fresh tube preamp/stompbox

[birt]

its finished (except for the leds and probably i'll need a new rectifier)

a little info:

the left stompswitch is an A/B to choose between the loop (with the preamp of my 2203) and the preamp itself.
the middle one is to put the preamp in front of the loop instead of using the loop OR the preamp.
the right switch is a bypass switch to feed the guitar signal directly in the loop.

i made the rectifier out of some old 1n4004's i found but i fried them because they drop the voltage for 80% or something.. that ain't good. the rest seems to be ok.

here are the pics: http://sic.fotopic.net/c402596.html

[Peter Snowberg]

That is a thing of beauty!

GREAT job!

It is very impressive that you made the box too!

[birt]

That is a thing of beauty!

GREAT job!

It is very impressive that you made the box too!

actually i didn't make the box.

i found it at my grandma's garage.. my grandpa must've made it a couple of years ago (he died 2 years ago, sad cos he was a tv/radio tech and could have learned me a lot and i really liked him) and tough it has ugly corners and looks like a tank ran over it a couple of times, i liked it.
so it was just lying around waiting for a project

[Paul Marossy]

Well, at the very least, it will always remind you of your grandpa.  

[EdJ]

Ziet er goed uit Bert!
Hoe klinkt ìe?
Groeten,Ed

[smashinator]

he died 2 years ago, sad cos he was a tv/radio tech and could have learned me a lot and i really liked him

My grandpa was a hearing aid tech/designer.  Not only did he know electronics inside and out (from what I hear), but he was also a great teacher (I know that first hand).

It would have been great to be able to call him and ask about stuff.  Well, I'm glad I got to know him anyway.  My little brother barely remembers him.

[birt]

Ziet er goed uit Bert!
Hoe klinkt ìe?
Groeten,Ed

nog niet bij gebrek aan gelijkrichter... er is trouwens een topicje over op gitaarnet.nl  :wink:

we won't be anti-social so here's the translation:

"how does it sound?"

"there's no sound yet because there is no rectifier, and i made a dutch topic too on the dutch board"

:lol:

[birt]

the tube gets about 7,4v on the heaters instead of 6,3, is that really bad or should it handle it?

[Paul Marossy]

That's a little high. I believe that it is standard to not exceed 10% less/more than 6.3V on those heater supplies. It will work with 7.4V, but the tube probably won't last as long. But, hey, preamp tubes are pretty cheap.  :wink:

[petemoore]

can one put a voltage regulator on a heater circuit? Not too much current ??

[Paul Marossy]

Yes, you could use a LM317 adjustable voltage regulator. The kind of current for a single 12AX7 preamp tube running at 6.3V is well below the maximum current that the LM317 can handle. The only hitch with using that voltage regulator is that there is a voltage drop associated with using it - I thought it was 2V, but I don't remember for sure. If you use a 5V voltage regulator, then the voltage would be too low. I would probably use a couple of series resistors to knock the voltage down a little bit. A pair of 10 ohm 1 watts would probably get you there.

[birt]

i was also thinking to use some resitors, but i had no idea what values.
and i still have to install the 6 leds.. can that take the voltage down a bit?

[Paul Marossy]

Six LEDs will drop it some, depending on how much current your transformer is delivering and how much current you let the LEDs have.
Six LEDs at 10mA each would be 60mA, which may put enough of a load on the heater circuit to get you within the 10% +/- tolerance for the tube heater voltage. I'm not sure how much current the typical LED can handle, though.  :oops:

Here's a nifty page to help size LED resistors: http://www.muzique.com/schem/led.htm

[puretube]

a series diode or two (e.g.: 1N4001) will drop Uf by about 0.6....0.7V
per diode, without producing much heat ( - take 2 - )...

err, you`re using DC, don`t you ?

[birt]

a series diode or two (e.g.: 1N4001) will drop Uf by about 0.6....0.7V
per diode, without producing much heat ( - take 2 - )...

err, you`re using DC, don`t you ?

i'm using ac for the heaters

[Paul Marossy]

Ah yes, series diodes. I always forget about that one. Would it work only with DC?

[H.Manback]

Nope, it can work in AC as well but you will have to double the amount of diodes, since you need them for each phase. Just put diodes parallel to the ones you would use in DC.

It might hum now I think about it, since for a small amount of time there is no current because of the turn on voltage. If you are dropping it 1.4 volts it might get nasty...

But you can always add a voltage divider, no problem. What is the typical impedance of those heaters anyway? You'll have to take that in to account when choosing values for your voltage divider.

[puretube]

they draw 300mA @ 6V3