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Old 17th Aug 2020, 11:14 am   #61
ORAWA01
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Default Re: ATU vs. Preamp vs. Active Antenna

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Different receivers are built with different antenna impedances in mind. Get it much wrong and it can seem pretty deaf

In general, broadcast and cheapish short wave receivers were designed to go with high impedance antennae like long wires.

Amateur radio stuff was designed for 50 Ohm antennae for transmit, so the receiver had to be optimised for the same and it was assumed that other antennae would be handled by an ATU. Professional gear went for 50 Ohms as the default.

So my amateur radio gear is somewhat off song when I just shove a wire out of a window as a temporary antenna when I'm away from home and just want to have a listen on the bands.

A loop antenna with a built-in preamp could be arranged for either of these situations.

David
My HA-600 has no PL259 antenna socket at the back, but it has just 2x screws for the wire connection for the antenna. I take it is made for high impedance only antenna input. But I think some of the caps inside has gone leaky and resistive too. I was going to recap it, but with the MLA30 working well with the HA-600, I was not sure if it had to be recapped.
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Old 17th Aug 2020, 12:36 pm   #62
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Default Re: ATU vs. Preamp vs. Active Antenna

I had a look at the schematic for the HA-600, and as I suspected, it has much in common with my old Realistic DX-160, i.e. about 12 transistors and a couple of FETS. The aerial input circuitry is really fairly crude (similar in both sets).

Somewhere, there is bound to be a HA-600 users group on the web; until a few months ago, probably on Yahoo, and there will be loads of information about what problems and what improvements people have made on the set. I would definitely seek that out before starting a mass recap. The most likely caps to deteriorate are electrolytics, mostly found in the AF circuits, but the ones which would tend to cause loss of RF sensitivity will be ceramics and perhaps silver mica which are much less likely to have deteriorated. The odd dry joint may well be more likely.

The manual does quote a sensitivity figure and provide some very basic alignment data. Do you have a reasonable signal gen to test it?

B
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Old 18th Aug 2020, 10:40 am   #63
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Default Re: ATU vs. Preamp vs. Active Antenna

Yes, I have a vintage Heathkit 9V battery operated signal generator, and a Chinese Made Signal Generator FY-6800, and also a 20 Mhz vintage Oscilloscope still works.

The HA-600 works OK with the MLA30 mag loop, but some part of the band 4 - 6 Mhz is dead quiet, which suggests it lost the sensitive in that edge of the band all together, and with a good long wire antenna, it just doesn't receive anything on all SW bands. So recapping and alignment are badly needed for the set, I would say.

It works great on LW and MW as it is with the long wire or the MLA30, so it is fine for a domestic set.
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Old 19th Aug 2020, 8:14 pm   #64
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Default Re: ATU vs. Preamp vs. Active Antenna

Hi,

I have an HA-600 and although its not the most sensitive of radios on the higher frequencies I would also suggest a realignment (as per the manual) before any recapping.
My HA-600 still has the original capacitors and works as well as it did back in the 70's.

Good luck,

Peter
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Old 21st Aug 2020, 11:27 pm   #65
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Default Re: ATU vs. Preamp vs. Active Antenna

Hello Peter

With the MLA30 loop, my HA-600 seems working really well. But as I said earlier, between 4-6 MHz, it is deaf. 7-8 Mhz is medium. It hears the strong stations but not the weak ones. And above 15 Mhz, total deaf again.

As you suggested, it is needing realignment. Maybe it doesn't need recapping yet? Just realignment? I will need to download the manual, and give a try.

Due to its single conversion? / direct conversion? receiver design, I am not sure, which is right, but it seems very dynamic radio on reception. I like it. I think it is a fun classic receiver. Mine has no band noise on HF due to being deaf but fed my the MLA30 high active antenna current, it works very well between 9 - 13 MHz, as if it is tuning FM stations with squelch on. Great sounding on LW and MW for the local stations too. It looks like a great boat anchor.

Thanks & kind regards.
J.
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Old 21st Aug 2020, 11:42 pm   #66
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Default Re: ATU vs. Preamp vs. Active Antenna

Attached is the copy of the manual I looked at and it has some hand written notes at the back about substitute transistors. It's the usual single conversion (455kHz IF) and even uses a ceramic filter just as does my DX-160.

