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Old 13th September 2008, 06:17 PM   #1
Renron is offline Renron  United States
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Default Warning: new SS relay question / No flame I

Ok, being a newb... I am trying to figure out if this will work or just make pretty blue smoke when I turn it on.

Power supply for an Aikido 6SN7 line preamp. 4 Valves which (according to the reference table at the back of my Aikido users guide) says the B+ with above tubes pulls about 10mA. max per valve. This gives a total B+ I of ~40mA, this information also corrisponds to the Tung-Sol application chart which states ~10 mA draw per valve with plate voltage of 250V - 300V

I would like to use a SS photocoupler relay to switch on the B+. (After a delay from an Amperite TDR tube).
The relay is a Panasonic AQV-254. It is rated at 400V / 150mA.
I have a 3V output on my transformer which I could rectify, or I could steal from the heater DC (which turns on first) with a resistor circuit to obtain the correct switching voltage and current.

Question is can I run the B+ through the SS relay or will it spike at turn on and fry the relay?
Link to relay PDF

Thanks for any and all input

Ron
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Old 13th September 2008, 06:51 PM   #2
Renron is offline Renron  United States
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I also found a Teledyne BS60D4A another SS relay, 600Vrms and up to 4A. 3.7V - 10V control voltage....even better! $10.74 at Mouser
I think I found a winner!

Link to 600V 4A Relay


Input, as always, accepted graciously.

Ron
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Old 13th September 2008, 07:33 PM   #3
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Triac based! Once you turn B+ DC on, you can't shut it off.
AC, with a zero crossing 120 times per second, no problem.

Why then would the spec sheet say "DC control"? Cause
DC controls the optoisolator, not because DC is controllable.

This could work, but where you put it makes the difference.
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Old 15th September 2008, 04:53 PM   #4
kevinkr is offline kevinkr  United States
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Ken's right about that, but you might be able to use an opto-mos switch to do the job.

More to the point though is why you think you need to delay the B+. Voltages here are moderate, and cathode stripping is not an issue with the tubes you are using in this Aikido.

(Tubes like the 6AS7/6080/6336/6528 are a notable exception as are some tungsten/thoriated tungsten dhts)

Using relays to delay B+ in a pre-amplifier can be a pretty good way to generate an ear jarring pop when the relay closes mandating the use of a muting relay on the output. This can also be fatal for solid state amplifiers and the speakers connected to them. Using a tube rectifier or just letting the B+ come up as the tubes warm up is a pretty good way to reduce the severity this issue. With SS amps a shunt connected muting relay at the pre-amplifier output is strongly recommended. (Short the output to ground until warm up is complete using a time delayed relay.)

Incidentally flames are a pretty rare occurrence here, and generally reserved for these You needn't worry..
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Old 15th September 2008, 06:18 PM   #5
Renron is offline Renron  United States
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KevinKR, KenP,

Thanks for the input, you said the same things as SY regarding the non-use of a B+ delay on a Preamp (W.O.T.)....cool, less work for me! The reason I wanted to delay the B+ was that specs on 6SN7s say the heater takes ~11 seconds to come up to full power(warm up temp).

Good point about the shunting of the (output)? or (input)? signal to prevent damage to my SS amp. How did you know? Are you spying on me??? I've got a Conrad Johnson SS amp that powers my Scottmoose/Planet10 designed small Thors.

Perhaps I'll use the Amperite Delay relay tube to shunt signal.
Is it on the input or output???
me thinks output, but not sure.

I was planning on NOT turning on the source or SS amp until AFTER the preamp had warmed up. Is that not enough to prevent damage to the SS amp or my speakers? New to this and appreciate the help.

Ron
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Old 15th September 2008, 08:58 PM   #6
kevinkr is offline kevinkr  United States
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Quote:
Originally posted by Renron
KevinKR, KenP,

Thanks for the input, you said the same things as SY regarding the non-use of a B+ delay on a Preamp (W.O.T.)....cool, less work for me! The reason I wanted to delay the B+ was that specs on 6SN7s say the heater takes ~11 seconds to come up to full power(warm up temp).

Good point about the shunting of the (output)? or (input)? signal to prevent damage to my SS amp. How did you know? Are you spying on me??? I've got a Conrad Johnson SS amp that powers my Scottmoose/Planet10 designed small Thors.

Perhaps I'll use the Amperite Delay relay tube to shunt signal.
Is it on the input or output???
me thinks output, but not sure.

I was planning on NOT turning on the source or SS amp until AFTER the preamp had warmed up. Is that not enough to prevent damage to the SS amp or my speakers? New to this and appreciate the help.

Ron

Hi Ron,
A mute relay always goes on the output of a pre-amplifier. It provides protection in the event that you forget to sequence the components properly - and you or someone else eventually will. The other thing is that the relay should mute the instant the power is turned off for the same reason.

Use a shunt configuration to short the outputs to keep the contacts out of the signal path.

Given the requirements I would make sure that the time constant of the supply powering the mute relay is short. (Use a dedicated winding with a bridge rectifier and a small cap.) Don't use a lot of filtering as you want it to open literally as soon as the power is removed. Use the thermal delay relay to provide the just the delay and look at configurations to bypass it and shut it off once it has done its thing - that is so that if there is a power interruption it will mute the pre-amp and prevent dc transients from getting to your power amplifier.

