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Vintage Amateur and Military Radio Amateur/military receivers and transmitters, morse, and any other related vintage comms equipment.

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Old 3rd Aug 2018, 5:57 pm   #41
ms660
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Default Re: HRO and BC348

So far as I can make out the chassis braiding to the top cap screen of the 1st IF valve was fitted to the later all glass models eg: models M and MX that had the Xtal fitted inside the phasing box, the earlier types had a plug-in Xtal that plugged in to the top of the phasing box, I remember taking the Xtal out on my plug-in one to give it a clean.

You can see the braiding in the HRO M topside chassis layout in this manual:

http://www.cryptomuseum.com/df/hro/files/hro-5.pdf

Lawrence.

Last edited by ms660; 3rd Aug 2018 at 6:03 pm. Reason: Link added
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Old 3rd Aug 2018, 6:15 pm   #42
Jon_G4MDC
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Default Re: HRO and BC348

Interesting, either I have one with an internal crystal or I have just the box having the internal crystal as a spare. Evidence long gone if it is the latter.

Will remember to look at it next chance I have.

Yes washing the crystal from the plug in one is usually beneficial.

It's also instructive to pick off some IF from the box and feed it into a DSP dongle
SDR. Set for 1 MHz bandwidth it shows very nicely how well the coil box tracks across the dial. If the noise bump stays centred on 456k across the whole range you are doing well.

One of mine crossed over completely.
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Old 3rd Aug 2018, 6:25 pm   #43
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Default Re: HRO and BC348

Another give away that it's a later all glass valve job is the pressed steel gearbox cover, early ones were cast.

Lawrence.
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Old 3rd Aug 2018, 6:31 pm   #44
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Default Re: HRO and BC348

Well spotted.

Have you done any alignment of coil boxes? I have no idea how they did that.

The obvious capacitors are not hard to tune with the right tool but swinging the loop in
the middle of the coil former to set inductance? Only a brave man would try that with the HT on!
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Old 3rd Aug 2018, 6:55 pm   #45
G4YVM David
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Default Re: HRO and BC348

My front panel

Someone asked about bandspread...yes, I have a few bandspread coil packs including what I am told is a rarity...one for 15m.
Not all of my coil packs work - the topband one for example is known to be u/s and they may be others. I haven't yet had a chance top even try them all, let alone try to open them for fixing.

David
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Old 3rd Aug 2018, 6:56 pm   #46
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Default Re: HRO and BC348

Quote:
Originally Posted by Jon_G4MDC View Post
Well spotted.

Have you done any alignment of coil boxes? I have no idea how they did that.

The obvious capacitors are not hard to tune with the right tool but swinging the loop in
the middle of the coil former to set inductance? Only a brave man would try that with the HT on!
Yes, I've tweeked coil boxes, just C though not L.

The one I used the most was what I call the HRO Senior (plug-in Xtal) nice receiver, it was my favourite if I'm honest, always been a fan of the HRO receiver, it's a nice elegant simple design, that receiver had it's original set of four (1.7-30MHz) matched serial number (to the receiver) band spread coil packs so was really good for the amateur bands, for other general SWLing I had a Reception Set R106 MKII (HRO 5t) that had a full set of non bandspread coil packs that covered 50kHz-30MHz

Lawrence.
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Old 4th Aug 2018, 10:54 am   #47
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Default Re: HRO and BC348

Hi I did do some coil setups as per this write up. But to be honest I have re-read it several times this morning and I cant get my brain on the right wavelength!!! It did work effectively as I recall as originally I could not get the coil to track in by trial and error adjustment. National must have had a systematic approach but would not be dealing with coils designed and tracked for one model being used on another as many of us are. Lucky is the person with matching serial numbers!!

There is also a link in the thread from Andrew giving more of the maths behind these coils.



https://www.vintage-radio.net/forum/...d.php?t=111382

Pete
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Old 7th Aug 2018, 6:33 am   #48
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Default Re: HRO and BC348

Some of the BC348's had a built in power supply. Be sure to add a fuse to it.

The one I have came with a note in what had been the PS compartment telling me that the PS had shorted out and the radio had caught fire. No fuse was ever designed into the PS.
Also note that the round cap cans that look like a little "pot" with mica or micarta on the top are failing a lot. If you decide to keep it, I would suggest re-capping. They contain paper dialectric caps and the acid in the paper is causing them to fail.

All in all a pretty good for its time, and very rugged receiver.
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Old 7th Aug 2018, 11:36 am   #49
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Default Re: HRO and BC348

Quote:
Originally Posted by G3VKM_Roger View Post
The G2MI marking may not mean that the holder owned your HRO but it might be a reference to the logging scale setting of that receiver on 3650kHz. G2MI in Bromley (erstwhile RSGB President) used to read the RSGB news and Log scale 337.5 could have been 3650, a likely freq for the news. Stick a sig gen on it and see what the dial reads!
David, did you check to see if that dial reading corresponded with 3650kc?

73

Roger/G3VKM
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Old 11th Aug 2018, 4:15 am   #50
G4YVM David
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Default Re: HRO and BC348

No Roger, Ive been busy and distracted by a friend's death.
I shall have a look today though, thanks for the reminder

David
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Old 11th Aug 2018, 6:27 am   #51
G3VKM_Roger
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Default Re: HRO and BC348

Very sorry to hear that, David. I don't have a "classic" HRO yet (although I'm getting one in October) so I can't make a measurement myself. I expect there's little difference between the dial readings of individual sets?

73

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