|
Homebrew Equipment A place to show, design and discuss the weird and wonderful electronic creations from the hands of individual members. |
|
Thread Tools |
21st Mar 2020, 1:24 pm | #1 |
Octode
Join Date: Mar 2020
Location: Blackburn with Darwen, Lancashire, UK.
Posts: 1,572
|
Building a collection of bits so I can play. Ex mil and Ebay
I hope this section is relevant to this? Please move if not.
As I am now sort of retired and wishing to play more in electronics, I had a hankering to get back into valves of some form, so looking around as one does on Ebay, came across a site selling old cold war comms gear. I picked up a couple of 'guard receivers' from and aircraft set, they basically have wire ended valves of the type ECC70 and EF732, in mil spec. These are a.m. receivers for 243MHz , initially I want to check they work, but lack a few things such as a proper pin out and suitable power supply. To sort out the power supply I have decided to look into a couple of buck type HT units on Ebay again, one as pictured below has just turned up. 12 Volts input and variable up to a couple of hundred volts. The output is up to +390 Volts, 0 Volts - 390 Volts from 8 to 32 volts DC input, the 0 Volts is tied to the 0 Volts input so it not isolated for the DC input. the plan is to use this with another DC step down buck regulator to give me 6.3 Volts DC from 12 Volts. I am just wondering if anyone else on the forum has done this before me and can suggest any pit falls, or, if anyone else has played with the guard receivers and got them to work? The next stage will be to strip one of the receivers and build something with the bits. Adrian |
21st Mar 2020, 2:21 pm | #2 |
Nonode
Join Date: Dec 2012
Location: Stockport, Greater Manchester, UK.
Posts: 2,106
|
Re: Building a collection of bits so I can play. Ex mil and Ebay
Wow, "DC-DC Step Up Down Boost Buck Voltage Converter Module +45-390V / ±45-390V", pos and neg outputs, 390V max at up to 5A total, must order one
__________________
- Julian It's good here |
21st Mar 2020, 2:36 pm | #3 |
Octode
Join Date: Mar 2020
Location: Blackburn with Darwen, Lancashire, UK.
Posts: 1,572
|
Re: Building a collection of bits so I can play. Ex mil and Ebay
You confused me there, the maximum input current is 5 Amps it says the output maximum could be 40 watts, to keep it more reliable I doubt I would ever push it past 25 watts, which at say 275 Volts would be around 90mA max. It has two holes for a small 12 Volt fan supply so I expect this would get hot if pushed.
There is a better one that I also have on order which does two outputs and is designed with a valve amp in mind, it will provide between 150 and 420 Volts for HT and 1.2 to 12 Volts for filament. Grand cost of just under £12, I was wondering about the battery portable type receivers but again until I get my hands on one would not know if the outputs are isolated or common ground. Adrian |
21st Mar 2020, 3:22 pm | #4 |
Dekatron
Join Date: Sep 2005
Location: Seaford, East Sussex, UK.
Posts: 5,997
|
Re: Building a collection of bits so I can play. Ex mil and Ebay
The most likely issue will be RF noise.
|
21st Mar 2020, 5:27 pm | #5 |
Hexode
Join Date: Apr 2012
Location: Chorley, Lancashire, UK.
Posts: 260
|
Re: Building a collection of bits so I can play. Ex mil and Ebay
I tried one of the boards which gives a filament supply plus a variable high voltage. As soon as a few milliamps were drawn the voltage dropped precipitously! I only required about 20mA but it would only deliver this at an inadequately low voltage. It failed after very little use so I built my own. I adapted Tony Thomson's design (Radio Bygones issue 163) to run off 12v rather than 6v. This uses a couple of BFY transistors to produce a square wave output that is then fed to the secondary of a transformer (still available from CPC in Preston for £6.86) and then rectified. With a bit of extra smoothing this works very well as a power supply for my pantry transmitter at vintage car events - along with my Beethoven Super Minor portable radio.
Mark |
21st Mar 2020, 5:52 pm | #6 | |
Octode
Join Date: Mar 2020
Location: Blackburn with Darwen, Lancashire, UK.
Posts: 1,572
|
Re: Building a collection of bits so I can play. Ex mil and Ebay
That is quite possible, it says it runs at 75KHz so this could be an issue for receivers, possibly need to place in a metal box and add some extra filtering?
Quote:
Thanks for the heads up, I need to build a small test load. Adrian |
|
21st Mar 2020, 8:24 pm | #7 |
Dekatron
Join Date: Jan 2004
Location: Newcastle upon Tyne, Tyne & Wear, UK.
Posts: 8,194
|
Re: Building a collection of bits so I can play. Ex mil and Ebay
Hi Adrian, you may find a simple mains transformer and rectifier asa used in 50's radios works well enough. Power through a variac for variable output and used Si rectifiers.
If you really get the bug then buils a nice valve based variable voltage (and current limited HV PSU and beware it can bite. I'm afraid Golbourne has been cancelled or you might have got one there Ed |
21st Mar 2020, 8:54 pm | #8 |
Moderator
Join Date: Mar 2012
Location: Fife, Scotland, UK.
