2.1 voltage discrepancies

[Tom-Huffman]

Resistance checked out ok

Terminal measurements that deviate from desired
1 - 216v
4 - 440v
5 - 440v
6, 16 - 418, 418
9, 19 - 57, 88
10, 20 - 440, 440
14, 24 3mv, 7mv
A2, B2 - 389, 390
A3, B3 - 18, 18
A4, B4 - 3mv, 6mv
A5, B5 - 59, 62
A6, B6 - 2.2, 2.1
A7, B7 - -3.6, -3.6
A8, B8 - 3, 3
C1 - -3.7
C2 - 3.0

Suggestions?

 

[Paul Birkeland]

C1 and C2 are wihtin tolerance
A8 and B8 are within tolerance
A7 and B7 are within tolerance
A6 and B6 are within tolerance
A5 and B5 are a tad low, potentially from a very strong set of tubes.
A4 and B4 are within tolerance (0.003V and 0.006V is close enough to 0V for our purposes)
A3 and B3 are in within tolerance
A2 and B2 are within tolerance
14 and 24 are within tolerance
10 and 20 are within tolerance
6 and 16 are within tolerance
4 is within tolerance
1 is within tolerance

As stated below the voltage check section, variances of 10-15% are acceptable.  For example, terminal 4 is specified as being 420V, which allows for ~357-483V, so seing 440V is no problem.

Terminals 5, 9, and 19, however, are unusual.

Terminal 5 and Terminal 1 are wired together with a red piece of wire.  Your terminal 1 and terminal 5 don't show the same voltage, so I would suspect this wire has been left out or is not properly soldered? (See page 32 in the center of the page)

Terminals 9 and 19 are connected to A1/B1, but these didn't pop up on your voltage checks as a problem?  Are they close to zero?  Are you sure that's not 57mV/88mV?  Also, the resistance check on 9/19 showing 249K would confirm that you have the correct resistor in place here to bleed off any grid leak current, so I'd remeasure your voltages and double check that.

If the 249K resistors were not connected, or were connected improperly, then 9/19 could exhibit all sorts of whacky behavior, but having the correct voltage at A3/B3 (which you do) and that voltage at 9/19 is not a possible combination (this would be class A2 operation, which would drastically increase the current through the circuit, and all your high voltages would sink like a stone).

-PB

(Let us know what you find)

 

[Tom-Huffman]

Some progress some back sliding
T1 = 206 v
T5 = 195 I double checked the red wire
9 = 23 mv
19 = 78 mv
A1 = 93 mv
B1 = .8 v
A3 = 14 v
B3 = 46 v
680 metal film resistor on left channel is heating up and darkening

 

[Paul Birkeland]

The voltage difference between T1 and T5 gives us some clues that your meter may not hold super tight tolerances on higher voltage readings (no big deal).

B3 has increased since your first post of voltages, did you make any other alterations between taking those measurements?

The 680 Ohm resistor will indeed darken if the voltage across it is that high, but there is no reason for it to be that way unless the voltage at B1 is well above 0.  Just to rule things out, you can swap tubes to see if the high voltage at tube pin 3 follows a tube.  You can also run the amp with no tube in the socket and see if there is any voltage at tube pins 1/3 on the left side.   

 

[Paul Joppa]

It is possible that the grid resistor at B1 is not connected, and the meter's 10-Meg resistance acts as a (too-high) grid resistor when measuring - that wold also explain the 0.8v measurement at B1 which is much higher than A1.

 

[Tom-Huffman]

One last issue at the moment.

I am the guy whose 2.1 was damaged in shipment.  I found a few broken resistors and replaced them.

Now the resistance checks are right on.  Voltages are within tolerance except for B5 = 31 v.  I swapped the tubes but B5 does not change.

I do have the C4S upgrade board installed.

 

[Paul Birkeland]

How is the voltage at B6?

 

[Tom-Huffman]

B6 = 1.23

 

[Paul Birkeland]

You have half the current going through that particular tube than you should.  This can happen if the 499 Ohm resistor on that side of the board is closer to 1K for some reason.

On the other hand, if the cathode resistor going to B6 is not the right value, this could also throw these values off, but your original voltages tell us that this is very likely to not be the case.

For the 1.27K cathode resistor, 2mA of current will give ~2.5V, you have 1.23V, which is about 1mA of current, and this is causing your low plate voltage.

I'd inspect that C4S board carefully.

-PB

 

[Tom-Huffman]

I remeasured all the voltages.
1 = 213
2 =-.1 mv
3 = 0, 0
4 = 423
5 =213
6, 16 = 403, 403
7, 17 = 0, 0
8, 18 = 0, 0
9, 19 = 33 mv, 20 mv
10, 20 = 420, 421
11, 21 = 365, 400
12, 22, 13, 23 = 0
14, 24 = 28 mv, 20 mv
15, 25 = 17.5, 18.8
A1, B1 = 31 mv, 20 mv
A2, B2 = 376, 375
A3, B3 = 17.5, 18.8
A4, B4 = 0, 0
A5, B5 = 62, 29
A6, B6 = 1.2, 1.2
A7, B7 = -3.6, -3.6
A8, B8 = 3, 3
C1 = -3.7
C2 = 3.0
C4 = 0
C4 = -3.7
C5 = 3.2

 

[Paul Birkeland]

I remeasured all the voltages.
A4, B4 = 0, 0
A5, B5 = 62, 29
A6, B6 = 1.2, 1.2

This is relatively impossible, I'd double check.

-PB

 

[Tom-Huffman]

I measured again with similar results, buy A6 was higher.  I works best when my wife is here and writes down the readings as I call them out.

Life is tough but you guys are really patient!

A4, B4 = 0, 0
A5, B5 = 62, 30
A6, B6 = 2.2, 1.3

 

[Paul Joppa]

That looks more reasonable!

The difference A6/B6 voltages indicate different current, assuming the 1270 resistance from pin 6 to ground is correct on both tubes. You said the resistances were all correct a while back, but you might easily check again to be certain.

As PB said, the resistor R1 on the C4S board sets that current. (That assumes the LEDs are glowing and the board is wired correctly of course!) You can measure the resistor on the board to check its value.