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Interesting 5E3 trick

4/6/2006 6:13 AM
Interesting 5E3 trick
I recently built a 5E3 with a slighly undervoltage power transformer (250-0-250V) and discovered a neat trick while troubleshooting it. Using the 5Y3 rectifier, the amp had a B+ of 283v and a power output of 6.6 watts. This looked a bit low, so on a hunch I replaced the 5Y3 with a 5AR4. This raised the B+ to 324v, and the power output increased to around 11 watts. Hmm, two different output power settings by simply switching between rectifier tubes of different efficiencies...
4/6/2006 6:59 AM
Al Lang

What were the differences in tone?
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4/6/2006 8:27 AM
what trannie did you use? Did it fit in the chassis cutout? I want to build a 6BQ5 amp using the 5E3 chassis and that is the voltage rage I need. Do you know any of the trannie ratings?
4/6/2006 8:56 PM
Andy B.

You may find this helpful.  
4/7/2006 11:04 AM
registered users only.....
4/7/2006 11:18 AM

might as well register then, that forum is as good as this one!
4/7/2006 11:56 AM

Indeed the 18 Watt website is great!!  
The PT I'm using in this amp is an old Hallordson I found NOS at a hamfest a few years back. It's rated at 250-0-250VAC @ 70mA, which is a little wimpy for a 5E3 but it works pretty good, only 5V or so of sag on B+ from idle to full output with the 5AR4. It does get warmer than I'd like, so it will get a fan eventually.  
The Hallordson PT won't fit on a 5E3 chassis as it is an above chassis mount. You may be able to find a Hammond that will work though, some of their PT's have secondary taps for different voltage outputs.  
I'm not sure of the tonal differences with the different rectifiers, sounds pretty good with either one. I used it with the Chinese 5AR4 on a gig last night for the first time, it was just a bit too loud (into an EV12L) to overdrive with the band. I plan to try the 5Y3 next gig. That might drop the power a bit and allow a bit of grit at a more usable level.  
BTW that's what is so interesting about the mod, you can swap tube rectifiers for different playing situations. There are a lot of different 5V filament octal base rectifiers available that might give different results. IIRC the 5AR4 has less of a voltage drop but more sag, where the 5Y3 has a larger voltage drop but less sag. And you could always insert a solid state rectifier for no voltage drop or sag. All this with no modifications. You would need to make sure that none of the rectifiers allow voltages to get too high so that the tubes or transformers get cooked, hence the reason for the lower voltage PT.
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