1st build, need a little help

DFMoore · Post by **DFMoore** » Sat Dec 31, 2011 8:57 pm

I am building an Eagle 100 and RJ suggested I get a little help from you. I have the amp wired, the tubes light up but I only get a very, very low distorted volume. Any Ideas.

Phil_S · Post by **Phil_S** » Sat Dec 31, 2011 9:16 pm

It's hard to tell. The last picture is a bit small to see details.

I think, for starters, it looks to me like you have a serious wiring "violation" that needs to be corrected before you attempt to power up again. Your mains ground (green) at the IEC inlet is going to the circuit board. You do not want to mix the mains ground with the circuit ground. It is a major safety issue. It also introduces all the noise from your mains supply into the circuit. The mains ground gets it's own through the chassis bolt near where it enters the chassis. The wire should provide enough slack so that when there is a mishap and the IEC inlet is disloged from its mount, that will be the last wire to get pulled. Use a screw, a toothed washer, a ring lug soldered to the green wire, and a bolt. Many people double bolt or otherwise secure or lock down this important safety ground.

I think our amp may be eating the signal before it gets to the output. If this is your first build, a common error is input jack wiring. How about a few close ups of the build. I suggest dividing it into 3 sections, plus a close up of the input jack. Also, you may want to look for an unintended ground.

While you are at it, please give us voltage readings at the + side of each filter cap, and at the tube sockets.

ampgeek · Post by **ampgeek** » Sat Dec 31, 2011 9:17 pm

Sweet looking build there DF! Love the wicker grilled cab!

If you are comfortable poking around a live amp with your volt meter (lethal voltages present!!), you should measure, record and share the voltages at each tube pin.

9 times out of 10, this will lead to identification of the problem.

Cheers,
Dave O.

cbass · Post by **cbass** » Sat Dec 31, 2011 9:22 pm

Its hard to see in the pic.But it looks like Pin 9 on the 12ax7 is going to where the pin 8(cathode) should go.Pins 4and 5 should be tied together on one side the other side of the filaments should go to pin 9.

DFMoore · Post by **DFMoore** » Sat Dec 31, 2011 9:55 pm

OK, I moved the ground from the IEC. The 6H2N-EB Tube voltages are as follows: 1-112; 2-0 (i get a buzz when I touch the pin); 3-0; 4 and 5 3.1 AC (Heaters); 6-140; 7-0; 8-1.

6N6C Tube voltages are as follows: 1-18;2 and 7 Heater- 3.1AC; 3-321; 4-280; 5-0; 6-0; 8-18.

How should the input be wired? I have the end post of the cable/jack going to a 68K Resister then to the #2 preamp tube pin. I have a 1 meg resister jumping to the center jack post, and the center jack connected to the ground post, which leads to a ground.

cbass · Post by **cbass** » Sat Dec 31, 2011 10:02 pm

Sorry Didn't realize the kit came with a 6H2N.

ampgeek · Post by **ampgeek** » Sat Dec 31, 2011 10:06 pm

It looks like one half of the pre-amp triode isn't conducting.
Check wiring/componants from pin 3 to ground against the schematic. If cathode resistor is by-passed, make sure the capacitor is oriented properly (+ side to tube).

If all good there, try another tube.

Can you easily post a schematic?

Good luck,
Dave O.

cbass · Post by **cbass** » Sat Dec 31, 2011 10:07 pm

Pin 3 on the 6h2n should have somewhere around 1.5volts

DFMoore · Post by **DFMoore** » Sat Dec 31, 2011 10:15 pm

Attached you will find RJ's layout.

kwijabo · Post by **kwijabo** » Sat Dec 31, 2011 11:13 pm

it is a little tough to see on that size picture/resolution, so maybe my eyes aren't picking out the detail they need to but here's what i see -

the 6H2N pre-amp is not wired as the layout shows. i've never used that tube so i'm not familiar but just comparing layout-to-your build, pin 8 should be the cathode - going through a resistor/capacitor to ground. it looks like you have pin 9 doing that and pin 8 is just sitting there floating.

since its a self-biased circuit, if you leave the cathode floating, theres no guarantee the grid will be at the appropriate voltage with respect to the cathode. the closer the grid is to the cathode (i think) the following happens: it wouldn't conduct (low-to-no volume) and would have almost no headroom (distortion you hear). can you confirm pins 8 and 9 are wired correctly?

cbass · Post by **cbass** » Sat Dec 31, 2011 11:25 pm

I can't see a wire coming off of pin 8.Is there a conection going threw the 1k5 resistor to ground?

DFMoore · Post by **DFMoore** » Sat Dec 31, 2011 11:46 pm

Yes, pin 8 is being used, (yellow wire) goes to the 1.5 resister. 9 is floating unused.

cbass · Post by **cbass** » Sat Dec 31, 2011 11:55 pm

Ok i see now.Sounds like you either have a bad tube or something is wrong with the wiring around pin3 You should not have 0 volts there.That means that half of the tube is not conducting.

You have some suspect looking solder joints.You can run some of the leads down in the turret holes.
Make sure you have a good ground conection for that 1k5.(check with a meter)

DFMoore · Post by **DFMoore** » Sun Jan 01, 2012 12:08 am

So should the 1.5 go directly to ground? The layout had it going through a 47K then to ground.

cbass · Post by **cbass** » Sun Jan 01, 2012 12:18 am

I think that should be a 47 ohm to ground not 47k

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