EL34 Champ - Simple Standby?

[theundeadelvis]

Hey guys! It's been awhile since I fired up the soldering iron, and I decided to dust off the EL34 Champ and see if I could finish her off. Got it finished after sorting out a hum issue, and it sounds awesome! After I wired it up it occurred to me I should consider installing a standby since it uses a diode rectifier.

My questions is what would be the simplest (but reliable) way to insert a standby into this baby? Thanks in advance! It feels good to be soldering again!

Here's the layout I used:

[sluckey]

Maybe the neatest way would be to use a DTST switch and break both red wires before the diodes.

Or you could use a SPST to break the red/yel HT CT.

[theundeadelvis]

Does either method have an advantage? Thanks so much for your quick response!

[Fresh_Start]

Here's the Valve Wizard's discussion of standby switches:
http://www.freewebs.com/valvewizard1/standby.html
Don't necessarily agree with everything there but the basics are covered.

If it's important for this build, a "progressive" triple throw, double pole (TTDP) switch would allow you to avoid drilling another hole in your chassis.  Switch positions would be Off/Standby/ON, with one pole switching the high voltage just like your "AC Switch" now and the other pole between the diodes and that 150 ohm dropping resistor.  Wish I could think of a way to mount that resistor on the switch but it's late...

AES sells this switch IIRC part #P-H520.  Wish Doug would carry it.

Cheers,

Chip

[rzenc]

Breaking both red wires with DPST switch will eliminate all high voltage from circuit, you can allow heaters to warm-up before applying voltage and start to suck current. Also, it is safer if you want to mod something while keeping the heaters hot - just remember to properly discharge power supply caps before attempting to stick your iron/hand into something. It would help to if you install fuses before the stand by switch, in case of shorts, it will not melt the switch.


Some food for thought:

http://www.freewebs.com/valvewizard/fuses.html

Hope this helps

Best Regards

Rzenc

EDIT: Chip responded at the same time... so I changed the link from stand by to fuses...

[loogie]

Don't necessarily agree with everything there but the basics are covered.

I've read those words before, but often there's no explanation -- and often where Merlin is concerned.  What don't you agree with? 

On a scale of one to ten where one is 'What is a soldering iron?' and ten is 'Hi, my name is F. Langford-Smith' I'm about a two. So I really am curious.  I've read everything I can find, including as much of F.  Langford-Smith as I can understand.  I'm still working on the frontispiece.

[sluckey]

Maybe the neatest way would be to use a DTST switch and break both red wires before the diodes.

Or you could use a SPST to break the red/yel HT CT.

Does either method have an advantage?

I think so. Both are equally effective, simple, and easy to do, and don't require moving any components or modifying the board. You could also put a switch between the diodes and that 150Ω/5W sag resistor, but then you really need another eyelet or turret. Or you could put a switch in the cathode of the output tube like my Magnatone does (effective, but I don't like this method).

So, what is "your" purpose for a STBY switch? My purpose is to keep the amp hot and ready to go at the flip of a switch like those good ole ss amps. Nobody likes to wait 30 seconds for an amp to warm up. 

[jhadhar65]

*After I wired it up it occurred to me I should consider installing a standby since it uses a diode rectifier.

A standby in that amp will be more trouble than it's worth, regardless how you implement it, unless you do it for your convenience.  Power amps with multiple tubes can benefit from other performance/tone features using certain standby schemes involving breaking the cathode ground path for some/all of the power tubes, but this won't apply to your amp.  I'd probably spend my solder time in that amp tweaking component values or something instead of worrying about a standby switch.

[theundeadelvis]

Thanks for all the replies! If I implement one, I'll go with Sluckey's suggestion.

jhadhar65 - I was concerned with giving the tubes time to warm up to prevent premature wear on the tubes, but after reading the Valve Wizard article I see that it may not be anything to worry about. So, I may just forget the standby all together. Thanks again!

[jojokeo]

Dude, this is a simple mod to do w/ little work. http://www.rru.com/~meo/Guitar/Amps/Kalamazoo/Mods/standby.html

[Fresh_Start]

Question:  if your standby switch cuts the power transformer's center tap connection to ground, will capacitors on the power rail retain their charge?  Seems to me like they would, even if you have a bleeder resistor on the power rail.  I know that cutting the DC rail itself allows the caps to discharge if you have a bleeder resistor.