Given that it works on some bands but not on others, probably the first job would be to get some switch cleaner on the band switch (if not already tried).

B
Attached Files
File Type: pdf 4028_Lafayette_HA600_receiver_manual.pdf (1.26 MB, 91 views)
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Old 22nd Aug 2020, 12:12 am   #67
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Thank you for the manual. Managed to download it OK. Ah... single conversion it was. Thanks for your confirmation.

It works on the part of the freq. (9 - 13 Mhz) in a band, but as it is tuned down to the other side of the band, then it gradually becomes deafer. And at the edge of the analogue tuning scale, it is totally deaf. So, it seems not to do with the band selector switch, but looks like it has lost sensitivity on the portion of the band = the worst part is between 4 - 6 Mhz. And as the tuning passes 7Mhz it gets better, and it is really good from 9 - 13 Mhz.

It sounds great on the 40m and 80m band SSB at nights, when the volume is set to MAX, and RF control rolled down, but adjusted for the comfortable sensitivity, it really sounds like a good valve receiver.

J
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Old 22nd Aug 2020, 9:07 am   #68
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Default Re: ATU vs. Preamp vs. Active Antenna

These sets are well over 40 years old now, so if they haven't already had a "mid-life" going over, they may well benefit from one. With the DX-160, I've read that they were quite variable as they came out of the factory, both in terms of build quality and alignment (the HA-600 may well have been built in the exact same factories). Yours sounds like it is fundamentally fine - just needs a little TLC to get it back to 100%.

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Old 23rd Aug 2020, 12:08 am   #69
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Default Re: ATU vs. Preamp vs. Active Antenna

I have an old HA600A (different RF stage from the HA600 but otherwise very similar).

If anything, my set is too sensitive. It's better with the RF gain / attenuator control backed off. If your set is deaf on some parts of its ranges, that definitely implies a need for alignment - or possibly a fault in the RF amplifier circuit.

I replaced all the electrolytics some years ago and did a full realignment, all of which improved the performance.

Bear in mind that these are basic SWL receivers from 50 years ago. The image performance on the highest range is very poor, but OK if the set is used with an outboard preselector.
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Old 23rd Aug 2020, 10:40 am   #70
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Default Re: ATU vs. Preamp vs. Active Antenna

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I replaced all the electrolytics some years ago and did a full realignment, all of which improved the performance.
This issue of "mass recapping" is always interesting and has been addressed previously on the forum. When I changed all the electrolytics on my DX-160, all the ones which came out tested fine for capacitance (I don't have an ESR tester) and I didn't notice any improvement in performance. However, there was a chap on the forum recently saying he done a mass re-cap and things seems to have deteriorated (possibly a bad joint or some other problem on the PCB?).

My Avo valve tester stopped working last year and investigation revealed that all of the low value (1uF) electrolytics had ceased to function as capacitors. As it's a lot of work to remove the boards from that chassis, I decided at that point to replace all the electrolytics (though there aren't that many).

I have an ageing Kenwood TS 530 and it's possible that one or two caps on that could be on their way out, but I think I'll investigate and replace selectively rather than do a mass-recap.

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Old 23rd Aug 2020, 12:20 pm   #71
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Default Re: ATU vs. Preamp vs. Active Antenna

Replacing capacitors (and other components) needs to be done intelligently.

The two extremes are:

Replace everything!
The full shotgun approach. The disadvantages are you waste money on bits that didn't need changing, and you do so much work, the spectre of bad joints, errors and other service-induced faults arises. You can introduce multiple faults, while fault-finding techniques tend to assume that there is a single fault with collateral damage. It becomes an awful lot harder to troubleshoot multiple faults randomly scattered. The advantages are that if you are eventually going to have to replace a lot of parts then it's labour efficient to swap a lot in one session with the thing dismantled, and if done well, and if the new parts are actually better than the old ones, the finished thing should be reliable.

Replace only the bad parts!
The advantages are: lowest parts cost and minimum intrusion. The disadvantages are that you can wind up playing whack-a-mole with the item repeatedly failing as you keep going in to find and replace the one part that died. Screw threads and cabinet parts can wear out or just get tired from all the dismantling. If you decide to test all the parts and replace only the ones that do not test good, there is about the same effort in testing as in replacing, and the testing may need you to have specialist equipment.

