Automatic Disconnect for ST 70

I recently upgraded a Dynaco ST 70 tube amp. The old tubes seemed to survive the inconsistent AC power we have in this part of Maine, but newer rectifier tubes are evidently more delicate. The first did not survive the first few flickers in the power on a windy day a few weeks ago.

I'm wondering if there is a quick disconnect I can use that would shut the power off immediately when there is a sudden short interruption in the AC power. I've looked at surge protectors, but don't see that these would trip if the power is just briefly interrupted. I suppose I can buy more tubes, or only use the amp on days that seem unlikely to have power interruptions, or move to another part of the state, but a way to shut the amp off automatically seems a better choice if such a device exists.

Thank you, tna

TNA,
What may work would be a 120 vac latching relay. When the power is interrupted
the contacts will open. You will need a manual momentary switch (push button) to
re-energize the relay coil once the power is restored. Do a google search for this
simple circuit.

Kevin

The VTA relay board would be a good option for you VTA Relay Board. Or at the very least in your environment the rectifier tube socket diode mod described here (yellow sheet mod). Diode Mod

The relay board opens upon power failure and times out for 17 sec. upon each power reapplication. The yellow sheet diode mod adds solid state diodes on the rectifier tube HV AC inputs. During a power failure the diodes prevent reverse arcing through the rectifier tube. I use a variation of the yellow sheet mod using instead one diode on the rectifier output. Either of these will only help your situation.

I use SSR to turn on poweramps, these i feed via 12V from my preamp ( takes a few mA )
But in your case i'd go with a variant :
Install an ssr, then two toggle buttons ( really cheap ones will do)
Additinally you will need a 4.5V flashlight battery ( or 9V ), a 100ohm resistor and
maybe a 1n4007 diode.

The first toggle will connect the battery to the ssr, making it close. As it closes
i will use any suitable power ( rectified filament ?) through a resistor to keep
the ssr in ON state. The second toggle will shortcirquit the ssr control input, thus shutting the amp down.

To clarify : you amp will have one "on" button and one "off" button. The battery
will serve as "bootstrap" and will last very long. If the amp is in "on state" and
power fluctuates it will torn off.

In my last implementation of ssr ( in a vta70) a have the ssr in paralell with the
ordinary cirquit breaker, thus either "on" from preamp or "on" with the breaker
will turn it in ( for those cases where i use the amp without my usual preamp).

TN Allen,

I am an electrical engineer. I can tell you what we do in industry to protect against power flickers. Try a uninterrupted power supply, or UPS. It plugs into your outlet and has a battery backup and inverter. If your power flickers the UPS automatically kicks in and keeps power going. When power comes back on the UPS goes back into charge mode to charge the battery. They work great and are not very expensive. You can even get them at Sam's Club.

The system would not let me post a link. Go to Amazon.com and search for uninterrupted power supply and check it out.

The ones Amazon have are used mainly with computers and home entertainment equipment. I hope this helps.

Ed Cheek

Thank you for the information, all of the ideas seem good. I'll look into them in detail tomorrow. Perhaps something I can plug the amp, preamp, turntable, tuner and CD player into would be a good idea, although a circuit inside the amp also makes a lot of sense to avoid trouble in a situation where I might not have the external device.

.

There are several manufacturers that GFI outlet modules and power strips with remote controls out that allow reset and on-off functionality. The GFI system has been bulletproof for me in Costa Rica where we have a nightmare power grid with voltage spikes and quick on off incidents almost daily. I am even considering building one of these into into the chassis of one of my custom amps.

Get this: http://www.amazon.com/Belkin-Conserve-Switch-Energy-Saving-Protector/dp/B003P2UMNK

It works great. Momentary outage requires a manual restart so you can't short-cycle your equipment. Also, you can plug in all your audio devices to this power strip and control power remotely - eliminating standby power usage.

Every VTA customer should get either Bob's Time Delay Relay built into their system - or one of these power strips.

My TV and entertainment toys were drawing about 60 watts even when they were not on. Using this power strip I can basically "unplug" everything without crawling behind my components. BTW, 80 watts 24x7 here in California, where electricity is $0.30/kwh, is $210/yr!

BTW, 80 watts 24x7 here in California, where electricity is $0.30/kwh, is $210/yr![/quote]

I've thought we pay too much at about $.15/KWH(most of that is "delivery"), but $.30/KWH is outrageous!

I've been looking at the various possibilities, and plugged the amp, preamp & etc. into a Tripp Lite Isobar I've had for 20 years. I'm thinking though of the internal circuit as well, seems good insurance as 2 5AR4's cost about what the VTA kit costs.

Thank you for all the suggestions. tna

Kind of on the same topic, here at KSC, we're demoing these powerstrips with a "remote" on/off that you can hang on the wall like a lightswitch. Easy off for all those "vampire" power drains.

Tom

http://www.amazon.com/Belkin-BG108000-04-Conserve-Energy-Saving-Surge/dp/B001GQ2W6W