I need some help!
I just built a tube driver, using my own PCB layout, going by the General Guitar Gadgets schem. I get signal out up until the tube. For the power supply I am using a 25.2V CT connected to a diode bridge, filter caps, and finally a 7812 and a 7912...to get +12v and -12v.
Pin 4 is connected to +12v and pin 5 is connected to ground. Pin 9 is not used at all.
The tube doesn't even look like it is heating up, no glow at all. :(
Also, this is the first time I have worked with tubes, so I am clueless.
Please help.
Also, I used a 12AT7 that was given to me. Not, a 12AX7. I assumed it would aleast let me know if the circuit worked.
Hmmmm.... if you have 12 volts between 4 and 5 you should have two glowing filaments in there, if you don't, one of the filaments is probably broken which will sure stop and sounds from getting through.
Measure the resistance between pins 9 and 4 and then 9 & 5. My guess is that one of those will show as an open circuit.
The gain on a 12AT7 is a little over 1/2 of the AX7, but you should be getting sound for sure.
Good luck,
-Peter
what Pete is saying is good advice.
For sure check the resistance on the valve (tube) with your DMM. Also don't forget some tube sockets can be a bit flakey; check this out:
I built a tube project once, the heaters didn't warm up and I got no sound at all.
I fiddled with the tube socket, I think I took the tube out, pushed the contacts for the pins 4 and 5 a bit with a small screwdriver, put the tube back in and hey! the filaments started to glow and I got groovy tube tone.
All I can say is don't be afraid to look very closely at your circuit and do what needs to be done to make it work. Remember RG's rule, if everything is right, it can't *NOT* work - so, check *EVERYTHING*
Good luck
Well, I found something out shortly after posting.
If you wire the tube up backwards, the tube won't work!
I miss understood how to identify the numbering of the pins, but I looked in an old tube amp repair book, and there it was plain as day. So, everything is fine...it works, but I hope it sounds better with the 12AX7 I put an order in for last night.
Thanks.
Excellent! :D
It's the old "bottom view" "top view" thing.
You'll find quite a difference between the AT7 and the AX7.
Take care,
-Peter
Thanks Pete and George.
I do hope there is a difference between the AX7 and the AT7, because right now it doesn't quite sound like a buddy of mine's Tube Driver (an original BK Butler model).
Also there seems to be quite a bit of hum going on. This may be because it is not housed in a metal enclousure and the puts are connected on a breadboard to the rest of the ckt.
I will have to borrow his real Tube Driver and check for any differences and so on. Also I will probably take it to class with me sometime and look at the power supply on a scope and see what is going on. Wouldn't think there would be much hum using regulators. But, maybe I can isolate the problem.
Thanks again.
I recently bought all the parts for the ggg tube driver project but have been holding off on the build because I read some posts on here and emailed jd and learned that there is hum and noise heard with this pedal built the way it is on ggg. I have been waiting until jd has a chance to go through it. Judging by all the recent updates I am guessing he is really busy with stuff so I am trying really hard not to bug him, but I can't wait to get a tube overdrive stompbox in my pedal arsenal.
If you would, post your status on this pedal after you get it all together. I'd really like to hear how it went.
Thanks, Matt.
Well I got the Tube Driver all boxed up in a 125C size box from Small Bear.
Still get the annoying hum. I have an original TD to compare mine to. It does hiss a little but not the lower freq hum I get with mine. So since the only difference is the power supply and the bypass. I assume my problem is in the power supply. Also noticed that the original TD has up to +/-16V running to the tube. Wouldn't think that would affect the hum.
So, Thursday I will take mine to class and look at it on the scope. See if we can pinpoint the problem.
In the mean time I am going to order some 15V regulators.
Interesting, keep us posted if you will.
THanks, Matt.
you happen to have the transformer inside the box, too?
P.S. caps big enough?
I mounted the transformer inside the box, on the other side of the box - 6 inches away from the circuit board.
Its a Mouser 25.2CT 1.0A transformer. Pretty bulky.
I used 1000uf caps after a full wave rect. bridge, and that goes to a 7812 and 7912 Vreg's. and then 10uf caps after those.
this was found by google on my ever busy find to check out what the talk is about:
http://www.generalguitargadgets.com/v2/diagrams/tube_driver_sc.gif
the following is different from your description:
GGG powers the tube from the 12V AC.
