Stand-by switch question.

[Red2112]

Hi,

I know it's not a stompbox, but you folks have allot of experience.  I would like to install a bulb rocker switch as a standby switch to my Epiphone Valve Junior head (it doesn't have one, just a power switch).

Aim a newbie to electronics.  The bulb rocker switch is rated 250v 16A, but I don't know where to get the lead from to power the bulb of the rocker switch, I would guess it has to come from the power transformer.

Here's the EVJ stock scheme:
http://www.euthymia.org/DIY/VJstock.jpg

and here is the rocker switch:
http://www.ondaradio.es/esp/detalle.aspx?id=969

Any help would be much appreciated, thank you.

Regards,


Mike

[d95err]

What do you want the standby-switch for?

[Red2112]

What do you want the standby-switch for?

Hi d95err,

Thank you for your interest.

The Epiphone Valve Junior is a 5watt class A valve amplifier.  To preserve the life of the el84 and 12ax7 power and pre tubes, a standby switch would be nice, but not mandatory.  It could live without one, I know and yes tubes are cheap, specially this one that only runs on two tubes.  But for the price of the rocker switch and some wiring, why not.  Thanks again d95err.

Good care.

[petemoore]

  The PV classic 30 has no standby, many amps dont'.
  I think that setting volume to 0 on the amp sufficeintly reduces output, and tube loading so that the tube life can be extended..as output tubes are not doing output when in a non-warmed up state.
  I'm not sure so ask is there a difference in tube life if the slight background noise of a volume control turned all the way down is effective than a standy which lifts B+...either method can be used improperly, both can have malfuncions.

[jonathan perez]

my traynor has never been put on standby, as has been running off of the same tubes for nearly 20 years.

[jlullo]

mike,
i did this and it worked great!

i used a dpdt switch, and basically broke the connection with the red wire at T2....
make sure you use shielded wire.  i didn't, and of course, added to the hum


jonathan

[jlullo]

i think it is a nice feature to have, if nothing else, for testing the stompboxes we make.... i turned mine on and off a hundred times while iw as making adjustments, and now having the switch makes it a lot easier for me.

[sfx1999]

From what I've heard, standby switches don't make a large difference in tube life. Actually, leaving an amp in standby for extended periods can cause what is known as cathode stripping. I don't think that really makes a large difference either if you don't do it so much.

Anyway, all you need is a SPST switch in between the bridge rectifier on there and R12/C6/T1. That's how it is on my homebrew amp. The only problem is you may get a pop when you switch it on/off.

By the way, don't think that because your amp is in standby, you can't get shocked. You still can due to the charge in the capacitors.

[spud]

From your statement (regarding being a Newbie to electronics) and your question, I would advise you NOT TO TRY THIS.  

Tube amps have high voltage/high current inside them.  Enough to kill you if you don't know what you are doing.  Even experienced people get shocked because of mistakes due to fatigue/rushing/etc.  Don't take this wrong - I am only trying to keep you safe.

If you still insist on pursuing this, read up on it first.  Go to one of the Valvejunior sites or AX84.com, 18watt.com, GEOFEX (tube FAQ), etc - all have safety material and information that you MUST READ before you start to mess with your VJr.  

It might seem like a simple thing, "insert switch here",  well, from looking at the schematic that amp has no bleeder resistors on the filter caps.  Those caps can hold their charge for quite a while after power is cut off.  Also, from the schematic I can't tell what the PT puts out but if they are running the EL84 according to spec, the tube should be getting at least 250v on its plate plus a bias current of ~65mA - that can kill you, no lie.  Go to this link and read the part on Ventricular fibrillation - YES, 1mA across your heart can kill you!

http://en.wikipedia.org/wiki/Electric_shock

I just found a schematic at S2amps that lists the voltages: 354V B+1, 322V B+2, 298V B+3.

Before you start to mess with your VJr, please read up on Tube Amp Safety.  

If you don't understand what I've written (not just the English aspects) but the technical information I've tried to convey, you should take the VJr to someone who is competent at Tube Amplifier repair and ask them to make the mod - I'm serious - this stuff can kill you.  

