Forum sponsored by:

benchtop power supply

Search for: in Thread Title in

Terryd	12/09/2011 00:04:03
1946 forum posts 179 photos	Posted by Steve Garnett on 11/09/2011 23:27:46: ..............................................And Terry, that's a gap-bed lathe. If you size it by looking at the imperial bricks in the wall behind it (about 3 rows/ft), the faceplate on it has to be best part of 6' diameter, so I reckon that an 8' chuck is just about within its capability. You probably wouldn't lose the chuck key in a hurry though... Hi Steve, You may be right, I wouldn't quibble. I remember working at Davey Ashmore in Teeside and we were casting hopper bells for blast furnaces and I seem to remember that the charging bell was about 24 ft diameter and the loading bell about 12ft diameter. These were pit cast and then turned on what might be called vertical lathes (after much fettling and prepping) to create the sealing ring around the edge of the bells. Fascinating stuff, and this equipment was destined for the steel plants of N Spain around St Sebastian I believe - if my memory serves me well , these were along with some enormous rotating molten steel torpedo railway trucks we designed for the plant in order to move molten iron from the blast furnace to the basic oxygen converters in it's molten state without the cooling stage of pig iron production, Nostalgia ain't what it used to be (sigh) Best regards Terry Edited By Terryd on 12/09/2011 00:06:54
Ian S C	12/09/2011 15:37:42
7468 forum posts 230 photos	OOPS, sorry to disapoint you Terry, its only a 8" chuck, quite large enough for me. Got a mate just down the road how has a lathe with 16" chucks, I think its a Pratt with about a 6' bed,1930 vintage, hes just got a Colchester of a similar age, and not much smaller, have not had a good look at it. He seems to collect worn out vintage machinery, that includes tractors. Ian S C
ian weeks	13/09/2011 22:43:48
33 forum posts	Thanks les for the information and sorry about the delay in replying. had a good look at the old radio tonight and some stuff I had got together a few years ago in preparation for having a go at it . I did find a schematic for a power supply on the uk vintage radio repair and restoration website but it was for a 90v ht and 1.35v lt supply .it used a 'voltage quadruple circuit' which I didn't undersatand so put it to one side for a long winters project The radio I have is 135v ht and 2v lt I will need to spend time relearning stuff I must have Known 40 odd years ago! ,or perhaps you know of a website that would have a ready made circuit diagram? Kind regards Ian
Steve Garnett	13/09/2011 23:11:48
837 forum posts 27 photos	2v DC for the heaters is relatively easy - although it has to be pretty smooth DC or you get to hear a lot of hum. Your real difficulty is the 135v, and although a quadrupler circuit would work fine, I think (there's very little current needed), it's not the way I'd do it. What's probably easiest these days is to have a second transformer running from the secondary of the first one (the one that's supplying your heater 2v), only connected so that the primary is the output. That gives you an isolated supply back into the hundreds of volts, and a simple rectifier, reservoir cap and zener stabiliser is all you are going to need to produce an adequate 135v supply from it. You can get four 33v 5W zener diodes from Rapid electronics for 19p each, and put them in series. All you need to do then is calculate the value of resistor you'll need to drop whatever secondary voltage you end up with down to 135v, allowing for a few milliwatts through the zener chain, and you're there. If this isn't clear from the description, I can sketch it out for you. Edited By Steve Garnett on 13/09/2011 23:12:54
Steve Garnett	13/09/2011 23:25:38
837 forum posts 27 photos	For the 2v supply, you could use something like the circuit we were discussing on page one, only using a MIC29152WT variable regulator. This gives 1.5A at voltages down to 1.25v. I'm sure that those valve heaters aren't that hungry! If I recall correctly, it's only around 25mA per valve they need.
Les Jones 1	14/09/2011 09:13:52
2292 forum posts 159 photos	Hi Ian and Steve, I was going to suggest more or less the same solution as Steve as one of the possible solutions. (Assuming you want to power it from the mains and not a set of nicad cells etc.) I was thinking of using a 6 volt transformer which would be rectified, and regulated for the 2 volts with an LM317 regulator. (A switching regulator would be better but more complex as a linear regulator would have to dissipate more power than used by the valve heaters.) I think the valve heaters use about 200 mA each. I remembered the type of valve I used when I was a child to build a radio control receiver for a model boat. It was a "PM2" and I found the heater current from the web. For the 135 volts the 6 volts AC from the first transformer would be stepped up to about 100 volts AC the way Steve suggests which when rectified and smoothed would give about 140 volts DC. A transformer rated to give about 13.5 volts when used normally would give the correct voltage but the nearest you would find would be 12 volts. Another solution for the 135 volts would be a 24 - 0 - 24 transformer with a voltage doubler used in the normal way. Probably the cheapest way to get capacitors for smoothing the 135 volts is from the cheap low energy bulbs you sometimes see being sold for about 10 P each. Les.
