Simple Tube Preamp 60 second Mute - why wouldn't this work perfectly?

[john65b]

OK, go easy on me please... need advice before I do something stupid...

Looking to add a 60 second delay the simple way (I know there are many timer circuits, but this seems like a slap in and forget for cheap)

SQUARE D 9050JCK13V20

Pros
Heavy Duty contacts - Octal base - DPDT - 120VAC Coil - timer dial range .6 to 60 seconds

See attached - 120VAC on Pin 2-7 activates 60 second relay - Left / Right channel outs to pins 1 / 8, ground on 4 / 5, final Preamp outs on pin 3 / 6.

Can this be as simple as this for less that $15 (Used)?
Since 120VAC, dangerous? Better sticking with lesser voltages?

 

[Kay Pirinha]

Yes, for security reasons you don't want 120 Vac mains voltage next to signal carrying pins in an octal tube base.
Best regards!

 

[Schmitz77]

For what reason this delay should be any good?
In practice, nobody needed a relais in a tube pre.
There are some tubes with a controlled heater warm up time. This offers enough delay and was often use in the old days.

 

[Kay Pirinha]

Controlled warm up time means that any tube in a series heater chain encounters the same time to heat up. It hasn't anything at all to do with delayed start.
Best regards!

 

[john65b]

I have a nasty series of pops and cracks from a DIY tubeamp that have damaged downstream amps upon startup... once preamp circuit warmed up and stable, no issues at all.

I know I can just count to 60 and turn on amp after preamp, but would like a better, automatic solution....

 

[rayma]

Use a DC operated, NC relay that matches the DC filament voltage in the preamp.
The relay switches the audio output either unmuted, or shorted to ground.

Upon power on, after a preset delay, the relay opens and then the audio is available.
Upon power off, immediately remove power to the relay to mute and prevent turn-off noises.

You could use the 120VAC relay to switch the filament DC to another relay for audio muting.

 

[john65b]

Yup, the 6.3vdc (in parallel to tube heaters) instead of 120VAC relay coil voltage is obviously a better solution (duh)...

Will start looking... I kinda like the octal socket setup tho...

 

[rayma]

You can use both relays, as in post #6.

 

[john65b]

I do not understand why I would want to delay the heater circuit 60 seconds while full B+ is being applied...urban myth?

Forgive my ignorance....

 

[rayma]

The DC coil relay is powered by the DC filament supply. The filament supply is not switched by the relay.
The relay switches the audio output short to ground on and off.

You could use the 120VAC relay switched contacts to interrupt the connection between the DC filament
supply and the coil of the DC relay, and use the programmable delay of the 120VAC relay for the turn-on delay.
This way you could use the 120VAC relay instead of an IC timer for the turn-on delay of the muting DC relay.

 

[anchorman]

I don’t understand the problem here. If you want there is no signal/audio being switched by this timer, which is worrying to the Germans, and maybe should be for you. Wire it so that when the preamp is switched on, it starts the timer, and when your 60 seconds are done, it turns on power to your power amp. I’d wire the coil so that it is switched on with the preamp, get a double pole switch, or hook it up with one leg post switch and the other to the neutral, so that it turns on when the preamp turns on.

I’m curious what is causing the pops and cracking.

 

[anchorman]

Most such timer relays can switch 10-20 amps, which should be plenty for an outlet for your power amp, and if this one won’t, have it turn on a relay that is powerful enough to switch the mains power on for your power amp. Keep it simple, don’t mess with your signal path, or tube filaments if you don’t need to (and you don’t!).

 

[anchorman]

This timer is good for 10 amps, so unless you’ve got some ungodly large power amp, you should be good to go. Do yourself a favor and get a simple octal relay socket with screw terminals and put it in its own box with an outlet, or inside the preamp if there’s space in the cabinet.

 

[john65b]

This would be a better solution - 12vdc supply...and $12. DPDT delay relay.

0 to 60 minutes, not a bad solution...

I would rather have this delay on preamp out than amp input... I am trying to protect my amp.

 

[mickeymoose]

I do need to ask: Have you tried to fix the preamp?
What if the preamp gets worse or intermittently noisy? E

 

[john65b]

I did mention it was a DIY tube preamp? Getting noises and crackles on startup come with the territory with DIY tube preamps.

I have yet to see a commercial tube preamp that does not have a startup muting circuit, and now understand why.

Cant really be leaking output coupling caps as it would not just happen on startup, yes?

 

[mickeymoose]

Yes you said DIY. I would look for a cap with DC potential across first. Unlike transistor amps tubes, should not do that. E