GEC BRT400D Communications Receiver

[Orthicon]

Hello to fellow members,
I have just been given a GEC BRT400D, in fabulous condition and working. I confess to being a complete and utter newcomer with regards to communications receivers, and would be extremely greatful for any information or advice. I do have some specific questions that would be of particular interest;

Approximately what year would the D variant have been manufactured?

How many different variants were made, and what were the differences?

How reliable are the original capacitors that were fitted?

Does anyone have a component list and a component layout specifically for the D variant?

Ian.

[Dave757]

Hi Ian,

The highest model letter I have ever seen was the BRT 400K, but I think
the only ones I have seen are the B D and K. I haven't got a djvu reader
but if its any use to you, BAMA has a BRT 400 manual listed under GE.

I think they were all 1950's sets.

Kind regards

Dave G0ELJ

[Orthicon]

Dave,
unfortunately the particular manual you refer to covers the earlier models, which had a slightly different component layout, but with very different component values, especially in terms of the resistor values.

thanks anyway.
Ian.

[Rupert Bullock]

Hello Ian,
You have a very nice receiver there in that BRT 400D and it will keep you warm in the winter too.
I have some A3 sized copies of the 400D and E circuit and component list. I can post to you if you let me know your address in a PM.
I don't know about all the different versions but the D is the "standard" model, the E includes a 500kc/s calibrator and DN and EN versions have a 9kc/s rejector filter in place of the standard 1kc/s AF filter.
The 400 models are table mount and the 19" rack mount versions are 402.
My own RX is a slightly sorry 402E which I need to spend a good few hours on to return to how it was some years ago.
I hope this helps.

Rupert

[Orthicon]

Thanks Rupert,
Private PM sent.

Ian.

[Orthicon]

Just out of interest, all the capacitors in the set are the originals -all are metal bodied and shrouded in a clear pvc type covering. Many are manfactured by Hunts - see photos.

Unless showing signs of oozing or leakage are they pretty much ok to be left alone, or should all of them be replaced?

Any advice is much appreciated.

Ian.

[HamishBoxer]

Most likely ok Ian.

[glowinganode]

Originally Posted by Orthicon

Just out of interest, all the capacitors in the set are the originals -all are metal bodied and shrouded in a clear pvc type covering. Many are manfactured by Hunts - see photos.

Please see this thread, you may be able to provide useful information.
Cheers,
Rob.

[Andrew Sinclair]

Hello Ian,

I restored a BRT400K a few years ago.

According to my copy of "A guide to Amateur Radio" by Pat Hawker, the BRT400 was in production from 1947 to 1967. My 1961 Radio Communication handbook has an advert for the BRT400K.
The BRT400K had mostly miniature valves such as 6BA6, 6BE6, EL84 as opposed to the mostly B8B based valves in the earlier versions. I think the older valves were out of production by the time the K came along.

These are good sets. The detector has particularly low distortion, making it very good for listening to AM.

The power supply uses small value oil filled paper capacitors rather than the usual electrolytics for smoothing. To reduce the HT ripple it has a smoothing valve V13 (EL84 on a BRT400K) which sits across the HT rail and is fed with a sample of the HT ripple. The valve gain is adjusted to cancel out the hum. I have not seen this done on any other radio.

My example had a lot of electrically leaky metal cased capacitors. Ones to watch out for are C112 which is in the grid circuit of the smoothing valve. If this leaks the valve draws an enormous HT current. On my example it had melted the wiring harness under the chassis, along with much other damage.

Most sets have a capacitor between the 1st AF stage and the output valve (often referred to as THAT capacitor). If it leaks then this valve also draws a huge current and damages other expensive components.

On the BRT400 series there are three capacitors C103 , C109 and C110 which can cause this sort of failure. The leakage from all three adds together. The output valve grid resistor is 4.7M ohm just to make things worse!

I would strongly recommend changing all these capacitors for piece of mind. At least measure the signal grid voltages of the two power valves and check that they are close to 0V.

Good luck with your restoration.

Andrew

[Orthicon]

Thanks Andrew,
I will replace the capacitors you have mentioned just to be on the safe side as a preventative measure.

My set uses mostly B8B valves with only three of the valves being miniature. The S130 Cossor branded valve gives off a particularly mesmerising purple glow.

It has a very low serial number, so I would think from you info it is an early Fifties made model.

I also have a copy of an advert for the later BRT400K, which I have attached, - it maybe the same as yours. The BBC definately had no shortage of them judging from the photo!


Ian

[Andrew Sinclair]

Hello Ian,

I have heard that the audio quality of these sets was so good that the BBC was able to re-broadcast transmissions using this receiver.

The AGC circuit is unusual in that it has DC amplification. Most sets have a simple diode.
There should be a paxolin panel on top of the mains transformer containing some power resistors and the mains voltage selector links. This has a second panel on top with ventilation holes. On all examples I have seen, the paxolin is burnt black and crumbling away. If yours is in good condition, it has probably not seen much use.

If your set is a table model, it is worth checking that the blanking plate is fitted inside the left hand side hand hold cast into the side panel. (I don't mean the chrome handle on the front panel.) This plate was added to later sets to prevent finger contact with the mains selector links when lifting the set while running. Please ask if my description is not clear enough.

Andrew

[glowinganode]

I seem to have acquired one of theses sets today at Harpenden.
Watch this space.
Rob.

[turretslug]

Nearly as good for the biceps as an AR88. At least most have 'andles.

I had one years ago, well built or what.

[dave walsh]

I particularly recall [because I didn't know this set at all] a story in [Radiophile ?] that one was found in a scrap yard having been run over by a lorry and buried in the mud! After a thorough housing (hosing) inside and out, it was left to dry and then worked first time!
Dave W

[Sean Williams]

Oh dear Rob!

Still, it is a nice looking beastie - I've got some spare railway sleepers here if you want to reinforce the bench!

[glowinganode]

I've had a chance to look mine over, it's in suprisingly original condition internally.
I've made a start on replacing (restuffing) the caps, both KT81's were dissipating around 30W a piece!
It must be an early model, loctal front end and EF91 I.F.
Strikes me as being an Anglicised AR88, the tuning gearbox and coil pack arrangement look suprisingly familiar.
Rob.

[turretslug]

We've all heard of "that cap"- well, the one between HT and V13 g1 is "that cap- with a vengeance"!

[glowinganode]

That was the first one I replaced.
The HT voltage increased 40V after so doing, I estimate V13 was drawing 100mA!
Rob.