Improved regulation. - UK Vintage Radio Repair and Restoration Discussion Forum

Boater Sam · 23rd Jul 2018, 7:35 pm

Whilst constructing wall warts for my transistor radio collection, I make PP7, PP9 and PP10 falsies using surplus non regulated 9v and 12v power packs, I use mainly LM317T adjustable regulators. With these I can make power packs from 6v to 18v with ease.
I have found them to be good, minimal hash on the radios, robust and cheap.
But I have been making these for years. Stocks are running low. At 99p for 10 from China they are outstanding value.
The thought occurred that things have moved on and I should maybe update to something better next time I restock.
Is there a better regulator at a fair price?
No surface mount tech though!

Nuvistor · 23rd Jul 2018, 8:09 pm

At 99p for 10 I would get 100, should last you a while and you have proven design that works. I would only look for something new when you are near then end of the 100.

dseymo1 · 23rd Jul 2018, 9:19 pm

You've been lucky!
I bought a few from China a while ago; they regulated OK, but went O/C as soon as they were asked to pass a few mA.

Diabolical Artificer · 24th Jul 2018, 6:38 am

Looked on Farnell - http://uk.farnell.com/w/search/prl/r...earchlookahead and they have 64,000, but look underneath and it looks like you could be right Sam. However it says this - Market demand for this product has caused an extension in lead times, delivery dates may fluctuate.

I use the LM317AHV which is a bit higher voltage. If it ain't broke.....

Andy.

Mooly · 24th Jul 2018, 8:14 am

The abilities of the regulator as seen at its destination are severely diminished simply due to the effects of the cable from wall wart to equipment. In other words the advantage of increasing the regulator performance, even many times over, is totally swamped by the remote location of the regulator.

Boater Sam · 24th Jul 2018, 8:57 am

A case for 98% silver gold plated one way HiFi audiophool cable then?
It was not the precision of regulation I was concerned with, rather the purity of the DC without hash.
I used to use 78xx series regulators with base resistors to trim the output voltage but found that the output had a lot of switching pulses that cause background noise sometimes.
Sam.

turretslug · 24th Jul 2018, 9:42 am

The 78/79xx series have a noisy internal reference followed by what is effectively a wideband, low impedance power amp making output noise very difficult to eliminate- some RF applications end up using pi-filtering on the output. Perhaps in the case of the 7805, they were expected to have extensive rail filtering for spiky logic applications anyway, so device noise wasn't a high concern. The LM317 family use a much quieter bandgap reference. It may be an oldie, but I like the 723, as the reference is available at a pin and can be filtered as much as you like before applying to the rest of the circuit- it does need external pass transistors for any appreciable output current and several other peripheral components though, so not quite an easy modular block like three-terminal regulators.

paulsherwin · 24th Jul 2018, 10:28 am

You probably know this already, but a typical transistor radio doesn't actually need a regulated supply unless you want to squeeze every last mW of output from it. You just need to ensure that the off load voltage isn't excessive (say 10V for a PP9 set) and that the voltage doesn't sag too much at reasonable volume levels. A regulated supply is preferable, but it does add cost, complexity and a little noise.

kalee20 · 24th Jul 2018, 12:44 pm

I've had noise issues with the LM317 - I was using it to regulate the 2V filament supply to a 3-valve radio, but could hardly hear stations through the hash! It took me a while to pinpoint the source of the interference.

So now, I bypass regulators as near as possible to the IC. And for sensitive applications, I use a downstream LC filter. Yes, it hurts regulation a bit, but so far that has not been a problem.

Boater Sam · 24th Jul 2018, 12:45 pm

Quote:

Originally Posted by paulsherwin

You probably know this already, but a typical transistor radio doesn't actually need a regulated supply unless you want to squeeze every last mW of output from it. You just need to ensure that the off load voltage isn't excessive (say 10V for a PP9 set) and that the voltage doesn't sag too much at reasonable volume levels. A regulated supply is preferable, but it does add cost, complexity and a little noise.

Understood Paul but I have found that transformer wall warts have only a bridge rectifier and electrolytic cap inside and the voltage can be over 15v off load.
Even with the load of a 7 transistor radio they are over 11v sometimes, my germaniums don't like it.
I often use 12v warts regulated down to 9v as I have a seemingly endless supply.
Sam.

Terry_VK5TM · 25th Jul 2018, 1:55 am

There are more modern versions of the LM317 - LM1117 etc - but the trade off is lower current handling (800mA for the '1117) and lower maximum input (20v).

Old adage - if it ain't broke, don't fix it, just stock up on the LM317.

AC/HL · 25th Jul 2018, 11:29 am

For basic uses like this, a simple zener stabiliser would be more than adequate.

23rd Jul 2018, 7:35 pm	#1
Boater Sam Banned Join Date: Dec 2013 Location: Middlewich, Cheshire, UK. & Winter in the Philippines. Posts: 3,897	Improved regulation. Whilst constructing wall warts for my transistor radio collection, I make PP7, PP9 and PP10 falsies using surplus non regulated 9v and 12v power packs, I use mainly LM317T adjustable regulators. With these I can make power packs from 6v to 18v with ease. I have found them to be good, minimal hash on the radios, robust and cheap. But I have been making these for years. Stocks are running low. At 99p for 10 from China they are outstanding value. The thought occurred that things have moved on and I should maybe update to something better next time I restock. Is there a better regulator at a fair price? No surface mount tech though!

