Tube preamp relay click on start up

[Reachahighernoon]

OK so I built a tube preamp with 3 12AX7's running on 190VDC to the plate and 12V to the heaters. I use a SMPS to convert 12V to 190V and the whole thing is powered by a 12V 1A wallwart

On start up, when everything is cold, I plug the power and I hear audible clicking coming from the relay for several seconds until the tubes warm up, when the tubes are warm, nothing but standard operating noise

This is the schematic, any help would be appreciated

[Manfred]

What is the circuit of the 12V supply?
The cold resistance of the 12AX7 is about half of the hot resistance which increases exponentially and is reached after about twenty seconds.
It could be that the 12V power supply or the heater winding of the transformer is weakly rated.
Then the ripple voltage before the voltage regulator could be so high that the output voltage of the regulator follows this and the relay switches off and on in time with the ripple frequency until the tubes are warm up.

[Reachahighernoon]

What is the circuit of the 12V supply?
The cold resistance of the 12AX7 is about half of the hot resistance which increases exponentially and is reached after about twenty seconds.
It could be that the 12V power supply or the heater winding of the transformer is weakly rated.
Then the ripple voltage before the voltage regulator could be so high that the output voltage of the regulator follows this and the relay switches off and on in time with the ripple frequency until the tubes are warm up.

OK so I dont know about the circuit, it's a 12V wallwart that was recommended to me for this application, it is a switching power supply and not transformer based

I noticed that a similar issue happens on a similar preamp I built but it has no relay and only 2 tubes, the status LEDs switch on and off but for a shorter period of time cos the 12V supply only has to deal with 2 tubes instead of 3

I noticed that a lot of tube based pedals have a large cap before the heaters, I think this is the issue especially after you said "ripple"

[plush]

My assumption is that SMPS wall wart goes into hiccup mode due to large inrush (especially if there's a lot of filtering/bypass caps present), then stabilizes after some time. This explains relay clicking.
Some SMPS don't like huge capacitive loads and/or don't have any intelligent inrush control.

[Reachahighernoon]

My assumption is that SMPS wall wart goes into hiccup mode due to large inrush (especially if there's a lot of filtering/bypass caps present), then stabilizes after some time.

Which is weird cos these are the same wall warts that Effectrode sell

Wait wait, no they are not, the ones Effectrode use are rated at 1.5A and 18W, the ones I used are rated at 1A 12W. I just tried the Effectrode ones and they dont make that weird clicking

[plush]

My assumption is that SMPS wall wart goes into hiccup mode due to large inrush (especially if there's a lot of filtering/bypass caps present), then stabilizes after some time.

Which is weird cos these are the same wall warts that Effectrode sell

I'm not really sure how relay control is implemented in effectrode and what capacitive load do they have.
I'm also not sure how do you control your relay.

The circuit you've provided is not complete and is missing some details. which may be critical for our investigation.

[Reachahighernoon]

My assumption is that SMPS wall wart goes into hiccup mode due to large inrush (especially if there's a lot of filtering/bypass caps present), then stabilizes after some time.

Which is weird cos these are the same wall warts that Effectrode sell

I'm not really sure how relay control is implemented in effectrode and what capacitive load do they have.
I'm also not sure how do you control your relay.

See my edit please

Also, my relay control is really simple, its just a switch that connects the coil to ground

[plush]

See my edit please

Well, I guess, we can mark this one as solved, right?

Reason = smps going into hiccup due to inrush.

Those provided by Effectrode may have higher inrush limit or deal with it in a different way.

[Reachahighernoon]

See my edit please

Well, I guess, we can mark this one as solved, right?

Reason = smps going into hiccup due to inrush.

Those provided by Effectrode may have higher inrush limit or deal with it in a different way.

Yeah pretty much, I guess the circuit is fine

I was sure this had something to do with the output current of the power supply

Thank you kindly

I assume a thermistor will help me? Or is the issue solely related to the supply?

[Manfred]

My assumption is that SMPS wall wart goes into hiccup mode due to large inrush (especially if there's a lot of filtering/bypass caps present), then stabilizes after some time.

Which is weird cos these are the same wall warts that Effectrode sell

Wait wait, no they are not, the ones Effectrode use are rated at 1.5A and 18W, the ones I used are rated at 1A 12W. I just tried the Effectrode ones and they dont make that weird clicking

The maximum inrush current of all filaments together is about 1.9 Amps for all tubes.
The mean value until the heating is finished is about 1.5 Amps.
The nominal value after the heating is 0,9 Amps.
Therefore I think that the power supply is too weak.

[plush]

I assume a thermistor will help me? Or is the issue solely related to the supply?

Yep, NTC placed in series with VCC should work.
Relay soft start with a timer/voltage reference is also an option.

[Reachahighernoon]

I assume a thermistor will help me? Or is the issue solely related to the supply?

Yep, NTC placed in series with VCC should work.
Relay soft start with a timer/voltage reference is also an option.

I just searched "tube amp inrush current" and thermistors id what came out

Thank you guys for the help

What value though? 100K? The schematics for typical thermistors it says 10ohm

[Manfred]

Regulated PSU with Softstart:

RegulatedPSU_Softstart.jpg (24.15 KiB) Viewed 1137 times