Thanks for the schematic diagram, Steve.

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Some days ago, I stumbled upon some nice 3D X-Ray images of what the author claims to be an ALA1530 amp, but that version uses only a couple NPN transistors. Do you know when did they redesign the amp with j-fets and how does it compare to the simpler bipolar version ?

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73,
Caaarlo.

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Secondary of T1 is not more overcrossed like in Wellgood amp ALA clone?

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Hi, F.

Some of George's information with respect to the transformers is confusing, which he has tried to correct, but it can still catch you out.

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There is a 50 / 50 chance that you will accidentally connect them the wrong way around when building a copy (I certainly have). But the poor performance when incorrectly connected is very noticeable and easily corrected.

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Regards,

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Martin

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On Mon, Jul 22, 2024 at 11:04 PM, Francesco Caizzi wrote:

The critical part is the phase relation between the the 1-turn feedback windings an the main secondary winding. With? the wrong phasehift, the negative feedback turns into an unwanted. positive feedback. There is one way to do it right, but there are three ways to do it wrong: upper winding wrong phased, lower winding wrong phased, both windings wrong phased.

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regards

Fred

In a message dated 7/23/2024 9:09:20 AM Central Daylight Time, dl4zao@... writes:

Hi everyone

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As the owner of an ageing ALA1530LN since Wellbrook ceased trading I have been trying to find a replacement amp unit before mine finally succumbs to the wet & windy English weather.? With the sad death of Andy Ikin we know there will be no possibility of the design being sold and marketed and I have seen with interest a number of variants ranging from the Chinese clone Wellgood ALA1530LN to a number of recent schematics on this board yet all seem to vary slightly making it difficult for a novice such as myself to try to construct a new head amp.

My ultimate aim is to produce a new head amp for personal use only that will fit into a 65mm round conduit box that should retro-fit direct into my existing loop, and so as a first step I have produced a schematic drawing upon a number of the existing circuits to produce a compromise design for an ALA1530LN clone and I have uploaded it to the files section here:

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/g/loopantennas/files/ALA1530%20combined%20schematic.pdf

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As this is still a work in progress I haven’t indicated transformer phasing dots yet.

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There were, however, some design questions that I hope other members might be able to clarify:

1. Ferrite beads – there seems to be a variation in the value of ferrite beads used and I wondered how critical their value was?

2. In some designs there are 2 series (parallel) diodes between the diodes connecting the loop connection to ground and some just have a pair of parallel 1N4148’s. I presume the latter is correct.

3. Some circuits show a single 82pF across the loop in connection whereas most show each loop connection having an 82pF connection to ground.? Again I assume the latter to be correct.

4. A number of designs include two 51ohm resistors across the output of T1 running to ground in parallel with a 100ohm trimpot but I don’t understand why both?? If the source voltages on Q1-Q8 need to be equal then surely just the trimpot will suffice and if the exact voltage id not absolutely critical then I would think the trimpot could be omitted.

5. Some designs have a 10pF capacitor across the output of T2 but most do not, presumably this serves little purpose?

Sorry for all of the questions and I hope members might be able to help with my lack of knowledge.

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Thanks in advance

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Chris Sentance

On Tue, Aug 13, 2024 at 04:49 AM, chris.sentance wrote:

In some designs there are 2 series (parallel) diodes between the diodes connecting the loop connection to ground and some just have a pair of parallel 1N4148’s. I presume the latter is correct.

If you want to protect the loop against static atmospheric voltages to earth, you need to connect the diodes to ground. Ground means real ground/earth, not GND/minus of the amplifier.

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regards

Fred

On Tue, Aug 13, 2024 at 04:49 AM, chris.sentance wrote:

4. A number of designs include two 51ohm resistors across the output of T1 running to ground in parallel with a 100ohm trimpot but I don’t understand? why both??

It may be as simple as a 100Ω pot was more available than a 50Ω pot.

Also the adjustment will be less touchy, easier to set.

???????????????????????????????????????????????????? Mikek

I hope I'm not puttng my foot in my mouth but I didn't realize Andy had passed away...I thought he simply retired.

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Jay

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On Tue, Aug 13, 2024 at 08:06 AM, Mikek wrote:

Also the adjustment will be less touchy, easier to set.

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The parallel resistors also reduce power dissipation in the pot. Without them the pot will get quite warm, reducing its life.

Hello from France

Thanks to Steve and all the OMs of this Groups for this topic/wellbrook_traced_out_loop_amp thread, which is very interesting.

As always with Mouser and DigiKey, the transistors mentioned have several references

Due to these conditions, what are the optimal references to carry out the realization of this preamplifier?

Best Regards

Bernard

Hi again

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I'm still confused about the VR1 trimpot and resistors R1 & R2 in parallel because some circuits include the trimpot and some do not.? Therefore if VR1 is omitted the source to GND resistance is 51ohms, however with the addition of the trimpot this resistance would fall to 25ohms so surely only one of these can be the optimal value.

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Thanks

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Chris

Chris, why do you want to re-invent the wheel?

From Everett, N4cy you can get naked or assembled boards. Steve AA7U has posted the appropriate circuit diagram and bom. Suitable transistors had been discussed in depth in recent threads.

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regards

Fred