Farnell Bench Power Supply LT30-2 - UK Vintage Radio Repair and Restoration Discussion Forum

MightyMouse · 11th Sep 2010, 5:37 am

Hello,

I've just acquired a: Farnell Bench Power Supply Model LT30-2

0 to 30V at 2Amp's x 2 with analogue meters and current limiting.

I'm hoping that someone has a copy of the service manual or the circuit diagram.

Thank you

Stockden · 11th Sep 2010, 9:24 am

Hi,

I have a copy of the manual in PDF. Let me have your email address via a PM and I'll send it to you.

Hugh

MightyMouse · 11th Sep 2010, 11:06 am

That's great. Thank you.

Clint

AC/HL · 11th Sep 2010, 7:04 pm

Thanks Hugh for my copy too

Dickie · 12th Sep 2010, 9:41 am

And thanks for mine as well

Stockden · 12th Sep 2010, 11:05 am

Glad to have been of service!

Hugh

percih70 · 21st Apr 2011, 11:39 pm

Hello

New to vintage radio but I also need a circuit drawing for a Farnell LT30-1 - great if you could help.

Regards

Harry

Stockden · 22nd Apr 2011, 8:51 am

Hello Harry,

The same manual covers both variants. Since I seem to get regular requests for this manual (and the file size is within the forum limits) I've posted it here.

Hugh

WME_bill · 22nd Apr 2011, 4:14 pm

for MightyMouse. The early versions of the Farnell LT30 series used discrete active devices in the error amplifiers, instead of the IC's. If the IC version of 1976 helpfully posted by Stockden does not match yours, send me a PM for the circuit of the Discrete 1975 version. The text of the manual is the same. The LT30-1 is rated 1amp, LT30-2 is 2Amp. The LT30-5 is 5 Amp, with more series transistors. All models 30V. Bill m0wpn

fastfourier · 2nd May 2011, 6:34 am

Hi WME_bill,

I've got a really old LT30-2! I had no idea it was that old - but yep, it's all transistors. I would much appreciate it if you could send me the circuit! One side of it is kaput!

thanks

owen

WME_bill · 2nd May 2011, 9:12 pm

for FastFourier. I attach the circuit diagrams for versions of the LT30 power unit. You will note that by chance the discrete is the 1amp version, and the IC is the 2amp version, so has a few more series pass transistors. Bill m0wpn

Mooly · 13th May 2011, 7:52 am

Many thanks to Stockden and WME bill for the diagrams. A diagram makes it so much easier than "busking" it when working on anything.

I have two of the 30v 1 amp PSU's picked up at a NARSA event around 20 years ago. Both have been faultless... and one of them I modded with a small "opamp/ transistor" virtual earth arrangement connected to the (unused for me) sense terminal. So as well as 0 to 30 volts I have a split rail - /0/ + of whatever the main output is set too... for example setting the output to 24 volts gives -12/0/+12 etc at up to 100ma. Very useful.

So thanks again...

ARMUREF5F · 9th Aug 2011, 6:59 pm

Thanks for the PDF file.
I can now repair my L30-5 PSu
best regards

Tim · 10th Aug 2011, 12:48 pm

From comparison of the transistor versions of the LT30-1 and LT30-2, I think it's possible to convert the former into the latter by simple addition of an extra 2N3055 and resistor and modification of the meter shunt/s. One would have to do some mathematical jiggery pokery interpreting the current scale too of course. But it doesn't look impossible.

I was just wondering as I have a spare unit.

What do others think?

ronbryan · 10th Aug 2011, 4:48 pm

Is the mains transformer and main rectifier the same for both the 1A and 2A version?

Ron

Tim · 10th Aug 2011, 8:35 pm

Not sure, but not difficult to change. It's about a 3" cube. (45-0-45) The other winding is rectified and used to power the innards and for sense/reference, but I would imagine current consumption is negligible.
The rectifier diodes might have to uprated too, again not difficult.

richard.cs · 19th Oct 2013, 12:04 pm

I know I'm reviving an old thread here but I thought this might be useful or of interest to people.

My I've just had my LT30-2 apart, fixed it and then gone hunting for manuals and schematics, a little bit in the wrong order maybe. Mine is the discrete transistor one and both of the current limit LEDs had failed. I wasn't expecting it to be so old until I opened it up! Date codes put it about 1977.

Anyhow these LEDs appear to be connected as shown on the schematic but were clearly not foreseen when the PCB was laid out with components stretched to the wrong pads, etc. I've also got a few other components slung across the back of the PCB that aren't on the schematic at all. For example I have a capacitor B-C across VT4. The power on LED appears to have been slung across the 50V d.c. supply rather than run half-wave from the transformer. I've taken a good selection of photos whilst it's apart.

high_vacuum_house · 20th Sep 2015, 7:27 pm

Good evening,
I have just been fixing my L30-2 power supply. Many thanks for the manual the circuit diagram helped a lot

One of the coarse voltage adjustment pots had gone crackly and the o/p voltage could jump wildly if you booted the table.

