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Hi guys I have been looking at adding a "Power On Time Delay Relay Circuit" to my power amp.
What I have seen is that I can instead of putting a relay between the two HT cables of the secondary
just put one on the center tap to ground of the secondary. Can this work?
I'm using a GZ34 or similar tube.

Sure, but if you're worried about HV breakdown, just use a proper relay, like an Omron G6RL-1-ASI-DCx (where x is your voltage used by the delay). Cheap and have a 5KV breakdown rating between coil and contacts, 1KV between open contacts and can switch 400V. I use one in my DynaMull for a standby and it switches 475V regularily just fine with no failure for 5 years now

Thanks Geek for the reply, I just checked the price it's quite affordable also, the G6RL-1-ASI DC12 is 3,36 Euro from Mouser.
I saw that it is a single NO NC contact, would there be a benefit if I used a duel contact relay that was bridged ?
also would I have any concern about an inrush when the contacts are made?

6B4G wrote:... would there be a benefit if I used a duel contact relay that was bridged ?

Not really, tubes are low current, high voltage devices. This is a 10A relay!

...also would I have any concern about an inrush when the contacts are made?

Nope! Mechanical relays are unlike their SS cousins that don't do inrush currents. The "break" is harder on the contacts than the "make".

Cheers!

Thank you

In my VERY VERY first prjects, I used a "tube delay", the thing that looks like a relay but contains a heater and a bimetal switch. This one switched a standard realy. Very simple and and worked fine.

If I may ask... why is it necessary that you want a Power On Time Delay Relay Circuit?

With power amps using large cathode tubes, it reduces the "cathode stripping" effect.

For preamps, I use them to short the outputs for 30 seconds until it warms up. Otherwise you risk a low frequency, high voltage ramp. Tubes with OPT's and coupling caps are immune, but SS, especially pure DC ones, will blow speakers and transistors

Cheers!

Please define large tubes in question. All the information I have read suggests that only high voltages on certain tubes will result in cathode stripping. Other than that its just a myth.

Cathode stripping is a myth, for indirectly heated cathodes

But that doesn't stop all the HiFi mags and most DIY forums saying the sky is pink and deep space is hot