Hoffman Amplifiers Tube Amplifier Forum
Amp Stuff => Tube Amp Building - Tweaks - Repairs => Topic started by: NotSure on February 21, 2016, 08:45:56 pm
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Seems to me as simple as the Champ type builds are, it depends on the transformer you intend to use, right? The circuit in general is about the same, but there are a lot of tweaks from Weber, Kendrick, Hoffman, Mojo, etc. Seems the critical piece of all these versions is which power transformer you buy, and what you have to do with the varying wire colors coming out of each. So is it safe to say you need specific instructions specific to the transformer you buy. If not, how do you adapt a generic power transformer to a Champ circuit from any of the above mentioned circuit tweaks?
Cheers,
Dave
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So is it safe to say you need specific instructions specific to the transformer you buy.
yes
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You could just use a 350 volt battery.
Since that is awkward, we want to find some way (any workable way) to get 350V of DC from the _AC_ in our wall-outlets.
There are many ways to do it. Different AC volts, different rectifier schemes, and yes different color leads.
I'm not sure the choice of transformer makes any real difference to the final sound.
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thats all there is to it.....if you get a transformer that puts out what you need, and use the rectifier that works in your build....any amplifier can be built
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Hate to say it, but watch eBay. I've purchased a bunch that way. Most sellers don't really have any idea what the specs are, but sometimes you get lucky and there's a part number visible in the posting that you can cross reference. Make SURE your current ratings are where you want to see them, not only for the HV but also for the filament windings too. The Champ 5Y3 draws 2amps @ 5v, which is pretty much standard, but if you swing up to a 5U4, you'll fry the same transformer, since that tube has a 3a filament current demand. Also, don't underestimate the 6.3 current winding. Some of the octal power tubes are current hogs! I just purchased a pair of Stancor PT's that the seller pulled out of two old V-M tape players, and they fit the Champ bill perfectly. I think he's got another two still out there.
Pete
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Of the two transformers, the output transformer needs to be single-ended specific due to differences in the actual construction.
I my last project, a tweed Princeton (very similar to a Champ & SE), I used an OT that I had on hand that was much larger than required & had to adjust components to deal with the overall bassy-ness of the amp.