Don't necessarily agree with everything there but the basics are covered.

I've read those words before, but often there's no explanation -- and often where Merlin is concerned.  What don't you agree with?  

On a scale of one to ten where one is 'What is a soldering iron?' and ten is 'Hi, my name is F. Langford-Smith' I'm about a two. So I really am curious.  I've read everything I can find, including as much of F.  Langford-Smith as I can understand.  I'm still working on the frontispiece.

I'm probably a "2" as well.  Maybe a "1.5" since I don't know who F. Langford Smith is.  

Merlin's at least an "8".  My problem is that he sometimes expresses opinions as if they are irrefutable facts.  Also, he has strong preferences in terms of amp circuit design and the resulting tone.  Nothing wrong with that.  Unfortunately, it can be hard for a newbie to figure out when Merlin (or Kevin O'Connor for that matter) is explaining a fact vs. describing a personal preference.  It's more a question of style than substance.  

I've learned a lot from Merlin's website and his posts over on AX84, and I certainly don't want to seem ungrateful.

Jack Darr would be the polar opposite for me. I can't believe I didn't read Darr's book first!

Hope I haven't offended anyone with this explanation.

Chip

[Shrapnel]

Question:  if your standby switch cuts the power transformer's center tap connection to ground, will capacitors on the power rail retain their charge?  Seems to me like they would, even if you have a bleeder resistor on the power rail.  I know that cutting the DC rail itself allows the caps to discharge if you have a bleeder resistor.

It would be no different, without a bleeder resistor, those caps will take a might long time to discharge on their own.

Merlin's at least an "8".  My problem is that he sometimes expresses opinions as if they are irrefutable facts.  Also, he has strong preferences in terms of amp circuit design and the resulting tone.  Nothing wrong with that.  Unfortunately, it can be hard for a newbie to figure out when Merlin (or Kevin O'Connor for that matter) is explaining a fact vs. describing a personal preference.  It's more a question of style than substance.  

I've learned a lot from Merlin's website and his posts over on AX84, and I certainly don't want to seem ungrateful.

Jack Darr would be the polar opposite for me. I can't believe I didn't read Darr's book first!

Hope I haven't offended anyone with this explanation.

Chip

Almost everyone will state some opinion as cold-heart canonical fact. Dan Torres is an example, along with Pittman, O'Connor (whom you already mentioned,) and others. I think part of it is  some of them feel "I'm THE Guru who knows how to exploit the Mojo." In other cases, "It's just how I do it," and in other cases, "Mystify them, for if they knew full fact from fiction, I'd have more competition or be out of a job."

No offense here. I think from what you describe, although Merlin tries to explain well, it gets into the "how I do it" category, and perhaps he feels the audience for his book already has some knowledge, therefore devote the space to more technical details than a "beginners" book. If Merlin chimes in, I know we will know where he's coming from.

[HotBluePlates]

Question:  if your standby switch cuts the power transformer's center tap connection to ground, will capacitors on the power rail retain their charge?  Seems to me like they would, even if you have a bleeder resistor on the power rail.

If there is no bleeder resistor, the caps will hold their charge unless some warm tubes pass enough current as they cool off to discharge the caps somewhat.

When you disconnect the center-tap, the winding "gyrates around itself" and there's no hard reference allowing the rectifier diodes to be forward-biased and pass current. So that's no voltage in.

With no bleeder resistors, there's "no resistance" to ground, and no path for the caps to discharge. Really, there is ESR in the caps and they will eventually discharge, but this could take a very long time. Longer for higher capacitance.

Hot tube cathodes could be a bleeder resistance for a second or 2. Might discharge the caps some. But I've been bitten by more than 400vdc from caps that were discharged but did not have bleeders or a jumper placed to keep them at ground potential. The particular caps had memory-effect happen because I left the amp sitting long enough after discharging (and didn't recheck cap voltage) that it built back up. Let me tell you it hurt! 

Almost everyone will state some opinion as cold-heart canonical fact.

Guilty.