Posts: 22,871
|
Re: Building a collection of bits so I can play. Ex mil and Ebay
For a step up/down converter without a gap in the middle, or having to switch mode, look up the SEPIC converter (Single-Ended Primary Inductance Converter - not really a helpfully clear name)
I use them at about 600kHz so they could easily be set to fit in the long/medium-wave gap. There's a reasonable application note by National Semiconductor that explainds the things and the design calculations. David
__________________
Can't afford the volcanic island yet, but the plans for my monorail and the goons' uniforms are done |
21st Mar 2020, 9:18 pm | #9 |
Octode
Join Date: Mar 2020
Location: Blackburn with Darwen, Lancashire, UK.
Posts: 1,572
|
Re: Building a collection of bits so I can play. Ex mil and Ebay
Thanks all for the responses, yes the current situation is going to make getting out and finding parts a bit more difficult, but so be it, it seems to be necessary.
I have done a bit of testing and initially it looks promising. A) I loaded both positive and negative outputs to 0 Volts with 11K Ohm resistors (3 x 33K) I was able to take the output Volts from 100 up to 300 Volts before my small 12 Volt bench PSU started to go into current limit. I had a small fan blowing on the six resistors I used as a load, see pic below. So 27.5 mA in each leg The output heat sink was warm to the touch although it was getting air flow from the same fan. I make the calculation that each leg would have had 27.5 mA in each leg, just over 8 Watts so 16 watts output total. Also when the positive output is set for 300 Volts the negative output is higher at 313 Volts, it only regulates on the positive output the neg side is left to it's own devices. B) Then I switched to a single output load of 5K5 Ohms and repeated the output setting up to 300 Volts, I had to put a 200K Ohm resistor in the negative leg to stop the Volts exceeding -400 Volts. With 300 Volts at the positive terminal the negative was now at 394 Volts,and as the output caps are only rated to 400 Volts it looks as though some load is needed on both outputs. Again I ran the unit for a few minutes, heat-sink warm to the touch and this would have been 55 mA in the positive leg. I can not let you know how much ripple there would be as no scope on the output, but I think the 16 Watts at 300 Volts output would be enough for me to power a small valve unit for the time being. So I think it may work for me to do some playing, without plugging anything across the mains. One has to be careful that no ratings are exceeded which looks like it is easy to do if you do not load both outputs. Lastly, I think the output switching transformer is just centre tapped, there are two large diodes on the bottom of the board one from each end of the transformer secondary, and they just go to 10uF 400 Volt caps. Just wondering about turning the diode and cap around on the negative side to see if it would work giving me two 0 V to positive HT Voltage outputs, I can see no reason why not? Adrian |
21st Mar 2020, 10:09 pm | #10 |
Octode
Join Date: Mar 2020
Location: Blackburn with Darwen, Lancashire, UK.
Posts: 1,572
|
Re: Building a collection of bits so I can play. Ex mil and Ebay
Last comment on this for tonight, No I can not just reverse the diode and cap on the normally neg output, I get some stupid voltages. The regulated side works OK but when set for something like 70 Volts the other new positive side will not go below 150 Volts even with 33K loads on both outputs, so the negative dc voltage must provide some form of feedback that I can not see.
Adrian |
21st Mar 2020, 10:19 pm | #11 |
Pentode
Join Date: Nov 2018
Location: Freckleton, Lancashire, UK.
Posts: 232
|
Re: Building a collection of bits so I can play. Ex mil and Ebay
Hi Adrian
good to see you on this forum ! I had cause to use a SMPS to generate both positive and negative outputs and it's not as easy as you may think because the main output usually has the feedback control as you might expect but the flyback used to generate the aux output is effectively un regulated. However in my case that is what I wanted as it gave an indication of the mains input voltage ! There's more to it than that but I'd have to dig out my notes from a few years back. 73 Tim
__________________
Building and tinkering for over 50 years, from 807's to digital amateur TV. |
21st Mar 2020, 10:55 pm | #12 |
Octode
Join Date: Mar 2020
Location: Blackburn with Darwen, Lancashire, UK.
Posts: 1,572
|
Re: Building a collection of bits so I can play. Ex mil and Ebay
Hi Tim this has both pos and neg outputs was just seeing I could reverse the neg to a second pos, Nope!
|
22nd Mar 2020, 12:08 am | #13 | |
Nonode
Join Date: Oct 2008
Location: Warsaw, Poland and Cambridge, UK
Posts: 2,677
|
Re: Building a collection of bits so I can play. Ex mil and Ebay
Quote:
This type of converter is cheap and simple but makes fairly inefficient use of the transformer core, which is why it's only popular up to about 50-100W or so. Anything larger than that tends to be a forward converter. Chris
__________________
What's going on in the workshop? http://martin-jones.com/ |
|
24th Mar 2020, 6:14 pm | #14 |
Octode
Join Date: Mar 2020
Location: Blackburn with Darwen, Lancashire, UK.
Posts: 1,572
|
Re: Building a collection of bits so I can play. Ex mil and Ebay
Well I have moved forward a little. I have wired up to a guard receiver using three buck converters.
DC Volts are 135, 225 -15 and 6.3. I am using an equally vintage IFR 1000A test set to provide a 243 MHz signal to the receiver and the scope section is showing the af out. Sorry for all the wores. This basically proves to me that the receivers I got for stripping down work as they are, so if I build something and it does not work that will be down to me. Adrian |