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Old 30th Apr 2021, 6:49 am   #21
ChristianFletcher
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Default Re: Lafayette Model HA-600A VERY DEAF

The Circuit I’m publishing are from the 600A manual so if it is wrong it the manufacturer that made the mistake. Thanks for the note on performance that’s interesting. The set is picking up broadcast stations quite loudly and does resolve a few SSB stations on 80 but I have total silence between stations. I have the set connected on a long wire without an ATU. The strange thing is if I connect a signal generator it takes a level of 400uV - 600uV to hear a tone a reasonable level. The set is deaf on all bands.

I don’t think possible detuning the front end could explain this magnitude of difference between the antenna and the signal generator source.

I did sense check with an older Lafayette valve receiver and it could happy resolve 1uv from the same signal generator

looking at the first filter built into the IF can, I can see it looks slightly melted with a large blob of solder on the outer can, but it did respond to peaking. Using a audible signal tracer and demodulation probe I cannot hear anything until the final IF stage. I notice the final IF stage didn’t respond to peaking so that may be worth a little more investigation.

I did test the RF FET on the peak tester and it reported it as a Zener diode but I have found these testers can miss report RF transistors. I have ordered a MPF102 so was going to try and change it out

It’s not proving an easy set to work on the components legs are corroded and don’t probe easily. I am more familiar with working on valve sets and a the signal levels I am measuring are small to none existent.
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Old 30th Apr 2021, 10:11 am   #22
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Default Re: Lafayette Model HA-600A VERY DEAF

Just to add a bit more detail could someone suggest the best method of probing, testing the RF front end and the IF strip. I am not familiar with transistor radios and don’t have a similar radio to for cross referencing etc. Regards test gear I have everything as my main interest is repairing test equipment so no shortage of equipment.

Thanks Chris
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Old 30th Apr 2021, 10:55 am   #23
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Default Re: Lafayette Model HA-600A VERY DEAF

A reasonably fast 'scope with 10:1 probe (adjusted for squarest square-wave trace from the calibrator) will accurately show up levels through the front-end, just remember that L21 between FET1 and TR1 is at a low impedance and will show a drop in voltage compared with the input.

I love this little example of the Japanese takeover of amateur radio manufacturing. Lafayette had been a manufacturer but changed to a re-badger of Japanese equipment. The consequence is that this radio became very simple to manufacture once all the customised components had been sourced, yet it all worked elegantly. Just look at the bandspread tuning capacitor, as shown on Radiomuseum in pictures 13 & 14, which is a double triple-gang to give different bandspreads on the amateur bands

I'd love to identify the manufacturing company. It does indeed look very much in the style of the Realistic DX-160. Can you see any date codes anywhere to narrow down on the date of the set?
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Old 30th Apr 2021, 11:30 am   #24
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Default Re: Lafayette Model HA-600A VERY DEAF

The DX-160 has a pretty good service manual, including detailed alignment info and specific details of how to do testing. It's 13MB, so I cannot attach it, but you should find it on google, or PM me with your email address.

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Old 30th Apr 2021, 12:26 pm   #25
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Default Re: Lafayette Model HA-600A VERY DEAF

Quote:
Originally Posted by Julesomega View Post

I'd love to identify the manufacturing company. It does indeed look very much in the style of the Realistic DX-160.

GRE Japan and later GRE America rings a bell, although it may have just been the scanners it manufactured.
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Old 30th Apr 2021, 6:14 pm   #26
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Default Re: Lafayette Model HA-600A VERY DEAF

Thanks everyone and I will download that manual I’m sure it will help. I did try the scope but I couldn’t see anything but noise at the low v/div setting. I need to explore further I think.

Thanks
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Old 30th Apr 2021, 6:36 pm   #27
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Default Re: Lafayette Model HA-600A VERY DEAF

Increase the sig gen level until you can see it clearly: it won't be a realistic operating situation, but you are only trying to ascertain the signal gain of the first three stages. That said, I suppose the AGC will be fighting against you
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Old 30th Apr 2021, 7:30 pm   #28
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Default Re: Lafayette Model HA-600A VERY DEAF

I think I may monitor that AGC line out of interest

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Old 30th Apr 2021, 10:58 pm   #29
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Default Re: Lafayette Model HA-600A VERY DEAF

Taking a quick look on Google, the HA-600 seems only to have a user manual, in to which some service info is included. The DX-160 has quite separate user and service manuals.

I saw a suggestion on one site that said the HA-600 was actually built by Trio and that may well be true of the 160 also. The comment about many such radios of the era was that build quality was rather variable, a good one being a lot better than a bad one, seems to be common.

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Old 1st May 2021, 5:10 am   #30
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Default Re: Lafayette Model HA-600A VERY DEAF

Oh it’s definitely come out of the Trio factory from the design of the tin but having done a number of 9Rs and other Lafayette’s HE-40 the soldering on this 600A is terrible every joint looks dry. I have quite a few videos where i revived a 9R and another Valve Lafayette. The construction styles are really identical
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Old 1st May 2021, 10:04 am   #31
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Default Re: Lafayette Model HA-600A VERY DEAF

Quote:
Originally Posted by ChristianFletcher View Post
Oh itís definitely come out of the Trio factory from the design of the tin
Yes, I also had the impression that these were made by Trio.

If aligning this radio according to Table 3 in the manual it is worth checking where the filter peaks before starting. It may not be exactly 455 kHz - mine turned out to be 456.8 and I aligned the IF coils, and centred the BFO, at that frequency.

As with similar "entry level" SWL radios of the period with a 455kHz IF, the highest range has terrible image performance. I used mine with a passive preselector.

Front end circuit, as drawn by me 50 years ago:
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Old 1st May 2021, 3:42 pm   #32
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Default Re: Lafayette Model HA-600A VERY DEAF

From memory, some of those Lafayette radios were sold as kits, in the style of Heathkit, Knight-kit etc.

If your radio is a kit-built one, your fault-finding may well include identifying and rectifying construction-mistakes made by the original assembler. I've seen gear sold at hamfests etc. that was built-up kits and could clearly _never_ have worked as assembled [2.2K and 220K resistors interchanged, for example].
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Old 23rd May 2021, 7:52 pm   #33
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Default Re: Lafayette Model HA-600A VERY DEAF

Just before closing the Thread wanted to confirm as suspected it was the front end FET was at fault. This has been replaced with a MPF102 and the sets working quite well. Perhaps a little too sensitive if anything.

Fix video here https://youtu.be/pKjCVnifkIU
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