There are strong proponents of both these approaches, and they're both wrong

The best answer is "It depends"

How good is your standard of workmanship? How diligent are you about finding genuine (not faked) parts and fitting them the right way round? If you're good, you'll dodge the disadvantages of shotgunning.

How good are you at fault finding and deducing which parts are duff... and which were collateral damage? Do you have the appropriate test gear? If you're good, then maybe the one part at a time approach looks better.

What is the history of the equipment? Has it had a hard life? If so then shot gunning becomes appropriate.

Are there any known problem components? Waxies, Rifas, tin whiskers masquerading as transistors? You might want to do a hybrid approach. Swap the known troublemakers without a backward glance, then look at the rest on an individual basis.

I bought a Revox B261 VHF/FM tuner. It was ex-BBC. They used these for programme quality monitoring and also sometimes for rebroadcast. They are excellent tuners, but the ex-BBC ones have sat in a hot rack running continuously for well over 10 years. It wasn't cheap.

It worked, but had a background hum. Inside I found one reservoir capacitor in the PSU had been changed. The replacement wasn't one of the known reliable makes, just whatever was handy, I suppose. In went something I trusted more. No difference.
Testing around I found the culprit, a low value part in a regulator circuit. Replaced and away went the hum. The tested part was a small one and had a very large ESR.
So I decided to give all the other electrolytics a stab with the ESR meter. About 80% of the physically small ones were high ESR, and about 25% of the ones in larger cans.

The cause was overall heat rather than ripple current heat because small signal parts were worse off than the reservoirs. Small capacitors have a larger surface area to volume ratio than larger parts, so the area of the seal is extra big per volume of water being retained, so they dry out faster if internal heating from ripple current isn't significant.

So I made the decision to replace the lot. But it was a rational decision founded on inspection and evidence.

Did it work better?

Yes it did. Some of the small capacitors had gone high enough in ESR to raise the low frequency roll off points. Also, the resistance exhibited by electrolyte fluids isn't necessarily linear.

This is a rather serious radio. It doesn't mess about using FM tuner specific ICs. The IF strip is a series of general purpose devices, the discriminator uses a coax delay line. The stereo decoder is made of several general purpose devices. Not an integrated decoder chip in sight. No ceramic filters either, but a hand-tuned multi-pole LC Bessel-transitional design.

In some hifi circles, 'recapping' is so popular they even invented a word for it, and they tend to perform it blindly with out assessing whether it is needed or appropriate. It's become an act of faith. As for 'alignment' they seem to have a small number of sainted wizards who seem to be the only people thought to be able to do anything other than ruin the equipment.

But, open your eyes, switch on your brain, and you can do wizardry yourself. It isn't even difficult. Of course, you don't get to wear the cloak and the pointy hat unless you're a denizen of the appropriate internet groups....

So when I see the word 'recapping' I tend to give a gulp, and expect not exactly the best work, done blindly. Possible with quite good, if overpriced parts. I'd rather see words along the lines of: "I found so many of the xxxxx parts rshowing high ESR I decided to replace the lot" or "I was beginning to suspect a bad batch in manufacture"

There is nothing wrong with a pre-emptive strike if you have a reason and can see the target. Done blindly you can shoot yourself in the foot.

David
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Old 26th Aug 2020, 6:13 pm   #72
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Default Re: ATU vs. Preamp vs. Active Antenna

Great post, David. Thank you.

I am not good at repair or restoration of old radios, but I have recapped every caps on this 1940s Murphy Radiogram which was working but had trouble with popping sound and deaf sensitivity on SW. It had mostly original paper caps and was obvious that these caps gone bad. So I think I replaced about 30 caps in total, and it took many days, because I did it about 2 - 3 every night when I had time to do it.

In the end, every cap was replaced with high quality hifi grade caps, and voila, it worked like NEW. It sounded very nice. And I sold it, because it took much space in the room.

Someone from Edinburgh came, and loaded it into his car, paid me cash. He was very happy when he got home, and thanked me in the email.

So, I was quite happy with the work at the time, and I repaired a couple of old valve HF transceivers mainly the PSU. It was also replacing the bad caps and resistors job. It worked as well. But I must say, it was just good luck. I don't don't know much or enough about technical or theoretical side of vintage Electronics. I am trying to learn more.

