How much current is enuff...

[JoeCon]

Guys

So when your looking at power xformers and you see the current rating how do you know what's enuff for your circuit? Do you add the anode current of the tubes you're using and make sure you got more than that total?
Whats needed to run 2 6V6 vs. 2 EL34??

Thanks...

[xtian]

Quickie calculator for you:

http://www.dreamtone.org/Calculate_Current_Form.htm

[randalp3000]

Quickie calculator for you:

http://www.dreamtone.org/Calculate_Current_Form.htm

I like this but the voltages always seem really high. I wonder if the voltage at first cap is unloaded?

Someone posted the math on here awhile ago and I wish I could find it.

[morcey2]

Quickie calculator for you:

http://www.dreamtone.org/Calculate_Current_Form.htm

I like this but the voltages always seem really high. I wonder if the voltage at first cap is unloaded?

Someone posted the math on here awhile ago and I wish I could find it.

What's with the "Subtract 6 Volts if using a choke before first capacitor" nonsense? If you're using a choke-input filter, the voltage at the first cap drops to 70% of a capacitor-input filter setup with the same transformer and current draw.

The voltages seem a little high, but pretty close. Current draw seems a little low, but, again, pretty close. There will be some variance depending on biasing, operating condition, and on the OT primary impedance.

Matt

[randalp3000]

300-0-300, 4 EL84's, 3 pre, GZ34 = 408VDC? I get around 345VDC with cathode bias. I think even unloaded I only get around 360-370.

[rp]

If you're designing an amp then you should work it all out correctly but if cloning just follow those before you, at least as a minimum. With small Fenders I always beef up the PT, Champs and Deluxes to 120mA mainly cause that's what Hammond 300 series I use offers. I've owned origs of small Fenders and those red hot PTs always freaked me out even though they have lasted for decades. I actually prefer the sound of my 5E3, 5F1, 5C1 clones with the stiffer PT. But don't overdo it, besides needless weight it can get really stiff/fast feeling, almost like going to SS rectification, if it's too much.
For the heaters don't over do it, keep it close to what you actually need. I thought overrating would be clever but you'll get above 6.3V. For Rectifiers I like to spec 3A unless size is an issue, that way I could use a 5U4G to drop voltage.

[matt h]

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[wyatt]

The voltages seem a little high, but pretty close. Current draw seems a little low, but, again, pretty close. There will be some variance depending on biasing, operating condition, and on the OT primary impedance.

Well, they are inversely related.

300-0-300, 4 EL84's, 3 pre, GZ34 = 408VDC? I get around 345VDC with cathode bias. I think even unloaded I only get around 360-370.

It's using the rectifier coefficients multiplied by the posted primary.

SS = 1.41
GZ34 = 1.36
5V4 = 1.33
5U4 = 1.24
5R4 = 1.19
5Y3 = 1.13

300v x 1.36 = 408v

This ignores a lot of caveats and possibilities; ...aside from diodes, the rectifiers aren't nearly as exact as this...circuits don't always use the load spec'ed by manufacturers, etc. But the idea is for a ballpark.

[ToneMerc]

You need to look at the exact circuit... that calculator is a fine idle condition ballpark... but without knowing your operating point, conditions, and power supply design.

I agree and IMHO that calculator doesnt even make a good ball park calculator.

TM

[matt h]

(deleted)

[JoeCon]

Matt h

I get what your saying but I see a xformer with the voltage I want and it's available with 100, 120, 150, 200, and 250 mA. And the difference can be up to $40/$50 and being a Yankee I'd like to save the $$ if possible. Sure I could do the 250mA even if I need only 100mA but I'd just be getting it cause I don't really know what I need.

How do get enuff but not way more than enuff??? What tube charateristics are you look at for current draw?

[matt h]

(deleted)

[JoeCon]

Matt

Sir, excellent, that's just what I needed. I know you wanna go over for safety reasons, no sense stressing every component. But why just run a 250ma when a 180 will be more than enough.

Thanks....

[matt h]

(deleted)

[John_P_WI]

Joe,

Read Aleks's (VacuumVoodoo) excellent write up about half way down the first page here:

https://tubeamparchive.com/viewtopic.ph ... er&start=0