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Components and Circuits For discussions about component types, alternatives and availability, circuit configurations and modifications etc. Discussions here should be of a general nature and not about specific sets. |
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22nd Dec 2012, 6:40 pm | #1 |
Triode
Join Date: Aug 2005
Location: Woking, Surrey, UK.
Posts: 34
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120 volt battery
All,
I've just got a GEC 4046 on the workbench. Problem 1: what to do about batteries. I've seen a number of designs for 90volt eliminators but does anyone know the whereabouts of a 120 volt eliminator (perhaps with 2 volts for the LT)? I'd prefer not to take the multiple PP3 route if at all possible. Thanks Simon |
22nd Dec 2012, 7:34 pm | #2 |
Dekatron
Join Date: Jan 2004
Location: Newcastle upon Tyne, Tyne & Wear, UK.
Posts: 8,194
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Re: 120 volt battery
Hi Simon, cheap PP3's are a good start for testing, but for real use you need an eliminator.
A lot of the designs use voltage multipliers from a lowish voltage to derive the 90 volts; simply add an additional stage of diode and resistor. The theory is normally found if you Google "cockroft/ walton voltage multiplier". The LT supply is usually from an LM317 regulator chip with a bit of crafty circuitry to get it to work down to 2 volts, with possibly a crowbar circuit to protect valuable filaments. You may also need a GB supply, which can be virtually anything with a chain of resistive dividers for the voltages required. Ed |
22nd Dec 2012, 7:34 pm | #3 |
Dekatron
Join Date: Feb 2005
Location: West Cumbria (CA13), UK
Posts: 6,127
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Re: 120 volt battery
Why not?
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22nd Dec 2012, 7:44 pm | #4 |
Dekatron
Join Date: Feb 2009
Location: Chesterfield, Derbyshire, UK.
Posts: 3,755
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Re: 120 volt battery
You could use an LT mains transformer and back feed the secondary with the appropriate voltage to arrive at 100/110V secondary. It works for me.
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22nd Dec 2012, 9:00 pm | #5 |
Dekatron
Join Date: Jan 2005
Location: Oxford, UK.
Posts: 17,843
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Re: 120 volt battery
Good quality PP3s need not be expensive, e.g. http://www.ebay.co.uk/itm/10-DURACEL...item230b9cf162
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22nd Dec 2012, 9:13 pm | #6 |
Guest
Posts: n/a
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Re: 120 volt battery
A 20V RMS transformer with two voltage doublers one positive and one negative would give about 120V. With modern cheap large capacitors there will be no hum. Or this https://www.vintage-radio.net/forum/...ad.php?t=66030 would last for ages.
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22nd Dec 2012, 9:58 pm | #7 |
Retired Dormant Member
Join Date: May 2009
Location: Norwich, Norfolk, UK.
Posts: 717
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Re: 120 volt battery
I tend to put two transformers back to back, i.e. the 2nd in reverse. The low AC voltage can be rectified and regulated for the heaters (and any dial lamps) and the higher AC voltage can be half wave rectified and a single smoothing cap used for the 120 volts. A suitable resistor will drop any excess voltage as the current is low.
I buy cheap wallwart adaptors from car boots for this purpose. Rob |
23rd Dec 2012, 1:02 am | #8 |
Hexode
Join Date: Nov 2009
Location: Chertsey, Surrey, UK.
Posts: 456
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Re: 120 volt battery
I have tried cheap wallwart type adapters but most have terrible regulation, but I have used two wallwart type transformers back to back and neon voltage regulation tube controlled transistor to make a 230v in 90v isolated and regulated power supply.
The older heavier wallwart type adapters have better regulation. |
23rd Dec 2012, 9:40 am | #9 |
Retired Dormant Member
Join Date: May 2009
Location: Norwich, Norfolk, UK.
Posts: 717
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Re: 120 volt battery
Regulation of the ht supply does not seem to much of an issue as long as it does not rise too high. I did try using an LM317 but it didn't offer any improvement in use.
The current drawn by these battery sets is only a few milliamps and easily supplied by a small transformer. Regulation of the LT side is of course far more important as the battery valve filaments are fragile but a LM317 copes well as it only has to drop a couple of volts at low current. Rob |
23rd Dec 2012, 5:49 pm | #10 |
Dekatron
Join Date: Feb 2007
Location: Leominster, Herefordshire, UK.
Posts: 16,535
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Re: 120 volt battery
Not particularly crafty. A LM317 works down to 1.25V (tail direct to 0V a la 7805 etc) and any higher voltage within its limits just needs two resistors to program. Add a couple of capacitors for stability and a heatsink if it's dissipating more than about a watt and that's it- apart from extras like crowbars or why.
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23rd Dec 2012, 6:20 pm | #11 | |
Triode
Join Date: Aug 2005
Location: Woking, Surrey, UK.
Posts: 34
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Re: 120 volt battery
Quote:
Any volunteers or thoughts on specification beyond covering HT 90 and 120V and LT 2V? |
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23rd Dec 2012, 6:47 pm | #12 |
Guest
Posts: n/a
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Re: 120 volt battery
I made this https://www.vintage-radio.net/forum/...2&d=1227122816 it has 60, 90 & 120V HT, 2V LT and variable negative grid bias, one of the advantages of using the voltage multiplier approach is that you can easily tap down for various HTs.
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23rd Dec 2012, 8:03 pm | #13 |
Rest in Peace
Join Date: Apr 2011
Location: Matlock, Derbyshire, UK.
Posts: 1,378
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Re: 120 volt battery
And here is another. There are many ways of doing the job, just use what components you have.
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27th Dec 2012, 3:33 pm | #14 | |
Dekatron
Join Date: Feb 2007
Location: Lynton, N. Devon, UK.
Posts: 7,079
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Re: 120 volt battery
Quote:
You do need to do this as a few microvolts of broadband noise on the LT line is effectively in series with the input signal! |
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27th Dec 2012, 8:35 pm | #15 |
Dekatron
Join Date: Jan 2004
Location: Newcastle upon Tyne, Tyne & Wear, UK.
Posts: 8,194
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Re: 120 volt battery
As Kalee20 has said, LM 317's need a big cap on the output. Best combination is an e-cap and a 0.1 plastic type. You should then also add a diode in inverse parallel back across the chip. This is to discharge the output cap at the same rate as the input.
If the input goes down first the chip is quite likely to die. Ed |
27th Dec 2012, 9:48 pm | #16 |
Dekatron
Join Date: May 2008
Location: Derby, UK.
Posts: 7,735
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Re: 120 volt battery
Not a plastic 100nF, ideally, but a ceramic one; which has a lower self-inductance.
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28th Dec 2012, 7:35 pm | #17 |
Dekatron
Join Date: Feb 2007
Location: Lynton, N. Devon, UK.
Posts: 7,079
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Re: 120 volt battery
That may be an old wives' tale. Most small plastic capacitors are metallised film with sprayed-on end electrode connections, thus effectively forming the same geometry as multilayer ceramics.
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29th Dec 2012, 8:15 pm | #18 |
Retired Dormant Member
Join Date: May 2008
Location: Preston, Lancashire, UK.
Posts: 428
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Re: 120 volt battery
Small PCB transformers are quite cheap. I just take three of them with 250V primaries and 15-0-15 secondrys. Connect the primaries in parallel across the mains. Connect the three ends of the 15-0-15 (30V) in series and you get 90V AC. Feed this into a normal bridge rectifier and smoothing circuit and it comes out at about 120 Volts. Rather simple, but it works OK for me.
Bob |