Odd 'ripple' in regulated Filament supply

[moamps]

It's interesting to note that the frequency display shows 110.96Hz...

It is obvious that the readout flickers between 120.xx and 119.95. This is expected because the distance between the dips also changes slightly depending on the load change (Pk-Pk voltage flickers too between 1.0 and 1.1V).
Finally, the scanning frequency of the display and camera should also be taken into account.

 

[abbey road d enfer]

It is obvious that the readout flickers between 120.xx and 119.95. This is expected because the distance between the dips also changes slightly depending on the load change (Pk-Pk voltage flickers too between 1.0 and 1.1V).
Finally, the scanning frequency of the display and camera should also be taken into account.

Yeah, good catch!

 

[Lee_M]

I think I had originally used the 338 because I was using an 18V xformer series wired, with much lower current demands- but due to the current requirements of this specific project I parallel wired to get the 5.5A at 9VAC. I suppose flipping out to the 1084 for this one is a reasonable change given how cheap they are.

If you're still using the same transformer and this is only intended for preamp tubes (I'm assuming this is for a specific design, rather than a bench PSU or something which needs to be more versatile), is it possible for you to wire the transformer up for 18v secondary again, and run the tube heaters on 12.6v instead?

That reduces the heater current by half (your [email protected] draw will be reduced to [email protected]), the change won't bother your transformer (5.5A@9v = 2.75A@18v), and the rectified 18v would then become about 25v, which gives you a lot more headroom for your regulator to work properly.

Then you could probably add a very low value series resistor (no more than a few ohms, but a lot of watts) between C1 and C3 to make a CRC filter, which will shave off a little bit of the excess voltage (reducing some of the strain on the regulator, otherwise the silicon has to dissipate over 20W on it's own) and should clean up the supply ripple a bit.

Obviously, disregard this all if you're using preamp tubes which don't have 12.6v heaters.

 

[amplexus]

If you're still using the same transformer and this is only intended for preamp tubes (I'm assuming this is for a specific design, rather than a bench PSU or something which needs to be more versatile), is it possible for you to wire the transformer up for 18v secondary again, and run the tube heaters on 12.6v instead?

That reduces the heater current by half (your [email protected] draw will be reduced to [email protected]), the change won't bother your transformer (5.5A@9v = 2.75A@18v), and the rectified 18v would then become about 25v, which gives you a lot more headroom for your regulator to work properly.

Then you could probably add a very low value series resistor (no more than a few ohms, but a lot of watts) between C1 and C3 to make a CRC filter, which will shave off a little bit of the excess voltage (reducing some of the strain on the regulator, otherwise the silicon has to dissipate over 20W on it's own) and should clean up the supply ripple a bit.

Obviously, disregard this all if you're using preamp tubes which don't have 12.6v heaters.

The project is all on PCB's- so rewiring for 12.6V isn't practical across 12 tubes and 5 boards.

That said the solution was just using a 15VAC/6A transformer, and then as you said, i dropped a 1R/100W chip resistor in between C1 and C3 which brought me down to a nicer Vin-Vout differential on the regulator. Then I heatsinked the shit out of the Resistor and the regs, and added a fan to the enclosure. Things are still warm, but everything ticks along beautifully, and regulation for both Filament and B+ is spot on.