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Old 7th Nov 2018, 11:33 am   #1
its ur aerial
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Default GEC BRT400 receiver.

Been offered a GEC BRT400 in working condition, never seen or used one, does their performance compare with a AR88 for example, I believe the BBC used them, for monitoring.
All comments appreciated.
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Old 7th Nov 2018, 11:43 am   #2
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Default Re: gec brt400

They're OK, but there's a lot packed into the case so they run catastrophically hot and suffer accelerated component-failure as a result.

As with any receiver that's 50+ years old, expect to replace a lot of leaky capacitors!
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Old 7th Nov 2018, 1:16 pm   #3
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Default Re: GEC BRT400 receiver.

Don't forget the muscles when you collect it!
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Old 7th Nov 2018, 1:38 pm   #4
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Default Re: GEC BRT400 receiver.

^Wot they say^! Potentially, it's an excellent radio- it follows the relatively conventional and established architecture of the likes of HRO, CR100, AR88 etc, but in an era when the market was awash with high-performance comms-orientated receivers from WW2, the BRT400 tried a bit harder with circuit detail, particularly as regards AGC performance, low-distortion detection and good audio fidelity. Unfortunately, the design crams rather more componentry than an AR88 into a shorter chassis and it must be one of the most challenging sets to work on. To compound the problem, with the CR100 and the AR88, the RF section can be removed from the main chassis as a "sled" for easier overhaul but the BRT400 has all the RF section screening seam-soldered to the main chassis making this part of the set something of an access nightmare. Not impossible, just very difficult and trying!

Further more, there's a lot of power consumed- a similar number of valves to an AR88 take about twice the HT power. The signal valves represent an early approach to low-noise performance, taking quite high anode current, the AF output is a beefy KT81 with nearly an amp of heater current and, as if that wasn't enough, another KT81 provides active smoothing. All that makes for a whopping mains transformer, hemmed in on the busy chassis with a gently-charring choke barbecueing it from underneath and a couple of big tubular wire-wounds roasting the terminal panel on top. Check the loom here carefully, the insulation chars and crumbles and as it carries mains and HT AC, it's no trifling problem.

It's a shame that they didn't relent to a chassis a few inches deeper, more like the AR88. It does have a certain "post-war kitchen appliance" charm with its chroming and pastel colours, at least compared to many dour and utilitarian comms receivers.

TBH, not for the faint-hearted, though an aspiring key-hole surgeon might relish it!
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Old 7th Nov 2018, 2:24 pm   #5
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Default Re: GEC BRT400 receiver.

They certainly look great and if one was ever offered me then my hand would be up.
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Old 7th Nov 2018, 10:15 pm   #6
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Default Re: GEC BRT400 receiver.

Was this GEC's one and only attempt to produce a comms receiver?
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Old 7th Nov 2018, 10:39 pm   #7
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Default Re: GEC BRT400 receiver.

Depends of whether they already owned Marconi at the time, I suspect.....
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Old 7th Nov 2018, 10:42 pm   #8
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Default Re: GEC BRT400 receiver.

I had one of these for some years in the '70s. Lovely to look at, very nice to use, with sensibly large ergonomic knobs. Mine had had a product detector fitted (by some previous owner) otherwise un-molested.
One thing I recall about it was the complete (I think) absence of electrolytic caps. Hence the active smoothing arrangement. The power consumption is alarming, though.
Would benefit from an EF183 in the 1st RF amplifier position, as the sensitivity was not terribly good at the HF end of the coverage.
There is a service manual on the "Boat anchors" website. http://bama.edebris.com/manuals/ge/brt400/ Tony.
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Old 7th Nov 2018, 10:52 pm   #9
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Default Re: GEC BRT400 receiver.

No. it wasn't GEC's only attempt. They later did the RC410 transistorised, synthesised job which was much more of an epic.

The BRT400 is probably the last hurrah of the simple architecture of a down converter to a 450-odd kHz IF.

