Need help with a Crack build.

[Reid]

This is my first build and I thought I was careful but- am getting some odd readings. They were not that far off so I plugged it in, the small tube glows faint and the large tube does absolutely nothing. The fuse does not blow and their is VERY faint sound thru the headphones turned all the way up. If anybody has any ideas on how to get this up and running I would really appreciate it.

Thanks

The readings are:

1-* 

2-*

3-0

4-*

5-*

6-2.48

7-2.92

8- bounces a bit but will settle at 0 or 0.2

9-2.96

10-2.48

12-moves around will settle at 0 or 0.1

13- Jumps around have gotten it to settle near the 270 mark but will try again and it will start at 200 then go up slowly up and then down.

14-0

20-0

22-0

Red-RCA-94
Black-97

Ground lug moves a bit but will stop on 0.1 or 0

 

[Grainger49]

If the tube glow is questionable then measure from one of the heater pins to the other heater pin on the tube socket.

On the large tube socket those are pins B7 and B8.  On the small tube those are A4 and A5.

This is AC voltage and should read 6.3V AC.

This is what makes the tubes glow.

 

[Doc B]

The resistance readings look OK. Please give us your voltage measurement readings as well.

 

[Reid]

Doc.

I was in the process of taking volt reading and touched the backside of 20 or 21 and blew a fuse. Went out a bought 1/2 amp 250 volt fuses and they are blowing every time I switch the unit on now. Does it matter the orientation of the pins on the large tube? My readings up until the fuse blew were:

1-87

2-177

3-0

4-179

5-178

6-0.60 or so and it jumps around.

7-180

8-0

9-Moves around a lot-160 to 80 to 0

10-0

11-0

12-0

13-179

14-0

15-197

20-0

21- all over 397 to 197 to 007

 

[Laudanum]

The 6080 tube socket is keyed and the tube should be keyed at the base and only go into the socket one way.  Sometimes the key may be chipped off in which case, yes, pin orientation would matter.
Im not an expert here but I would suggest double checking the orientation of the diodes (terminals 18 - 21).  Also, double check your transformer wiring between transformer terminals 6,7 and 9,10.  You probably didnt short your meter probe to ground at 20 so it was probably at 21 or off the diode lead that attaches at 21.   I would think that it may be possible that you blew that diode.  But again, not being an expert I dont know for sure or what else might be suspect.  If it is only the diode/diodes, I believe that Rat Shack carries the 4007's.  But Doc or others will offer more definitive advice.  Mine should just be food for thought ... mainly, double check the diode orientation.  Also, the fuse included with the kit is a slow blo type if I am not mistaken.  Im not sure if a fast acting fuse would be ok even if everything was fine with the amp.

 

[Laudanum]

Scratch the slo-blo fuse.  That was for a power supply I built.  It should be a standard fuse like you purchased.

 

[STURMJ]

Several of us have had the fuse problem, Doc has said that the fuse should be 1 amp 250v.  See the quote here:
http://www.bottlehead.com/smf/index.php/topic,930.15.html
That may be your only problem. But if it is not, it should keep you running long enough to troubleshoot.

 

[Grainger49]

The oddest thing.  New capacitors draw quite a lot of current when first turned on and not ever after.  I have experienced this startup problem before but after you get it on you will not have a problem if the power supply is properly wired (no reversed diodes etc.).

 

[Laudanum]

I dont think that Reid had the blowing fuses until he shorted his meter probe to ground while checking voltage at terminal 20 - 21 ... where a diode is located. 
I had this problem with fuses blowing at power up in a vintage tube bass guitar amp that I fixed before.  I remember getting the advice that if the fuse DID NOT blow with the tubes removed then I should consider a bad tube.  If the fuse DOES blow with the tubes removed, consider a bad ps diode.  The fuse did blow with the tubes removed and I ended up replacing a diode that tested bad and problem was fixed.  Maybe the experts can chime in if the same troubleshooting would apply here, I dont see why it wouldnt.  With the fuse blowing problem being reported only after Reid shorted his meter probe to ground, I would think it would be worth considering. 

 

[Reid]

Thanks- everyone with your help so far. I made a pretty large mistake. I did not know that the large tube was keyed inserted it and the black part broke. I now have the proper alignment and clean music out of the red channel. Also it does make a difference if you use a quick blow or slow blow fuse from RadioShack. The quick blow would go every time I turned the unit on, no problems with the slow blow. The red led at A3 is now on but must have a bad solder that I am going to fix it flashed on and off as I touched it with the probe.

Here are my new volt numbers and some are off.

1-84

2-164

3-0

4-164

5-145

6-0 but jumps around a bit.

7-102

8-0

9-145

10- 1.348 then will bounce near the 0 mark.

11-0

12-0

13-163

14-0

15-186

20-0

21-209

A1-144

A2-0

A3- 1.59 The red light came on when I put the probe- loose need to fix.

A4-0 bounces a bit.

A5-0 bounces a bit.

A6-84

A7-0

A8- 1.5

A9- 5.9

B1- 84

B2- 168

B3- 104

B4- 81

B5- 168

B6- 103

B7- 130

B8- 0 but move around a bit.

 

[Grainger49]

I dont think that Reid had the blowing fuses until he shorted his meter probe to ground while checking voltage at terminal 20 - 21 ... where a diode is located.  .  .  .  

I appreciate the correction.  It is my bad for not knowing which thread I'm in.  It seems to me if he shorted across a diode that the capacitors not the diodes would take the brunt of the AC that gets passed.  But I'm not sure what voltage got shorted.

Reid, one other thing for those reading the posts.  If you put in both the expected and measured voltages it keeps us from looking at the voltage check page and back to the assembly to see what is attached to the terminals.

 

[Laudanum]

Are you sure that your meter isnt reading a small amount of DC millivoltage at terminals B7 and A9 instead of full DC VOLTS?  Those are directly off of the transformers 6.3V AC secondary and shouldnt show any signifigant DC voltage.  You have some others that are about 50 volts high at Terminal 5, 9 and A1 that Im not sure what to make of (and I would think that B4 would be high as well but apparently isnt).  But B7 and A9 stand out in my novice brain as possibly being suspect measurements.  Hang in there Reid, one of the techies will get you through it.