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Old 17th Jun 2020, 6:34 pm   #1
ribbonmicsrus
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Default HRO M 1.7-4.0Mz Coil problem

Just nearly finishing restoring an HRO M, all coil packs have calibrated nicely except the 1.7-4MHz pack.

Originally it didn't work, this was due to dry joint between pins 1-3 on 2nd RF stage grid coil. Problem is pack will not tune correctly, cannot get tracking correct at all. The oscillator is set up correctly, the only clue I have is that the tuning of the grid of the 2nd rf stage appears a lot flatter than the others, this was the coil with the o/c between pins 1-3.

Cannot see any signs of corrosion on the coil that might cause low Q, any ideas, all joints are now good!

Andy
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Old 17th Jun 2020, 6:51 pm   #2
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Default Re: HRO M 1.7-4.0Mz Coil problem

Please would you expand on what you are tuning?

Is it just the capacitor at the HF end or are you adjusting the inductance of the 2nd RF grid coil as well?
I remember having one coil pack of this range in the "awkward squad".

In the end I used a DSP dongle kludged in the mixer IF out to view what it was doing. You could see the effect of adding a bit of hand capacity to each tuned circuit and it would tell you whether it was right or else high/low at each end of the range.

Last edited by Jon_G4MDC; 17th Jun 2020 at 6:58 pm.
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Old 17th Jun 2020, 7:11 pm   #3
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Default Re: HRO M 1.7-4.0Mz Coil problem

Hi Jon
Yes, using that technique for checking which way the bottom end needs to go, it just won't track correctly and as I said the tuning is flat on the capacitor, I might re-wind the coil. going to attach pack to spectrum analyser and see if can compare with the 0.96 to 2,04 pack I have to get some idea of Q.

Andy
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Old 17th Jun 2020, 9:06 pm   #4
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Default Re: HRO M 1.7-4.0Mz Coil problem

OK Andy. Flat tuning of the capacitor can be just that the whole coil is wrong across the range.

When you say "using that technique" - I'm guessing you mean adding hand capacity and is it getting better or worse?

A spectrum analyser can't tell you much about Q. I think rewinding the coil would be a mistake unless you are very sure...
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Old 17th Jun 2020, 9:53 pm   #5
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Default Re: HRO M 1.7-4.0Mz Coil problem

Jon
I can sweep the coil in-situ,no power, with the analyser with TG and see what is happening.I agree the coil winding scenario is a no go unless absolutely certain.

Andy
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Old 17th Jun 2020, 10:04 pm   #6
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Default Re: HRO M 1.7-4.0Mz Coil problem

Ah - you have an SA + tracking generator. That changes the game.
Then we must discuss how to couple it up.

It might make it easier or else harder. I'm pleased you will preserve the original coil for now. Rewinding is the last resort!
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Old 17th Jun 2020, 11:22 pm   #7
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Default Re: HRO M 1.7-4.0Mz Coil problem

Some coil packs have screws to change them from general coverage to amateur band bandspread coverage. You wouldn't happen to have LO in one range and one of the RF stages in another?

David
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Old 18th Jun 2020, 12:06 pm   #8
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Default Re: HRO M 1.7-4.0Mz Coil problem

Hi David /Jon

No, these are all general coverage coils, set of 9, from 50kHz to 30MHz without padder screws.

However, after dismantling my working 3.5 to 7.3MHz coil pack 2nd RF stage section, I have discovered that someone has fitted the same one in the 1.7 to 4MHz one and added extra capacitor to try and bring it down!!!

So now looking for a 1.7 to 4MHz complete coil pack as don't trust if anything else has been bodged!
73

Andy G3UEQ
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Old 18th Jun 2020, 1:29 pm   #9
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Default Re: HRO M 1.7-4.0Mz Coil problem

Oh, well, at least you've got it down to the cause. If someone's mucked it up, you can relax and blame them. If I never get to a root cause I wind up blaming myself.

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Old 18th Jun 2020, 9:39 pm   #10
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Default Re: HRO M 1.7-4.0Mz Coil problem

Good find... I still have a pile of scruffy coil packs that I was working through.
I should get back to that given the current situation. It was one of those projects that ground to a halt somehow.
I think it was that same frequency range that I bought NOS from a shop in Goldhawk Road Hammersmith in about 2005...
It's one of those in the picture at left - Queen of the HRO!

Later edit: Perhaps this could warrant splitting off a new thread? The setting of the vanes on the HRO tuning capacitor is a subject I have always wanted to get to the bottom of. They mount on the shaft using grub screws and so they can be adjusted. Is it correct that they all align together 3xRF and 1x LO or is there some offset for the LO gang? My several examples have all got screw indents so they prefer to take up a certain position. I'm doubting that is actually best for performance. I can find no info on the subject - does anyone know better? Shuffling the moving vanes for the right lateral spacing with the fixed vanes is hard enough but then there is the "angle of advance" - rather like in an ignition distributor.