GEC threw a good bit more effort into the design of each stage and used expensive parts and expensive labour-costing construction methods. It is probably the best of its class, quite a bit better than the CR100, a bit better than the HRO and AR88.

But the writing was on the wall. Good image rejection needed multi-superhets and the appearance of SSB on the scene needed proper shaped multi-crystal filters. THe BRT400 sounded splendid on AM broadcasts and was useable on CW, but SSB left it behind.

Having and restoring or just keeping up with the maintenance demands of this hot-running beastie is something you'd do for historic reasons. If you need to ask about it, you probably aren't historically connected to it, and I'd say it probably isn't the right radio for you.

It's perhaps the best sounding set for MW/shortwave AM broadcasts, if they only still broadcast broadband AM. Sadly, thet went down the pan with the regularised 9kHz spacing bandplan.

If you want a high performance radio with valves, the Racal RA17/RA117 is far more complex, yet easier to maintain... but it's not good for SSB.

If you want SSB for the amateur bands and oceanic aviation, then the RA1772 is maybe the way to go. You lose the valves, but gain a fabulous receiver.

Given the difficulty and frequency of repair a BRT400 is not the right receiver to have if you want to use it.

It is the right receiver to have if you are attracted to the BRT400 specifically, maybe because of its BBC history?

David
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Old 8th Nov 2018, 3:06 pm   #10
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Default Re: GEC BRT400 receiver.

Many years ago, I acquired one of these at a price that simply could not be argued with - so a lucky find! However, I simply could not discover how the case came off! - Perhaps I didn't try hard enough! Anyway, it seemed to working fine 'as is' - so I sold it via an on-line auction site - and I do believe it ended up in Germany.
So no, I would not want another one, either as the owner nor as a repair for someone.

Al.
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Old 8th Nov 2018, 4:12 pm   #11
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Default Re: GEC BRT400 receiver.

I have had a BRT402 languishing under the bench in my shed for probably 25 years. I did get it going for a while but had to give up after one of the switchable bandwidth IFT's developed a fault. After spending too much time dismantling the thing and dealing with hard to get at components I threw the towel in, and there it has remained, unmoved all this time. Weighs a ton too! And no, this thread hasn't inspired me to have another go at it. It has two friends to talk to under there...CR100's.
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Old 8th Nov 2018, 8:28 pm   #12
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Default Re: GEC BRT400 receiver.

A few (not that many) years ago, I was working in Lincoln and took the opportunity to browse Birkett's- in one box, there were a number of NOS IFTs that I recognised as using the same moulded base and can size as the BRT400 with its not-so-great scheme of trimmer capacitors adjusted through large holes in the top of the can (so that they accumulate dust). Stupidly, I clean forgot to enquire as to exactly what they were whilst continuing to while away time in this Aladdin's cave of electronics. Naturally, it's entirely possible that they were associated with some other GEC RF device, but the memory jog is tantalising. It seems that one of this set's Achilles heels was flashover and failure of the final IFT winding (overwound overcoupling link) when tuned to a strong signal with AGC malfunctioning, or simply switched off.

I think that the overall gist of the thread is that an AR88 would probably be less strife!- not as pretty, needs a few inches more shelf-depth and you'll have to choose between one with MW or LF coverage, but a whole lot easier to maintain with more widespread spares and extensive knowledge base.

Apparently, earlier desk-case BRT400s had a nasty surprise lurking- when putting fingers into the LHS hand-recess for moving, finger-tips could come into contact with distinctly spikey mains transformer terminals!- this was corrected in later versions. A contrast with the notably safe AR88's topside.
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Old 8th Nov 2018, 9:57 pm   #13
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Default Re: GEC BRT400 receiver.

