Finished build of Crack and all was well for first 8-10 hours, but a hum has appeared in the right channel only. Volume level, presence or absence of input device or switching input leads does not alter the level or channel of the hum. It takes about 4 minutes after power up for the hum to appear. Tapping on the small tube with a pencil has little to no effect. Tapping on the large tube causes a slight decrease in the level of the hum before it quickly returns to the previous level. In addition, the tapping can be heard through the headphones. Tapping on the transformer bell will cause the hum level to decrease slightly and quickly return, but the tapping is not audible through the headphones. Similarly, the same results seem to occur when tapping the middle side top plate, but perhaps to a lesser extent. Rechecked the resistances and voltages obtaining the following values (my values):
1 * (28k & rising)
2 * (64k & rising)
3 0 (0.1)
4 * (61k & rising)
5 * (85k & rising)
6 2.4k (0.1 - ground mod on phono jack, 2.49k before mod)
7 2.9k (3.01k)
8 0 (0.1)
9 2.9k (2.95k)
10 2.4k (0.1 - ground mod on phono jack, 2.49k before mod)
12 0 (0.1)
13 270k (270k and slowly rising - took about 8min)
14 0 (0.1)
20 0 (0.1)
22 0 (0.3)
B3 2.9k (3.01k)
B6 2.9k (2.95k)
RCA grnd 0 (0.2 L, 0.2 R)
RCA pin 90k (95.2 L, 96.8 R)
Voltage
1 70-90 (86.4)
2 170 (176.5)
3 0 (0)
4 170 (176.4)
5 70-90 (83.4)
6 0 (0)
7 100 (111)
8 0 (0.001)
9 100 (107)
10 0 (0)
11 0 (0.001)
12 0 (0)
13 170 (176.6)
14 0 (0)
15 185 (198.2)
20 0 (0)
21 206 (219.2)
A1 90 (83.1)
A2 0 (0.001)
A4 0 (0)
A5 0 (0)
A6 90 (85.8)
A7 0 (0)
A9 0 (0)
B1 90 (85.7)
B2 170 (176.1)
B3 100 (111.5)
B4 90 (83.0)
B5 170 (176.0)
B6 100 (107)
B7 0 (0)
B8 0 (0)
Checked AC after DC test: IEC N-L 122.8, Transformer T1-T2 122.8, T4-T5 6.00; T7-T8 168.4, T9-T10 168.4
Ground mod on phono jack was done before I started listening. Resistance & DC values are similar to first test.
Also tested several ground points from IEC ground lug to: top plate (far end of chassis); T3; Pot grnds; RCA grnds; phono grnds; T12, T14, T20, 9-pin socket center, 4 & 5; 8-pin socket 8, T8, T11, T16 and T17 all were 0.1.
1 * (28k & rising)
2 * (64k & rising)
3 0 (0.1)
4 * (61k & rising)
5 * (85k & rising)
6 2.4k (0.1 - ground mod on phono jack, 2.49k before mod)
7 2.9k (3.01k)
8 0 (0.1)
9 2.9k (2.95k)
10 2.4k (0.1 - ground mod on phono jack, 2.49k before mod)
12 0 (0.1)
13 270k (270k and slowly rising - took about 8min)
14 0 (0.1)
20 0 (0.1)
22 0 (0.3)
B3 2.9k (3.01k)
B6 2.9k (2.95k)
RCA grnd 0 (0.2 L, 0.2 R)
RCA pin 90k (95.2 L, 96.8 R)
Voltage
1 70-90 (86.4)
2 170 (176.5)
3 0 (0)
4 170 (176.4)
5 70-90 (83.4)
6 0 (0)
7 100 (111)
8 0 (0.001)
9 100 (107)
10 0 (0)
11 0 (0.001)
12 0 (0)
13 170 (176.6)
14 0 (0)
15 185 (198.2)
20 0 (0)
21 206 (219.2)
A1 90 (83.1)
A2 0 (0.001)
A4 0 (0)
A5 0 (0)
A6 90 (85.8)
A7 0 (0)
A9 0 (0)
B1 90 (85.7)
B2 170 (176.1)
B3 100 (111.5)
B4 90 (83.0)
B5 170 (176.0)
B6 100 (107)
B7 0 (0)
B8 0 (0)
Checked AC after DC test: IEC N-L 122.8, Transformer T1-T2 122.8, T4-T5 6.00; T7-T8 168.4, T9-T10 168.4
Ground mod on phono jack was done before I started listening. Resistance & DC values are similar to first test.
Also tested several ground points from IEC ground lug to: top plate (far end of chassis); T3; Pot grnds; RCA grnds; phono grnds; T12, T14, T20, 9-pin socket center, 4 & 5; 8-pin socket 8, T8, T11, T16 and T17 all were 0.1.