5E5 with bigger iron - more power?

[yankeerob]

I've built a 5E5 clone, which I've done quite a few times already, only this time I thought I'd experiment with some bigger iron to see what would happen.

Normally I use a 150mA 340-0-340 PT with all the usual whistles and bells - sufficient 6.3V and 5V windings etc and a 5K6 OT and they produce a fairly consistent 28W output.

This time I thought I'd try building the same amp with a bigger set of iron - I had a 200mA 360-0-360 lying around with plenty of 6.3 and 5V current and a 5K OT so that's what I've used. It's weird but the amp produces around 25W as is (not what I was hoping for!!)...

In it's current state it's got 445V B+ straight off a 5U4 rectifier, 405V plates, 430V screens and around 32.5V on the cathodes (common cathode follower, 250Ω/22uF). I thought this a bit odd and am wondering if I need to drop the cathoder resistor value to make this beast go? I'm not that great at working these things out and haven't found any relevant info on this sort of situation... Anyone got any Ideas?

Like I said it's a straight 5E5 build but with bigger iron. I've attached the schematic of the build.

Many thanks...
Rob

[Daver]

Do you really have 25 more volts on the screens than the plates? That seems odd considering you have a 1.5K resistor to drop voltage between them. That suggests a lot of resistance in the OPT if that's a correct reading.

[Old Tele man]

P = I * V

...so, if you can get more " V " from the power supply and the output tubes can be driven harder to conduct more " I ", then "yes," you'll get more " P " from the amp.

...but, consider *where* each of those increases might come from:

1) more " V " means bigger PT or less voltage-drop across the rectifier
2) more " I " means lower Zpp OT
3) more " I " means output tubes having higher " gm " value
4) more " I " means more drive-signal from PI

...in reality, a HEFTIER (more "iron") OT only gains you lower frequency response.

[Bruce / Mission Amps]

I'm using a custom 35-40 watt OT and 180ma watt PT in my 6L6'd Chicago harp amp.
When switched into cathode bias mode, it makes about 22 watts max clean with a GZ34 rectifier @ 425vdc and around 32-34 watts clean in fixed bias.
With a combination resistor and choke node, my screen voltage is about 2-3 volts less then the plate voltage

[yankeerob]

Hi Bruce... pleased to make your acquaintance and thank you for your input... this is what I've come to accept about this circuit :-D

I should have also let everyone know that we've tucked our tails in and are reverting the chassis to the 150mA 340-0-340 PT and 5K6 OT...

Thanks to everyone for all the input!!!

[Bruce / Mission Amps]

And I meant 180ma PT... still had watts on my brain... ha ha