170 Volt Amplifier Power Supply - UK Vintage Radio Repair and Restoration Discussion Forum

John12868 · 28th Jan 2009, 12:44 pm

Hi Guys,

I've found on the net the schematic for an amplifier using PCL82's using a 170 volts power supply. It uses rectified mains, using diodes, 47 uF capacitors, a 22R resistor, a 10H choke, more 47uF caps finally outputting 172 volts.

My questions are:-

1. Would this be suitable as a "universal" amplifier Power Supply for homebrew amplifier projects?

and

2. I know the choke is used to provide smoothing for the DC output. How critical is this smoothing to the supply voltage?

Regards

John

GMB · 28th Jan 2009, 1:13 pm

If this is rectifying the mains directly, without a transformer, then the answer to your question is that it isn't at all suitable.

davidw · 28th Jan 2009, 1:18 pm

Sounds like a non isolated power supply ,ie, NO mains transformer.As such it is, in my opinion, potentially dangerous to connect to earthed equipment.
Can you show us a diagram?

edit..GMB types quicker than me!

julie_m · 28th Jan 2009, 2:06 pm

Quote:

Originally Posted by John12868

I've found on the net the schematic for an amplifier using PCL82's using a 170 volts power supply. It uses rectified mains, using diodes, 47 uF capacitors, a 22R resistor, a 10H choke, more 47uF caps finally outputting 172 volts.

Rectified and smoothed UK mains would be around 300V. Are you sure this isn't an American circuit?

I think you'd be better off using a transformer.

John12868 · 28th Jan 2009, 4:46 pm

I have a copy of the schematic at work, but I can't find it on the net at the moment, so I will post it tomorrow.

It's a foreign diagram, however, its rectifying 250 volts.

Modifying my original post slightly, by using a mains isolating transformer, would it be possible to rectify and output 170 volts, and would it also be suitable as a universal power supply?

Regards

John

John12868 · 28th Jan 2009, 4:55 pm

I found the link

http://www.geocities.com/foltransvac.../PCL82Page.htm

ppppenguin · 28th Jan 2009, 5:12 pm

Stay well away from the power arrangments shown here. They are bad enough for 110V mains as shown; for 240V mains they would be lethal. This is the polite version. My real opinion would not be allowed in this forum.

Apart from the lack of isolation, the designer has assumed that the mains supply is balanced wrt earth. This is certainly not the case in the UK and probably not in most other countries.

The amp design may be quite reasonable though finding a suitable output transformer is the hard part.

Phil G4SPZ · 28th Jan 2009, 5:35 pm

The only safe mode of operation would be via a 110 volt isolating transformer with the secondary centre-tapped to earth, as with a transformer used on building sites.

That's a problem with the internet - anyone can publish a design, however unsafe, and unsuspecting people may follow it and get hurt.

John12868 · 28th Jan 2009, 5:45 pm

Ah, well, back to the drawing board as it were

Cheers

John

Brian R Pateman · 28th Jan 2009, 6:26 pm

In view of the fact that several of us have picked up on the safety aspects of this thread I am closing it.

We have discussed these aspects more than once.

Thread closed.

Regards,

28th Jan 2009, 12:44 pm	#1
John12868 Retired Dormant Member Join Date: Nov 2006 Location: Crayford, London, UK. Posts: 181	170 Volt Amplifier Power Supply Hi Guys, I've found on the net the schematic for an amplifier using PCL82's using a 170 volts power supply. It uses rectified mains, using diodes, 47 uF capacitors, a 22R resistor, a 10H choke, more 47uF caps finally outputting 172 volts. My questions are:- 1. Would this be suitable as a "universal" amplifier Power Supply for homebrew amplifier projects? and 2. I know the choke is used to provide smoothing for the DC output. How critical is this smoothing to the supply voltage? Regards John

28th Jan 2009, 1:13 pm	#2
GMB Dekatron Join Date: Aug 2003 Location: near Reading (and sometimes Torquay) Posts: 3,099	Re: 170 Volt Amplifier Power Supply If this is rectifying the mains directly, without a transformer, then the answer to your question is that it isn't at all suitable.

28th Jan 2009, 1:18 pm	#3
davidw Heptode Join Date: Sep 2006 Location: Woodbridge, Suffolk, UK. Posts: 643	Re: 170 Volt Amplifier Power Supply Sounds like a non isolated power supply ,ie, NO mains transformer.As such it is, in my opinion, potentially dangerous to connect to earthed equipment. Can you show us a diagram? edit..GMB types quicker than me! __________________ Dave G1AGK. My perception is my reality! Last edited by davidw; 28th Jan 2009 at 1:19 pm. Reason: timing!

28th Jan 2009, 4:46 pm	#5
John12868 Retired Dormant Member Join Date: Nov 2006 Location: Crayford, London, UK. Posts: 181	Re: 170 Volt Amplifier Power Supply I have a copy of the schematic at work, but I can't find it on the net at the moment, so I will post it tomorrow. It's a foreign diagram, however, its rectifying 250 volts. Modifying my original post slightly, by using a mains isolating transformer, would it be possible to rectify and output 170 volts, and would it also be suitable as a universal power supply? Regards John

28th Jan 2009, 4:55 pm	#6
John12868 Retired Dormant Member Join Date: Nov 2006 Location: Crayford, London, UK. Posts: 181	Re: 170 Volt Amplifier Power Supply I found the link http://www.geocities.com/foltransvac.../PCL82Page.htm

28th Jan 2009, 5:12 pm	#7
ppppenguin Retired Dormant Member Join Date: Dec 2003 Location: North London, UK. Posts: 6,168	Re: 170 Volt Amplifier Power Supply Stay well away from the power arrangments shown here. They are bad enough for 110V mains as shown; for 240V mains they would be lethal. This is the polite version. My real opinion would not be allowed in this forum. Apart from the lack of isolation, the designer has assumed that the mains supply is balanced wrt earth. This is certainly not the case in the UK and probably not in most other countries. The amp design may be quite reasonable though finding a suitable output transformer is the hard part.

28th Jan 2009, 5:35 pm	#8
Phil G4SPZ Dekatron Join Date: Apr 2005 Location: Bewdley, Worcestershire, UK. Posts: 4,748	Re: 170 Volt Amplifier Power Supply The only safe mode of operation would be via a 110 volt isolating transformer with the secondary centre-tapped to earth, as with a transformer used on building sites. That's a problem with the internet - anyone can publish a design, however unsafe, and unsuspecting people may follow it and get hurt. __________________ Phil Optimist [n]: One who is not in possession of the full facts

28th Jan 2009, 5:45 pm	#9
John12868 Retired Dormant Member Join Date: Nov 2006 Location: Crayford, London, UK. Posts: 181	Re: 170 Volt Amplifier Power Supply Ah, well, back to the drawing board as it were Cheers John

28th Jan 2009, 6:26 pm	#10
Brian R Pateman Nonode Join Date: Jun 2005 Location: Western Lake District, Cumbria (CA20) - UK Posts: 2,136	Re: 170 Volt Amplifier Power Supply In view of the fact that several of us have picked up on the safety aspects of this thread I am closing it. We have discussed these aspects more than once. Thread closed. Regards, __________________ Brian