You power from the DC ?
Loads the rect/caps too much > ripple hum!
(the heaters don`t bother - but the audio does!)
I am powering the tube after the V regulators, which would be a stable source a DC voltage.
Is this not a good idea?
I could easily change it to running straight off the transformer.
Its 25.2V CT. So I could just pick one side of it (25.2Vac/2 = 12.6Vac), and run it to the heaters?
increase the caps on the side you heat the tube from to 2200uF;
or try one time to heat with 12V6 AC, and listen if the hum sounds different;
if possible, turn the x-former 90deg around, and listen if the hum changes while moving.
The first time I built a Shaka Tube, I had the transformer internally mounted. It hummed no matter what I did. I found ways to minimize it, but not eliminate it. When I reworked it, I used a wall wart instead, and voila! No more HUMMMMM.
Rotating the xfmr 90 degrees may help some, but I have my doubts that it will elminate the hum. But, if you do try it, let us know if it works. 8)
I hooked the heater up by running one side to the + side of the FW rectifier. And the other to ground. Seems to have reduced the hum a little, but its still there.
I may go to Radio Shack and see if they have any 2200uF caps, I don't have any on hand.
The thing I don't understand is that the original I have uses 250uF caps, a smaller sized transformer and it still doesn't hum!
Well, I will keep trying.
A 2200uF cap is going to be pretty big. Hopefully you have the room inside of your enclosure for it...
BTW, I don't think RS is going to have that, but you never know.
The 250uF caps in the original unit are probably still more than is needed. Tube amps use filter caps that are way smaller than 250uF. I personally think your heater supply may be causing some of the hum. Maybe you could put a couple of resistors to ground off of the heater supply as a noise reduction tactic - kind of like what is on the Firefly schematic. I'm not sure what values you would need to use in this case, though.
Just got back from RS...$3.99 for one 2200uF Cap!! Axial leads, that stinks!
Anyway, I will stick that in there after lunch. I will try to seperate the heater with a resistor on the ground side to see if that helps.
I am just wondering if the transformer has anything to do with it.
Also, I took the transformer and moved it every which away, didn't help.
that big cap is needed when heating from the same rectified voltage as what the rest of circuit sees as B+.
it`s not needed when heating from AC 12V (i don`t mean pulsating 16V or so rectified/unsmoothed).
When heating AC, usually a trimpot of 50 to 100ohm/2Watt is used to balance out the filament hum: outer lugs to the 12V, wiper to ground.
But sometimes it will work grounding one side of the filaments direct.
(swapping pins 4&5 s.t. helps.
Also: in tube-amps the caps can be smaller, because only the circuit asks for juice from B+; NOT the heaters!; most of the time, they have chokes.
Another reason for hum can be wrong layout: if all the heater juice goes thru the same wire/trace as the signal: hum!!! seperate the leads, and have them connected only at the minuspole of the big cap.
If heating with AC: tightly twist the wires, keep`em far away from the rest of the circuit, and keep`close to the chassis
Oh yeah. I forgot about the choke part. :oops:
And it is very true that the layout is important. Sometimes a signal path will pick up a hum from another part of the circuit. I always tightly twist my heating filament leads and keep them close to the chassis and as far away from everything else as I can get.
well, so far I tried everything....so now I am going to copy the original PCB trace for trace part for part.
I've looked at it so many times now, this should only take a minute.
I believe I will even wire the bypass switching up the same way.
Reminds me of my first Shaka Tube build. :(
Hope you get it working the way you want it to the next time around. You might want to ask the forumites here if they have built this one. I seem to remember reading that the Tube Driver thing at GGG had some problems...
I believe the problem is in the layout, mine or the GGG one.
So I am in the process of copying the real thing.
Let you know how is goes.
The results are in ----- the problem was my layout!
I now I have an exact copy of an original Tube Driver. Actually I didn't have another 2200uF, which is what the original used, along with a pair of 220uF and a 470uF. I used a 1000uF and three 470uF caps. It didn't seem to mind.
Anyway, right now I am very happy (and tired). :lol:
congrats! glad to hear...