Power Relay

[keaster]

Hey all, did some searching and came up with nothing
I have a power relay with a contact rating of 5A @ 250AVC

to quote the data sheet
Max. switching capacity
2500 VA, 240 W (NO) 625 VA, 120 W (NC) 1250 VA, 120 W (NO/NC High-capacity)

http://www.components.omron.com/components/web/PDFLIB.nsf/0/4F7D9D9CA026C97E862573930070AC4F/$file/G5LA_E_0609.pdf

I want to use this to switch on the high voltage after a set delay time to allow the heaters to warm up.

I know in tube audio the current is very low but higher voltage would I be safe to use this relay or would the higher voltage still cause a problem?

Thanks in advance

 

[bob91343]

I don't feel you will have a problem. In your application, the relay is not required to break current, as it only drops out when the power is removed. Thus any contact arcing will be minimum, and occur under power-off conditions.

 

[VictoriaGuy]

What sort of rectifier circuit are you using?
In guitar amps the 'Standby' switch is often in the HV CT line to avoid switching HV.

 

[keaster]

Tube rectifier, so you think it would work that way?

 

[VictoriaGuy]

Yes, interrupting the HV center tap works fine as a standby switch.
Just search on "standby switch center tap" and you will find lots of info and discussion.
Check out the Fender 57 Deluxe Reissue as an example.
57 Deluxe complete schematic
(I don't know why they put the diodes in the HV feed to the rectifier tube...somebody online suggested inrush/pop prevention?)

 

[VictoriaGuy]

When I was looking around for that schematic, I came across (music electronics forum) a post by 'Enzo' where he makes some good points (IMO):
Quote:
NO guitar amp needs a standby switch really. The only reason they are put on there is to allow the amp to remain warmed up but not producing sound. There is no "best" way to do it. You can open the PT CT, you can open the PT secondaries before the rectifier (Marshall), you can open them after the rectifier(Fender). You can open the B+ line after the first filter but before the plates. You can open the B+ after the plates, but killing the screens(Peavey).

You can open the cathode lead from the power tubes. You can short the opposing control grids together on the push pull output.

The standby doesn't really protect the tubes from anything. At the small currents and low voltages of guitar amps, the vaunted cathode stripping just is not an issue.

 

[VictoriaGuy]

Note Enzo's reference to 'low voltages' in tube guitar amps.
He probably has experience with HV tube RF tubetransmitters /RF amplifiers where B+ voltages above 1000v aren't rare.