Resistance cks OK voltage descrepancies

[Tom-Huffman]

Resistance checks were right on except for 2 and 14 which were 13K and may be OK

Start - Finish AC voltage = 167 v
A1 to A4 = 2.5 v
C1 to C4 = 2.5 v
2A3s to not glow

Diodes oriented correctly
LEDs oriented correctly but no light
Transistors oriented correctly
I have confirmed to 12AT7 wiring to the PCB above it

HV+ = 449

Terminal voltages
1 = 440 v
2 = 175 v
3 = 0
4 = 440
5,6,7,8,9,10,11 = 0
12 = 440
14 = 167
15 = 440
16 = 0
17 = 440
18 = 0
19 = 440
20 = 0

A1 = 0
A2 = 445
A3 = 445
A4 = 0
C1 = 0
C2 = 445
C3 = 445
C4 = 0

1A = 445
1B = 445
OA = 174
OB = 166
Kreg both = 2.5
-reg both = 0

[rlyach]

Tom,

This is just a hunch. Did you check your 4 pin tube sockets to see that the larger holes are facing the back of the chassis (closer to the hum pot)? It appears that you are not getting any cathode current on the 2A3's. Reversing the tubes could cause this. This would also explain why no glow. Your filament pins are not connected to the filament windings.

[Tom-Huffman]

Knowledge plus a hunch = excellence

Everything is in line but two pair -

Terminal 2 and 14 = 167 v
OA, OB = 167

A few zeros are reading 15 to 18 mv

[rlyach]

Glad to hear it is working now. I don't think the 167V on the 12AT7 anodes is a problem. That number will be tube dependent, and will vary a lot. The design is tolerant to this and it will not affect the performance. I am sure someone can chime in with a range of acceptable values. Also, terminals 2 and 14 will not match exactly unless you are very lucky and get a tube where both triodes inside the 12AT7 are perfectly matched.

[Paul Birkeland]

167V is an unusually strong 12AT7, certainly no problem there.

-PB

[Tom-Huffman]

One last check before I check to see if it makes music.

Left hum pot .096 to .071 with .000 mv in between.
Right hum pot .110 to .067 with .000 mv in between.

Is this normal?

[Tom-Huffman]

Please check my previous post as well about the hum pot measurements.

I went ahead and hooked up the system with minimum components - Stereomour, DAC, CD transport and speakers.  Result?  No sound at all.

[rlyach]

Tom,

It appears that something is not right in the signal path. What voltage did you get on terminals 5 and 11? I am just checking to see if your output transformers are hooked up correctly. Also check to make sure the coupling cap between terminals 1 and 5 and between 11 and 15 are in place. The funny thing is that you seem to be getting hum on the speaker terminals as evidenced by your humpot measurements but no sound. I would expect much more hum than .1mV max though. I would expect the humpot measurements to get has high as 10 to 100 mV. The next thing to look at is to see that your input is wired correctly. Trace your inputs through the selector switch and the volume pot to make sure there is a connection from the RCA jacks to the output of the volume pot. If that is OK check the other coupling capacitor between terminals 2 and 4 and between 12 and 14. Keep us posted on your progress. You could also post a picture of the underside of your build. Perhaps something will pop out.

[Tom-Huffman]

5 = 58 v
11 = 60 v
I am starting the signal tracing now from input to volume pot

[Tom-Huffman]

I continuity checked each input to the selector switch and then to the volume pot.  All are correct.  I will remeasure all voltages and send to you.

[rlyach]

Tom,

This is a little baffling. Your cathode voltages are good and the output transformers are connected. I looked at your build and I did not see anything obvious. I noticed you are using a 16 ohm secondary wiring for your output transformers. I also assume you have the proper source selected when you tested for sound (switch position) and the volume was not at the lowest level. I drew up the schematic you had before you fixed your tube sockets and in your old configuration you would have had the full 445 volts between the grid and cathode of the 2A3's with 249K ohm current limiting resistor. This can damage the tubes but since you are getting the proper current now I assume the tubes are functional. I will wait to see all the DC voltages to see if that sheds any light on the situation.

Randy

[Tom-Huffman]

As previously posted, all input to selector switch and then to volume pot checked out

Here are the new voltages.
hv+ = 400
1 = 370
2 = 176
3 = 0
4 = 12 mv ??
5 = 58
6 = 0
7 = 0
8 = 0
9 = 0
10 = 0
11 = 60.8
12 = 13 mv ??
13 = 0
14 = 167
15 = 369
16 = 58
17 = 401
18 = 0
19 = 400
20 = 61
A1 = 58.8
A2 = 372
A3 = 18 MV
A4 = 58.8
C1 = 61.5
C2 = 369
C3 = 20 MV
C4 = 61.5
IA = 400
1B = 400
OA = 176.5
OB = 167.7
Kreg = 2.5
-reg right = 0
-reg left = 0

[rlyach]

Tom,

All the voltages look reasonable. The 400V is a little high but not too far out. Everything else is right in line with where it should be. I noticed that your volume pot was all the way down when you made these measurements. I re-looked at the way you had it hooked up before and there was only 1200 ohms limiting the grid current on your tubes. I am starting to wonder if you blew a grid connection inside the tubes. Do you have another pair of 2A3's to try? Perhaps PB or Paul or Doc can comment on the possibility of damaging the tubes.

Randy

[Doc B.]

Are your speaker cables making good contact with the metal of the binding posts?

[Tom-Huffman]

No extra tubes.  This is my first 2A3 project.

Speaker connections are via Kimber banana plugs.  However, I did have trouble getting my interconnects to seat properly because they were so tight.  I will try a cheap pair.

Question:  should I be able to see the 2A3s glow?  I have never seen that but they do get hot.