But for this HA-600, I am not sure what to do with it. It works very nicely on MW and LW. It sounds great. But it was deaf on SW. Now it is paired with the new MLA30 active loop antenna, and it works OK on SW too, but there are some dead spots in the tuning = 4 to 6 MHz there is no reception just silence.
And above 13 Mhz is also silence.

So it will need some work for sure. I have not even opened it up yet, and had no chance to peek inside. But it will be done one day. I have been enjoying listening DX BC mainly recently with the new antenna MLA30 wired up to other radios. Minds you the HF bands is still very poor, but MW bands is good. I was chasing a lot of LPAM stations in UK on MW and LW. It was a great fun.
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Old 26th Aug 2020, 9:13 pm   #73
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Default Re: ATU vs. Preamp vs. Active Antenna

Well done! It takes a lot to get folk in Edinburgh to make a foray outside their city it must have been good.

No-one was born with much knowledge. Everyone who knows something learned it one way or another. Trying to force it in is painful and not terribly effective. Doing things, getting a bit of advice here and there, reading things and taking on new knowledge by a slow process of immersion and absorption seems to be a better way. It's more comfortable, and the results are better lasting.

I think you've got to the level where you could benefit from a dependable signal generator to check the sensitivity of your radio across all the bands.

A cross check is whether other receivers, if connected to your antenna, are insensitive in the same region.

Is it the set, the antenna, the location, or are the bands dead in that range? All these happen from time to time.

David
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Old 27th Aug 2020, 8:26 pm   #74
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Default Re: ATU vs. Preamp vs. Active Antenna

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It works on the part of the freq. (9 - 13 Mhz) in a band, but as it is tuned down to the other side of the band, then it gradually becomes deafer. And at the edge of the analogue tuning scale, it is totally deaf. So, it seems not to do with the band selector switch, but looks like it has lost sensitivity on the portion of the band = the worst part is between 4 - 6 Mhz. And as the tuning passes 7Mhz it gets better, and it is really good from 9 - 13 Mhz.
Is the antenna trim control working properly?
At any point on the main tuning dial, it should be possible to turn the trimmer and get a definite peak in the signal (and noise). There can be a big difference in receiver gain depending on whether it is set correctly.
If it doesn't peak in some parts of the waveband, there is probably something wrong with the front end alignment.
If it doesn't peak anywhere on any band, check whether it has become disconnected.
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Old 28th Aug 2020, 11:26 am   #75
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Default Re: ATU vs. Preamp vs. Active Antenna

Thank you David

And, yes the antenna trim of the HA-600 seems working well. It peaks fine on 9 -13Mhz. But on the same band, if it tuned down to 6 Mhz to near 4 Mhz, the receiver gets totally silent. The antenna trimmer has no effect on this portion of the band.

Because the HA-600 is not sensitive on the whole, the good point is that, there is no band noise even on LF of HF. It will pick up a signal, and when I peak it with the trimmer, it comes up with good loud signal. When tuning around the band, it is totally quiet, and can only hear the signal itself when it is on the freq. just like as if squelch were on.

So, if one is not interested in chasing the weak DX signals, but just likes to listen to the local stations or strong European signals, this HA-600 is fine as is.

But for chasing the weak signal, it will need to be tweaked and re-aligned I think. I will one day open the chassis, and have a good look inside, and also do some testing with my old Heathkit signal generator and Oscilloscope. Maybe this will have to be a separate thread for troubleshooting soon.

But another point I learned from this is, that the active magnetic loops work great with the old insensitive radios like the HA-600.
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Old 28th Aug 2020, 1:44 pm   #76
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Default Re: ATU vs. Preamp vs. Active Antenna

You won't need to remove the covers to do a realignment. It sounds as if the IF is fine as some bands are okay, so just do the RF alignment as described in the manual. All adjustment points are accessible through holes in the bottom cover. Its actually better if the covers are fitted whilst doing this alignment.

Good luck,

Peter
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Old 28th Aug 2020, 2:25 pm   #77
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Default Re: ATU vs. Preamp vs. Active Antenna

Great advice, thank you Peter.
I will give it a go. cheers.

J.
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