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Old 1st May 2017, 2:53 pm   #21
Radio Tech
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Default Re: GEC BRT402D Receiver.

And here is another two pictures, the capacitors within this section were well and truly hidden, I found the only way I could get to these was to remove the coil, (spanner job) and then first remove the larger of the three capacitors then the two smaller ones, an 0.1uF and two 0.01uF. On replacement, I added an extra earth tag and then positioned these capacitors so that they were much easier to get to (see second photo). There are three more capacitors that are going to be tricky to get out, one of them being in the third coil pack section nearest the mains transformer, but there it is, I am sure I will find a way of dealing with it.

Regards

Ken
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Old 1st May 2017, 3:13 pm   #22
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Default Re: GEC BRT402D Receiver.

Keep up the good work. Seeing what you have done so far I'm glad I didn't take it on.

Al
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Old 1st May 2017, 5:05 pm   #23
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Default Re: GEC BRT402D Receiver.

Good work and a interesting read . I find that mine runs far cooler on 120v than it does on 240/220v .
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Old 1st May 2017, 8:14 pm   #24
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Default Re: GEC BRT402D Receiver.

Though out-of-band for discussion of this specific receiver, I find the same beneficial cool-running-when-on-120V effect with my Eddystone 840A. In-cabinet series mains-droppers and sweaty regulator-feed resistors are the enemy of cool running . . ..
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Old 1st May 2017, 8:53 pm   #25
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Default Re: GEC BRT402D Receiver.

Good stuff, I hope all the painstaking work is satisfyingly fruitful- the pictures reminded me that the RF coilboxes are so full of components that they ended up fitting a couple of decouplers externally and looping the leads through rivet holes! If anyone ever asks why someone needs a few different sizes of needle-nose pliers, point them at a BRT400. I also remember thinking that GEC ought to have punched a dozen or so 3/8" holes in the chassis plate between that big choke and the mains transformer to encourage a bit of convection (I normally think and speak metric but that would be inappropriate here....).

Hopefully, the valves will at least be good enough to get the set going- I suppose there's a gamble with ex-professional kit in that it might be low hours and quickly declared redundant, or sat in a rack for decades running virtually 24/7 being cumulatively fried with neighbouring sets, then dumped unloved in a yard for a while.

Sometimes, you get a hint of a manufacturer's principal interest from the way kit is made- Eddystone were apparently into decorative die-casting and wrinkle paint before their radios, and the BRT400 shouts "kitchen appliances" with its sturdy but precise steel foldings, pastel paintwork and chroming and the hefty Berco wire-wound pots and tubular power resistors. The huge signal terminals on the rear panel look as if they were originally made for connecting up cookers. Comms receivers tend to be a dour and functional bunch but the BRT400 must be one of the more attractive looking examples.
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Old 2nd May 2017, 2:21 pm   #26
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Default Re: GEC BRT402D Receiver.

The lower voltage and smaller component suggestions to lower the wattage are interesting. Given what David said [in post 12] about a "quart in a pint pot" design, I suppose the usual "fix" re providing ventilation holes would not apply! As it's for home use, perhaps a mesh cage rather than a box would help. You would sometimes get that in TX's of the period.

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Old 5th May 2017, 12:21 pm   #27
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Default Re: GEC BRT402D Receiver.

Hi folks

Yes indeed it is a pain staking task to take on and thank you everyone for their input so far, to date I have replaced 98% of the caps that is the paper types the manufacturer used, I did find one mica cap s/c and the anode load resistor burnt out which was in the early stages of the set. Now got the BFO working but at the moment got to find out why there is no signal getting through, all the valves have HT Volts on their anodes so a bit more investigation as to why no signal. I will but another picture or so shortly.

And yes I do agree they do run hot especially those resistors on top of the mains transformer.

Best wishes

Ken
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Old 5th May 2017, 4:46 pm   #28
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Default Re: GEC BRT402D Receiver.

