power switch options

hello all

so a power switch on the back of my st-70 is not ideal. reaching over hot tubes in a shelf is a hassle. couple options i see...

relocate to the mono/stereo switch (runs 120v through the critical audio signal traces... sounds bad)
use a relay at the mono/stereo switch but since i only have the heater tap i could run a 6v relay to control the 120v power in the back.
use a 12v trigger signal from my reciever to auto turn on/off but this would require a whole new circuit with relay

anyone done this?

thanks
jason

buschfsu wrote:hello all

so a power switch on the back of my st-70 is not ideal.  reaching over hot tubes in a shelf is a hassle.  couple options i see...

relocate to the mono/stereo switch (runs 120v through the critical audio signal traces... sounds bad)
use a relay at the mono/stereo switch but since i only have the heater tap i could run a 6v relay to control the 120v power in the back.
use a 12v trigger signal from my reciever to auto turn on/off but this would require a whole new circuit with relay

anyone done this?

thanks
jason

Yes, bet an even better solution: use a SSR ( solid state relay)
Se http://n.manet.nu/vta70/ pictures from my vta70 build.

Some comments:
the SSR is connected in parallell with the existing power switch, thus
amp may be used in absence of external control voltage.
The control is connected with a isolated rcaplug mounted in the unused fuse
As control 12V DC from preamp is used , but SSR accepts 3-32V

I also mounted an IEC connector instead of the "knot-on-power-cable".

I moved the on/off switch from the back to the "mono/stereo" position. I ran the twisted wires carefully along the bottom of the chassis. There is NO hum. I think Bob's idea is best, but I do like the power switch in front.....

One very nice feature of the SSR device is that it connects and disconnects at the zero crossing.
Thus there is no turn on pop ( won't be heard in a tube amp but may disturb other equip. ) and no turn off pop . This is something a hardware switch or magnetic relay cannot do.

That SSR is an interesting option that I've never seen before. I see Digikey has them for around $48.

I purchased one of these, to solve my problem. Never have to leave the chair! This one is non-latching, which leaves the relay off, in response to a power outage.

https://www.amazon.com/gp/product/B001Q9EFUK/ref=oh_aui_detailpage_o08_s00?ie=UTF8&psc=1

corndog71 wrote:That SSR is an interesting option that I've never seen before.  I see Digikey has them for around $48.  

You may find these significantly cheaper :
http://www.ebay.com/itm/Groove-End-LED-Indicator-Light-DC-AC-Solid-State-Relay-10A-24-480VAC-3-32VDC-/291557662911?hash=item43e230e0bf:g:cU0AAOSw~AVYuL-K

peterh wrote:

corndog71 wrote:That SSR is an interesting option that I've never seen before.  I see Digikey has them for around $48.  

You may find these significantly cheaper :
http://www.ebay.com/itm/Groove-End-LED-Indicator-Light-DC-AC-Solid-State-Relay-10A-24-480VAC-3-32VDC-/291557662911?hash=item43e230e0bf:g:cU0AAOSw~AVYuL-K

That is considerably cheaper. Unfortunately they do not ship to the US.

Found cheaper ones on ebay.

mazeeff wrote:I purchased one of these, to solve my problem. Never have to leave the chair! This one is non-latching, which leaves the relay off, in response to a power outage.

https://www.amazon.com/gp/product/B001Q9EFUK/ref=oh_aui_detailpage_o08_s00?ie=UTF8&psc=1

That "never have to leave the chair" part sold me!
I bought two.
And BTW, those tubes only give you the heat treatment when you're turning the rear switch OFF.

I have a power switch in mind that i never got any chance to implement;
it consist of 2 buttons one red and one green, 1 diode+ resistor+uF cap and a 9V battery + a green LED with resistor, All energizing an SSR with the few mA that the SSR needs

Function is described as :
the green button connects the 9v battery + to the control line connected to the SSR, thus
energizing the SSR. This starts teh amp.
When amp starts, a suitable AC ( filament ?) is rectified with the diode, smoothed by the uF and
keeping the control line energized, the button may be released at this moment.
If mains should fail ( brownout or simular) the amp won't restart.
Stopping the amp is done with the red switch that shorts the control line to ground.

A green LED also powered from the amp indicated that the amp is on .
The 9V battery might be replaced by a few Nimh batteries, these could be trickle charged by
the holding voltage, but honestly i thing this makes life more complicated. A single 9V batter
used one second each time amp is started will last for a long time.
The uF cap should be large enough to keep the recitfied AC above 3V, but small enough to
make maneuvers reasonable, a guess is 10uF 25V


Sadly enough all amps i have used last decennium has a mechanical switch, thus i have not
got the motivation for the above thing.

When I assembled my MK III's I used one of these in each amp: https://www.amazon.com/gp/product/B01BR3B9XU/ref=oh_aui_search_detailpage?ie=UTF8&psc=1
Have worked very well. These have seen daily use for the last year with no problems. They are mounted in the front of the chassis.