The Wellgood Magloop Amp
 

Just a few months after starting work on this two-transistor device, I have finally finished it ;D.

It needs 'setting up' by adjusting a small, 25-turn resistive trimmer (RV1) to balance the two transistors. In the original design, the amp used a pair of 2N2222's, but in line with various recommendations (including the Wellgood site) I used a pair of 2N3866's. Of course, these transistors take appreciably more current and have been fitted with heat sinks. The amp is designed to operate at 12V.

The recommended way of setting the bias is measure the voltage across RV1 (see attached) and adjust to minimise it. As a cautious way of approaching this, I started off with just 6 volts on the board and adjusting RV1 went well, and so too at 8 and then 10 volts, but at 12 volts, the minimum setting is not stable.

The two transistors are drawing ~127mA (total) and running at 48 and 54'C. RV1 is also getting quite warm, running around 50'C. The voltage across RV1 climbs from ~0mV to around 10mV fairly quickly; I've not left it running very long, so I don't know how far it may go.

I'm not quite sure what's causing this but I guess it could be transistors which were not too closely matched (I need to dig out my notes but I think the pair I used add gains of something like 180 and 195) or whether the 100R trimmer is an issue; it's rated at 0.5W, and it's sandwiched between the transistors and so it's being pushed a bit.

Any insights would be welcome.
Thanks

B

Re: The Wellgood Magloop Amp
 

No image. Could you make .pdf so everyone could view it please?

Re: The Wellgood Magloop Amp
 

There you go.

B

Re: The Wellgood Magloop Amp
 

Deciding to side-step the thermal issues by running the amp at 10V, I'm now sat listening to some some G stations and some D stations working each other on 80m. The background noise level seems to be low and the S-meter is hitting the end stop hard with some signals. The receiver is a Realistic DX-160 and the 1m loop is in the shack (bedroom), a couple of feet from my running desktop and inside a house with numerous wall warts.

Brief excursions up to 12V, and then back down as low as 6V makes no audible difference. At 10V, I=107mA.

That's quite pleasing.

B

Re: The Wellgood Magloop Amp
 

It sounds like you've sorted it Barrie. 107mA at 10V doesn't sound out of the way.

Just to recap for anyone unfamiliar with the 'Wellgood' and 'Wellbrook' amplified loop receiving aerial:

The 'Wellgood' loop which Bazz has built is a clone of the 'Wellbrook' commercially made amplified loop, but whereas the Wellbrook is made on a piece of stripboard using two 2N2222 transistors, the 'Wellgood', devised by Dr George Smart, is built of a purpose designed compact printed circuit board.

There's been much debate about which transistors to use to optimise performance.

2N2222 transistors, which are small and cheap.(typically 18p each from UK suppliers).

Gary Tempest (not on this forum) had earlier designed a 5-transistor loop antenna using 2N5109s, which was published in the BVWS Bulletin, and kindly donated one to me. He'd built it 'Manhattan style' and I later devised a printed circuit board for it, and built another one, which worked fine. (I wrote that up in a thread on the forum and included the artwork for the PCB).

Gary later devised what might be termed a clone of the 'Wellgood', again using a Manhattan style board. This too featured in the BVWS Bulletin. As I was interested to see how the simpler 2-transistor design worked, I devised a PCB for it and built that version.

I'd installed the loop for the 5-transistor version on the outside gable end of my wooden workshop. It consisted of 15mm copper plumbing pipe in a 2M square. Up to that point, I'd used what many incorrectly refer to as a 'long wire' aerial - a 60ft end fed wire, which only becomes a 'long wire' at frequencies above 14MHz, but that's another story.

For the two transistor version, I made a 1m diameter loop of 15mm tube - the same dimeter as a Wellbrook loop. I've installed that on the gable end of the loft in my brick garage in the same orientation as the one on my shed. There's no discernible difference in performance. Appreciably higher signal strength and lower noise levels as compared to a wire aerial.

Gary in his 'Wellgood Clone' design again used 2N5109s, but I used 2N3866s which had been kindly donated by David, 'Radio Wrangler'. I tested them on a Peak Atlas DCA55. The Hfe ranged from 165 - 190, and I chose two with similar gain. They're a good bit larger than 2N2222's so if compactness is called for, they might pose a problem.

I fitted heat sinks to the transistors and their temperatures stabilised at 45 degrees C (113 F). I guess they'd get considerably hotter without heat sinks.

I Set RV1 on the PCB to midway then checked the supply current. If the amp draws around 100mA, that’s a good sign, but if it’s low - say 25mA - the circuit is in oscillation and Gary advises that the secondary wires of T1 will need to be reversed. With the circuit stable, RV1 is adjusted so that both transistors pass roughly the same current. With a current meter in the power lead, when balanced by adjusting RV1, the least current will be drawn. (In my case, 95mA).

