Yamaha T50 C

[lowell]

Hello,
I'm curious if someone might help a bit with some parts in this amps switching circuit. It seems that when the relay is grounded it switches the power supply from 3 optos to the other 3 optos as well as an LED in parallel. I find it cool that this is all controlled from a half wave rectified heater supply. I guess I have a couple specific questions.

What value DC relay would I need for this? I think it'd be 4vdc but please confirm.

What are these opto-isolators? I don't see any part # reference or values.

Finally if I were to use this switching circuit for a cathode/fixed bias switch would opto-isolators work? I'm just not sure what the ratings of these components are.

[Enzo]

Well, it is full wave rectified, but that doesn't much matter.

SInce you ought to see about 4.5v of DC< I suspect a plain old standard value 5v relay would work. I have never seen a 4v relay, does someone actually make them?

I don;t know which optos Yamaha used, but if you are building your own circuit, use whatever optos you want. They are running off the same 4.5v supply, so adjust the external current limit resistor to suit.

[lowell]

enzo thanks... yeah duh on my part bout the half wave. i was thinking bridge, not full wave, my bad.

How much current can these things take? Not on the power rail but on the side that has the resistance?

[lowell]

oh and what are these called on mouser?

[Don Moose]

How much current can these things take? Not on the power rail but on the side that has the resistance?

It's not the current, so much as the power (see attached). 175mW, derating 3.9mW per degree C above 30.

I think you'd be a ton better off using an N-channel MOSFET in parallel with your cathode-bias-mode resistors. Very hardy parts and super easy to use.

Here's my fifth of a nickle:
- Go ahead and use a VTL5C1-like part to switch off the fixed-bias-mode source, that's really low current (and power).
- Use an N-channel MOSFET to shunt the cathode-bias-mode components.
See R.G.Keen's MOSFET Follies article for more info.
- Keep that 1-ohm cathode resistor in the circuit in both modes - connect it between the MOSFET's Source pin and GND - so you can easily measure the bias current in both modes
- Make CERTAIN that the fixed-bias source comes back on BEFORE you shunt the cathode-bias components ... it's better to go super cold bias for a bit than the super-hot bias of leaving the grids at or above GND even briefly.

Hope this helps!

[lowell]

thanks Don... boy those Vactrols are pricey!!! $10!?

[Enzo]

VTL5C1 sells at Allied for $5.30 each.

For the others just search VACTROL there.