Paper in oil capacitors.

[Electronpusher0]

Originally Posted by bikerhifinut

My personal concerns with Voltage doublers are the hammering they give the PSU capacitors, I will need to refresh my memory but I think a voltage doubler needs csapacitors that can handle very large ripple currents? That I guess can be mitigated by being able to use lower voltage rated caps or to get a better margin? And again, I may have the wrong end of the stick, but does a voltage doubler put a bit more strain/load on the mains transformer? i.e you have to halve the current rating (Ohms law?).

A.

With the doubler circuit I attached to my post the capacitors are only being charged once per full mains cycle ie half wave rectification so indeed you are right the ripple current is higher than full wave rectification but modern Electrolytic capacitors are able to carry this.
However since one capacitor is being charged on the positive half cycle and the other on the negative half there is current flowing in the transformer during the entire mains cycle exactly as it would in full wave rectification so there is no extra strain on the transformer or derating required, normal VA calculations apply.

Peter

[Electronpusher0]

Originally Posted by bikerhifinut

I see where you are coming from, and it certainly opens out the choice of transformers as you'll easily find an inexpensive toroid with 2 x 60V secondaries that will give you 120v and then use another one for the heaters.
A.

For my valve amp I used an inexpensive 2 X 60v torroid as you suggest but I made sure to buy an open torroid, ie one that had not been filled with epoxy.
I was then able to overwind with sufficient turns for the heater secondaries. I wound two secondaries simultaneously (Bi-filar) to give 2 X 3.15V which I then connected in series with the centre tap connected to ground.

Obviously I chose a torroid with sufficient VA for both HT and Heaters.

Peter

[ms660]

Some Schades curves for half wave, full wave and voltage doubler, as good as flat for most apps once critical C (reservoir) is used.

Lawrence.

[G6Tanuki]

If you don't want to use electrolytics, it could be worth you looking at 'motor capacitors' which are available remarkably cheaply and in high-voltage ratings. The Italian Ducati company offer a range, some of which are specced for use in 3-phase 440VAC applications.

Example: https://uk.rs-online.com/web/p/polyp...itors/3888061/

[Lucien Nunes]

Compton's first series of post-war electronic organs used exclusively PIO capacitors for reservoir and all smoothers of the 15+15W amplifier based on popular octal beam tetrodes, supplied via two popular octal directly-heated rectifiers in parallel. CLC for the main HT - typically 10H @400mA tuned by 0.25μF - followed by RCRC for the preamp, all C's 8μF. The PSU chassis was slightly smaller than the PA but much heavier. Early versions with triode-connected output stages used no electrolytics in the circuit at all. The tetrode and ultra-linear versions that followed had cathode bypass electrolytics, but the PSUs retained PIO parts until they switched to solid-state amplification in the 1960s.

However, in the early 60s they introduced some smaller models with physically more compact single-channel 20W amplifiers all on one chassis. These still had CLC smoothing but with a much smaller choke and 32+32μF electrolytic reservoir and smoother, served by an indirectly-heated rec. The hum in both cases is admirably low, but the toe-injury potential of the models with the big choke and 8μF caps is very high indeed. The inertia in changing these to use electrolytics may have been influenced by the expectations of longevity. Subject to service contract, they were guaranteed for 21 years!