Grampian 506

[ms660]

Note that in the photo in the link I posted what appears to be the radio earth connection is connected directly to the chassis.

For what it's worth I've reverse engineered a basic schematic for the output stage/power supply to the best of my ability from that photo, might post it up later on.

Lawrence.

[Newgirl2013]

Hi Chris
Thanks very much
I'll just make sure the mains plug is connected the right way round
When I was repairing TVs I had one come in for repair and found the mains plug was connected wrong
Reconnected the plug correctly
Repaired the TV and returned it to its owner to find the chassis live
Some idiot had connected the mains socket wrong way round
Rewired it correctetly and charged the customer accordingly
Shaz

[Techman]

If it's typical Grampian, then there'll be metalwork connected to one side of the mains that can potentially be touched by the user. Making sure that it's connected the correct way round is the obvious first step, but what if the neutral connection goes open circuit or the house socket is wired incorrectly as you've found once yourself and the whole thing becomes live? If it has double pole switching, I've found (once with bitter experience when I was a youngster in a garage stood on a damp concrete floor) that it's always the live side of a double pole switch that fails permanently 'on', so the whole set becomes live just as you switch it off and happen to be touching the metalwork at the same time. That's the reason that I personally detest double pole switching on live chassis equipment - neutral should always really be hardwired all the way through without going through any switching and only the live should be switched.

However, having just said all of the above, I'm against modification around the mains input circuitry of radios etc. There's potentially legal issues with doing this, so best left as originally designed and if you're concerned about safety, then my personal advice would be to get hold of a proper purpose made isolation transformer to plug all such stuff that you may have into externally, leaving the set as 'original'. Personally, although many recommend these RCD trips and circuit breakers, I'm not convinced that they offer enough protection and would always go down the separate isolation transformer road.

[Newgirl2013]

Of course the best way is the common old Neon Mains tester
The Grampian uses a single pole on off switch which is missing so included in the selection of spares needed is a replacement Single Pole Switch
Shaz

[Nuvistor]

Having the neutral hard wired is ok until the wall socket is incorrectly wired then the chassis is live even after switching off and when the Grampian was made there were a lot of two pin sockets in use.
The makers of all the live chassis sets I dealt with had taken a lot of effort to keep any possible live parts well insulated.
Grampian seem to have different thoughts.

[Newgirl2013]

Obviously no Health and Safety in Grampian's day

[Techman]

Yes, back in the day when there were two pin sockets with some folk also using lamp holders to plug into, double pole switching was a reasonable idea. Nowadays, when it's all 13 amp 3 pin plugs and sockets and all electricians are supposedly properly trained and certified then single pole switching with this sort of kit is a better idea.

If Lawrence susses the circuit out, then perhaps more will come to light regarding the circuitry. Grampian are very variable, some of their kit seems better than others, but mostly it's dangerous - in the wrong hands, that is.

[Newgirl2013]

It would be a good idea if someone could post a Circuit Diagram for the 506
I already have one for the Grampian 462, but, sadly not one for the 461

[ms660]

Attempt at reverse engineering schematic for the AF amp section for the Grampian 506, based on photo's in the links to date.

Bits might be correct, bits might not be correct, can anyone with good specsavers confirm either way?

Note....Suppressor grids and connections are not shown.

Maybe the OP can post some top side and under chassis pics etc to give us a further understanding of the circuit?

Lawrence.

[Newgirl2013]

Hi Laurence
I've noticed on my 506 there was a double Smoothing Capacitor (Missing)
The guy I got the Grampian from told me from memory he thought it was a 16+16 350V

[Techman]

If you post several good, close up photos of the underside of the chassis, 'someone', I'm mentioning no names (Lawrence), 'may' be able to work something out from them - I make NO promises on his behalf!

I actually own one of the safest items ever made by Grampian, it's a large parabolic reflector, and it has no electrical connections connected to it whatsoever. Hang on! You could fit a Grampian microphone to it and go out early one morning with it connected to a Grampian live chassis PA amplifier, onto the damp grass and listen to the dawn chorus - what a way to go!

Edit to say - Lawrence is already two steps ahead!

[Nuvistor]

Hats off to you Lawrence, my specs are not good enough. The circuit you have drawn look good, I don’t think there will be a lot wrong with it.

[Newgirl2013]

How do I post pics on here?

[Nuvistor]

https://www.vintage-radio.net/forum/...b3_attachments

[Newgirl2013]

For some reason I've tried posting a pic but it won't post

[Nuvistor]

You have pm.

[Newgirl2013]

Hi Frank
I've sent you a pic of the underside

[Station X]

Originally Posted by Newgirl2013

How do I post pics on here?

https://www.vintage-radio.net/forum/...ad.php?t=77650

[Nuvistor]

Three photos.

[ms660]

I think I've managed to work out a good chunk of the radio section, I'll post up a reverse engineered schematic tomorrow if I can draw one up ok.

Lawrence.