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Simple Tube Preamp 60 second Mute - why wouldn't this work perfectly?
Simple Tube Preamp 60 second Mute - why wouldn't this work perfectly?
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Old 3rd November 2020, 01:10 PM   #1
john65b is offline john65b  United States
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Default Simple Tube Preamp 60 second Mute - why wouldn't this work perfectly?

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?
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Last edited by john65b; 3rd November 2020 at 01:19 PM.
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Old 3rd November 2020, 02:41 PM   #2
Kay Pirinha is online now Kay Pirinha  Germany
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Yes, for security reasons you don't want 120 Vac mains voltage next to signal carrying pins in an octal tube base.
Best regards!
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Old 3rd November 2020, 07:04 PM   #3
Schmitz77 is offline Schmitz77
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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.
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Old 3rd November 2020, 07:15 PM   #4
Kay Pirinha is online now Kay Pirinha  Germany
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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.
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Old 3rd November 2020, 07:21 PM   #5
john65b is offline john65b  United States
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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....
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Old 3rd November 2020, 07:31 PM   #6
rayma is offline rayma  United States
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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.

Last edited by rayma; 3rd November 2020 at 07:49 PM.
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Old 3rd November 2020, 08:24 PM   #7
john65b is offline john65b  United States
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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...
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Old 3rd November 2020, 08:36 PM   #8
rayma is offline rayma  United States
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You can use both relays, as in post #6.
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Old 3rd November 2020, 08:52 PM   #9
john65b is offline john65b  United States
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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....
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Old 3rd November 2020, 09:01 PM   #10
rayma is offline rayma  United States
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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.

Last edited by rayma; 3rd November 2020 at 09:03 PM.
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