I decided to replace the coarse voltage pot with a 10 turn Spectrol 5K lin resistor. This really improves the voltage control and I can now tweak the output to within 10 to 20mV of a desired output. I am really happy with this modification and I might repeat this with the other channel and possibly the current limiting controls.

I also replaced a snapped off banana terminal but beware as I found out the hard way, some of the Maplin banana terminals the threaded portion is a little larger in diameter and would not fit through the little output PCB behind the terminals.

A quick clean and also to remove all of the old calibration and PAT testing stickers and it is a really nice bench power supply.

Many thanks,
Christopher Capener

Refugee · 20th Sep 2015, 10:23 pm

I have kept a copy of the PDFs as I own a single channel model and they will be useful if anything goes wrong with it.
Cheers.
Ref.

emeritus · 22nd Sep 2015, 10:57 am

I have saved the PDFs as well for possible use with my own L30. The coarse voltage adjustment of mine has also gone crackly, but in a part of the range I do not normally use: another "round tuit" job!

I remember a Farnell advert of some 30 years ago consisting of a photo of an original L-30 standing next to their then-current model, with the caption "Our Biggest Rival", and a comment to the effect that their main competition to sales was the large number of their highly reliable older models still performing sterling service.

11th Sep 2010, 5:37 am	#1
MightyMouse Retired Dormant Member Join Date: Jun 2010 Location: London, UK. Posts: 2	Farnell Bench Power Supply LT30-2 Hello, I've just acquired a: Farnell Bench Power Supply Model LT30-2 0 to 30V at 2Amp's x 2 with analogue meters and current limiting. I'm hoping that someone has a copy of the service manual or the circuit diagram. Thank you

11th Sep 2010, 9:24 am	#2
Stockden Heptode Join Date: Mar 2008 Location: Forest of Dean, Gloucestershire, UK. Posts: 648	Re: Farnell Bench Power Supply LT30-2 Hi, I have a copy of the manual in PDF. Let me have your email address via a PM and I'll send it to you. Hugh

11th Sep 2010, 11:06 am	#3
MightyMouse Retired Dormant Member Join Date: Jun 2010 Location: London, UK. Posts: 2	Re: Farnell Bench Power Supply LT30-2 That's great. Thank you. Clint

11th Sep 2010, 7:04 pm	#4
AC/HL Dekatron Join Date: Nov 2003 Location: Heckmondwike, West Yorkshire, UK. Posts: 9,642	Re: Farnell Bench Power Supply LT30-2 Thanks Hugh for my copy too

12th Sep 2010, 9:41 am	#5
Dickie Octode Join Date: Sep 2004 Location: St. Albans, Hertfordshire, UK. Posts: 1,478	Re: Farnell Bench Power Supply LT30-2 And thanks for mine as well __________________ Regards, Richard, BVWS member

12th Sep 2010, 11:05 am	#6
Stockden Heptode Join Date: Mar 2008 Location: Forest of Dean, Gloucestershire, UK. Posts: 648	Re: Farnell Bench Power Supply LT30-2 Glad to have been of service! Hugh

21st Apr 2011, 11:39 pm	#7
percih70 Retired Dormant Member Join Date: Apr 2011 Location: Glasgow, UK. Posts: 1	Re: Farnell Bench Power Supply LT30-2 Hello New to vintage radio but I also need a circuit drawing for a Farnell LT30-1 - great if you could help. Regards Harry

22nd Apr 2011, 4:14 pm	#9
WME_bill Octode Join Date: Oct 2007 Location: Exeter, Devon, UK. Posts: 1,554	Re: Farnell Bench Power Supply LT30-2 for MightyMouse. The early versions of the Farnell LT30 series used discrete active devices in the error amplifiers, instead of the IC's. If the IC version of 1976 helpfully posted by Stockden does not match yours, send me a PM for the circuit of the Discrete 1975 version. The text of the manual is the same. The LT30-1 is rated 1amp, LT30-2 is 2Amp. The LT30-5 is 5 Amp, with more series transistors. All models 30V. Bill m0wpn

2nd May 2011, 6:34 am	#10
fastfourier Retired Dormant Member Join Date: May 2011 Location: Toronto, Canada Posts: 1	Re: Farnell Bench Power Supply LT30-2 Hi WME_bill, I've got a really old LT30-2! I had no idea it was that old - but yep, it's all transistors. I would much appreciate it if you could send me the circuit! One side of it is kaput! thanks owen Last edited by Brian R Pateman; 2nd May 2011 at 7:23 am. Reason: Quote of preceding post is not required.

13th May 2011, 7:52 am	#12
Mooly Octode Join Date: May 2011 Location: Lancashire, UK. Posts: 1,351	Re: Farnell Bench Power Supply LT30-2 Many thanks to Stockden and WME bill for the diagrams. A diagram makes it so much easier than "busking" it when working on anything. I have two of the 30v 1 amp PSU's picked up at a NARSA event around 20 years ago. Both have been faultless... and one of them I modded with a small "opamp/ transistor" virtual earth arrangement connected to the (unused for me) sense terminal. So as well as 0 to 30 volts I have a split rail - /0/ + of whatever the main output is set too... for example setting the output to 24 volts gives -12/0/+12 etc at up to 100ma. Very useful. So thanks again...

