Hacker P-18 power supply

[Nukeybrown]

Has anyone got any info on this power supply , schematic etc as I have one in a hacker vhf herald but it has a 35v 1000uf cap across the battery terminal , not sure if it's been put their due issues with the one in the psu which is 40v 220uf.

[Nukeybrown]

Is it that rare?

[GeoffK]

As no one else has answered this, if you measure the voltage across the capacitor to make sure it is correct for the radio, a 1000uF is usually ok as a smoothing capacitor, the 220uF is a bit small as a smoother.

[Nukeybrown]

I understand this but schematics for this would be great. 220uf might sound low but it's what hacker put into it so should be correct , 1000uf not sure if this has been put in afterwards or is part of the set up for a p18. Just strange how I can find very little bordering No information about this power supply.

[GeoffK]

Can't help with the schematics though small linear supplies can be usually be drawn out if they can be accessed, probably no more than a transformer, rectifier diode, a zener and series transistor and a few caps and resistors. Could be the designer made it for average listening levels where a 220uF would have been enough, and a 1000uF would have of course been larger and more expensive.

[Station X]

Can you post a picture of the PSU please. Someone might recognise it.

[Nukeybrown]

Here's pics.

[Station X]

That PSU gets a mention in post #5 in this thread:-

https://www.vintage-radio.net/forum/...ad.php?t=11940

[Nukeybrown]

Surely if Hacker put in a 220uF cap that would be correct?

[Station X]

That 1000uF- capacitor isn't part of the RP18 PSU, it's part of the radio. If the circuit diagram for your Hacker VHF Herald doesn't show it then it shouldn't be there.

However is possible that someone has added the capacitor because the 220uF unit inside the PSU has failed or problems were being experienced with smoothing.

[Nukeybrown]

It's no part of the schematics as someone has obviously soldered it to the top of the battery terminal.

[julie_m]

220 µF sounds a bit stingy for a PSU smoothing capacitor, but might just about be OK for an 18 volt supply, if this radio uses two PP9s in series.

Adding capacitance here won't hurt, anyway. Anything that will physically fit, will be fine, and will reduce power hum.

[Nukeybrown]

The only issue with that is when batteries are put onto radio instead of the psu the distortion level is off the scale when turned up. Not sure if it's related or another issue

[Nuvistor]

if it is similar to the VP408 PSU from Hacker, note the 408 is variable, it will be a straight forward linear PSU with a series regulator transistor. They made 9 volt versions, same size as a PP9.
it should be an easy circuit to fix, the circuit for the 408 is in post 11, link below, thanks to Mark. Hopefully apart from being variable it will be very similar.

https://www.vintage-radio.net/forum/...d.php?t=107374

Frank

[Nukeybrown]

Thanks frank , I have a 408. Just haven't really looked at that for similarities in caps etc yet only got the p18 on thur this week and been restoring a rp10 since then.

[Station X]

You could do forum members a favour by reverse engineering your P18 PSU and posting a circuit on here, much as mhennessey did with the VP408.

Members would then be able to comment on whether 220uF was a suitable value for the capacitor.

[Herald1360]

If function is more important than originality, I'd be inclined to replace everything after the reservoir capacitor with a TO 220 7815.

My VHF Herald runs quite happily from an AC wallwart feeding a bridge/reservoir/7815 combo.

[Nuvistor]

My VHF Herald runs quite happily from an AC wallwart feeding a bridge/reservoir/7815 combo.[/QUOTE]
That would be good enough for me.

Frank

[AC/HL]

This is mine, the capacitor & bridge are a bit OTT, but they were available at the time.
Works perfectly on 15V.

[Nukeybrown]

That's not the same as mine though, that's a standard power supply with smoothing. Mine's official Hacker with an internal cap.