I picked up a BRT400 cheaply several years ago with the intention of restoring it. It certainly looked great, with the enormous edge-lit tuning scale and separate bulbs for each band. The design seemed interesting with the active smoothing and, as as boxdoctor noted, complete absence of electrolytics. The amplified AGC system seemed neat. However, it did look like the whole thing had been designed to maximise power consumption.

It turned out that the (huge) mains transformer had shorted turns, not surprisingly given the barbecue heat in there. I got as far as finding a replacement that would have fitted and been adaptable, but then realised that the amount of under-chassis work needed was going to be too much for me. I decided to cut my losses and pass the receiver on.

I would love to have got it going, though, and have had it on display!

Chris
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Old 8th Nov 2018, 10:10 pm   #14
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Default Re: GEC BRT400 receiver.

I have one.

As has already been mentioned, the unconventional power supply arrangement is a big problem - on the receiver I have the original transformer had already been replaced by a real mess of transformers and bodgery.

I ended up rebuilding the PSU with a different transformer, and conventional smoothing, I took advantage of my transformer having a HT voltage that was far too high, and floating the centre tap above ground via a string of power resistors to give me a bias supply for the rest of the receiver.

I have to say, it is a delight to use, and well worth all the hard work repairing it - the hefty output stage and well designed RF bits really make broadcast listening a pleasure.
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Old 8th Nov 2018, 10:37 pm   #15
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Default Re: GEC BRT400 receiver.

Quote:
Originally Posted by turretslug View Post
with the CR100 and the AR88, the RF section can be removed from the main chassis as a "sled" for easier overhaul
Does it really? I never knew that when I had an AR88. The RF section just looked like a square screened box that was fixed.

Cheers

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Old 8th Nov 2018, 11:40 pm   #16
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Default Re: GEC BRT400 receiver.

Quote:
Originally Posted by Radio Wrangler View Post
No. it wasn't GEC's only attempt. They later did the RC410 transistorised, synthesised job which was much more of an epic.
David
I have one here (RC410R), stored on behalf of my radio club. The set is ex the RMS Queen Mary and was subsequently part of an operational amateur radio exhibit at Bletchley Park. A very interesting and unusual design.

"Epic" would probably apply to the task of getting it back to working order as one of the synth boards is on SRBP and has warped badly due to heat. And also to the amount of detail in the service manual, right down to component level and taking up 4" of shelf space.

Not so much a job for a rainy day, as for an entire monsoon season. I suspect that restoring a BRT 400 would be a doddle in comparison...

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Old 8th Nov 2018, 11:43 pm   #17
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Default Re: GEC BRT400 receiver.

It does indeed- I expect that in many sets the fact that the RF assembly is underslung from the main chassis is concealed by decades of dust and tarnish but removal of around a dozen screws around its periphery and the disconnection of a similar number of wires plus release of the tuning drive (and no doubt one or two other things that I've omitted!) allow it to be removed. At that point, it's only "quite large" and "quite heavy", i.e. vastly more manageable than the complete chassis! A whole lot easier to root out the Micamoulds, gone-sky-high composition resistors, etc. When I overhauled mine, I further removed the screening panels on RF and oscillator sections that face the IF strip so as to drill and fit them with a row of feedthrough capacitors in the appropriate places for all the heater, AGC, +150, +250 etc. rails, feeling that this made re-connection easier and neater. OTT, really, but it was a case of "while it's all out, it's only a few more minutes work". It also made it easier to access the IO valve bases and their components while they were removed.

Crossed with m0cemdave!
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Old 9th Nov 2018, 12:14 am   #18
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Default Re: GEC BRT400 receiver.

The RC410 I had was one of the prototypes.

I had it running with all the cascaded switches and their Geneva-wheel linkages working freely. Operation was very unreliable due to tracks cracking on the warping SRBP boards.

I toyed with the idea of making FR4 boards and transferring the parts across, but the tediousness of tuning convinced me to save my effort. Nice filters, awkward AGC. Pig to tune - only 100Hz steps if you kept using the clunky push-pull tuning speed 'gearchange' and you always had to fiddle the fine tune pot. Nice filters.

