am i gonna melt my valvecaster doing this?

[pinkjimiphoton]

was dicking around with my valvecaster that haveyouseenhim sent me a board for eons ago.

i bought a bunch of russian 6n2p ev's on the bay a while back.. some circuits they work well, others not so well... the pinout is a bit different. so i bought some socket savers and figured i'd make my own adapters.

first try? not so great. i bent pin 5 to pin 9 of the socket saver, soldered them together. nipped off the bottom of pin 9 on the russian tube side, and tied it to pin 8 <k, cathode> as its the center tap of the heater supply on a 12a_7, but on the 6n2p it just connects to an internal shield. i made sure everything was insulated, and decided to try it in my valvecaster first, before trying in a guitar amp.

of course, wasn't thinking... the valvecaster runs at 12vac, on a 2 amp wart. the 6n2p is SIX VOLT OPERATION ONLY, not 6/12 like a 12axwhatever. so i plugged in the adapter, something started smoking, i pulled the power. stinky cloud of funky nastiness disipated  a bit, and i tried again... without the adapter. believe it or not, fired right up still!! with the 6n2p wired as stock right into the 12ax7 socket. sounded GREAT!! i was surprised, actually... the tube is glowing brightly, i guess it SHOULD be as the heaters are running at double their rated voltage!!!




but here's the thing... the sucker sounds KILLER! it has more headroom than it ever had in the past... was always a fuzzy noise maker, nothing really great... just fun to play with. but with this mistake, it sounds more like an actual stage in an actual amp.

the tubes are dirt cheap and sound good. the pinout issue i'm dealing with for the amps... but the question is, am i gonna cook the valvecaster running it with a 6v tube at double the heater voltage?

i'm guessing the higher heater voltage equates to a larger electron cloud being released from the cathodes, without having to raise the plate voltage higher, but i dunno if that's actually possible.

the only side effects i've noticed so far beside the increased headroom are the tube actually GLOWS now like it would in an amp, and its putting out actual HEAT which it never used to do... all day long, and the box it was in would stay cool to the touch. now it gets warm. not too hot to touch, and doesn't seem to get any hotter, but it gets warm to the touch, i'd guestimate the casing is around 120 degrees <its full of holes to dissipate heat, too>

remember, i'm no EE, just a 10 toed freak of a monkey with a breadboard, willing to let that magick smoke out of ex - pensive old obscure rare parts in pursuit of #FuzzyGoodness so you don't have to.... so i need advice.

if its gonna smoke the circuit, i'll go back to the 12ax7 <5751 in there actually, was what was in there> but if its not crazy dangerous, i may just stick with the 6n2p.

what do you think? as always, when dealing with tubes, even low volt stuff, always be careful.

if this is a safe hack, it may  be worth trying is what i'm thinking. i'll try and get some stupid video if anyone wants to see it.

thanks guys

btw, to make adapters to use 6n2p russian tubes <wicked cheap but military grade> get some socket saver adapters from tubedepot or similar... they have a screw thru them and you can take them apart...

inside, bend pin 5 to contact pin 9, solder. nip off pin 9 close to the socket for the tube <the top> and insulate it so no shorts are possible.

now pin 4 becomes one side of the heater, and pin 9 the other side. pin 5 is not used. so you end up using 8 of the 9 pins.

pin 9 of the 12AX7 is the center tap of the heater supply. on the 6n2p it connects to an internal shield. you COULD connect it to ground <many reccomend connecting it to k/cathode, but i don't cuz in guitar amps your cathode usually has an RC network connected to the preamp tubes, and i don't think ya wan an internal shield connecting to the ac heater supply... sounds like an antennae situation to me, potentially> but its not really necessary.

when i get done tinkering and testing, i'll up some photos.

anyways... as always... thanks in advance!!

[PRR]

Small tube heaters can exceed 10,000 Hour life.

At 2X design voltage, this becomes approximately 1.2 Hour life.

(I suspect that outright heater failure expected life is really well past 10K hr, so you may get several hours on a tube.)

The extreme temperature may hasten secondary troubles like cathode material depositing on grid which makes the grid go wild.

But hell. Live hot, die young, leave a handsome corpse.

[pinkjimiphoton]

Small tube heaters can exceed 10,000 Hour life.

At 2X design voltage, this becomes approximately 1.2 Hour life.

hahahah, its been running all day in my shop, still seems to be going!!!