9th Aug 2011, 6:59 pm	#13
ARMUREF5F Retired Dormant Member Join Date: Aug 2011 Location: Albi, France Posts: 1	Re: Farnell Bench Power Supply LT30-2 Thanks for the PDF file. I can now repair my L30-5 PSu best regards

10th Aug 2011, 12:48 pm	#14
Tim Dekatron Join Date: Jan 2003 Location: Bradford on Avon, Wiltshire, UK. Posts: 3,310	Re: Farnell Bench Power Supply LT30-2 From comparison of the transistor versions of the LT30-1 and LT30-2, I think it's possible to convert the former into the latter by simple addition of an extra 2N3055 and resistor and modification of the meter shunt/s. One would have to do some mathematical jiggery pokery interpreting the current scale too of course. But it doesn't look impossible. I was just wondering as I have a spare unit. What do others think? __________________ "Nothing is as dangerous as being too modern;one is apt to grow old fashioned quite suddenly."

10th Aug 2011, 4:48 pm	#15
ronbryan Octode Join Date: Jan 2003 Location: Guildford, Surrey, UK. Posts: 1,960	Re: Farnell Bench Power Supply LT30-2 Is the mains transformer and main rectifier the same for both the 1A and 2A version? Ron

10th Aug 2011, 8:35 pm	#16
Tim Dekatron Join Date: Jan 2003 Location: Bradford on Avon, Wiltshire, UK. Posts: 3,310	Re: Farnell Bench Power Supply LT30-2 Not sure, but not difficult to change. It's about a 3" cube. (45-0-45) The other winding is rectified and used to power the innards and for sense/reference, but I would imagine current consumption is negligible. The rectifier diodes might have to uprated too, again not difficult. __________________ "Nothing is as dangerous as being too modern;one is apt to grow old fashioned quite suddenly."

19th Oct 2013, 12:04 pm	#17
richard.cs Triode Join Date: Feb 2011 Location: Southampton, Hampshire, UK. Posts: 46	Re: Farnell Bench Power Supply LT30-2 I know I'm reviving an old thread here but I thought this might be useful or of interest to people. My I've just had my LT30-2 apart, fixed it and then gone hunting for manuals and schematics, a little bit in the wrong order maybe. Mine is the discrete transistor one and both of the current limit LEDs had failed. I wasn't expecting it to be so old until I opened it up! Date codes put it about 1977. Anyhow these LEDs appear to be connected as shown on the schematic but were clearly not foreseen when the PCB was laid out with components stretched to the wrong pads, etc. I've also got a few other components slung across the back of the PCB that aren't on the schematic at all. For example I have a capacitor B-C across VT4. The power on LED appears to have been slung across the 50V d.c. supply rather than run half-wave from the transformer. I've taken a good selection of photos whilst it's apart.

20th Sep 2015, 7:27 pm	#18
high_vacuum_house Octode Join Date: May 2003 Location: Belper Derbyshire Posts: 1,935	Re: Farnell Bench Power Supply LT30-2 Good evening, I have just been fixing my L30-2 power supply. Many thanks for the manual the circuit diagram helped a lot One of the coarse voltage adjustment pots had gone crackly and the o/p voltage could jump wildly if you booted the table. I decided to replace the coarse voltage pot with a 10 turn Spectrol 5K lin resistor. This really improves the voltage control and I can now tweak the output to within 10 to 20mV of a desired output. I am really happy with this modification and I might repeat this with the other channel and possibly the current limiting controls. I also replaced a snapped off banana terminal but beware as I found out the hard way, some of the Maplin banana terminals the threaded portion is a little larger in diameter and would not fit through the little output PCB behind the terminals. A quick clean and also to remove all of the old calibration and PAT testing stickers and it is a really nice bench power supply. Many thanks, Christopher Capener __________________ Interests in the collection and restoration of Tefifon players and 405 line television

20th Sep 2015, 10:23 pm	#19
Refugee Dekatron Join Date: Apr 2012 Location: Worksop, Nottinghamshire, UK. Posts: 5,553	Re: Farnell Bench Power Supply LT30-2 I have kept a copy of the PDFs as I own a single channel model and they will be useful if anything goes wrong with it. Cheers. Ref.

22nd Sep 2015, 10:57 am	#20
emeritus Dekatron Join Date: Jan 2012 Location: Brentwood, Essex, UK. Posts: 5,339	Re: Farnell Bench Power Supply LT30-2 I have saved the PDFs as well for possible use with my own L30. The coarse voltage adjustment of mine has also gone crackly, but in a part of the range I do not normally use: another "round tuit" job! I remember a Farnell advert of some 30 years ago consisting of a photo of an original L-30 standing next to their then-current model, with the caption "Our Biggest Rival", and a comment to the effect that their main competition to sales was the large number of their highly reliable older models still performing sterling service.