Separate names with a comma.
Discussion in 'DIY Effects Forum' started by Mr. Lumbergh, Dec 25, 2016.
Cool thread. You are the man, Lumbergh
I'll give it a try then; worse comes to worst I get a pair of NOS tubes as was suggested. I am going to be building a regulator circuit to help keep it quiet if nothing else; researching this online suggests hiss can be a real problem. This would also give me the opportunity to use the power supply as my ground and keep signal ground separate so I don't introduce the capacitance of the enclosure and circuit into the signal.
Any actual chinese or russian tube will work. No need to go NOS.
Just use a good power supply and the circuit should work like expected.
All the best,
This is an interesting project. I'm looking forward to the final results.
It's trivial. You wire an 36 Ohm, 1W resistor in series with the heater.
@Mr. Lumbergh I just saw a pedal in a guitar shop in Las Vegas that looked very similar to your build, in appearances anyway. I peeked around the side of the glass case it was in to see if it had a price on it and was hit with a bit of sticker shock. They were asking north of 400 bones for it!
1w resistor is not enough. 5V at 0.3A is 1.5W. Even a 5W would get pretty hot and changing resistance as well with more heat building up.
A regulator would be better but you need a pretty big heatsink - maybe the steel(?) case and isolated.
All the best,
You're right. I checked my notes (I built this over a year ago). I used a 5 W resistor. But, the resistor heat is not significant. I checked it, and the resistance didn't change over 20 minutes. Even if it did, it's the heater circuit. It's extremely tolerant of changes. Even if the resistor changed by 20%, your voltage across the heater changes by 0.8 V, which is a 6% variance, and you're not going to hear it.
I haven't made much progress; took everything back off the panel to drill a few more holes. I've added Fat switches and a voltage regulator to prevent noise. Regulator circuit is done and mounted to a board.
The last couple weekends have been busy and/or frustrating and I'll be out of town for this next one, hopefully soon I'll be able to get back into it.
And it would have been a 20Ohm resistor but the regulator is really the better way.
@Mr. Lumbergh cool decision to use a regulating circuit to make the supply thing stable.
All the best,
Yeah, it's really very simple. A diode to make sure I don't wreck it if I insert the wrong plug accidentally (the circuit is negative ground unfortunately), a .1uF electrolytic cap, and a 7812 regulator chip. I put a hole in the back of the enclosure to hard-mount the 7812 to the case as they can get pretty hot; the case will act as a heatsink. Didn't turn out I needed it, at least with the power supply I had available; I was reading just under 11V when I had it plugged in, but it didn't heat up at all.
No. R=V/I. If you're running positive voltage into pin 5 and grounding 4 (or vice-versa; it doesn't matter), the operational resistance of the heater circuit is 12.6 V/0.15 A = 84 Ohms. 84/R = 12.6/(18-12.6) gives 36 Ohms.
If you're running positive voltage into pins 4 and 5, and grounding pin 9, the operational resistance of the heater circuit is 6.3 V/0.3 A = 21 Ohms. 21/R = 6.3/(18-6.3) gives 39 Ohms.
It would never be a 20 Ohm Resistor.
Of course, all that is assuming your heater circuit is reliably 42 Ohms per side, which it isn't, and it doesn't matter. Since it's the heater, you're not going to hear even major variations in the heater circuit resistance. A lot of people build these with a 15V or 18V supply directly into the heaters, and live with the fact that their tube only lasts 4000 hours.
Yes, if you are using just one tube which he is not.
All the best,
Ah, you're running a resistor and both tubes in series, with the heaters running in parallel within each tube. I just split it out as two parallel circuits with separate resistors for each tube, and then running the heaters in series within each tube.
Using the 20 Ohm resistor reduces your part list, but dissipates 1.5 W through that resistor. Using separate resistors cuts the power dissipation for each resistor in half, which isn't nothing if you're worried about your resistors running hot.
I wouldn´t have used a resistor anyway. The resistor was your idea to get rid of the too high voltage.
Anyway burning voltage into heat is always a bad thing to do and hopefully @Mr. Lumbergh gets great results using the normal 12volt and the regulator.
Building a full supply with 6.3V just for the heaters and the additional needed B+ for the tubes would be a bit over the top I guess and not very usefull for the low voltage tube abuse - sorry, starved plate - but I think nothing compares to a full run with high voltage and great use of way above 50V.
But that would be a part of another thread.
Back on topic, sorry.
Peace and all the best,
In any case, if I were to do it again, I'd use a 12V wall wart, run that directly to the heaters, and use a voltage doubler to run the plate at 24 V, adjusting the gain resistors to get the breakup I wanted when I was pushing it. LT1054's can handle the 12V input just fine, and can supply more than enough current to drive the unit.
I've not made much progress on the wiring, but I did get a possible layout together. I found out, while I was designing this, that JHS made a dual OD they call the Double Barrel. Oh well; theirs ain't tube. Let me know what you think:
The contrast between the text and graphic isn't good in this PNG export; hopefully it turns out a bit better on the final print. The black circles won't show up on the final print; they're just there as a reference to the holes for the pots so I could better locate the rest of the details.
@Mr. Lumbergh that looks great, 5 bullets hit the target xD
I like it.
All the best,
More progress today, both with the wiring and the finish:
Pa Lumbergh built the base of the enclosure out of oak and pine, so I figured I'd add a bit of color to make it look like a proper red oak. I'll be following up with a coat of poly before the build is done.
That's an epic pedal build...