Re: [sdiy] vcr delay line?

[Roman]

this is delay line used in TVs. It uses ultrasonic waves traveling thru piece of crystal to achieve long delays. At angled end there is actuator and receiver. Acoustic wave bounces 8 times before reaching the receiver, hence it has much longer way to go in comparing with overal crystal size. It's easy to draw the travel of the wave. The squares are dumpers not to let the whole crystal wibrate, and reduce crosstalk between wave paths.
The delay time is 64us (microseconds). It's the time of 1 TV signal line. The delayed signal is needed to recover color information for next line, as it is somehow multiplexed with something else. This is for SECAM system AFAIR.
It's been long time, I may remember it wron, but the idea is more or less like described.

Roman

---- Wiadomość Oryginalna ----
Od: jhno <ear at heldscala.com>
Do: synth-diy at dropmix.xs4all.nl
Data: Sun, 16 Jan 2005 09:13:44 -0800
Temat: [sdiy] vcr delay line?

> i was looking inside a dead vcr and a big blue rectangular component caught
> my eye. it looked like a fairly large plastic capacitor - however, it was
> clearly labelled, 'DELAY LINE'.
> 
> when i tugged on it hard enough, the blue shell came loose. the 4-pin base
> was still attached to the PCB. inside the blue shell was this weird piece
> of plastic with polka dots on it and a cutaway where the four wires
> attached. there was also a partial overlay of some other kind of plastic,
> and a little rubber spacer.
> 
> a nice picture of all these elements, except the spacer, can be viewed at
> 
> http://heldscala.com/delayline.jpg
> 
> ....what is this thing?
> 
> jhno
> 
> 
>