Hello folks

Just got a bit of a snag with the progress, went to check the crystal and found the glass envelope it was supposed to be in parted company with the rest of it, its like a B7G valve and its frequency is 455K/C so now got to find one from somewhere.

Ken
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Old 5th May 2017, 6:28 pm   #29
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Default Re: GEC BRT402D Receiver.

Does lack of an envelope stop it working? I wouldn't expect its operation would require a vacuum.
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Old 5th May 2017, 6:51 pm   #30
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Default Re: GEC BRT402D Receiver.

I'm guessing it will work but maybe not on frequency and maybe not for long.
Airborne rubbish will settle on the plate and things will go downhill from there.
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Old 5th May 2017, 8:25 pm   #31
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Default Re: GEC BRT402D Receiver.

I might be able to help with a replacement, I'll try and have a look over the weekend.
ATB
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Old 6th May 2017, 4:12 pm   #32
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Default Re: GEC BRT402D Receiver.

Mine (a 402K) needed a linking plug on the back panel to let the VFO through - it had been designed for diversity mounting with a shared VFO. I just bridged it out at the LO valve.

Cheers,

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Old 9th May 2017, 5:09 pm   #33
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Default Re: GEC BRT402D Receiver.

Hi folks

I found another cap in an awkward place, and the only way you can get to it was to unsolder all the connections to the small tag board seen on the right of the picture, and go in there with a soldering iron and aim for the joint. But so long as you get the old cap out at least you have the lead to grab hold of and snip it short.

Still not resolved as to why I cant get some signal through though,

Best wishes

Ken
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Old 15th May 2017, 11:05 am   #34
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Default Re: GEC BRT402D Receiver.

Hi folks and those following this,

I have narrowed the problem down to the first two RF stages on the front end, but can't work out why at the moment any signal injected into these stages will not get though. I injected 455kc into where C49 is on circuit and that comes right through to audio stage and the S meter shows this but nothing via V1 and V2 which are RF amplifiers attached to tuned circuits.

Best wishes

Ken
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Old 15th May 2017, 11:33 am   #35
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Default Re: GEC BRT402D Receiver.

Are V1 & V2 voltages ok? What frequency are you injecting into V1 & V2?

Lawrence.
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Old 15th May 2017, 12:22 pm   #36
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Default Re: GEC BRT402D Receiver.

I forgot to ask, is the Local Oscillator working?

Lawrence.
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Old 16th May 2017, 11:10 am   #37
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Default Re: GEC BRT402D Receiver.

I'm assuming yours is a rack mount (being a 402), in which case it's quite possible the LO has been disabled. Mine had coax running to the back panel for an external VFO, which has now been removed - it was corroded and replacement seemed like unnecessary clutter in an already tight space.
73,

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Old 16th May 2017, 2:33 pm   #38
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Default Re: GEC BRT402D Receiver.

Hi Lawarence, voltages seem ok on V1 and V2, I tried injecting various frequencies such as 1mhz, 200kc, 1500kc in the aerial socket but nothing, and yes Colin it is the rack mount version and yes the thought had crossed my mind about the LO being either disabled or not working so that is my next step to check this out, at the moment all I get is a mushy noise and a few crackles but nothing tunable.

Best wishes

Ken
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Old 19th May 2017, 9:04 am   #39
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Default Re: GEC BRT402D Receiver.

Hi folks

Bad news about the set, the mains transformer gave up and started to smoulder, so I have now had to resign and give in on this after all the time I have spent on it and the set is only fit for the scrap yard, very disappointing I know, but that is it, the end of the line.

Regards

Ken
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Old 19th May 2017, 10:46 am   #40
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Default Re: GEC BRT402D Receiver.

Sorry to hear that Ken, it's a big pain to have invested all that time, effort and componentry only to have that happen. I wouldn't be surprised if years of hot running- quite possibly in the professional environment of being pretty much permanently powered- had thoroughly cooked that big lump of a transformer and made the insulation brittle and carbonised. It's a big enough radio as it is without resorting to the "HRO option" of an umbilically-connected power-pack, though not out of the question and it would keep things cooler!,

Colin.
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