[Red2112]

Hi and thank you all for your prompt reply and concern.  Thank you very much!

A special thanks regarding your concern for my health.  Yes, I did do allot of reading before I put my hands inside the EVJ, as I did have a special concern regarding charged caps, even before I swapped the tubes for a TAD EL84 and a TAD 12AT7, never the less swapping the tranny for a Hammond 125ESE.  Aim very cautious when I don't know something or new to it.  A future project is building a 18 watter, but till I have everything very straight, I wont even start something like that, and of course allot of reading and research.

Just for the record, the version 2 of the EVJ dose have a resistor bleeder, if I remember correctly its R-14 (220k).  Just in case I built this to discharge the caps to ground, but lucky enough the bleeder resistor was there.  All though, you can´t trust the bleeder resistor to do its job.







I would never consider someones concern for my health as a offence, thank you very much Spud    I hope this dose serve other newbies as a warning as well, very Important!

Regarding a two pin SPST switch to T2, aim aware of that too.  I just thought I would look better with a bulb rocker switch in yellow next to the power rocker switch which is red.  Yeah I know, it just looks fancy    You can throw things at me now...

As for tube life and the standby switch, yep allot of folks agree that you don't need it.  I just guess aim getting hooked to all this modding thing, electronics and of course, my EVJ head 

Thanks again folks, very nice of you and good care,


Mike

[sfx1999]

How are the TAD tubes?

Have you tried JJs? Their ECC83-S is my favorite 12AX7 so far, and I like their EL84.

[Red2112]

How are the TAD tubes?

Have you tried JJs? Their ECC83-S is my favorite 12AX7 so far, and I like their EL84.

Hi sfx1999,

I'll tell ya how my story went.  When I went to my local shop in search of tubes so I could swap the stock Sovitek tubes on the EVJ, they only had TAD for the EL84 and Sovitek for the 12AX7.  So I picked up the TAD EL84, swapped that, and at least I did notice the difference (some folks cant).  But I didn't like how the brake up came out with the Sovitek, TAD combination.  Its hard to explain, its was just too harsh and muddy, boomy sounding like.  The week later, I picked up a TAD 12AT7 and the result over all was great!  Less volume, but much better break up and more definition, I was (am) very happy with that.  Two weeks later, I swapped the OT tranny for a Hammond 125ESE, and now, well.... Aim very happy!

I will pick up a TAD 12AX7 soon and try it out, but I think I will stay with the 12AT7 cuz its right for the sound aim looking for.  I think TAD´s are very good, and might even try some of there premium stuff.  I do hear the JJ´s EL84 sound real good, so In the future I will try one out.

I think swapping tubes is a cheap and great way to get new tones out of your amp, so I will experiment with that in the future 

Here's a short clip of how they sound on the EVJ...

http://www.youtube.com/watch?v=7cEFNR8y5Aw

TAD´s site...

http://www.tubeampdoctor.com/index.php?language=en

Good care

[jlullo]

red,
how did the transformer swap turn out?  i was thinking about doing that myself next (along with fixing this ground hum!)

you're right, the bulbed switch would look pretty sweet  

i like your discharging rig!

[Red2112]

red,
how did the transformer swap turn out?  i was thinking about doing that myself next (along with fixing this ground hum!)

you're right, the bulbed switch would look pretty sweet  

i like your discharging rig!

Hi Jlullo,

The swap for a Hammond 125ESE or DSE went great! Its the best mod you can do to the EVJ, apart from tubes and getting rid of the hum if you have a AC rectified version.  The version 2 head (which is what I have), is DC rectified so the hum issue is done stock.

The Hammond OT, just makes such a great change.... you will have a nice smile on your face once you do it, believe me.

