milliamp question

paisley_tele · Post by **paisley_tele** » Thu 04/17/08 8:10 pm

would 150ma trans be ok for a 5u4gb , 4 el84 , 12ax7 , ef86 build

what_wires · Post by **what_wires** » Thu 04/17/08 8:35 pm

150mA at what ouput voltage? If it is let's say 285V, the total output at 100% efficiency is about 42 watts. You can easily get 36 watts from a quartet of EL84's that aren't running anwhere near 100% efficiency. If they are running at a favorable 85% efficient, you'll need to supply about 44 watts just to run the output tubes.

In short, I would go for at least 200mA to avoid overheating/toasting the PT.

Pressed_Rat · Post by **Pressed_Rat** » Thu 04/17/08 8:56 pm

You also need to consider the the heater and rectifier current draw, if you haven't already done this.

That 5U4GB is going to draw around 3 A from the 5 VAC supply; not reflected in the 150 mA supply. So you need to make sure the 5 VAC supply is rated at 3 A.

The EL84s draw 0.76 A each, the 12AX7 draws 0.3 A, and the EF86 will draw 0.2 A. These all draw from the 6.3 VAC supply, so your 6.3 VAC should be rated at 3.54 mA. Round it up to 4 mA.

what_wires · Post by **what_wires** » Fri 04/18/08 3:11 am

Pressed_Rat wrote:You also need to consider the the heater and rectifier current draw, if you haven't already done this.

That 5U4GB is going to draw around 3 A from the 5 VAC supply; not reflected in the 150 mA supply. So you need to make sure the 5 VAC supply is rated at 3 A.

The EL84s draw 0.76 A each, the 12AX7 draws 0.3 A, and the EF86 will draw 0.2 A. These all draw from the 6.3 VAC supply, so your 6.3 VAC should be rated at 3.54 mA. Round it up to 4 mA.

P_R, you are confusing filament current with HV current and mA with A.

paisley_tele · Post by **paisley_tele** » Fri 04/18/08 7:10 am

the tranny is 660v or 540v @ 150ma . 6.3v @ 5A , 5v @3A.

so according to the spec it will work . right

what_wires · Post by **what_wires** » Fri 04/18/08 10:53 am

You'll have plenty of heater current but you are pushing it on the HT current capacity.

paisley_tele · Post by **paisley_tele** » Tue 04/22/08 7:15 am

so is there a certian yes or no ?

what_wires · Post by **what_wires** » Tue 04/22/08 8:43 am

Most transformers are conservatively underrated. With your exisiting iron you will be running at or or over this rating. If it is Hammond iron, you can probably get away with it. I would watch PT temps though.

paisley_tele · Post by **paisley_tele** » Fri 04/25/08 2:23 pm

the build calls for a choke to . will it still be ok ?

what_wires · Post by **what_wires** » Fri 04/25/08 2:24 pm

Sure, a choke shouldn't raise the current consumption too much.

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