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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 30th Jul 2018, 6:01 pm   #1
G4YVM David
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Default HRO and BC348

I have recently acquired both an HRO with boxes of coils and a BC348. Why did I do this? Who knows. I wanted to listen to both and compare them I guess. It's fun. They compliment my 1154/1155 pair quite nicely but take up huge amounts of space so how long I will keep them, who can tell.

I adore the tuning dial on the HRO...what a genius of sleight of hand...turn the dial, watch the numbers change before your very eyes!

The 348 of course is a sexed up version of the 1155. It is somehow a better looking set, like American cars...the same as ours but different...



That's all, no questions, just thought I'd share my enjoyment.

David
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Old 30th Jul 2018, 6:14 pm   #2
HamishBoxer
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Default Re: HRO and BC348

Wonder which power supply you have with the HRO? The dog kennel or the other one?
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Old 30th Jul 2018, 6:59 pm   #3
Jon_G4MDC
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Default Re: HRO and BC348

BC348 with 915kHz IF is not a good choice if you live near 300kW on 909kHz as I do with R5 from Brookmans Park. It is always there as a spare BFO with modulation...
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Old 30th Jul 2018, 7:08 pm   #4
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Default Re: HRO and BC348

My PSU is the 686S...which I read is the battery unit, so it must have been modified if thats the case as it obviously (to me!) runs of house mains! Is this the Dog kennel one?

D
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Old 30th Jul 2018, 7:23 pm   #5
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Default Re: HRO and BC348

The Dog Kennel psu is prone to transformer failure,I have both mains one,s and a battery version.Though need to check on model numbers.

The better psu is square.
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Old 30th Jul 2018, 7:43 pm   #6
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Default Re: HRO and BC348

Thanks.

Well mine was owned at one time by G2MI, now SK and never known to me. I know this because he pencilled in the lid "G2MI. 36 50 LoG33 75", whatever that means!

I cant find any serial number in any of the usual places on the HRO so cant yet date it accurately. I think, because it has plastic insulator at the aerial bind posts and screw terminals, that it is post '39.

Theres a warning in y manual about shorting the speaker terminals if they are unused. Well, it looks to me that thet have not been used nor shorted...it was sold with phones to me. In the manual it says use speaker of 7000 ohms. If I use a modern speaker (much less than 7000) I find it works just fine (which I find odd), so do you think I will do ny damage by using this speaker?

D
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Old 30th Jul 2018, 7:51 pm   #7
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Default Re: HRO and BC348

Running the receiver without a feed to the anode risks damaging the screen grid, that's why the shorting link is recommended when using the headphone socket for headphones.

The primary of any old bog standard valve output transformer can be connected to the loudspeaker terminals, the secondary will drive a bog standard low impedance loudspeaker no problem.

The HRO is my all time favourite old time comms. receiver.

EDIT: Don't forget that some of the adjustable IF tuning capacitors have HT on them, same goes for the S meter set zero pot shaft....And what's on the rear chassis apron.

Lawrence.

Last edited by ms660; 30th Jul 2018 at 8:06 pm.
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Old 30th Jul 2018, 8:21 pm   #8
G4YVM David
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Default Re: HRO and BC348

Thanks. My speaker o/p drives a modern speaker just fine as is...very loud in fact, plenty of umph.

There seems to be ht on many places in an HRO...the coil packs for one! I wonder what engineer smirked as he realised THAT little beaut!

D
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Old 30th Jul 2018, 8:27 pm   #9
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Default Re: HRO and BC348

Quote:
There seems to be ht on many places in an HRO...the coil packs for one! I wonder what engineer smirked as he realised THAT little beaut!
That's why it was designed with a B+ switch....always switch it off when removing/inserting coil packs.

