First time builder - failed voltage check [resolved]

[shroomalistic]

redid a4 and a5 still same results.

my meter is a sperry dsa-500.  its about 25 years old,  used it in my old heating and ac days

 

[shroomalistic]

my brother dropped off his multimeter,

T01: 190
T02: 207
T03: 0
T04: 208
T05: 191
T06: 0
T07: 192
T08: 0
T09: 191
T10: 0

a3: 0
a4: 3.1v
a5: 3.1v
a8: 18v

 

[shroomalistic]

i double check the new wire resistors and they were grounded.  UPS says the package was damaged in transit. 

I had a couple more that ordered off ebay and they are working

T01: 144
T02: 160
T03: 0
T04: 160
T05: 145
T06: 0
T07: 144
T08: 0
T09: 145
T10: 0

a3: climbs slowly till it hits 200 then starts over
a4: 3.1v
a5: 3.1v
a8: 14.4

 

[shroomalistic]

i checked the 12au7 for resistance
saw in another post to check a9 to a4 and a9 to a5
a4 is 0
a5 is 7

 

[Paul Birkeland]

Your voltages have now gotten worse and neither side of the 12AU7 is conducting.  Can you verify that the 12AU7 tube itself is glowing?  You could also have loose wiring at B7/B8 or where the green wires land on the power transformer. 

The 14.4V at A8 suggest that the LED there is damaged, and this happens from excessive heat being applied to the LED during soldering.

A3 can't climb to 200V, as there isn't a source in the amp for 200V DC. 

Looking at your build photos again, A9 does not look particularly well soldered.

 

[shroomalistic]

looks like only one side of the 12au7 is glowing but im not sure what it would look like with both sides?

I bought a magnifying/light arm to help me threw the rest of this,  should have did that first.  I can actually see what im doing now.

I have another 12au7 on the way and ordered new leds from you guys.

i had to put everything up for now and only have a few hours window a day.  Cant have it laying out with 4 kids running around.

Ill resolder a9 first thing tomorrow.  Plus ill have a new multi meter here tomorrow also.

 

[shroomalistic]

Forgot to tell you guys, THANK YOU SO MUCH FOR HELP!

I really appreciate the time you are taking here.

 

[Paul Birkeland]

If one half of the 12AU7 is glowing, definitely recheck the joint at A4/A5.  If it's loose at one of those connections, that will cause half of the tube to not light up.

-PB

 

[shroomalistic]

i have checked that multiple time and reflowed it.

 

[Paul Birkeland]

You can pull the 12AU7 out and check the DC resistance between pins 9 and 4 and pins 9 and 5.  It should be a very low value.

 

[shroomalistic]

i checked the 12au7 for resistance
saw in another post to check a9 to a4 and a9 to a5
a4 is 0
a5 is 7

I did that too

 

[Paul Birkeland]

Is that the socket pins or the pins on the tube itself?

 

[shroomalistic]

tube its self,  its not zero,  there is just nothing on pin a4 to a9

 

[Paul Birkeland]

OK, zero would be the opposite of nothing, which is infinite. 

It's possible that the tube pins are a bit oxidized, and inserting them into a lump of steel wool a few times may clean them enough to restore operation.

 

[shroomalistic]

cleaned up the pins and still nothing on a4 to a9,  a5 to a9 still gives me 7

 

[Paul Birkeland]

It would be a good idea to try a different 12AU7 tube next.  Can you post pictures of the 12AU7 you have?

A bad 12AU7 still doesn't explain why you had such high voltage on terminal 9, but we'll address that when the front half of the amp is working properly.

 

[shroomalistic]

No clue when the nos tube will be here,  ordered it off ebay.

 

[shroomalistic]

so did i kill my tube?  Im a little worried now, should i put the new one in when i get it?

 

[Paul Birkeland]

It would be very difficult to damage that part of the tube. I would just give the replacement a go to see if both its halves light up.

 

[shroomalistic]

who would i contact to get another 12au7 tube?  Not sure whats going on with my ebay one.  If i can purchase or get a replacement from you guys,  I already have an order in for the LED's