ITV Channel 11 Test Transmitter.

[Murphyv310]

Strewth!!!!
405 down a phone line, nice 

[ppppenguin]

Don't joke about it, video has been sent down ordinary phone lines on occasion when nothing better was available for an OB. Probably not very far and with a some pretty heavy equalisation. how do you think DSL works

I'm not suggesting that these were necessarily installed in telephone exchanges, just that they shared -48V power arrangments.

[Mark Hennessy]

A lot of broadcast gear worked that way, FWIW. By all accounts, the battery rooms were scary places to be! They pre-dated me, sadly...

[ppppenguin]

I've been in an old style exchange battery room. When I was a kid the FInchley exchange (now 8346, 8349 and probably others, I'm on North FInchley) held an open day. Saw wonderful rooms full of clattering Strowger kit. The battery room was dank, dark and mysterious. A nasty acidic twang in the air. Each of the 24 cells was about 2 feet cube, at least that's how I remember it. Busbars perhaps 6"x1". Definitely not a nice place.

Some years later, c1983, the same exchange had another open day to show off their new TXE kit. Rooms full of silent Strowger replaced by something a fraction of the size. The battery room was light and bright, each cell no bigger than a car battery.

I can't imagine BT having an open day now at an exchange.

[Murphyv310]

Guys only a little banter to lighten things a little
're the TX it's uses 2N918's in the osc, the two multipliers and output buffer. The DC to DC converter uses 2 of 2N1613 transistors. The ring diodes are unknown to me and Google. They are marked thus.
HBP2
2970
345
Any ideas?

[AlanBeckett]

BT had a 'Video Telephone' Project in the late '60s. 500kHz Video over Telephone Lines. Bell tried a similar system - Picturephone? - but it never took off.

You didn't have anything in the Battery Room apart from the Batteries and some Isolators and Fuses because of the Explosion Risk.

Alan

[Geordie McBoyne]

From the Radiomuseum, details of the 2N918 silicon NPN transistor: http://www.radiomuseum.org/tubes/tube_2n918.html

The 2N1613: http://www.radiomuseum.org/tubes/tube_2n1613.html

These are mid to late sixties transistors, helps us to put a date for the modulator.

Geordie McBoyne.

[ppppenguin]

The 2N918 is a classic RF transistor, good up to VHF and just about low UHF. Don't think it was used that much in domestic sets though I could be wrong.

The 2N1613 is a very ordinary medium power TO5 can device. I think of it as being like a BFY50 etc.

[Brianc]

BBC Television Centre (God rest its soul) had a 50V battery room initially and there was a huge distribution system throughout the technical areas. Each studio had an incoming 50C did board with butterfly fuses etc. The room was similar the that described by Jeffrey except the battery comprised cells about 24" x 12" x 24" high and the busbars were smaller. Nevertheless, almost as frightening as an early RCA TV transmitter I saw in Iraq. That was in a wire cage and could be heard "bristling" - euch!  

[jimmc101]

HP 5082-2970 matched quad of hot carrier diodes?

Jim