Roberts R500 battery eliminator?

[Scotorvm]

Just wondering guy's if anyone has attempted a battery eliminator for an R500.

This model takes 2xPP9's, 3 wires leaving batteries to radio, red wire is 18/19v, yellow 9v, black (-).

I have found a surplus HP laptop charger, 19vdc, so the 18/19vdc is covered and can reduce to 9vdc. have vintage battery snaps so no alterations to be done.

Just not keen on how I get the cable into the set without drilling a hole

Replaced the AF117's inside the module with CCCP GT322b's, lifted a couple of pads but resolved ok.

Just need to replace the AF115, has a leg cut, so probably had a whiskers issue.

It's a cracking set for less than £20, very clean, brass aerial polished nicely, red case buffed with cherry blossom. Need to spray the Roberts badge, handle ok some loose stitching. Grilles ok, washed in soapy water. Turntable oiled.

Thanks.

[Herald1360]

Not attempted one, but would say the set has a slightly unusual PSU arrangement- 18V is only used for the audio stages, the front end is fed from the 9V midpoint. I would expect that it would work OK if the 9V "tap" from the laptop PSU is derived from a simple zener diode shunt regulator with about 10mA "no load" current into a BZX79-C9V1 or similar.

You could try using something like a three way 30AWG ribbon cable to get the power into the set without needing to drill any holes- it should be fine for the few 10s of milliamps intermittent load.

[Restoration73]

I think this is the first transistor Roberts with shortwave. Whilst I agree with the above,
this is probably a switch mode power supply and might cause some interference to
reception. Worth trying to see if this is a major problem.

Just not keen on how I get the cable into the set without drilling a hole

Foil conductors?

[Scotorvm]

Originally Posted by Herald1360

Not attempted one, but would say the set has a slightly unusual PSU arrangement- 18V is only used for the audio stages, the front end is fed from the 9V midpoint. I would expect that it would work OK if the 9V "tap" from the laptop PSU is derived from a simple zener diode shunt regulator with about 10mA "no load" current into a BZX79-C9V1 or similar.

You could try using something like a three way 30AWG ribbon cable to get the power into the set without needing to drill any holes- it should be fine for the few 10s of milliamps intermittent load.

Thanks Herald1360, great info, something for me to investigate

Cheers for taking the time.

[Scotorvm]

Originally Posted by Restoration73

I think this is the first transistor Roberts with shortwave. Whilst I agree with the above,
this is probably a switch mode power supply and might cause some interference to
reception. Worth trying to see if this is a major problem.

Hi Restoration73, was planning on having the PSU external to the set, with just the wiring entering, have ferrite cores that I can use, would this help with interference?

Cheers

[Scotorvm]

Originally Posted by merlinmaxwell

Foil conductors?

Thanks Merlinmaxwell, forgive my ignorance, can you expand on what you mean by foil conductors, please.

[Nuvistor]

Only way to check if it is interference free is to build and try it, certainly ferrite cores in input and output of the supply will help. Keeping the supply well away from the radio will also help.
If you can find a linear supply it would be a better option. Have you thought about rechargeable batteries? Two packs in place of the PP9’s. Using AA batteries should last a while between charges.

[Scotorvm]

Originally Posted by Nuvistor

Only way to check if it is interference free is to build and try it, certainly ferrite cores in input and output of the supply will help. Keeping the supply well away from the radio will also help.
If you can find a linear supply it would be a better option. Have you thought about rechargeable batteries? Two packs in place of the PP9’s. Using AA batteries should last a while between charges.

Thanks Frank, good call re the rechargeable batteries, a dozen AA's, 2 packs of 6 would work. I think the volts are a wee bit less per cell, but should be ok. Just would prefer a wired solution as I have a tendency to leave sets on..

[AC/HL]

The cure for that is to add a resistor to the earthy end of the volume control so that there is always a low level audio reminder.

[Scotorvm]

Originally Posted by AC/HL

The cure for that is to add a resistor to the earthy end of the volume control so that there is always a low level audio reminder.

Cheers Bill, that's a great tip, thank you