Tape Speeds - UK Vintage Radio Repair and Restoration Discussion Forum

14th Oct 2018, 5:51 pm

Why didn't tape speeds start with a multiple of two, that would save all this 7 1/2" or worse 15/16th etc. stuff.

julie_m · 14th Oct 2018, 6:07 pm

Just a historical accident?

IIRC the original German machines ran at 72 cm/sec, this was rounded up to 30 in/sec (= 76.2 cm/sec) because 30 has many factors, and it was not obvious that successive developments would be based on halving the speed each time. Someone might have gone straight with "triple play" at 10 in/sec, rather than 15 and then 7.5.

Or, if the firm developing the tape recorder for peacetime use had been metrically-minded and stuck with the original units, 72 cm/s would have stood three "halvings" before introducing a fraction.

llama · 14th Oct 2018, 6:22 pm

I'd always assumed they divided down from 10 feet per second - maybe used for wire recorders(?)
Graham

julie_m · 14th Oct 2018, 6:47 pm

A thingy just jumped across a whatsit in my memory then: something about an old recording device used by the BBC, with a flat steel tape running at 10 or 5 feet per second. Maybe that is where 30 in/sec (= 2 ft 6 in/sec) came from .....

I doubt the person who made the original decision is still around to ask, unfortunately .....

Restoration73 · 14th Oct 2018, 7:16 pm

I think this is the potentially lethal device
http://www.orbem.co.uk/tapes/blattner.htm

Ted Kendall · 14th Oct 2018, 8:05 pm

There are two, or perhaps three, strands here.

First there was the Blattnerphone - steel tape, running at 10 feet per second, longitudinal recording, DC bias and

dangerous to anybody within twenty feet, as the edges of the tape were razor-sharp. The Blattner patents were acquired by Marconi, who made a rather more civilised device with loop bins on either reel and thyratron control of the spool motors, so that a tape breakage resulted in a sudden stop rather than mayhem.

Although Lorenz made steel tape machines in Germany in the late 'thirties, RRG (German Radio) preferred the plastic-tape Magnetophon. Initially, broadcast versions ran at 1m/s, this speed necessitated by the quality of the early tapes and the use of DC bias. When RRG rediscovered AC bias (a happy accident - one day a Magnetophon started sounding phenomenally good, and was pulled into the workshop to find out why - the record amplifier was oscillating at tens of kHz), the tape speed was reduced to 77cm's, and it was at this stage that the technology was captured. The first non-German machines were more or less straight copies of the Magnetophon, and carried this speed over - I think it was Ampex who led the way with 30ips on the original 200 machine. The EMI BTR-1 ran at 77cm/s, which sets elephant traps for those remastering early tapes.

A lot of the Blattnerphone stories have been concatenated with tales of VERA, the BBC's linear video recorder. It ran half inch tape at 200 ips, with two-foot spools and lots of heavy engineering, but wasn't quite as dangerous as the Blattnerphone - at least the tape was plastic, even if the reels were still metal.

14th Oct 2018, 5:51 pm	#1
Guest Guest Posts: n/a	Tape Speeds Why didn't tape speeds start with a multiple of two, that would save all this 7 1/2" or worse 15/16th etc. stuff.

14th Oct 2018, 6:07 pm	#2
julie_m Dekatron Join Date: May 2008 Location: Derby, UK. Posts: 7,735	Re: Tape Speeds Just a historical accident? IIRC the original German machines ran at 72 cm/sec, this was rounded up to 30 in/sec (= 76.2 cm/sec) because 30 has many factors, and it was not obvious that successive developments would be based on halving the speed each time. Someone might have gone straight with "triple play" at 10 in/sec, rather than 15 and then 7.5. Or, if the firm developing the tape recorder for peacetime use had been metrically-minded and stuck with the original units, 72 cm/s would have stood three "halvings" before introducing a fraction. __________________ If I have seen further than others, it is because I was standing on a pile of failed experiments.

14th Oct 2018, 6:22 pm	#3
llama Octode Join Date: Jun 2006 Location: St Osyth, Nr Clacton, Essex, UK. Posts: 1,482	Re: Tape Speeds I'd always assumed they divided down from 10 feet per second - maybe used for wire recorders(?) Graham __________________ Half my stuff is junk - trouble is, I don't know which half!

14th Oct 2018, 6:47 pm	#4
julie_m Dekatron Join Date: May 2008 Location: Derby, UK. Posts: 7,735	Re: Tape Speeds A thingy just jumped across a whatsit in my memory then: something about an old recording device used by the BBC, with a flat steel tape running at 10 or 5 feet per second. Maybe that is where 30 in/sec (= 2 ft 6 in/sec) came from ..... I doubt the person who made the original decision is still around to ask, unfortunately ..... __________________ If I have seen further than others, it is because I was standing on a pile of failed experiments.

14th Oct 2018, 7:16 pm	#5
Restoration73 Nonode Join Date: Jun 2013 Location: Surbiton, SW London, UK. Posts: 2,801	Re: Tape Speeds I think this is the potentially lethal device http://www.orbem.co.uk/tapes/blattner.htm

14th Oct 2018, 8:05 pm	#6
Ted Kendall Dekatron Join Date: Jul 2008 Location: Kington, Herefordshire, UK. Posts: 3,670	Re: Tape Speeds There are two, or perhaps three, strands here. First there was the Blattnerphone - steel tape, running at 10 feet per second, longitudinal recording, DC bias and dangerous to anybody within twenty feet, as the edges of the tape were razor-sharp. The Blattner patents were acquired by Marconi, who made a rather more civilised device with loop bins on either reel and thyratron control of the spool motors, so that a tape breakage resulted in a sudden stop rather than mayhem. Although Lorenz made steel tape machines in Germany in the late 'thirties, RRG (German Radio) preferred the plastic-tape Magnetophon. Initially, broadcast versions ran at 1m/s, this speed necessitated by the quality of the early tapes and the use of DC bias. When RRG rediscovered AC bias (a happy accident - one day a Magnetophon started sounding phenomenally good, and was pulled into the workshop to find out why - the record amplifier was oscillating at tens of kHz), the tape speed was reduced to 77cm's, and it was at this stage that the technology was captured. The first non-German machines were more or less straight copies of the Magnetophon, and carried this speed over - I think it was Ampex who led the way with 30ips on the original 200 machine. The EMI BTR-1 ran at 77cm/s, which sets elephant traps for those remastering early tapes. A lot of the Blattnerphone stories have been concatenated with tales of VERA, the BBC's linear video recorder. It ran half inch tape at 200 ips, with two-foot spools and lots of heavy engineering, but wasn't quite as dangerous as the Blattnerphone - at least the tape was plastic, even if the reels were still metal.