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Topic: DIY Amp question for people smarter than I am... |
James Collett
From:
San Dimas, CA
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Posted 26 Sep 2019 12:32 pm |
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Hi everyone,
I'm trying to put together a decent tube pedal steel amp using the shell and power transformer from an old broken Pignose G60VR (60 watt POS amp). I know that I'm likely to be more successful building directly off of a schematic, but I want to see if I can make the existing transformer work. I'm basing my design off of the Fender AA1069 Circuit (late 60's Pro Reverb), but I'm ditching the reverb and tremolo--basically resulting in a 60-70w clean pedal platform. I know enough about electronics to tweak with component values to get the EQ curve, etc., that I'm looking for, but power supply design is somewhat elusive to me. Anything more complicated than a Fender Champ PSU feels like a balancing act that I'm not cut out for.
Anyways, after doing some homework and playing around with the Duncan PSU Designer software, this is what I've come up with. I used a voltage doubler to be able to reach the relatively high B+ voltage required of 435V, but overshoot it and use the 1.8k resister to drop the voltage down to where it needs to be. I'd love for there to be a simpler way to do this. The 110mA current tap is the B+ load (2x6L6), and the 50mA load is intended to cover the preamp/inverter tubes and then some. Does this schematic look sound? Is there anything crucial I'm missing? I enjoy the experimentation, but I don't want to cause a safety problem.
Thanks in advance for any and all advice!
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James Collett |
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J Fletcher
From:
London,Ont,Canada
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Posted 26 Sep 2019 4:01 pm
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Hi James
At full power , the pair of 6L6's will be drawing somewhere around 200 ma , and that will drop 360 volts across the 1.8 k ohm resistor . That's probably not what you want.
If you use a full wave bridge what does the high voltage end up as ?
You will need a bias supply for the 6L6's too . Somewhere in the -50 volt region. Should be adjustable to compensate for different sets of tubes.
Jerry |
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Jack Stoner
From:
Kansas City, MO
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Posted 27 Sep 2019 1:58 am
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I'm no electronics "design engineer" but that schematic and cap values look like something found in a solid state amp and not a tube amp.
I would bite the bullet and get a Fender/Fender replacement power transformer and use a proven Fender power supply design. As noted you will need sufficient current capacity and a negative voltage (around -51VDC) for the Bias. |
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Donny Hinson
From:
Glen Burnie, Md. U.S.A.
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Posted 27 Sep 2019 6:14 am
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| I'm no genius at this stuff, either, but I think you're going to run into a problem with a voltage-doubler. They do give you a high voltage, but at the expense of poor regulation and reduced power. If that transformer is rated at 200 or 250 ma, you'll likely get far less than that using it in a doubler circuit. Now, if you wanted lots of "sag", that might be tolerable. But since you're interested in clean power, you really ought to get a more suitable transformer and use a full-wave rectifier. |
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James Collett
From:
San Dimas, CA
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Posted 27 Sep 2019 6:47 am
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Thanks everyone! Yeah, in playing with the values I notice that a voltage doubler seems a lot more finicky than a full wave rectifier, but I can't get the voltage anywhere near high enough with a full wave. I'll take your advise and get the proper transformer. That will give me a 5v tap, too, so I can go with a tube rectifier if I want.
Thanks again!
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James Collett |
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Steven Paris
From:
Los Angeles
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Michael Brebes
From:
Northridge CA
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Posted 29 Sep 2019 12:53 pm
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Try this as a starting point. I would drop the inductor and first resistor.
http://www.standelamps.com/support/schematics/1964.html
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Michael Brebes
Instrument/amp/ pickup repair
MSA D10 Classic/Rickenbacher B6/
Dickerson MOTS/Dobro D32 Hawaiian/
Goldtone Paul Beard Reso
Mesa Boogie Studio Pre/Hafler 3000
RP1/MPX100 |
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Brandon Montgomery
From:
Colorado, USA
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Posted 11 Oct 2019 11:00 pm
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Hi
First thing: tube amps contain deadly voltage, if you are unsure about what you are doing, please take it to a qualified technician. Proceed at your own risk
I edited this after looking at the pignose G60VR schematic.
First off, what’s “broken “ about the Original amp? You’re probably making this harder than it needs to be to get a good sounding amp out of this pignose, a few simple mods to the existing circuit will save you time, money, and stomach lining.The schematic shows this amp to basically be a hot-rodded Marshall/tweed fender type architecture, a simple swap of tube type in the preamp (12AY7 v1, 12AT7 V2) will decrease the “overdrive “ and increase the headroom. Changing the slope resistor (R19) from 33K to 56K will tighten up the bass, and changing the mid pot (VR4) to 25k audio and clip out the 51K (R34) will give you a more familiar mid contour . If it were mine, I’d do these couple simple things and give it a listen, and then you can write down what you like/don’t like about it so you have a direction in mind for additional modifications. It looks pretty flexible with lots of potential for modifications.
I design and build tube amps for a living, happy to help if I can
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I swear they tuned it when I bought it
Excel Superb SD-12 C6/E9
Bludotone amp works Owner and resident solder Jockey |
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Mark Fowler
From:
Minnesota, USA
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Posted 24 Oct 2019 8:09 am Schematic
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The Pignose schematic shows you how to build the power supply and do you still have the boards from your amp?
Full wave bridge power supply.
Mark
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