Resistance Check Failure [solved]

[Rhok]

Hello Everyone!

I really hope someone can assist me with this, as I was so stoked for this project (and it was my tax return "gift", being only 22 living on my own in this economy this was a major investment for me!)

I'm failing resistance checks on terminal 13, potentially 20 (mixed results) and the center pin. Now before I continue, I'll admit I'm a total noob but am fairly technically inclined (not so much with electronics! but computers) had experience soldering, and generally fairly capable. But this particular project when it's gone south now I'm totally lost on where to begin troubleshooting.

I'm hoping someone here could assist/advise me on making my amplifier work - it's been such a crushing feeling to have issues after assembly!

Here are some general photos of my build to see if anyone notices any major issues that I didn't catch - additionally I had to replace the 270K 1W resistor because I had accidentally broke off one of the legs of the original don't know if that's part of the issue - the resistor itself reads correctly on a multimeter.

http://s752.photobucket.com/user/mikemathis3/library/

I can provide additional photos/will try anything, am low on materials but I need to get this to work I can't imagine abandoning the project.

Any help/advice is very much appreciated.

- Mike

[Doc B.]

Give us resistance readings and we can start to sort it out.

[Rhok]

Most definitely,

Before I provide the readings, as long as I'm grounded on the negative  can the positive touch any part of the terminal to receive an accurate reading, or should I be placing it somewhere specific?

[Doc B.]

Well, the qualifier is if the solder joint at the terminal is good, then yes, touching the probe anywhere on the terminal is fine.  If you think you have a bad joint, try touching the terminal with the black probe and the lead connected to it with the red probe. If you measure a high resistance you have found a cold solder joint and needs to be reflowed.

[Rhok]

1: 0.4
2: 0.4
3: 0
4: .35
5: varied 1.5 and dropping, or above
6: 2.483
7: 2.951
8: 000.7
9 2.934
10: 2.485
12: 000.9
13: 3.2 - very varied, but nowhere near 270k
14: 001.0
20: 0.650
22: 000.8
B3: 2.953
B6: 2.934

Ground Lug: 000.8

RCA: 098.4 on both roughly

Center pin: 000.6

I'm using a Fluke 87 True RMS  Multimeter which is very sensitive not sure if that's part of those 0's not reading a straight 0.

[Paul Birkeland]

It's pretty important to have units along with these measurements. 

0.4 could be 0.4 Ohms, or 0.4 Mega Ohms, which would be 400,000 Ohms.  You have an unusually nice multimeter for these measurements, it looks like it will just tell you what the units are.  For example, I see 2.951 and 2.934 on 7 and 9.  These are certainly in thousands of Ohms, which makes them OK.  (6 and 10 are certainly about the same)

Also, that meter will certainly measure the resistance of the wire in the leads.

The carbon composition resistor is not a particularly wise choice for the bleeder, can we send you a replacement?

[Rhok]

I have the multimeter's dial simply set on the Ω symbol for the measurements I'm providing. So I anticipate they are all Ohms and not Mega Ohms, how could I confirm the difference? I listed them exactly how they showed up on the multimeters display.

Of course I would accept a replacement - I had a hard time finding anything other than carbon for a 1W 270K resistor for my local and online search (unless it was coming from China).

I didn't bother to contact you guys in regards to that since it was my fault. Then again, the issues I'm experiencing are also my fault for not building the amplifier correctly - but now I'm desperate for any assistance lol.

[Paul Birkeland]

The meter will display a "K" or an "M" next to your value when it's not just Ohms.  It looks like they should appear near the bottom right corner of the display.

[Rhok]

I really appreciate the help - like I said, when it comes to this stuff I'm a complete noob.

Here are fresh results with appropriate markings.

1: 0.4 M - Varied results

2: 1.5 M - then it will continuously drop, varied as well. (did not encounter this last time)

3: 000.7 (does not read K or M)

4: Started at 0.600 M - descreases 1 per second - get very mixed results here as well

5: Started at 2.6 M - drecreases rapidly - also did not experience this last time.

6: 2.483 K

7: 2.951 K

8: 000.7 (does not read K or M)

9: 2.934 K

10: 2.485 K

12: 000.8 (does not read K or M)

13: starts at 0.600 M and slowly decreases.

14: 000.8 (does not read K or M)

20: starts 1.6 M and slowly decreases

22: 000.7 (does not read K or M)

B3: 2.951 K

B6: 2.934 K

RCA: 98.4 K (for both again)

Ground: 000.9 (does not read K or M)

Center: 000.8 (does not read K or M)

[Paul Birkeland]

I think you're ready for voltages.

[Rhok]

Tubes did not glow, the fuse is not blown (no visible detection and less than 1 Ohms reading on multimeter). Disconnected everything (as listed in the PDF instructions) - now what should I do?

[Paul Birkeland]

Test the AC voltage at the power transformer.  With the amp plugged in and powered on, you should get:

120V AC between power transformer T1 and T2
6V AC between power transformer T4 and T5
160V between power transformer T6 and T7

The 6V between 4 and 5 makes the tubes glow, but you won't get voltage there unless the incoming voltage at 1 and 2 is correct.

Do also note that there are two positions in the fuse holder that accept a fuse.  One is a storage box for an extra fuse, the other is a clip that is where the fuse needs to go for the amp to power on.

-PB

[Rhok]

Here are the latest results:

T1-T2: 123.1 AC

T4-T5: 6.58 AC

T6-T7: 179.1 AC

Additionally, I took a picture just in-case somehow this is not where the fuse is supposed to go - though there's no other way for it to make a connection otherwise. http://i752.photobucket.com/albums/xx165/mikemathis3/IMG_0710_zpsd18cdd37.jpg

[Paul Birkeland]

The 6.58V means that the tubes should glow.  I would inspect the twisted pair of wire leaving power transformer terminals 4 and 5 and going to B7/B8.  Wrap them around the solder tabs on the transformer and be sure they are well connected on both ends.

-PB

[Rhok]

Awesome, we're getting somewhere (the tubes glow! - it was awesome to see the filaments start to take life), one of the wires on B7 was not properly soldered - how easy it is to track something down if you know where to begin looking. I would presume to move forward with the voltage checks from here, but I will await further instruction. Additionally, I am not sure if the LED(s) should also light up at this stage, but they do not.

FYI I'm very impressed by the customer support for a DIY project, I feel confident that this will function in the end thanks to the provided assistance.