Roberts BR added to my collection

[bobhowe]

Hi after getting a Roberts P4A radio discussed on another thread i have just bought a Roberts BA as David Boynes was telling me that the B7G Miniature valve sets are very good performers as well . It needs a power plug & on / off switch knob . I have downloaded from this site the 1123 Trader sheet that covers the CR mains and battery set as well as the BR battery only version but some of the component values are different to the BR on the Trader sheet here is some pictures of the set kind regards Bob

Why the dark side? I had one of these, worked well, now at the Chiltern Open Air Museum in pride of place in the grown ups bedroom of the "Amersham Prefab".

[bobhowe]

Originally Posted by merlinmaxwell

Why the dark side? I had one of these, worked well, now at the Chiltern Open Air Museum in pride of place in the grown ups bedroom of the "Amersham Prefab".

Hi Just a bit of fun never had a battery valve set till i got the P4D an did not know how really got they are kind regards Bob

[FERNSEH]

Hi Bob,
Here's a picture of the internals of my Roberts model CR, the mains-battery version of your model BR.
Note the different chassis metalwork employed in the two models. No holes on the chassis in the battery only version where the mains power supply components are fitted in the model CR. That's real quality.

DFWB.

[bobhowe]

Yes David i agree the quality is really good the solder is great to work with no dry joints the components are easy to desolder no trying to pick out the wire that is wrapped round tag strips like other makes has any work been done on your set kind regards Bob

[FERNSEH]

The set was restored last year as a lockdown project. The actual receiver didn't need much work but special care was taken with the mains power section, with particular attention to the low tension supply.
Performance is excellent, receives BBC R4 on the long waveband loud and clear.

DFWB.

[bobhowe]

Originally Posted by FERNSEH

The set was restored last year as a lockdown project. The actual receiver didn't need much work but special care was taken with the mains power section, with particular attention to the low tension supply.
Performance is excellent, receives BBC R4 on the long waveband loud and clear.

DFWB.

Hi David did you put regulator in the power supply ? as looking at the trader sheet the low tension side would vulnerable to voltage spikes kind regards Bob

[FERNSEH]

"Hi David did you put regulator in the power supply ? as looking at the trader sheet the low tension side would vulnerable to voltage spikes kind regards Bob"
Hi Bob,
I didn't use an LM317 for the filaments. Tomorrow I'll take the chassis out and show the methods I employed to repair the power supply.

DFWB.

[bobhowe]

Thanks David that is a good idea if other forum members get the same set and it will save the valve filaments going OC if the low tension voltage gets high king regards Bob

[Herald1360]

Originally Posted by bobhowe

Hi David did you put regulator in the power supply ? as looking at the trader sheet the low tension side would vulnerable to voltage spikes kind regards Bob

With 5000uF and a choke in the LT supply, I doubt that spikes would be a problem, only longer term excess supply voltage. MRs tend to fail high rather than short too.

A series string of suitable diodes across the LT supply could provide the braces for peace of mind....

[bobhowe]

Originally Posted by Herald1360

With 5000uF and a choke in the LT supply, I doubt that spikes would be a problem, only longer term excess supply voltage. MRs tend to fail high rather than short too.

A series string of suitable diodes across the LT supply could provide the braces for peace of mind....

Hi without going OT my house mains voltage varies by about 7 volts sometimes it is high in the afternoon kind regards Bob

[ms660]

I can't remember for parallel connected but for series connected the trick originally was to run them at 1.3 Volts to help guard them against being over run due to voltage fluctuations.

Lawrence.

[Herald1360]

The same 1.3V would apply for parallel filaments. The difference being that (4 valve set assumed) a series filament string would have a total LT of 6.5V (3*1.3V + 2.6V) whereas the parallel filaments would simply have the 1.3V.