A receiver for sked working, not for hunting around.

I also had a Marconi H2900 which was worse! Sosin's Folly they called them.

David
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Old 12th Nov 2018, 7:43 pm   #19
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Default Re: GEC BRT400 receiver.

Quote:
Originally Posted by CarbonMike View Post
Was this GEC's one and only attempt to produce a comms receiver?
There may have been another one other than the RC410 family.

On p. 165 of his article "Trends in Receiver Front-ends", RSGB Bulletin, Sept 1963, pp. 161-167, Pat Hawker mentioned, but did not reference, a paper given by A. Cormack of G.E.C. The paper was titled "An H.F. Receiver and Synthesizer designed for use on H.M. ships", I.E.E. Convention on H.F. Communication, March 1963, pp. 299-306.

Pat's interest was in the design of the front-end and its strong signal handling performance. The design was single conversion with a 1.6MHz i.f. and a synthesizer which tuned in 100Hz steps. The paper does not go into the design of the synthesizer, noting that it had already been described elsewhere, ie E.S.Carint and E. Ribchester, "The Synthesis of High Purity Oscillations Suitable for Single Sideband Receivers", J. Brit. I.R.E March 1961, Vol. 21 No. 3, pp. 237-240.

I wonder if this receiver was a forerunner to the RC410 ?

Sadly the papers from the 1963 Convention are very hard to find. I know of only three copies in libraries in the U.K., and the British library does not appear to have one. The convention was organised by the Electronics Division of the I.E.E, and they published the papers as E.D. 4 (as shown on the spine), and not as a set of I.E.E conference proceedings which had recently been started. This was the first I.E.E convention on H.F. Communication since the Radiocommunication Convention in 1947 (J. I.E.E. Vol 94, 1947,part IIIA, Nos 11-16)

Finally, there was some discussion about the RC410 in a thread last year. See:
https://www.vintage-radio.net/forum/...d.php?p=940172
with some serious history from Synchrodyne.

73 John
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Old 12th Nov 2018, 9:20 pm   #20
John KC0G
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Default Re: GEC BRT400 receiver.

Quote:
Originally Posted by CarbonMike View Post
Was this GEC's one and only attempt to produce a comms receiver?
There may have been another one other than the RC410 family.

On p. 165 of his article "Trends in Receiver Front-ends", RSGB Bulletin, Sept 1963, pp. 161-167, Pat Hawker mentioned, but did not reference, a paper given by A. Cormack of G.E.C. The paper was titled "An H.F. Receiver and Synthesizer designed for use on H.M. ships", I.E.E. Convention on H.F. Communication, March 1963, pp. 299-306.

Pat's interest was in the design of the front-end and its strong signal handling performance. The design was single conversion with a 1.6MHz i.f. and a synthesizer which tuned in 100Hz steps. The paper does not go into the design of the synthesizer, noting that it had already been described elsewhere, ie E.S.Carint and E. Ribchester, "The Synthesis of High Purity Oscillations Suitable for Single Sideband Receivers", J. Brit. I.R.E March 1961, Vol. 21 No. 3, pp. 237-240.

I wonder if this receiver was a forerunner to the RC410 ?

Sadly the papers from the 1963 Convention are very hard to find. I know of only three copies in libraries in the U.K., and the British library does not appear to have one. The convention was organised by the Electronics Division of the I.E.E, and they published the papers as E.D. 4 (as shown on the spine), and not as a set of I.E.E conference proceedings which had recently been started. This was the first I.E.E convention on H.F. Communication since the Radiocommunication Convention in 1947 (J. I.E.E. Vol 94, 1947,part IIIA, Nos 11-16)

Finally, there was some discussion about the RC410 in a thread last year. See:
https://www.vintage-radio.net/forum/...d.php?p=940172
with some serious history from Synchrodyne.

73 John
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