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Epiphone Valve Junior - Tube Rectifier Mod


riantide

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Why would you want to? A Class A amplifier draws the same amount of current from the rectifier at all times while it's operating in Class A conditions, so there's no "sag." When you push it very hard, out of Class A conditions so it's clipping a lot, there's a small increase in plate current drawn due to "rectification," but it's very small compared to the increase in a cool-biased Class AB amp. I think you'll find there's little tonal difference between a tube and solid state rectifier in an amp like this. Not worth the considerable trouble to convert it. You can emulate the voltage drop of a rectifier tube by inserting a resistance equivalent to that of the rectifier tube you'd use (likely a 5Y3GT) at the amp's normal plate current draw between the rectifier bridge and first filter capacitor, but you still won't get much in the way of sag, you'll just lower the working voltage on the tubes a bit. (Which will give you a little less clean headroom, so you may notice a little more distortion that might make you happy.)

 

I think this is a great little amp just as it is.

"A cheerful heart is good medicine."
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Good points, Ricochet!

 

Another thing to consider would be the current drawn by the proposed rectifier-tube's heater-filament. I doubt if it's covered by the stock power-transformer; you'd either have to replace the p/t, or add another small transformer dedicated to its heater-filament. (This whole heater-filament current-draw type of thing is often overlooked when converting to different output-tubes, as well.)

 

I believe that Weber makes custom-tailored ss rectifiers that nicely emulate saggy tube-rectifiers to the customer's specs; they're generally made to pop into a tube-socket, but perhaps they'd make you one for internal, hardwired installation...

Ask yourself- What Would Ren and Stimpy Do?

 

~ Caevan James-Michael Miller-O'Shite ~

_ ___ _ Leprechaun, Esquire _ ___ _

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All the rectifier does is function as a part of the power-supply, so no signal goes through it. It can have an effect on the overall response and feel of the amp, mainly when pushed hard, but it also depends on the total design and all other components.

 

Note that many of the classic tube-amps that are considered standards to measure up to used SS rectifiers: Twin Reverbs, Marshall heads, Mesa/Boogies...

 

They contribute to a stronger sound and feel with more robust, tight in-a-good-way bass...

 

Not necessarily a bad thing, at all.

Ask yourself- What Would Ren and Stimpy Do?

 

~ Caevan James-Michael Miller-O'Shite ~

_ ___ _ Leprechaun, Esquire _ ___ _

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Yet another thing to consider for anyone who wants to do this anyway, is that the stock setup on the Valve Junior is for a full wave bridge rectifier, which doesn't use a center-tapped power transformer secondary. To go to a full wave tube rectifier, you'd have to replace the power transformer with one having a center-tapped secondary and twice the total number of turns on the secondary. And you'd have to have one with a 5V rectifier filament supply winding if you wanted to use one of the common 5V tubes. There are 6V heater rectifier tubes, but you'd have to look mighty hard at their heater-cathode voltage ratings.

 

It's a no-starter in my book.

"A cheerful heart is good medicine."
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Yep, the mod would end up costing as much as the amp did to start with. You'd be better off building one from scratch almost. A new power transformer alone will set you back $60 to $70 for a decent one and you may have to have a separate filament transformer just for the rectifier tube. $$$

Born on the Bayou

 

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