23rd Jul 2018, 8:09 pm	#2
Nuvistor Dekatron Join Date: Aug 2013 Location: Wigan, Greater Manchester, UK. Posts: 9,433	Re: Improved regulation. At 99p for 10 I would get 100, should last you a while and you have proven design that works. I would only look for something new when you are near then end of the 100. __________________ Frank

23rd Jul 2018, 9:19 pm	#3
dseymo1 Retired Dormant Member Join Date: Dec 2007 Location: Shropshire, UK. Posts: 3,051	Re: Improved regulation. You've been lucky! I bought a few from China a while ago; they regulated OK, but went O/C as soon as they were asked to pass a few mA.

24th Jul 2018, 6:38 am	#4
Diabolical Artificer Dekatron Join Date: Jul 2009 Location: Sleaford, Lincs. UK. Posts: 7,670	Re: Improved regulation. Looked on Farnell - http://uk.farnell.com/w/search/prl/r...earchlookahead and they have 64,000, but look underneath and it looks like you could be right Sam. However it says this - Market demand for this product has caused an extension in lead times, delivery dates may fluctuate. I use the LM317AHV which is a bit higher voltage. If it ain't broke..... Andy. __________________ Curiosity hasn't killed this cat...so far.

24th Jul 2018, 8:14 am	#5
Mooly Octode Join Date: May 2011 Location: Lancashire, UK. Posts: 1,351	Re: Improved regulation. The abilities of the regulator as seen at its destination are severely diminished simply due to the effects of the cable from wall wart to equipment. In other words the advantage of increasing the regulator performance, even many times over, is totally swamped by the remote location of the regulator.

24th Jul 2018, 8:57 am	#6
Boater Sam Banned Join Date: Dec 2013 Location: Middlewich, Cheshire, UK. & Winter in the Philippines. Posts: 3,897	Re: Improved regulation. A case for 98% silver gold plated one way HiFi audiophool cable then? It was not the precision of regulation I was concerned with, rather the purity of the DC without hash. I used to use 78xx series regulators with base resistors to trim the output voltage but found that the output had a lot of switching pulses that cause background noise sometimes. Sam.

24th Jul 2018, 9:42 am	#7
turretslug Dekatron Join Date: Nov 2011 Location: Surrey, UK. Posts: 4,400	Re: Improved regulation. The 78/79xx series have a noisy internal reference followed by what is effectively a wideband, low impedance power amp making output noise very difficult to eliminate- some RF applications end up using pi-filtering on the output. Perhaps in the case of the 7805, they were expected to have extensive rail filtering for spiky logic applications anyway, so device noise wasn't a high concern. The LM317 family use a much quieter bandgap reference. It may be an oldie, but I like the 723, as the reference is available at a pin and can be filtered as much as you like before applying to the rest of the circuit- it does need external pass transistors for any appreciable output current and several other peripheral components though, so not quite an easy modular block like three-terminal regulators.

24th Jul 2018, 10:28 am	#8
paulsherwin Moderator Join Date: Jun 2003 Location: Oxford, UK Posts: 27,972	Re: Improved regulation. You probably know this already, but a typical transistor radio doesn't actually need a regulated supply unless you want to squeeze every last mW of output from it. You just need to ensure that the off load voltage isn't excessive (say 10V for a PP9 set) and that the voltage doesn't sag too much at reasonable volume levels. A regulated supply is preferable, but it does add cost, complexity and a little noise.

24th Jul 2018, 12:44 pm	#9
kalee20 Dekatron Join Date: Feb 2007 Location: Lynton, N. Devon, UK. Posts: 7,088	Re: Improved regulation. I've had noise issues with the LM317 - I was using it to regulate the 2V filament supply to a 3-valve radio, but could hardly hear stations through the hash! It took me a while to pinpoint the source of the interference. So now, I bypass regulators as near as possible to the IC. And for sensitive applications, I use a downstream LC filter. Yes, it hurts regulation a bit, but so far that has not been a problem.

25th Jul 2018, 1:55 am	#11
Terry_VK5TM Nonode Join Date: Oct 2010 Location: Tintinara, South Australia, Australia Posts: 2,343	Re: Improved regulation. There are more modern versions of the LM317 - LM1117 etc - but the trade off is lower current handling (800mA for the '1117) and lower maximum input (20v). Old adage - if it ain't broke, don't fix it, just stock up on the LM317. __________________ Terry VK5TM https://www.vk5tm.com/

25th Jul 2018, 11:29 am	#12
AC/HL Dekatron Join Date: Nov 2003 Location: Heckmondwike, West Yorkshire, UK. Posts: 9,643	Re: Improved regulation. For basic uses like this, a simple zener stabiliser would be more than adequate.