THUNDERCHIEF build question

Barcode80 · November 09, 2006, 07:41:07 PM

I recently whipped up the vero of the thunderchief from torchy's layout:

http://aronnelson.com/gallery/album28/Thunderchief?full=1

but it doesn't have the wire leads labeled. can anybody shed some light so i can fire this bad boy up?

zyxwyvu · November 09, 2006, 09:05:58 PM

Looking at that layout and the one at http://runoffgroove.com/thunderchief.html, it seems the wires go like this:
left side:
- gnd
- vol3
- gain3
- gnd
- gain2
- in
right side:
- +9V
- gnd

Also, does anyone know if this layout is verified? It looks like there should be a cut track at the bottom, to the right of the 33k resistor, and the 1k and 470k resistors next the second transistor are swapped. Could be more, but that's all I saw when I looked.

KerryF · November 14, 2006, 08:35:07 PM

Barcode,

Have you finished building this yet?

Is the layout correct?

Barcode80 · November 15, 2006, 12:14:55 AM

i did finish it, and i got signal, but something is screwy because i've chenged out the last 2 jfets about 20 times now, and i can't get them to bias to correct voltage. it sounds relatively good, but until i can get this solved i can't handle the low output enough to warrant finishing it up quite yet. especially since i know how kickass this is supposed to sound. any ideas how to pull the voltage down on those two jfets? lowest bias i can get with the trimpot is about 6.3 volts, and it needs to come down to the 4.5 range.

zyxwyvu · November 15, 2006, 01:48:50 AM

Have you tried changing the 4.7k resistor as stated in http://runoffgroove.com/faq.html?

KerryF · November 15, 2006, 05:18:29 PM

Quote from: zyxwyvu on November 09, 2006, 09:05:58 PM
It looks like there should be a cut track at the bottom, to the right of the 33k resistor, and the 1k and 470k resistors next the second transistor are swapped. Could be more, but that's all I saw when I looked.

barcode... did you cut that track and switch those 2 values? just wondering if when I build it, its supposed to be like that.

Barcode80 · November 15, 2006, 05:32:32 PM

yes, after checking the schematic you do need to make that cut and swap the resistors. i'm working on revising torchy's layout and posting it in my gallery. i haven't yet tried the suggestion from ROG, i will when i get home today and post results.

Barcode80 · November 15, 2006, 07:51:54 PM

dammit, i changed the resistor to a 1k according to the ROG FAQ, and i still only get the following:

Q3 = 6.75 - 7.1

Q4 = 7 - 7.15

i'm about to give up on this layout, dismantle this build and rebuild it using a diff layout. this layout wasn't truly verified anyway, so it may be that a resistor is connected to the wrong part of the circuit and many other possibilities. anyone know which gallery has a verified layout?

KerryF · November 15, 2006, 08:11:31 PM

Dude! Wait...

Dont quit. I just traced the schematic and layout and found another error to fix!

the 1M and 470R at the 3rd J201 need to be switched. hopefully this does it for you. I just got to that part and then realized I needed to fix that.

Everything else is correct. Peace!

KerryF · November 15, 2006, 09:06:07 PM

A question about the mods...

Lead/Normal Switch: It says use the .68uF cap on 1 side, and the 10uF cap on the other side of the switch. The 10uF cap is electrolytic right? And it doesnt matter which way its placed in right?

Variac Control: It says to put a pot between the trim pots and the +9v. Whats a good value for that? 1k?

zyxwyvu · November 15, 2006, 09:30:28 PM

Quote from: call1800ksmyazz on November 15, 2006, 09:06:07 PM
A question about the mods...

Lead/Normal Switch: It says use the .68uF cap on 1 side, and the 10uF cap on the other side of the switch. The 10uF cap is electrolytic right? And it doesnt matter which way its placed in right?

Variac Control: It says to put a pot between the trim pots and the +9v. Whats a good value for that? 1k?

The 10uF should be electrolytic, and it's negative side should connect to ground.

For the variac, I would try some different resistors/pots to see which ones sound best. It seems like the kind of mod that would be pretty subjective. My best guess is a value around where the trimpots are set. I'm not sure how much that is, but maybe around 25k?

Barcode80 · November 15, 2006, 10:00:13 PM

okay, so that last correction to the layout fixed my bias issue for q3! now, i just have to eliminate whatever is wrong with q4, as it still biases around 7 no matter what i set the trim to.

KerryF · November 15, 2006, 10:04:41 PM

So I helped for once?!

Great! I will post pictures of mine in like 2 minutes.

KerryF · November 15, 2006, 10:08:16 PM

Pictures of my Thunderchief with Double Channel mod...

I still need to get a few capacitors to finish it though...

Barcode80 · November 15, 2006, 11:03:44 PM

are those lead bridges and solder bridges on purpose?

i'm going to try to redo this layout with the changes we've made. then i might try to build another one, leaving this on e intact, and see if i get the same results. anyone have any idea about q4 bias?

Meanderthal · November 15, 2006, 11:20:56 PM

Yeah, those are on purpose... he's putting the jumpers on the bottom for some reason. Should be ok.

KerryF · November 16, 2006, 08:22:09 AM

Actually they arent jumpers or being connected. Its leads that havent yet been clipped in case I need to change JFETs or a few other parts I dont have to many of.

Barcode80 · November 16, 2006, 08:24:39 AM

cheapskate

KerryF · November 16, 2006, 08:43:12 AM

No, its just that I dont have any good electronics stores here except a few crappy Radio Shacks.

petemoore · November 16, 2006, 10:39:40 AM

The 10uF cap is electrolytic right? And it doesnt matter which way its placed in right?
Unless it is marked NP nonpolar or BP bipolar [same thing], use the polarity marking '-' on the cap...connect that lead to the most negative side of the circuit.

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THUNDERCHIEF build question