Steve Garnett	14/09/2011 10:58:39
837 forum posts 27 photos	Well if it's a Bush portable and it uses the D series valves, most of them take either 25 or 50mA for the heaters, and even the output valves only take 100mA. What intrigues me slightly though is that these are all 1.4v heater devices. A typical late example is the Bush BP61 - uses DK96, DF96, DAF96 and DL96, and that means less than 200mA heater current in total. Which makes sense, because otherwise the L.T. battery life would have been truly awful. Ian, exactly what's the model number of yours? And are you absolutely sure it has 2v heaters? Incidentally I should perhaps mention that I used to repair these damned things for a living, and still have some of the valves! Also, I found a website with portable radio power supply information, including a link to the quadrupler design, and actually that doesn't look too bad. The page that links to it, and at least two more designs is here.
Ian S C	14/09/2011 11:49:36
7468 forum posts 230 photos	I made an HT power supply for a single valve battery set that I built years ago. It has an oscelator, 2 BC 108 , the output of these is fed into the secondry of a small power transformer, the out put from the transformer goes to a bridge rectifier, 2000uf capacitor, The open voltage is about 90 volts with a 9 volt input (The little 9V with the dome clips on top). The set uses a DAF 91. Not quite a workshop radio, its headphones only. Ian S C ps., LT is 1.5 v, so I just use a battery, either a C, or AA cell. Edited By Ian S C on 14/09/2011 11:53:17
ian weeks	14/09/2011 15:21:14
33 forum posts	Thanks everyone , I I think I follow steve and les' postings. Un fortunately I boobed in my first posting and referred to a 'bush' that is actually the old bush ac11 which is at my bedside having got in going about 10 years ago - even wife allows it as it's cabinet is lovely wood! The battery job is an eko b53 !!--sorry ! [b53 135v/2v bush 90 or so /1.25 ]Had intended to do a bit on the gear box I'm slowly making for the myford tonight when I get home but think I'll spend the time looking at the links mentioned and probable re -reading my old electronic primer- I think I know whereabouts it is in the attic!!!!!!!!! Thanks chaps -the avenues which one ends up going down are what makes this hobby so interestin regards Ian
Donhe7	14/09/2011 15:59:22
37 forum posts	Posted by ian weeks on 09/09/2011 23:31:52: Dear All, whist building the gear banjo in MEW issue82 I once again read the article in the same issue by peter rawlinson on electronics in the workshop. It took me back to the 'radio and electronics club at school many decades ago. I resolved to build the project at the end of the article as a 'nostalgia trip'. However I have a problem -the circuit shows 4 of the capacitors as 10 microfarad 35vw but the pictures show one of these as a physically much bigger beast of an electrolytic[ viz the one across the output of the bridge rectifier]. My problem is that a little bell is ringing in my head and saying that this capacitor should br bigger but my knowledge is so rusty I cant be sure and I can see no corrections to the circuit inn subsequent issues. Any advice would be appreciated Regards Ian Whilst not having seen the article on the power supply project, in my experience with 7805s and similar regulators, the input voltage is best kept as low as possible while still high enough to not drop below the voltage of the regulator. My own approach to the power supply situation is to use a large value electrolytic capacitor directly after the rectifier to give as smooth a supply voltage into the 78xx as possible to ensure that the ripple is virtually none existent and don't forget any low value "greencaps" on both the input and output of the 78xx, to prevent possible oscillation, which I believe is possible without them. donhe7
Steve Garnett	14/09/2011 18:57:40
837 forum posts 27 photos	Posted by Donhe7 on 14/09/2011 15:59:22: Whilst not having seen the article on the power supply project, in my experience with 7805s and similar regulators, the input voltage is best kept as low as possible while still high enough to not drop below the voltage of the regulator. The snag with this particular design as published is that it runs two regulators from a single supply, one of them being variable up to 20-something volts. So the poor old 7805 has to run from a relatively high rectified secondary voltage, because only a single secondary was shown. In an ideal world, this power supply would be better served with two secondary windings, rectifiers and reservoirs, and a much lower voltage feed to the 7805, as you suggest. Ekco B53? Ooh, that's old... uses old Mazda valves I haven't got any of. But I found a service sheet for the radio, and you need 135v at 10mA (not much) for HT, but for the heaters, you do indeed need 2v, and best part of half an amp in total to run them. (0.41A, to be precise). Which is why, when it was originally sold, it came without an accumulator to run the heaters - you had to provide that yourself as an extra. At least you could recharge that!
Les Jones 1	14/09/2011 20:16:53
2292 forum posts 159 photos	Hi Ian, I found this web page with some information on your Ekco b53 Ekco B53 info I think you have to join the forum to access the full information. Les.
Les Jones 1	14/09/2011 20:43:03
