A rectifier with 17v heater?

[CambridgeWorks]

I am in the process of starting to build a psu for my R1155.
I have several routes. One is to use the transformer mentioned below.
I have a transformer that as well as 6.3 and ct ht also has a 17V 0.3A winding which is to spare. To save excessive loading on the 6.3V winding, i would like to use a fw rectifier with this 17V winding. Any ideas? Any base really.
I am reluctant to use silicon diodes, but may have to. However, if I did use silicon, I could then use the winding for a PCL82 af output stage.
Thanks, Rob

[G6Tanuki]

What about a pair of PY31

http://www.r-type.org/exhib/abo0063.htm

or PY81 ??

http://www.r-type.org/exhib/abc0005.htm

Or a 12X4 (12v 300mA heater) and a series dropping resistor?

https://www.radiomuseum.org/tubes/tube_12x4.html

Available for under five dollars... https://www.tubesandmore.com/product...fier-full-wave

[ukcol]

How about a PY81, this is a TV boost diode with a 17v 0.3A heater and is good for 150mA of anode current. Only half wave of course though. But very common and cheap.

The dreaded crossed posts has stuck again.

Just an after thought - You cannot use two PY81s to take advantage of the centre tapped HT winding because you only have 0.3 amps available for the heaters but you could use 2 silicon diodes to feed the anode of a single PY81 and then you would have the slow warm up associated with the valve and full wave rectification.

[CambridgeWorks]

Thanks both.
Colin, I never thought of that! Like it. Was considering a delay switch or similar. Yes, it is to stop the sudden full ht before the rx has warmed up.
Since posting I also found another 6v txfmr I could fit in as well.
Thanks, Rob

[Boater Sam]

Even less heater current and still a delay start, could you use an EHT rectifier diode?

[turretslug]

14Y4? Or 2x EY91 with heaters in series? The latter would load the winding to 0.42A, but at least it would be a nice resistive 0.42A! I think that the problem with any thermionic option will be getting good, long-lasting, low forward voltage drop output current (i.e. cathode emission) with just 5W of heating power available- a modest power output stage would help here. If only there were 17V heater versions of the late-in-the-day, relatively efficient EZ80/81...

[Boater Sam]

117v heater rectifiers and a capacitor dropper for it? Or even a diode dropper, DC heater?
117Z3, 117Z4GT 0.04A?

[turretslug]

Invoking the dreaded silicon rectifiers- Use the 17V winding to power a delay timer and relay (rectified/smoothed 17V would happily operate a low-power HT-capable 24V relay, the world is your oyster here!).

[G6Tanuki]

The other option of course is a heaterless valve rectifier!

http://www.r-type.org/exhib/aaq0314.htm

https://www.radiomuseum.org/tubes/tube_0z4.html

That would be suitably 'period' - the WWII Canadian 52-set receiver 'universal' AC-mains/12V-battery PSU used one and it worked just fine.

[Bazz4CQJ]

Having retired the original PSU for my HRO (with its valve rectifier), and gone to silicon, I've also been looking at ways to limit the "excess" voltage present during warm-up.

One approach is to put some zenners in; they'll clamp the voltage until the valves conduct, and if you can get the values right, will then stop conducting when the volts fall. You can put a relay in series with zenners which will drop out (go open) when the voltage falls, which may make finding the "sweet spot" easier. The option to make the relay contacts feed HT to a suitable resistor, while the relay is pulled in, also helps. IIRC, I tested one setup using 4 off 70V zenners, which limited peak HT to around 280V, not too much above the normal working value, but high enough to ensure they didn't conduct when the HT fell back to ~240V.

I cannot recal whether the 1155 has a voltage stabiliser for the local oscillator. If is hasn't, including one will not only help keep the LO stable, but will also serve to limit the peak HT volts (to some extent) during warm up.

The warm up period is not too long, so the components' power ratings can be pushed a little.

B

[CambridgeWorks]

I looked at 0Z4 spec before posting as I think I have a couple. I was put off because I did not recall seeing them used much, so wrongly thought there was a snag. In fact, forward voltage dtop is very reasonable. No heaters either. I also like the relay and zeners idea.
Thanks all, you have been busy. Nice to get different ideas.
Thanks, Rob

[CambridgeWorks]

The 0Z4 will be without warm up delay I imagine? Also, do they generate any rf noise? Sorry if daft question, but I do not recall ever using them.
I am in no hurry, this rx has been here around 3 years so far, with just the occasional spurt of enthusiasm. Been tidying my shack and came across the said txfmr that was hiding under my bench with part of a chassis and a case.
Thanks, Rob

[G6Tanuki]

An 0Z4 will indeed produce HT as soon as it gets AC on its anodes. I've never had any issues with them generating noise; think of them as being like big neons - the turn-on and off depends on ionisation which is a [relatively] slow process compared with what you get in hard-vacuum or most semiconductor diodes. (You wouldn't want to use an 0Z4 to rectify the output of a SMPS as it just wouldn't be fast enough to do anything)

Rather than messing about with slowing the buildup of HT, I'd spend effort on HT stabilisation, at least for the LO and BFO. A receiver that drifts 500Hz HF or LF anytime someone turns the kettle on can be deeply frustrating!

[Herald1360]

0Z4s generate considerable "sharsh". I used one in a R1155 PSU as a lad- the improvement in S/N when it was subbed by a 5Y3 was considerable.

The 0Z4 came from a car radio with non synchronous vibrator- I now understand why its PSU was pretty much hermetically sealed inside a metal box!

[CambridgeWorks]

Ok. Thanks to all for your input. I have decided on a different transformer with thermionic valve rectifier and bigger case.
Rob