power supply recommendation for EL84 amp

chevelle · 6th January 2006, 02:36 AM

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?

tubelab.com · 7th January 2006, 03:04 AM

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.

SHiFTY · 7th January 2006, 12:58 PM

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...

chevelle · 15th January 2006, 08:02 PM

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.

DigitalJunkie · 15th January 2006, 08:12 PM

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!)

chevelle · 16th January 2006, 12:41 AM

68 convertible

6th January 2006, 02:36 AM	#1
chevelle diyAudio Member Join Date: Dec 2005 Location: Merrillville, Indiana	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?

7th January 2006, 03:04 AM	#2
tubelab.com diyAudio Member Join Date: Jul 2005 Location: South Florida	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. __________________ Too much power is almost enough! Turn it up till it explodes - then back up just a little.

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7th January 2006, 12:58 PM	#3
SHiFTY diyAudio Member Join Date: Jul 2002 Location: New Zealand	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...

15th January 2006, 08:02 PM	#4
chevelle diyAudio Member Join Date: Dec 2005 Location: Merrillville, Indiana	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.

16th January 2006, 12:41 AM	#6
chevelle diyAudio Member Join Date: Dec 2005 Location: Merrillville, Indiana	68 convertible

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