2292 forum posts 159 photos	Hi Ian, Here is some more information on your radio. Ekco B53 Site 02 Les.
Steve Garnett	14/09/2011 23:40:44
837 forum posts 27 photos	The one thing that's likely to have dried out in the radio is the two electrolytic capacitors, C23 and C25. They are relatively easy to locate, because they're mounted under clips. Because they won't have a ridiculously high working voltage, equivalents are still available - well, 160v ones are with very similar values to those shown are, anyway. I'm not suggesting that you actually buy them from RS components, because they'll make you pay for 5 or 10 of them, but to give you an idea of what you're looking for, have a look at their part numbers 707-6521 and 707-6360.
ian weeks	15/09/2011 08:31:38
33 forum posts	Thanks Steve , just read the posting and I am getting Quite fired up at the thought of having a go . will be a few weeks yet before I have enough spare time but the preparation and reading will be fun.Slowly but slowly the nuts and bolts are coming back. The only problem is explaining to my wife why I'm not concentrating on getting the steam engine prepared for the church christmas fair Santa Specials!! If [when] I run into questions I know I can count on everyone for extremely knowledgable advice---Ian
Donhe7	15/09/2011 12:48:51
37 forum posts	Posted by Steve Garnett on 14/09/2011 18:57:40: Posted by Donhe7 on 14/09/2011 15:59:22: Whilst not having seen the article on the power supply project, in my experience with 7805s and similar regulators, the input voltage is best kept as low as possible while still high enough to not drop below the voltage of the regulator. The snag with this particular design as published is that it runs two regulators from a single supply, one of them being variable up to 20-something volts. So the poor old 7805 has to run from a relatively high rectified secondary voltage, because only a single secondary was shown. In an ideal world, this power supply would be better served with two secondary windings, rectifiers and reservoirs, and a much lower voltage feed to the 7805, as you suggest. Agreed about the "poor old 7805", not an ideal situation. Pity a multi tapped or multi secondary transformer could not be used, the other alternative would be to use the pre-regulated supply for the input to the 7805, if it is possible to do so. With regard to the "battery valved" radio, there was a series about powering this type of equipment in an edition of an Australian "Silicon Chip" magazine some time ago, I think it was in the Historical Radio section, and if I recall correctly, used a transformer and voltage doubler circuit for the HT supply, but I cannot recall how the filament voltage was obtained. donhe7
Steve Garnett	15/09/2011 14:17:34
837 forum posts 27 photos	It's worth noting that it's the filament voltage you need to be careful with here - that's the one you don't want to overdo - but there again, you don't want to underdo it too much either. The HT supply is considerably less critical. Many of these older radios ran quite well on significantly lower voltages than they were intended to. There were rumours that with some radios of this type, you could still get results with the voltage down to 20-30! Don't think that they'd be very loud though.
Gordon W	15/09/2011 16:08:14
2011 forum posts	Why not do a full home workshop job? Make a lead acid battery and a vibrator to get the HT ? Sure there must be plenty of info. on t.net.
ian weeks	16/09/2011 19:12:37
33 forum posts	Dear All , Thank you all for your advice and help . Cruised past Maplins today and just had to stop. Between them and bits in the shed and attic nearly enough to make a start . the trouble is the reading and thinking bit is fun!! I have had a look at the 'stennings' circuit diagram and the LT circuit looks a goer for the required 2v[by adjusting the resistor values across the lm317]. Having taken on board your comments about the ht circuit and having 230v twin 24v output and 230v twin 18v output transformers in the spares [come in handy one day box] is the idea of using one of these as a 'step' up from the 15v seecondary winding a starter as per your earlier suggestion rather than the straigh't voltage quadruple' circuit shown? A. bearing in mind I'm a tyro and B. I would love to understand the voltage quadrupler circuit but don't [ Am on amazon for a more modern primer tonight].also just thought If used 24v transformer totally seperately wouldn't that get me pretty damn near required 138v using quadrupler circuit-- then drop it -feel free to shoot me down in flames. Thanks again Ian Oh And another project has arisen -Have had a chester e30 mill for 2 years lovely little machine little use as I mainly use my Theil but noticed an irritating jerk on the x axis when milling My friend came round tonight and helped me remove table- no wear on screw or nut or tangential gibs -all pristine BUT would you believe the machined feed screw nut has no positive location just 2 capscrews wich allow lateral movement no locating peg or key -nut thread pristine - looks like a big job to provide a positive location for the nut and or a longer acme thread cutting and milling new purpose built nut. The words ship and ha'pence o' tar come to mind !!-- Ian
ian weeks	16/09/2011 19:26:10
33 forum posts	Dear All - following on from 5 minutes ago ??just use 24v for both circuits and adjust values of components before lm317 ?? I would probably get calcs wrong!-Ian