(I suspect that outright heater failure expected life is really well past 10K hr, so you may get several hours on a tube.)

used to nuke really bad tubes with a tube tester when i was a kid, surprising how much abuse they can take
but once they pop, they're gone for good

The extreme temperature may hasten secondary troubles like cathode material depositing on grid which makes the grid go wild.

its still far colder to the touch than in any of my amps... you can touch the bottle, and its hot, but not burning hot.  in most of my amps, if ya touch the tubes, your skin will stay with them

But hell. Live hot, die young, leave a handsome corpse.

i couldn't leave a good looking corpse if i tried. or die young. soooo.....

[GibsonGM]

I think it's a live and learn, man.  Enjoy it while it lasts, and take note of how long it lives!   

Oh, I've had a few of those things...sounds JUST LIKE WHAT YOU ALWAYS WANTED and then - BAP - it's all gone.  Like those old classic VOX speakers I had slaved to may amp, but which were like 50W rated, and my amp put out 100W...it was like the Who at Monterrey for 2 sets, and then...silence.... 

[pinkjimiphoton]

hahahah i so totally get it parks

we'll see how it makes out, i'll bring it on tuesday nite to my gig and see if i can set the stage on fire

i wonder why it sounds so much better... its crazy!

the only thing i can imagine is the cathodes are pumping more electrons. more heat = more balls?

we'll see

i got a fire extinguisher next to my bench

[thermionix]

Everything sounds awesome right before it dies.

I'm not familiar with the valvecaster, but if it uses two tubes, you can run the heaters in series for (safe) 12V operation.  If you really want to keep the increased power and headroom, maybe raising the B+ will do it.

[italianguy63]

we'll see how it makes out, i'll bring it on tuesday nite to my gig and see if i can set the stage on fire

LOL.. reminds me when I saw Blues Traveler.  They had some seriously crappy equipment!  Guitarist's amp was billowing smoke all night.. I was waiting for it to fail, and the keyboardist had this Hammond B3 thing he had cobbled out of plywood.



I'll be watching for the smoke signals Jimi!!

MC

[rankot]

Try putting 15-18 ohm 3W resistor in series with heaters, it will drop voltage to acceptable range.

[italianguy63]

Try putting 15-18 ohm 3W resistor in series with heaters, it will drop voltage to acceptable range.

Killjoy!

[pinkjimiphoton]

bwahahahah!!!

i love how it sounds, really wicked different from the 12ax7, a lot more of a brassy marshally edge that reacts beautifly to guitar knob tweaks.

i had it running on the bench over 12 hours today, it sounds the same and stopped smoking  yesterday

so i'll take it as a win-win so far.

for the record, the 6n2p is a KILLER guitar tube. to make the adaptor, go to like tubedepot dot com or your fav vendor, and get an assload of socket savers. they're wicked cheap. get the ones with the long base and a single bolt going thru them.

all ya gotta do is bend pin 5 so it makes contact with pin 9.

ya wanna kinda bend it a little in an arc so ya can get the screw back thru. put some heat shrink on it for safety, and then solder it to the post right where the pin comes out of it. use a good solder joint with some heat  so ya get a good joint. <<<damn, me always talking about how good joints should be lol.. somebody cue innagaddadavida ffs>>>

once it cools for a second, take your trusty fiskars/dykes/whatev and clip it off right flush to the phenol first by the socket for the tube itself on pin 9. just whack it right the @#$% off. then cut it again, for safety, closer to where the pin is attached. i leave some room for wiggle, and the pin 5 if soldered solidly will make it hold in place well.

the only downside is ya gotta make sure you orient the tube properly, as now there will be two keyways with pin 5 gone. you don't need pins 4 and 5 both, as they are in parallel... you could use pin 4 or 5 to solder to pin 9, pin 9 is closer to pin 5.

in a 12ax7 pin 9 is the center tap of the two heaters. on the 6n2p its an internal shield that should be tied to ground. yeah. whatever. ya don't need to tie it to anything. i tried tieing it to the cathode as some suggested and it seemed to make it hum more. so just don't even worry about it. once ya make the adaptor, pins 4 and 9  will supply the necessary heater voltage.

sounds a lot like a 12ax7, very robust with a pronounced ringy midrange chime i haven't heard in a long time.

i'll post some pids tomorrow, too lazy tonite, its already 4:05 am here lol... but i got enough of 'em built tonite to tube my silkyn and princeton. gonna order some more and do my pro reverb up too... i tried them  in that and was freakin devastated at the tonal improvement from the jj's that i had in it.

anyways... stay tuned.

no fires yet