[Ericus Rex]

Hi all!

I'm sourcing parts for a slightly modified Jonokuchi amp I plan on building this fall.  The design has ss rectification but no provision for delayed B+.  Is there a simple relay option I can put in place to delay the B+ supply by 30-40 seconds?  I have the Morgan Jones book which does briefly describe a delay circuit but it uses 20 or so components!  Far too complex (and just about as many components as the whole amp design!).  I have perused Mouser for relays but am coming up with thousands of options with no real clue how to filter them down.  All help appreciated!

[mgalusha]

You can use something like a 5AR4 after the diodes to act as a soft start. SS rectification but the tube rectifier will warm up slowly. The penalty of course is the heater current for the tube. A time delay relay is of course an option. Or a 555 timer circuit with a relay.

Time delay relays http://www.surplussales.com/Relays/RETimeD-2.html
Thermal/vaccum tube time delays: http://www.surplussales.com/Relays/RETimeD-5.html

[Niteshade]

I don't think you have to worry about cathode stripping. If you are, the simplest way to do what you want is to install a standby switch that turns off the B+ when it's not in use. Put it before the main filter capacitor.

[zobsky]

Install a thermistor in line with the mains transformer (for slow start). Rig up a time delay relay to bypass  this thermistor after a short while (say 30 seconds).

[Ericus Rex]

Thanks Guys!  Good suggestions!

Mike, that's a real interesting option with the tube rectifier.  Sounds like a good compromise between using the rectifier solely as a soft start while keeping the speed of the diode rectification.  In order in implement it in this particular design I'd have to add a 5v tranny (the power trans doesn't have 5v outs...).  I was really hoping for a simple relay but those particular relays in the links are far more expensive than I can swing (the whole project will be around $250 - starting small here in my first diy trek).

Blair, I thought about the B+ on/off switch.  That method is used all the time in guitar amps.  I've never actually seen it used in hifi though.  I'll keep that one in mind but I was hoping for an automatic, worry-free option.  You're probably right about me being a bit overly cautious about the cathodes, esp. since there's no option put into the original circuit.

Zobsky, I've thought of the thermistor option but didn't think they'd give me the kind of time delay I'm looking for.  Do you know roughly what kind of time delay they offer?  I thought they only gave a second or two.  Why would I need the relay to bypass it after warm-up?  Do they not act like shorts once they're warmed up?  Sorry for all the questions.  I'm not very experience with the whole DIY thing and have very little knowledge of thermistors.

Thanks again for your help and all the great suggestions!

[gld]

You short them out after a couple of seconds because they do not sound good sonically!
And they can only pass so much current before they go boom!
gary

[DaveC113]

In my preamp, I wired the heater trafo separately from the HV trafo with 2 power switches, but in series so B+ can't be applied without the heaters turned on. Cost... about $3.

In my amp, I just use a 5ar4 rectifier, no diodes. I haven't tried the 5ar4 with diodes, I have a few NOS tubes so I'm not as worried about them failing as most new 5ar4s seem to do. 

[mboxler]

I was thinking about installing this switch in the Decware SE84C kit I'm building...

http://www.tubedepot.com/p-dpst-3way.html

Apologies to the OP.  This seemed like a good place to post a similar question.

Mike

[Ericus Rex]

Thank you all!  I decided to go with Niteshade's idea of using a standby switch.  Using the pot in Mboxler's link means that I can have the standby option without drilling a new hole in my design.  Thanks again!