<< First < Prev 1 2 3 Next > Last >>

All Topics | Latest Posts

Please login to post a reply.

Magazine Locator

Want the latest issue of Model Engineer or Model Engineers' Workshop? Use our magazine locator links to find your nearest stockist!

Find Model Engineer & Model Engineers' Workshop

You can unsubscribe at anytime. View our privacy policy at www.mortons.co.uk/privacy

Latest Forum Posts

*Oct 2023: FORUM MIGRATION TIMELINE*
05/10/2023 07:57:11
Making ER11 collet chuck
05/10/2023 07:56:24
What did you do today? 2023
05/10/2023 07:25:01
Orrery
05/10/2023 06:00:41
Wera hand-tools
05/10/2023 05:47:07
New member
05/10/2023 04:40:11
Problems with external pot on at1 vfd
05/10/2023 00:06:32
Drain plug
04/10/2023 23:36:17
digi phase converter for 10 machines.....
04/10/2023 23:13:48
Winter Storage Of Locomotives
04/10/2023 21:02:11
More Latest Posts...
View All Topics

Support Our Partners

Shopping Partners

Subscription Offer

Latest "For Sale" Ads

Reeves** - Rebuilt Royal Scot by Martin Evans
by John Broughton
£300.00
BRITANNIA 5" GAUGE James Perrier
by Jon Seabright 1
£2,500.00
Drill Grinder - for restoration
by Nigel Graham 2
£0.00
WARCO WM18 MILLING MACHINE
by Alex Chudley
£1,200.00
MYFORD SUPER 7 LATHE
by Alex Chudley
£2,000.00
More "For Sale" Ads...

Latest "Wanted" Ads

D1-3 backplate
by Michael Horley
Price Not Specified
fixed steady for a Colchester bantam mark1 800
by George Jervis
Price Not Specified
lbsc pansy
by JACK SIDEBOTHAM
Price Not Specified
Pratt Burnerd multifit chuck key.
by Tim Riome
Price Not Specified
BANDSAW BLADE WELDER
by HUGH
Price Not Specified
More "Wanted" Ads...

Get In Touch!

Do you want to contact the Model Engineer and Model Engineers' Workshop team?

You can contact us by phone, mail or email about the magazines including becoming a contributor, submitting reader's letters or making queries about articles. You can also get in touch about this website, advertising or other general issues.

Click THIS LINK for full contact details.

For subscription issues please see THIS LINK.

Digital Back Issues