Voltage doubler questions

[jon]

I build a simple amp using a bridge style voltage doubler. My pt has no ct. I've noticed that the voltage takes a very long time to stabilize, like 40 seconds. I'm wondering if my caps are to large 100uF.

[Structo]

Gotta schem?

[Phil_S]

Sometimes, the first few power ups with new caps are slow, particularly if they are not as fresh as you think. Try cycling on and off several times, and when it's on, leave it on for a few minutes. This should correct itself if the caps are otherwise OK.

I had this happen with a new amp on occasion, voltages not right, etc., and then suddenly it all settles in.

[jon]

Gotta schem?

As requested. On a side note I am unable to generate sufficient bias voltage.

[martin manning]

Disconnect the bias supply from the PT (no power tubes installed, of course) and see if the B+ stabilizes quickly. You will need to capacitatively couple the bias circuit into the HT to get negative voltage.

[jon]

I'm not sure I follow the idea of capacitor coupled negative voltage supply.

[ToneMerc]

I'm not sure I follow the idea of capacitor coupled negative voltage supply.

I was kind of figuring this was a bias issue. You would break the bias supply feed and insert a .05/400-600V cap between it and the HT supply point.

By chance, do you know the HT rating of that PT?

TM

[martin manning]

Same as Marshall did in some of their amps with FWB. Connect the bias supply to the HT with a 47n-100n cap and a 56k immediately afterward to ground. Now you have positive and negative voltage available to feed into the reversed diode.

[jon]

I'm not sure I follow the idea of capacitor coupled negative voltage supply.

I was kind of figuring this was a bias issue. You would break the bias supply feed and insert a .05/400-600V cap between it and the HT supply point.

By chance, do you know the HT rating of that PT?

TM

150-0 @ 220-240mA

[ToneMerc]

I'm not sure I follow the idea of capacitor coupled negative voltage supply.

I was kind of figuring this was a bias issue. You would break the bias supply feed and insert a .05/400-600V cap between it and the HT supply point.

By chance, do you know the HT rating of that PT?

TM

150-0 @ 220-240mA

So you should have about 423V or so unloaded, at half that current.

TM

[jon]

I'm at 400v unloaded

[Structo]

This is probably very obvious but the 100uF cap on the bias node should be electrolytic and have the + end to ground, correct?

[jon]

Oh I got that part down

[jon]

Disconnect the bias supply from the PT (no power tubes installed, of course) and see if the B+ stabilizes quickly. You will need to capacitatively couple the bias circuit into the HT to get negative voltage.

Would you mind sketching what you are referring to or pointing me to a known schematic?

[John_P_WI]

Disconnect the bias supply from the PT (no power tubes installed, of course) and see if the B+ stabilizes quickly. You will need to capacitatively couple the bias circuit into the HT to get negative voltage.

Would you mind sketching what you are referring to or pointing me to a known schematic?

Put a 100n 630v poly cap between the winding and the bias diode.