Last edited by Jon_G4MDC; 18th Jun 2020 at 10:08 pm.
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Old 19th Jun 2020, 11:24 am   #11
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Default Re: HRO M 1.7-4.0Mz Coil problem

Quote:
Originally Posted by Jon_G4MDC View Post
Later edit: Perhaps this could warrant splitting off a new thread? The setting of the vanes on the HRO tuning capacitor is a subject I have always wanted to get to the bottom of. They mount on the shaft using grub screws and so they can be adjusted. Is it correct that they all align together 3xRF and 1x LO or is there some offset for the LO gang? My several examples have all got screw indents so they prefer to take up a certain position. I'm doubting that is actually best for performance. I can find no info on the subject - does anyone know better? Shuffling the moving vanes for the right lateral spacing with the fixed vanes is hard enough but then there is the "angle of advance" - rather like in an ignition distributor.
So far as I can make out all the rotor sections should sit central to the stator sections eg: rotor plates equidistant to stator plates also the rotor plates of all four sections should all be dead flush with there respective stator sections when one of them is set to maximum capacitance, eg : they are all at maximum capacitance together, also with the tuning dial fully at the stop position in the direction direction of maximum capacitance the tips of the rotor vanes should be below the fixed vanes by 3/32"

Lawrence.
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Old 20th Jun 2020, 9:34 am   #12
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Default Re: HRO M 1.7-4.0Mz Coil problem

Thank you Lawrence for the info. That is pretty much how I have always set them up but I wondered if it was right.
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Old 22nd Jun 2020, 12:22 pm   #13
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Default Re: HRO M 1.7-4.0Mz Coil problem

Yes, the calibration data says to align together, I did mine with an LCR bridge and set them within 2pF, it seems to track OK. I did have trouble after redoing gearbox with cardinal sin of loosening grub screws on split gear shaft, eventually got everything back OK but found screws have to be very tight.

Andy
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Old 22nd Jun 2020, 2:02 pm   #14
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Default Re: HRO M 1.7-4.0Mz Coil problem

I cannot chip in with any help but am rather envious of the HRO. Been after one for a while but they all appear to be butchered and silly money on eBay.

Chris
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Old 22nd Jun 2020, 3:15 pm   #15
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Default Re: HRO M 1.7-4.0Mz Coil problem

Try a Wanted on the forum Chris,there just might be one available.I have had mine many years and original and very tidy too.

Also got both power supplies and I think the battery one as well.
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Old 14th Jul 2020, 8:20 pm   #16
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Default Re: HRO M 1.7-4.0Mz Coil problem

This interesting thread ran out of steam some weeks ago. Reading it again today reminded me that I wanted to convert one of these coil packs to cover a 500kHz range with the Muirhead dial reading actual frequency.

The main disadvantage of the HRO was the calibration graphs. It was all right in the day using a pencil to write the dial setting of your favourite intercept stations in the boxes on the front - but now...? I was dreaming of having a classic HRO that had the dial calibrated at 1kHz/div more like the RA17 but having only 0.5MHz range. The 1.7-4MHz coil with bandspread, it seemed to me, was the most likely for that to work.

Other bands could be reached by an up/down conversion technique in front of the RX. It would be a dream 80m receiver anyway.

Somewhere I have some cock-eyed spreadsheets that has measured results from the capacitor gangs and it tried to work out what trimmers and padders would make the stages track.

It's a pity there's not much more lock down left. I almost got back to it!
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Old 14th Jul 2020, 8:34 pm   #17
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Default Re: HRO M 1.7-4.0Mz Coil problem

Frequency counter?

They aren't really the spawn of satan and all his little demons... they can actually be quite useful and save you going mad trying to get the 'law' right to fit the scale.

David
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Old 14th Jul 2020, 9:51 pm   #18
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Default Re: HRO M 1.7-4.0Mz Coil problem

I was going to post a link to the "no-no-no-no" cat video on YouTube but I will save you all from that.
It's just what I want.

I might put an SDR in the back end of the IF as a Q5er but I was keeping quiet about that part.
A ~direct reading dial for an HRO on 80m will do as a start. No displays of any sort required HI.

I need to find the files again - it seemed to be getting quite close but probably it had some fatal flaw which would make the wheels fall off it.
Maybe this is straying off topic so if needs be it can become another thread at some point?

Last edited by Jon_G4MDC; 14th Jul 2020 at 10:14 pm.
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Old 15th Jul 2020, 10:10 am   #19
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Default Re: HRO M 1.7-4.0Mz Coil problem

Jon, I converted coil packs for 1KHz per division some years ago and they still work well. The project was published in VMARS' Signal. I modified packs for 1.8, 3.5, 7, 10, 14 MHz. If you were serious about modifying your radio I'd send you my original notes.
Best regards
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Old 16th Jul 2020, 8:10 pm   #20
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Default Re: HRO M 1.7-4.0Mz Coil problem

That is most interesting Andrew. You did several bands!

I was sure I was not treading a new path. Any info would be read with great interest.
The issue, as I anticipated it, since it was only theoretical, was needing to adjust the inductor value with some accuracy. The swinging loop ones are just evil to adjust. The ones with threaded discs inside only marginally less so.

Is this indicating we should start another thread perhaps? Feeling a bit like a hi-jack if we are not careful. It would a shame to go private with it - depending what you think?
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