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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 1st Aug 2018, 7:31 am   #21
G4YVM David
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Default Re: HRO and BC348

Ref the added transformer...I wondered that. I was about to look when i tuned to All India radio on about 1MHz and got distracted....SWLing.

D
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Old 1st Aug 2018, 9:54 am   #22
ms660
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Default Re: HRO and BC348

Don't forget that the TR switch on the AR88 and the B+ switch on the HRO have two different circuit regimes....

The TR switch on the AR88 does not isolate the HT from the sound output valves anode, the valves anode, output transformer primary and the tone correction capacitor that's connected between anode and chassis are connected to HT at all times.

The B+ switch on the HRO isolates all load circuits.

Lawrence.
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Old 1st Aug 2018, 10:43 am   #23
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Default Re: HRO and BC348

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Originally Posted by ms660 View Post
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.
Oops! I didn't get a manual with my HRO and now that I look at its rear panel I see that the speaker terminals are open (I've always just used phones.) and to make matters worse my BSW terminals have a wire link across them.

My RF stages appear to have survived lots of coil pack changes but I've no idea about the state of my 6V6.

Peter
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Old 1st Aug 2018, 11:41 am   #24
ms660
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Default Re: HRO and BC348

Out of interest, apart from the output valve, does the receiver that's the subject of this thread use metal IO valves or glass UX6?

Do any of the coil packs have bandspread?

Lawrence.
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Old 1st Aug 2018, 1:11 pm   #25
HamishBoxer
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Default Re: HRO and BC348

My HRO has glass valves.
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Old 1st Aug 2018, 5:02 pm   #26
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Default Re: HRO and BC348

Colin,
This is my HRO with the transformer mounted under the chassis. It is mounted over the HT link cut out which I carefully preserved in case any one wanted it back original. What is not shown is under the transformer I permanently mounted 2 series 6.8 Ohms WW ( 13.6 Ohms) resistors across the speaker terminals so that the transformer could never be completely open circuit. I cant remember but I think the transformer was 8 Ohms and the 13.6 was an arbitrary selection to give load but not excessive.

Pete
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Old 1st Aug 2018, 7:24 pm   #27
G3VKM_Roger
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Default Re: HRO and BC348

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Originally Posted by Colinaps View Post
Has somebody fitted a speaker transformer under the chassis? This is quite a common HRO mod to avoid nippy voltages on speaker terminals!
Can anyone recommend an "off the shelf" HRO output transformer?

73

Roger
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Old 1st Aug 2018, 7:57 pm   #28
ms660
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Default Re: HRO and BC348

https://uk.rs-online.com/web/p/audio...rmers/2106475/

Lawrence.
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Old 1st Aug 2018, 9:27 pm   #29
G3VKM_Roger
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Default Re: HRO and BC348

Thank you, Lawrence. That's a useful type.

Cheers

Roger
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Old 2nd Aug 2018, 12:26 pm   #30
Junk Box Nick
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Default Re: HRO and BC348

Quote:
Originally Posted by G4YVM David View Post
"G2MI. 36 50 LoG33 75", whatever that means!
I remember the regular Sunday morning GB2RS news broadcasts on 80m in the early 1970s. Due to ground wave the broadcasts used to work their way up country from various stations on the same frequency 3.65MHz. They might even have been on AM. My local one was from Derby and I think was from G2CVV, though I could often hear G2MI. After the broadcast was over, the operator would take calls under his own callsign.

G2MI, Bromley, Kent was the address of the RSGB QSL Bureau for many years.

I have an HRO but it's not been in use for years. I don't have a full set of coil packs and think those I do have have been adjusted at some point to tweak coverage. It's in the round tuit queue. Always fancied a BC 348. There was one brought into school for a while and gave us lots of break-time fun. I always liked the 'cheese segment' tuning dial. I'm sure there was one at NVCF but fortunately I was spent out by then...
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Old 2nd Aug 2018, 3:44 pm   #31
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Default Re: HRO and BC348

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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.
Some HROs have been modded by the fitting of a speaker transformer internally - this could, possibly, account for the performance

J
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Old 2nd Aug 2018, 7:26 pm   #32
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Default Re: HRO and BC348

If not familiar with the tuning dial/drive system and want to remove any of the bits for servicing/lubrication or whatever etc then check these two sites out first, in a nutshell the centre bearing hole in the tuning shaft bush is off-centre from the bushes outer bearing surface, the bush is also marked "top":

https://www.prismnet.com/~nielw/PW_N...l/hro_dial.htm

https://aa7ee.wordpress.com/2015/02/...pw-gear-drive/

Lawrence.
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Old 3rd Aug 2018, 2:24 pm   #33
G4YVM David
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Default Re: HRO and BC348

Sorry, I have been very busy. I shall examine the valves for IO as requested and feedback...
David
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Old 3rd Aug 2018, 2:47 pm   #34
ms660
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Default Re: HRO and BC348

Output valve aside, metal valves were used in the later versions, glass valves in the earlier versions, the plug-in Xtal was also dispensed with on the later of the glass valved versions and all of the metal valved versions.

Lawrence.
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Old 3rd Aug 2018, 3:26 pm   #35
G4YVM David
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Default Re: HRO and BC348

Mine seems to be all valves.
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Old 3rd Aug 2018, 3:39 pm   #36
ms660
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Default Re: HRO and BC348

Yes, they would be valves....

Looks like the late version of the all glass valve receiver, usually known as the HRO MX, the S meter scale was usually white on them.

Lawrence.

Last edited by ms660; 3rd Aug 2018 at 3:47 pm. Reason: correction
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Old 3rd Aug 2018, 3:51 pm   #37
G4YVM David
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Default Re: HRO and BC348

Mine is a browny amber S meter, which I have read means it started life as yellow amber and has aged. I still havent located a stamped s/n on mine. I have found a number, C390, stemcilled onto the chassis which may be a s/n 'repeat' but I am not sure. I need to remove the chassis from the case to see whether it is stamped out of sight by the aerial bind posts...but why it would be out of sight I can't understand.
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Old 3rd Aug 2018, 4:04 pm   #38
ms660
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Default Re: HRO and BC348

I had one that had a white scale, calibrated in mA, apparently at some point there was a shortage of certain types of meters during the war.

Lawrence.
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Old 3rd Aug 2018, 5:39 pm   #39
HamishBoxer
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Default Re: HRO and BC348

Mine is white and nought to one milliamp.
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Old 3rd Aug 2018, 5:41 pm   #40
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Default Re: HRO and BC348

Davids HRO is a curious one.
Either it has the internal crystal or else it is one without a crystal filter.
We haven't seen a front panel picture so can't tell if the controls are there.

Also interesting is the braid running from ground lug on crystal filter box / main tuning capacitor ground link. It is bolted to the top cap of the first IF valve.

None of mine have that... I wonder if it was to stop some kind of pickup at IF?

Thats the sort of tricks I have to get up to with the BC348 and 909kHz from Brookmans Park!
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