If you do decide to do the OT swap...  You will also need to swap R-10 and R-14 to bring down the OT from 7.5v.  The value of R-14 depends on the bias, but your safe around 250-270ohm/2 watt resistor and R-10 to 1k/3-4 watt even 5watt resistor (metal oxide).  If you have R-11 in there at 220k, then thats the bleeder resistor.  You also need to drill a new hole to adapt the new OT, as its three times bigger then the original OT. Change the orientation of the new OT to a horizontal position and drill a new hole.

Hammond 125ESE and DSE color codes:

Primary:
-Blue to T4
-Brown to T3

Impedance board:
-White to 16ohm
-Yellow to 8ohm
-Green to 4ohm
-Black as same
-Orange unused (cut and tape or use heat shrink tubing)
-Green and yellow, leave as is.

R-10 swap for 1k 3 or 4 watt, 5 watt is ok too.
R-14 swap for 250-270ohm 2 watt.

If your fancy with biasing (I wont try this yet), measure voltage from cathode to ground on pin 3 of EL84 and measure plate to cathode voltage on pin 7 and 3. Calculate dissipation I=V/R etc...  If the dissipation is more then 12w, increase the value of R-14, if its under 12w, decrease value of R-14.  I haven't calculated dissipation nor do I have a screen resistor in there, I just put a 270ohm value for R-14 which is more better then what comes out of the manufacturing site regarding bias.

I think I got you straight on this, but just in case, you can check with the Epiphone forum or 18watt forum, they have been very nice with me and helped me allot.  The only other mod I might do, is the input mod of R1 and 2.  Some good tubes and the Hammond OT is all you really need to do to have a nice sweet mojo tone on this amp 

All in all, it's about an hour's work...and its worth it.  Again, as mentioned before, use tube amp safety!

Hope it helps and enjoy your EVJ!

Regards,


Mike

[jlullo]

mike,
thank you so much for the information!  this will definitely be a sweet little weekend project for me!

thanks again!

jonathan

[d95err]

Tube amps have high voltage/high current inside them.  Enough to kill you if you don't know what you are doing.  Even experienced people get shocked because of mistakes due to fatigue/rushing/etc.  Don't take this wrong - I am only trying to keep you safe.

The risks of high voltages in tube amps are grossly exaggerated. The reason any site involved in tube amp building or modding has such BIG DISCLAIMERS is because of the US way of suing the sh*** out of someone instead of admitting to making a mistake. Every site has to protect themselves from blame in case somebody zaps themselves and for some reason decides to blame them...

In practice, getting zapped by B+  or line voltage is something most experienced tube amp builders have done many times and lived to tell about it (I'm not *that* experienced yet thogh...). You'll get a nasty sting, perhaps a small burn and if your really unlucky, you'll destroy an expensive component. Actually getting killed would require exceptional circumstances.

Ok, make sure there are no children around when you work with a tube amp, and think twice if you have a known heart condition. Otherwise, you should be fine. Also take some basic precautions like - one hand in your pocket - and so on.

I can think of a lot of things more dangerous than tube amp building (driving a car, crossing the street, getting drunk...)


EDIT: OK, just in case, I'll add a disclaimer: TUBE AMPS CAN CONTAIN LETHAL VOLTAGES WHICH CAN GET YOU KILLED! DON'T LISTEN TO ME AND CERTAINLY DON'T BLAME ME IF YOU ZAP YOURSELF!

[sfx1999]

Wait, you didn't cover soldering iron burns!!!

If you can get a hold of it, I've heard good things about Heyboer transformers.

[runmikeyrun]

I never trust the insulation on alligator clips.  Once you start getting up several hundred volts i picture the 8 year old chinese kid running the mold machine making them...   

I clip one end to ground and the other to a screwdriver with a very good insulated rubber or plastic handle and FREE OF ALL GREASE/OIL/DIRT which could conduct some of the juice up the handle to you.  I actually use a brand new one that has a rubber and plastic handle.  Then i hold the screwdriver and touch the end to the appropriate power tube pin to zap the juice out of it.  Then i check the voltage w/ a voltmeter on the amp PLUS any components i am about to work on.  I'm paranoid but after getting shocked once i don't mess around anymore.