But I think that most people don't intentionally mislead folks about amp stuff. In my case, I try to be objective and offer an opinion based on reading, research and experiment. So in my mind, the opinion is almost equal to fact. I suspect most people are the same; the opinions they offer seem so correct as to be the same as fact, at least to them.

You know, I'm glad we're on at least the 3rd iteration of the Hoffman Forum. I have been coming on here since maybe 2002 and have learned an enormous amount since them. I'm glad that some of my earlier posts (with significant errors) aren't still around!  But I learn new things all the time on here, and am grateful for everyone's facts and opinions. Without them, I would have a far porrer understanding of tube electronics.

I'm probably a "2" as well.  Maybe a "1.5" since I don't know who F. Langford Smith is.

The editor of the Radiotron Designer's Handbook.

Remember though, he was the editor. He had an enormous amount of books and articles to cite and steal from. Which is perfect when you're producing a book without opinion, as facts don't change.

[sluckey]

Question:  if your standby switch cuts the power transformer's center tap connection to ground, will capacitors on the power rail retain their charge?  Seems to me like they would, even if you have a bleeder resistor on the power rail.  I know that cutting the DC rail itself allows the caps to discharge if you have a bleeder resistor.

The caps would hold their charge just the same as if the switch were on the B+ rail. If you have a bleeder resistor it would/should be connected directly across the cap, so the cap will discharge thru the bleeder whenever you break the charging circuit, either by breaking the positive side (B+ rail) or negative side (HT CT).

The PT HT secondary is the source for all B+ current flow. The rectifier insures that current can only flow in one direction (because we need DC). Think of the HT secondary and the rectifier as a simple battery (call it a car battery). The cathode junction of the rectifier is equivalent to the positive post of a battery. The HT center tap is equivalent to the negative post of a battery. Your headlights don't care if you switch the positive or negative side to turn on or off.

[OPINION] I don't like breaking the CT. And if you have other circuits (such as a bias supply) that rely on that same CT, you may get some undesirable effects by breaking the CT connection. In the case of a simple amp such as the champ, it makes no difference.

[loogie]

Hope I haven't offended anyone with this explanation.

Heavens no.  No offense in any of this. 

Maybe I'm delusional, but it seems to me that Merlin sometimes gets picked on.  Nothing wrong with that, you've got to defend your work, I guess.  Maybe its because he's pretty active on the forums.  I'm glad for that.

The only book I'd rather read than his is the one PRR will write someday.  And please let it be full of opinion.

[HotBluePlates]

I'd read PRR's book too. I doubt he'd write one though... He'll probably say there are too many books out there already that say everything he would want to say.

But at least he'll probably also point you to those books. I'm grateful that he sent a bunch of them to me for reading material during my deployment.

[Fresh_Start]

PRR's book would be like The One Minute Manager for tube amps   Short, straightforward, and extremely dense in terms of really useful advice & info.  Hell yeah I'd buy it!

Actually, I've done a search for PRR's posts a few times just in case I missed something.  HBP's too for that matter.

Cheers,

Chip

[Shrapnel]

Hot tube cathodes could be a bleeder resistance for a second or 2. Might discharge the caps some. But I've been bitten by more than 400vdc from caps that were discharged but did not have bleeders or a jumper placed to keep them at ground potential. The particular caps had memory-effect happen because I left the amp sitting long enough after discharging (and didn't recheck cap voltage) that it built back up. Let me tell you it hurt!  

Been there, done that myself, hand to forearm (rested on chassis.) I'm glad that is as far as it went. It did hurt (but probably no more than a good jolt from an electric fence in my case.)

Almost everyone will state some opinion as cold-heart canonical fact.

Guilty.

But I think that most people don't intentionally mislead folks about amp stuff. In my case, I try to be objective and offer an opinion based on reading, research and experiment. So in my mind, the opinion is almost equal to fact. I suspect most people are the same; the opinions they offer seem so correct as to be the same as fact, at least to them.

You know, I'm glad we're on at least the 3rd iteration of the Hoffman Forum. I have been coming on here since maybe 2002 and have learned an enormous amount since them. I'm glad that some of my earlier posts (with significant errors) aren't still around!   But I learn new things all the time on here, and am grateful for everyone's facts and opinions. Without them, I would have a far porrer understanding of tube electronics.

