5E3 Power Mod Voltages

[Mikeb]

From the previous post... I changed out the PT in my 5E3 to a Heyboer 320-0-320, 150 mA and also changed to fixed bias. ( That has it's own set of issues, haha)

My voltages were 454, 443, & 307 prior to inserting the tubes (6L6WGC). After insertnig the tubes to voltages fell to 385, 370, & 258.

Is this normal? What are typical voltages?? I have looked through a lot of blogs and reference material but none have answered my question.

I need to know which voltage to reference when biasing the tubes. I am assuming the "in circuit" voltage is the one. When I go that high (47mA says Webers Bias Calculator) I get a bad hum.

Please help!!!

[sportster4eva]

How are you measuring the 47ma? through a cathode current sense resistor?
At 385v that's about 18w dissipation per tube, right within spec. 450v is about right for an unloaded measurement, but what is causing the other voltages to drop without any tubes plugged in?

[Mikeb]

Bias Meas.

I have a series socket running thru my Fluke

[stokes]

"My voltages were 454, 443, & 307 prior to inserting the tubes (6L6WGC)."
If those voltages are with no tubes at all,there is a problem in your power supply,as there shouldnt be any voltage drop in the rail,since there are no tubes to draw current,a leaky filter cap will cause hum.That bias you mentioned is for a 6L6WGB,with your 6L6WGC you can go to about 54ma at 385 plate volts.

[Mikeb]

Re: Power Mod Voltage reply

Thanks man... I have been looking into different reference material on this whole power supply string "thing".

It would seem that there would be a voltage drop along that string as there are series resistors between the filter caps of 4.7K and 22K, Yes, no, maybe so?

Thanks again... I'll keep digging ( a deeper hole or for information, whichever comes first, haha)

Mike

[stokes]

There will be no voltage drop across those dropping resistors between the caps with no load (tubes), if you are seeing a voltage drop like you quoted with no tubes you have something wrong.Most likely a leaky cap.With no tubes there should be nothing drawing current,with no current you wont get a voltage drop of more than 1 or 2 v's.You have a drop of 136v's at that last cap that is way too much and you have a leak or short,no doubt,there is no need to dig any further,that last cap and possibly the second one where you see 11v's are leaking current,but the 11v could be caused by the leaky last cap.If they are old caps I would suggest changing all of them,otherwise change that last one and see if the 11v drop disappears as well.

[Mikeb]

Power Mod - Voltage Assistance

Thank you! I am going to move forward with this advice. I thought it seemed excessive, but I dont have much exp. with tube circuits. But I suppose your point is straight electrical theory.

Again, thanks!