Hoffman Amplifiers Tube Amplifier Forum
Amp Stuff => Tube Amp Building - Tweaks - Repairs => Topic started by: Diverted on March 30, 2024, 10:45:44 am
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Hi all,
Getting ready to start building a champ circuit for a friend. I'm going to use a 104ma power transformer with a 275-0-275 secondary@104ma. With a GZ34 I'm hoping for around 350 or 360VDC loaded. Also using an oversized 10w OT (5/7K primary) and a choke. It will run into a 12" speaker per his request. The circuit will be similar to a Vibro champ with bass and treble controls, but tremolo deleted.
I have two chokes on hand and wondering if there are advantages of using one vs the other.
One is a 4 henry 50ma which should be enough as current from the 6V6 and 12AX7 is going to be around 40ma.
However I also have a 4 henry 90ma choke.
Is there any advantage of using the larger choke over the smaller one? I'm looking to get as much clean headroom out of this amp as I can. Will the 90ma version keep it cleaner, or is it just wasted iron/overkill?
Thanks!
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Is there any advantage of using the larger choke over the smaller one? I'm looking to get as much clean headroom out of this amp as I can. Will the 90ma version keep it cleaner, or is it just wasted iron/overkill?
If plate current will be flowing through the choke I would use the larger one. If only screen and 12AX7 current will flow through the choke I would use the smaller one.
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Thank you. Larger one it is. The OT is going after the choke.
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Here's the schematic I klodged together showing the choke and a filter cap before it added in. How's it look? Thank you!
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Here's the schematic ... How's it look? ..
Looks good!
I think it's wise to have the extra filter before the OT.
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If I could make 1 suggestion...
Your schematic shows 1 end of the heater circuit tied directly to ground, you can elevate the heater circuit easily by tying the ground end of the heater circuit to the cathode of the 6V6. Or, you can do the 100 ohm resistor to ground on both legs of the heater circuit, but tie them to the 6V6 cathode instead of ground. I've done that with both of my SE amps, it does seem to help with heater derived hum.
I don't remember where I originally found that information, it's been a long time ago now.
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Thanks Amber. That's a remnant of the schematic's original form. I just photoshopped a few old Fender schematics together ... I didn't bother changing the heater wiring or the two plug, death cap etc. I'm going to run artificial center tap to 6V6 cathode. Thank you!
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FWIW;
adding to what HBP said;
this is the last, Variant, of my standard PS I used it on a PP 6V6 Class A-ish. It's stiff, which helps keep clean, clean, until clipping or compression.
the choke would be the 750ohm.
I like having a "double-tap" that I can "adjust" the PA tubes B+
IIRC tap A was about 4vac ripple, B was <2vac.
PP has a natural "cancellation" that SE doesn't, so moving to tap B with a well bypassed PA cathode knocks hum down below 1 on the guitar volume. (my "hum" tolerance gauge; IF i can hear it with guitar volume on 2, FIX hum, IF it goes away on 1, play and be happy)
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That's a good idea. But I'm probably going to stick to the stock plate voltages in this one, the only addition I'm making besides choke and filter cap is a midrange/raw pot to kinda sorta phase in no tone control 5F1 preamp mode.