the other pin goes to the 6V6 cathode (about 15VDC reference).
DON'T DO THAT!
I'm gonna wire the heater the old school way, i.e., 1 pin connected to the 6.3VAC supply and one pin connected to ground.
Don't do that either. Old school is inferior to new school. If you are concerned with filament hum use a center tap (real or artificial) and connect the centertap to the 6V6 cathode.
And use a small cheap speaker that cannot reproduce 60Hz very well. :icon_biggrin:
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Like Sluckey stated about the center tap on the filament supply.
As this is a new build, you can take a lead from amps that use a Hum Balance pot (Ampeg, Guild, etc.). Connect pot terminals 1 and 3 to each filament lead. Connect pot terminal 2 (wiper) to the cathode of the 6V6. You should be able to dial most or all of the filament hum right out.
Jack
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I love 6SL7 tubes, and I use a humdinger plus approx. 50 volt elevated ground. The last one I did is quiet as a mouse. (or maybe the speaker's just not very good).
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I'm building a simple Champ style amp with 6SL7, 6V6 and 6X5.
Since you're interested in reducing hum, do this:
Look at the Champ schematic. See the place where the rectifier tube output connects to the 1st filter cap? Break that connection. Now insert a filter cap to ground (16-22uF, whatever you like), and connect a 250-500Ω resistor from this cap's + terminal to the + terminal of the former 1st filter cap. If you want a choke instead of that resistor, go for it.
What I described is adding an extra stage of filtering; the extra filtering should be before the OT connects to a filter cap, so that connection is at the 2nd filter cap (what was previously the 1st filter cap).
Modern builders don't use trash speakers in their amps, then are horrified to hear a 120Hz hum they need to fix. The problem is lack of filtering for a single-ended output stage, but the original amps largely hid this with speakers with very poor bass response.
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Thanks for the answers guys.
I'll try that hum balance pot trick first and see what it does. I'm usually not a fan of those, I've replaced to many of those in silverface Fender amps.
I'll also try the extra filtering stage. I'd like to stay away from it though since I do not have too much real estate so 1 more filter cap + 1 more big resistor might be problematic.
But it's sure good to know!
Thanks again,
V
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I'll also try the extra filtering stage. I'd like to stay away from it though since I do not have too much real estate so 1 more filter cap + 1 more big resistor might be problematic.
The thread seems to be gone from the forum now... In maybe 2010, a forum member built a VibroChamp and had hum issues. Until he added the extra stage of filtering prior to the output tube plate B+ node.
Since that thread, it pretty much became the standard suggestion to add a stage of filtering to any Champ build to avoid 120Hz hum (especially when a better-than stock or bigger-than-stock speaker is used).
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I'm building a simple Champ style amp with 6SL7, 6V6 and 6X5.
Since you're interested in reducing hum, do this:
Look at the Champ schematic. See the place where the rectifier tube output connects to the 1st filter cap? Break that connection. Now insert a filter cap to ground (16-22uF, whatever you like), and connect a 250-500Ω resistor from this cap's + terminal to the + terminal of the former 1st filter cap. If you want a choke instead of that resistor, go for it.
What I described is adding an extra stage of filtering; the extra filtering should be before the OT connects to a filter cap, so that connection is at the 2nd filter cap (what was previously the 1st filter cap).
Modern builders don't use trash speakers in their amps, then are horrified to hear a 120Hz hum they need to fix. The problem is lack of filtering for a single-ended output stage, but the original amps largely hid this with speakers with very poor bass response.
for a visual representation of what's described above, use the PS scheme in the 5E1 champ:
http://el34world.com/charts/Schematics/files/fender/Fender_Champ_5E1.pdf (http://el34world.com/charts/Schematics/files/fender/Fender_Champ_5E1.pdf)
--pete