The topic of receiving aerials crops up regularly on the forum and to my mind, an amplified loop will outperform any random length of wire, both in terms of signal strength and low noise. A loop scores on compactness and convenience too. A 1 Metre loop will fit on a balcony of an apartment, in the corer of a room, inside or outside a workshop, in a garden etc. It makes an enjoyable project for anyone with constructional skills, but for anyone not so inclined, there are countless users (including some on this forum) who are delighted with the commercial Wellbrook loop.

Lots of information in this earlier thread, with links to the Wellgood site of Dr George Smart and the BVWS articles by Gary Tempest, as well as the 2-transistor version I built:

https://www.vintage-radio.net/forum/...Wellgood+clone

Enjoy using the 'Wellgood' Barrie!

Re: The Wellgood Magloop Amp
 

Interesting project. I've added this to the "todo" list.

Re: The Wellgood Magloop Amp
 

That's a very interesting write up David.

Buzz, how close is your circuit to Wellbrook's? Is the circuit of the Wellbrook loop known? I assumed it was a commercial secret - or at least the more subtle aspects of the design - although I expect the Wellbrook loop to follow conventional loop antenna design.

However, Wellbrook Communications have made various changes and improvements over the years and it would be great to see a head-to-head comparison with the clone both in technical measurements and real-life performance.

For info: https://www.wellbrook.uk.com/loopantennas/Loop_Antennas

Re: The Wellgood Magloop Amp
 

Yes, the 'Wellgood' is a clone of the Wellbrook, except that the Wellbrook, surprisingly perhaps, uses stripboard whereas the Wellgood uses a PCB. As I mentioned in the other thread, Dr George Smart, M1GEO, had accidentally transmitted into his WellBrook ALA1530 Loop and killed it. George had been very impressed with the Wellbrook so decided to see if he could repair or replicate the amplifier.

A friend of George’s - Dave G7UVW - who works in an X-ray lab, was able to X-ray the Wellbrook amp (encased in potting compound) to assess the feasibility of replicating it. From the X-ray images it was apparent that the amp was made on Veroboard, with several capacitors, ferrite transformers, and two transistors, identified as being ZTX327.

From his ‘teardown’ of the Wellbrook, George Smart designed a ‘clone’ amplifier built on a neat compact PCB rather than stripboard. He named it the ‘Wellgood’ and outlined his ‘teardown’ of the Wellbrook in detail and the subsequent design that he developed. The circuit, full constructional details, including winding the two small binocular ferrite transformers, even the bill of parts with RS part numbers is on his website and I believe he is also able to supply PCBs, so for anyone who wished to build a ‘Wellgood’ with the minimum of hassle, head on over to Geoge’s website.

The ferrite transformers, the design of the PCB, the development of the project and other aspects are all George's work so it isn't identical to the Wellbrook. Here’s the link to George's website, where you can see the full story and X-Rays of the Wellbrook:

https://www.george-smart.co.uk/projects/wellgood_loop/

Re: The Wellgood Magloop Amp
 

Yes, as David has described, George Smart re-engineered the Wellbrook, but I did recently find a forum discussing mag-loops where some questions were being raised about whether it's possible that the Wellgood is not precisely the same; could some mistake has crept in. I'll try find that link and will post it. Winding transformer #1 in the Wellgood needs quite a bit of concentration. Apparently, the amp that Wellbrook are now selling is
different to the design which the Wellgood emerged from

I need to do some testing and comparisons now to see how well this is really working. This all started with me putting up a 5MHz dipole last winter, connecting it to my IC-718 and finding an S8 noise level. The Wellbrook is supposed to be good to 30MHz, but my Wellgood seems to be good on 80m but my first impression is that it falls off above that. I've not yet heard anything on 5MHz with it. I need to try it on the IC-718 now.

There's a huge amount of info about magloops on the internet, much of it is inconsistent or contradictory. There are many alternative designs to look at both in terms of the loop and the amp.

B

Re: The Wellgood Magloop Amp
 

Bazz - I have owned a Wellbrook 1530 since the late 90's (I think) and it's an excellent performer. I've also built a semi-clone using a kids' plastic hula hoop (one turn of wire inside) and the famous PA1M two-transistor loop amplifier.
It works fine, but with slightly higher levels of IMD at the sum and difference frequencies of the very strong MW stations within a few miles of here.
I've also made another version that is optimised for LF listening which gets a good signal from the SAQ transmissions on 17.2 kHz using more turns, different ferrite for the o/p transformer and a LPF to keep MW out. Without my lovely loops my hobby would be long dead due to local noise.

Re: The Wellgood Magloop Amp
 

Andrew; as far as I can recall, I think that every report I've ever heard about the Wellbrook has been very favourable. Quite something for a unit which originally used two plastic transistors on a piece of veroboard, according the the Wellgood site. Of course, the Wellbrook team probably spent a lot of time getting to that point.

Regarding the clones, this site is interesting http://valentfx.com/vanilla/discussi...ellbrook-clone

It's fairly long, so I printed it out in Word and edited and highlighted it anyone wants to see that.

B