I'm probably a "2" as well.  Maybe a "1.5" since I don't know who F. Langford Smith is.

The editor of the Radiotron Designer's Handbook.

Remember though, he was the editor. He had an enormous amount of books and articles to cite and steal from. Which is perfect when you're producing a book without opinion, as facts don't change.

I know I don't know everything, and I try not to let opinion stand as fact, but sometimes when we've picked up opinion as fact, and didn't recognize it as such, we do state opinion as fact. I agree, *Most* people don't intentionally do so. But there are all types out there. Including old crotchety men who unless you are there to spend money (then they're glad to see you.) If you want to try to talk "shop" then there's the door. (DON'T EVEN think of trying to pick their brain on anything about electronics, customer or not.) I know I personally try to keep my mouth shut here if I have no clue to an answer, rather than misguide someone and look dumber than I am. If I think I know, I may reply, then note that someone else can let me know if I'm wrong.

Ugh! and here we hijacked the thread somewhat... Simple Standbys. Only real differences in actual function, excluding those that just drop voltage, is the voltage potential and whether they're asked to work with AC or DC voltages. (Even then, the voltage droppers have those same issues.)

[ EDIT ] Oh yeah, and as mentioned, IF it is working on the center tap (and low potential) anything else that depends on that center tap going to ground is effected.

[loogie]

Ya, it would be filled with anecdotes, stories from the road, quick solutions to thorny problems, opinion and personal reflection, romance and intrigue.  Hell, it'll make a great movie.  I wonder who will play him?  I think Benicio DelToro.  Imagine a Kubrick-like tracking shot, only in 3D, along the turret board of a DR103.  Or maybe it will be a Saganesque type romp through the history of radio, automobiles, airplanes -- all the stuff he is an expert at, which is just about everything.

I must admit I just trawl for PRR, HPB, Merlin and Aiken.  I should never post.

[PRR]

> ESR in the caps and they will eventually discharge,

Act-shually.... Equivalent Series Resistance is never gonna discharge the caps.

All caps have leakage, a parallel resistance. Electros have a lot. Some caps specify it, though an exact spec is impossible. Some don't even bother, because if leakage mattered we would not use an electrolytic. Electros usually self-bleed to fairly low voltage in a minute to a couple hours.

But don't depend on that. As you note, a short discharge followed by open-circuit, an electrolytic will "recover" some voltage. Slightly like a "dead" car battery may come-back a bit if you turn-off the lights you stupidly left on, and let it rest a while.

MY over-stated opinion is that a Champ does _NOT_ need a standby switch "to save the tubes". The whole distinction with "receiving tubes" is that they CAN be hot-switched with cold cathodes. I.E. they CAN be used by non-techs who can not be trusted to pre-heat the tubes. (There's a whole another book for high-strung "transmitter" tubes which are only fired-up by professional technicians who are paid to know the procedures.)

If you need to shut-up (guitar change, sermon) without messing your Volume setting, you could kill B+ (usually at the rectifier) or short the signal at some convenient place.

Book? Movie? Open to suggestion. I am finally reaching a point in my life that I could take the thousands of hours a good book needs.

[DummyLoad]

Book? Movie? Open to suggestion. I am finally reaching a point in my life that I could take the thousands of hours a good book needs.

i wish you would! a book that is... and if you touched a bit on solid-state, that would be the icing! 

[theundeadelvis]

I decided to forgo the standby, and the amp is near done (just finishing up the cab. It sounds great. I've built a number of amps, and I really love this little guy. May have to get a KT77 and see what it sounds like.

1 more, really silly, question. All of the other amps I've built, I've run the indicator lamp from the heaters. The only lamp I have laying around is 120v, but I can't for the life of me figure out how to wire it. The way I wired it, it's on when the amp is off, and off when the amp is on?

Thanks again for all the info. You guys rock, and the forum phenomenal.

[PRR]

120VAC lamp across the transformer. Not the switch.

[theundeadelvis]

Thanks PRR! It was one of the moments where I had been staring at that amp for too long and just needed to walk away. No matter how I thought about it, nothing made sense.