Non-polarized doubler capacitor...can I change it?

[AlanInSitges]

Working on a late-50s Philips, 21TE123A (made in Spain for those who care about such things). Aside from using four(!) PY82 rectifier tubes, the power supply features a 200uf non-polarized electrolytic as the pump capacitor in a voltage doubler circuit. I've never seen this before, and as those capacitors are hard to come by I'm wondering if I can swap it for a normal polarized cap with the negative toward the AC.

After googling around a bit the consensus seems to be that I can, but it was less clear if I need to make any change to the value. Running a circuit simulation gives them same result with both types, but I figured I'd ask the experts here. What do you guys (and Sue!) think?

[Electronic M]

Never heard the term "pump capacitor" so a schematic might help clarify.
Assuming the capacitor gets reverse polarity which would necessitate a non-polarized cap.

You can make a non-polar cap out of 2 polarized caps of the same voltage rating and twice the capacitance connected in anti-series (connect the positives of both caps together and use the negatives as the terminals that connect to the circuit).

[AlanInSitges]

That term is from wikipedia, I never knew what to call them.

Here's the PS schematic, it's C140, right before the first diodes https://i.imgur.com/GVrBfyo.png

[old_tv_nut]

I wonder if the use of a non-polarized cap protects against a fault condition, like failure of V21 and V22 (or their removal with power applied)?

[ppppenguin]

No, it's part of the voltage doubler. Used to get over 200V HT (B+) from a 127V supply.

You can't use an ordinary electrolytic. The results will be messy.

I would use a motor run capacitor such as this: https://www.amazon.co.uk/200uF-Capac.../dp/B07Q7XRV54 I presume that internally this is a pair of electrolytics connected in anti-series as a previous poster has suggested.

Alternatively I'd rewire for a conventional rectifier arrangement and run from a 230V supply. In the UK and Europe this is the easiest answer. In the US you'd need an autotransformer to step up the line voltage from 120V to 230V.

Since the OP is in Spain and the mains voltage there is 230V then if he sticks with the original circuit he would need a 230V to 127V step down transformer.

Historical note: While Europe now universally uses 230V, some European countries used lower voltages in the past. These included Spain and Belgium.

[AlanInSitges]

Well the set is, um, set for 220V. I'm having trouble tracing where the current goes through that hairball of a voltage switch, but it seems like when it's in the 220V position the wire from pin 14 could simply bypass the capacitor, and the power supply then works like a normal full-wave rectifier? In this set C140 has vented its spleen all over the place, so I wanted to replace it but maybe it's easier to just disconnect it since the TV will never see 120V.

As an aside this is a pretty cool TV! It's unlike any American designs, but cool looking, and easy to service - you just have to unplug the CRT, yoke, and speaker, then remove two screws and the whole chassis just slides out into your lap. And it has, or had, a glossy laquer cabinet and big honkin speaker just like the Philips radios of the time. This one has some curious characteristics: buttons on the front that switch in and out high-and-low-pass filters in the video section, not sure what they're for, and it has a VHF-only tuner with no extra position between 13 and 2, even though it was sold back when they had already started the transition to UHF-only. Photo: https://www.vintageway.nl/images/pro...s/big/0748.jpg

Jeffrey there are tons of those step-down transformers here, nearly all of them in cool midcentury bakelite cabinets, that can be bought for pennies. My Predicta came with one, and I have a couple more.

[old_tv_nut]

Beautiful clean design, but I wonder if that speaker sounds best when the set is placed in a corner.

[old_tv_nut]

Originally Posted by ppppenguin

No, it's part of the voltage doubler. Used to get over 200V HT (B+) from a 127V supply...

I'm thinking that a polarized cap (of sufficient quality) WILL work in a doubler, but that this cap will see alternating voltage if V21 and V22 are removed.

[AlanInSitges]

Originally Posted by old_tv_nut

I'm thinking that a polarized cap (of sufficient quality) WILL work in a doubler, but that this cap will see alternating voltage if V21 and V22 are removed.

That jibes with what I've read elsewhere, that the NP ones were used for safety reasons, which didn't make sense to me until you said that.

[ppppenguin]

I've looked again. It's hard to work out exactly what is being switched by the voltage selector. In the 220V position I don't think you need C140 at all. Simply remove C140, R147 and R148. Then you would need to check the heater chain to see that all valves are getting a supply. It may be possible to remove V21 and V22 completely.