Troubleshooting Resistance Checks

[ksolis01]

Are all of your resistance checks right?  Don’t apply power again till all resistance tests pass. They are there to prevent damage when power is applied to a build with wiring problems.

I redid the resistance checks. The four offs ones were suppose to be *, varying resistance, but came back as zero exactly. Like, there were some * terminals that also went to zero but varied in resistance first. However, these four went to zero directly.
Terminal  Resistance
10          0
20          0
22          0
23          0

 

[Paul Birkeland]

22 and 23 are the incoming AC line.  If those are 0 ohms to ground, your fuse will blow or the breaker will blow that feeds that outlet.

10 and 20 are the outputs of the constant current sink and the cathode of each half of the 6080.  Since you have at least half of the amp where the 6080 cathode voltage appears correctly, this 0 is also inconsistent with the performance of your amplifier.

 

[ksolis01]

22 and 23 are the incoming AC line.  If those are 0 ohms to ground, your fuse will blow or the breaker will blow that feeds that outlet.

10 and 20 are the outputs of the constant current sink and the cathode of each half of the 6080.  Since you have at least half of the amp where the 6080 cathode voltage appears correctly, this 0 is also inconsistent with the performance of your amplifier.

10 and 20 now have a fluctuating values in the mili ohms. 22 and 23 still measure directly to zero. I resoldered any joint that wasn’t perfectly shiny and also found that the white wire from the top row, middle lug, of the volume pot wasn’t connected to 12L. What else should I be looking for?

 

[Paul Birkeland]

milli-ohms or mega-ohms?

 

[ksolis01]

milli-ohms or mega-ohms?

Sorry, meant mega-ohms.

 

[Paul Birkeland]

A milli-ohm is 0.001 ohms, a mega-ohm is 1,000,000 ohms.  The "milli" is a short, the "mega" is nothing to worry about.

 

[ksolis01]

I ran another voltage test. The missing white wire disconnection changed two of the values from the previous measurements, the new ones are bolded. I'll give it another look tomorrow to try to find any other bad connection. All of them are mechanically sound but will check if the copper is cut. I had a white wire break off when running a voltage check so there is a possibility that another wire is compromised.

Terminal    Voltage (DC)

Low Current C4S
IA        150V  (187.7)
OA 60-90V  (79.3)
KregA  3-6V  (1.936)
bRegA 150V    (187.7)
IB        150V  (148.1)
OB  60-90V  (54.6) (71)
KregB  3-6V  (12.9)
bRegB  150V  (148)

High Current C4S (D socket)
IA        190V  (190.5)
OA        150V  (148)
bA        0V  (0)
IB          0V  (0)
OB  90-110V  (81.4) (91.1)
bB        150V  (148.1)

High Current C4S (B socket)
IA        190V  (188.3)
OA        150V  (186.7)
bA        0V  (0)
IB          0V  (0)
OB  90-110V  (96.5)
bB        150V  (186.5)

Headphone Jack
Tip          0V    (0.01)
Ring        0V    (0.04)

 

[Paul Birkeland]

A broken wire will indeed do a lot of strange things.

You still have the same regulator issue present on one channel though. 

I'd pull the 6AQ5 on that channel and recheck the voltage across the 2.49K resistor.

 

[ksolis01]

A broken wire will indeed do a lot of strange things.

You still have the same regulator issue present on one channel though. 

I'd pull the 6AQ5 on that channel and recheck the voltage across the 2.49K resistor.

Got the voltage. However, I decided to do a second check after turning the amp off and the value for B side came out different while A was consistent.
A side:
210 v

B side: 54, 69

 

[Paul Birkeland]

The voltage across the 2.49K resistor on the center C4S board above the 12AU7.  It should be well under 5V on both sides.

 

[ksolis01]

The voltage across the 2.49K resistor on the center C4S board above the 12AU7.  It should be well under 5V on both sides.

Did another check. The b side 59V value was actually due to remaining 6AQ5 tube being loose on one side so it is 54V. What should I check since the values are way off 5V?

 

[Paul Birkeland]

I would suspect that the ground wire (or jumper) feeding that portion of the board is broken.