Lawrence.
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Old 30th Jul 2018, 8:58 pm   #10
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Default Re: HRO and BC348

G2MI I believe was a well known RSGB member?? Or did he produce rigs etc?
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Old 30th Jul 2018, 9:01 pm   #11
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Default Re: HRO and BC348

I don't know. I wish I could fathom his little code too. I bet it's blindingly obvious...
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Old 30th Jul 2018, 9:26 pm   #12
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Default Re: HRO and BC348

3650 was a frequency (3.650 MHz) used by the RSGB for news announcements for certain parts of the country....Maybe something?

Lawrence.
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Old 30th Jul 2018, 9:34 pm   #13
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Default Re: HRO and BC348

David,

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!

73

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Old 31st Jul 2018, 11:17 am   #14
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Default Re: HRO and BC348

Thank you Roger,president I remember now.Think that frequency was for GB2RS news service.

I still read on 1.990Mhz.
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Old 31st Jul 2018, 6:12 pm   #15
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Default Re: HRO and BC348

Quote:
Originally Posted by ms660 View Post
That's why it was designed with a B+ switch....always switch it off when removing/inserting coil packs.
But be aware that when the B+ switch is set to off the power-supply HT will charge to something rather-disturbingly-high [basically the peak voltage of the PSU HT secondary] and then when you've swapped your coil-pack and then flick the B+ switch you're dumping the 'highest-possible' charge from the PSU into the receiver circuits.

Which is *not good*.

This sort of unintended killer-voltage discharge - while maybe survivable with straight-from-the-factory new parts - is really stressful to 70+ year-old insulation. Us AR88 owners bypass the 'standby' position on the power-switch to safeguard our IF/audio-transformer insulation!
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Old 31st Jul 2018, 6:21 pm   #16
G4YVM David
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Default Re: HRO and BC348

I am a coward when it comes to mains and tend to switch the set off at the wall before changing packs.

Thanks though for the info.

On the coils I have tested, the frequency display is still in accord with the chart...which amazes me really. If it says such and such a freq will be on 123.5...there it is! I have so many packs though that I havent tried them all yet

D
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Old 31st Jul 2018, 9:55 pm   #17
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Default Re: HRO and BC348

The HRO manufactures instructions recommend switching the B+ switch to Off when changing coil packs as do the instructions in the EMER Technical Handbook for the Reception sets R106 MK I and MKII.

Switching it Off when removing/inserting coil packs and then On again never did any harm to any of the three HRO receivers that I owned and used over the years.

Lawrence.

Last edited by ms660; 31st Jul 2018 at 10:20 pm.
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Old 31st Jul 2018, 10:48 pm   #18
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Default Re: HRO and BC348

Tanuki and Lawrence are both eminently well qualified on the technical side AND ironically, have almost an equal number of posts I have followed the history of AR88 Output Transformers burning out off load over the years and the advice was always hard luck! until alternative ideas were brought forward but the protective by-pass was always employed for good reasons. Lots of people have commented that this was a surprising design fault in such a very well regarded radio but in the War Time rush Others have pointed out that in the "the moment" the thing was to keep going and [then] brand new spare OP transformers were on hand if a mistake was made. The only thing I'd say, as not very technically adept contributor is that I've read so much about the AR88 Trs disasters but nothing about any problems with the HRO switch yet On the face of it, switching off the power when you might have a bad outcome seems obvious but it doesn't mean there is no additional risk. On the other hand it can't be on the same scale as the already established AR88 problem can it?.

Dave W
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Old 31st Jul 2018, 10:59 pm   #19
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Default Re: HRO and BC348

The BC348 will be full of the micamould zero ohm resistors. Mike must have been the guy who made them as you won't find any mica in them. Most have already had the heater wiring changed to parallel and a PSU put in place of the dynamotor.
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Old 31st Jul 2018, 11:15 pm   #20
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Default Re: HRO and BC348

Quote:
Originally Posted by G4YVM David View Post
Thanks. My speaker o/p drives a modern speaker just fine as is...very loud in fact, plenty of umph.
Has somebody fitted a speaker transformer under the chassis? This is quite a common HRO mod to avoid nippy voltages on speaker terminals!

73, Colin
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