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Old 6th January 2006, 02:36 AM   #1
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Default power supply recommendation for EL84 amp

I'm putting together a mono amp which will use three EL84's wired in parrallel to a single op traf.

I will probably use a 5U4 rectifier and a 6922 input tube. Will my 150mz (270V) Hammond power transformer be adequate for current?
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Old 7th January 2006, 03:04 AM   #2
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Hey, anyone called Chevelle deserves an answer. Unfortunately you have not quite supplied all of the needed information. Looking through the Hammond catalog, I don't find a transformer that exactly matches your description. An amp with 3X EL-84 can draw anywhere from 120 mA to 200 mA. Most Hammond transformers are rated for a maximum DC output with a cap input filter. In this case a 150 mA transformer would be marginal. You can draw about 170 mA if you used a choke input filter. If you do this, keep the bias adjusted on the low side until you see how hot the transformer gets. A lot depends on available ventillation, and the intended use of the amp. If this is going to be a guitar amp, with the volume "cranked to eleven" a lot, I would look for a bigger transformer.
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Old 7th January 2006, 12:58 PM   #3
SHiFTY is offline SHiFTY  New Zealand
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I would suggest going Push-Pull and just using a pair of EL84s, the transformer would be happier.

Otherwise give it a shot and see if it gets too hot- if it does, switch to a GZ34 / 5AR4 rectifier (less filament current) and use a separate 6.3V transformer for all the tube heaters...
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Old 15th January 2006, 08:02 PM   #4
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It's a Hammond 270FX transformer. I was planing on resistive coupling
with a 1K load resistor, 40uf before and 40uf after, using a 5U4 rectifier. This is what I was hoping to work with.
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Old 15th January 2006, 08:12 PM   #5
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Quote:
Hey, anyone called Chevelle deserves an answer.
Amen Tubelab!

I just have to ask tho,What year is it?

(Mine's a '67,and I *love* it!)
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Old 16th January 2006, 12:41 AM   #6
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68 convertible
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