Figure out the input impedance of the CJ amplifier and size the coupling cap just large enough for -3dB at 5Hz or so, don't oversize - this will help to limit the voltage spike in the event of an "event."

I have used tube line stages with solid state power amplifiers and in the distant, primordial past modified commercial tube pre-amplifiers where necessary to work safely with SS amplifiers. (In most case the work was preceded by complaints from the prospective customer about blown amp fuses, and damaged woofers or worse.)
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Old 16th September 2008, 05:33 AM   #7
Renron is offline Renron  United States
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Quote:
Originally posted by kevinkr



Hi Ron,
A mute relay always goes on the output of a pre-amplifier.

Hey, I got one right!

It provides protection in the event that you forget to sequence the components properly - and you or someone else eventually will. The other thing is that the relay should mute the instant the power is turned off for the same reason.

Makes sense to me.

Use a shunt configuration to short the outputs to keep the contacts out of the signal path.

I'll do a search and see if I can find a schematic for the layout. Thanks.

Given the requirements I would make sure that the time constant of the supply powering the mute relay is short. (Use a dedicated winding with a bridge rectifier and a small cap.) Don't use a lot of filtering as you want it to open literally as soon as the power is removed.

OK, with ya up to this point, and I understand we don't want much bleed down time for the capacitors.

Use the thermal delay relay to provide the just the delay and look at configurations to bypass it and shut it off once it has done its thing - that is so that if there is a power interruption it will mute the pre-amp and prevent dc transients from getting to your power amplifier.

Got any circuits in mind....handy? Is the reed type relay prefered of the SS type?

Figure out the input impedance of the CJ amplifier and size the coupling cap just large enough for -3dB at 5Hz or so, don't oversize - this will help to limit the voltage spike in the event of an "event."

Damn it, I was doing good up until this point. please explain. I know what the coupling cap is, but am uncertain of the calculations involved or the formula to arrive at the proper size cap.

I have used tube line stages with solid state power amplifiers and in the distant, primordial past modified commercial tube pre-amplifiers where necessary to work safely with SS amplifiers. (In most case the work was preceded by complaints from the prospective customer about blown amp fuses, and damaged woofers or worse.)
Thanks for all your help, It sounds like I am talking with the right person!

Ron
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Old 16th September 2008, 04:13 PM   #8
kevinkr is offline kevinkr  United States
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Hi Renron,
Can't use a SS relay in the audio path, cmos and opto-mos switches can be used. (But NOT recommended!!)

The mute relay simply shorts out the audio path and most simply could be a dpdt type connected directly across the pre-amplifier output rca jacks. Connect it using the n.c. (normally closed) arrangement so that with no power applied the outputs are shorted.
You can also use a pair of spdt to minimize potential cross-talk in the relay.

I don't recommend reed relays because unless you are adept at their proper application and can choose the right one based on specs you are quite likely to end up with welded contacts. Omron, and others make suitable small signal relays - you want something with gold plating, bifurcated contacts that is rated for low current operation (10mA rating or less at the low end) otherwise you run the risk of contact reliability issues. Contact resistance in the range of 10 milli-ohms should be fine.

1/(2pi x R x C) gives you the -3dB corner I was talking about, but you need to know the input impedance of your amplifier. In any event a couple of uF ought to be ok if your amplifier has an input impedance of 10K or greater. (2uF driving 10K is -3dB at ~8Hz, IMO a bit high. I'd recommend 4 - 5uF for this scenario.)

Use a dpdt relay (as a "latch" relay) with the thermal delay relay.. Connect the coil in parallel with the output mute relay coil(s). Connect one N.O set of contacts across the thermal relay contacts, connect the other N.C. set of contacts in series with the thermal relay's coil. This creates an electromechanical latch that removes power from the thermal relay and bypasses its contacts when its contacts close. This allows it to cool down for the next cycle and improves its service life as well. If you want to add a manual mute switch on the output place it after the latch relay coil and before the mute relays.

You can use LEDS to indicate what state the mute circuit is in.

Use dc on all coils, with the previous proviso, put a reverse biased clamp diode across the latch relay coil, and if you add a manual mute place one across one of the two mute relay coils.

All coils must operate on the same coil voltage.
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Old 17th September 2008, 12:30 AM   #9
Renron is offline Renron  United States
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Kevin,
Thank you so very much for all your time and help.
You have given me much information to think about and read up on.
I will shunt the outputs on my preamp build with relays as you suggested.
Thank you VERY much for your help.
Ron

When finished with my preamp I'll post pictures on this site.
Don't hold your breath though, the Wifee has her list of priorities and honey-do's, I know the pecking order in my house. Really great wife, but the master bathroom has been under construction for >10 months, can't ask her to wait forever.

Thanks again for all your expert help and preventing me from damaging my other stereo equipment.

Ron
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Old 17th September 2008, 02:01 AM   #10
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Oddly enough I am working with mute relays and a b+ delay for a small PP pentode amp right now. There are three relays in total. One for switching the b+ and two for shorting the secondary of the output transformers. Not wanting to use long RC constants or the plain old 555 timer I wrote a small program in PicBasic for the 16F684 chip. Nothing special about that particular model, we just happened to have a bunch of them at work. Looking at assembly makes my eyes glaze over so I tried PicBasic and it worked well. The b+ is delayed for 30 seconds. At 28 seconds the mute relays turn on for 4 seconds and then shut off again.
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