Completed sex kit: No sound from right channel

[fullheadofnothing]

By shorting the two decks of the pot together, you have made your amp mono. Not the worst thing in the world, but you probably want it to be in stereo.

The purpose of this exercise was to determine where your problem is, and you have now proven that both channels of your amplifier work, but one channel is not getting signal. You have a bad solder joint or a short somewhere earlier in the signal path, either at the pot, or the RCA jack. Check your RCA jack closely to see if there is any solder bridging the pin to the barrel. It is also possible that the problem is in your source or the interconnect cables, but I assume you've already checked for that by swapping cables.

[Grainger49]

Nope, you have mono Left channel now.  Next you want to remove the wire/jumper.

But you have located the problem to before the volume control.  This means the connection at the pot from the left channel and at the RCA jack.  Touch up those two solder connections.  Verify continuity with your meter set on ohms from the metal on the RCA jack to the metal on the right side of the pot where the red wire comes in.

Or your source is not feeding both channels.  There are very few possibilities.

[Jim R.]

You may have also fried the carbon comp grid stopper resistor or have a bad tube socket.

-- Jim

[mcandmar]

As above shorting the connection eliminated all that, all that is left is 12" of cable and two RCA jacks.

[mpent]

My guess is maybe it's the cable because earlier on I thought it may be the jacks and I inserted new jacks which clearly did not correct the problem. So am I looking at the signal wire running from the right rca jack to the volume pot?

[Paul Birkeland]

After soldering the wire in connecting the middle lugs of the pot, I get sound from both channels.  So what does this mean?  Should I leave the wire in there and consider the problem rectified?

If you like listening in mono, you could indeed leave that wire there.

This suggests that you either have a bad connection from the center lug of the right jack to the outer lug of the pot for the right channel, or (more likely) you have excess solder shorting out the jack, or perhaps some metal-to-metal contact on the jack itself that can be cleared out.

When you look at the bottom of the right input jack, you should see the center post, then a ring of open space between that and the outer shell of the jack.  Can you see any metal bits in there shorting things together?

[mpent]

There really isn't an open space per say. If im looking correctly, there is the center post sitting in the ring.  Within the ring appears to be a white piece of perhaps plastic. That is the left jack. The right jack has what appears to be burnt flux in that area where the center post is seated. Aside from that, I touched up the lugs on the pot and the right rca jack and I am now getting sound from the right channel. Do you think that flux residue can be causing the problem??

[Paul Birkeland]

Yeah, some residue could be an issue.  Rubbing alcohol and q-tips would be your friend here.

On the bright side, you have whittled the problem down to only two components (level control and RCA jack), so the rest of the amp can be ignored.

[mpent]

Although this is another topic, I re-installed the C4S board again last night. One LED does not light. However my voltages are within range at pins 10 and 20. The OA side voltage is 54 and OB side is 76. OA side has the blown LED. I think I have a blown transistor which I have identified. Question is why do I get good voltages at the terminals and when I listen I hear no audible problems in sound?

[Paul Birkeland]

If you swap the inputs and outputs of the board, do the voltages change?

[mpent]

Would I accomplish the swap by reversing the wiring at terminals 10/20? Attaching the leads fro. 10 to 20 and vice versa? If not, how?

[Paul Birkeland]

Would I accomplish the swap by reversing the wiring at terminals 10/20? Attaching the leads fro. 10 to 20 and vice versa? If not, how?

I can't see how that would apply to either the C4S issue or the right channel not working.

The inputs/outputs on the C4S boards is the red and white twisted pair of wires that comes from IA/OA and IB/OB.

Is the right channel issue resolved?

[mpent]

The right channel issue is resolved. My other question had nothing to do with the right channel. Was asking why my C4S board "appears" to be working even though one LED is not lit. I am getting correct voltages at terminals 10/20. You asked whether the voltages change if I swap the inputs/outputs of the board. I am not certain how to perform that action.

[Paul Birkeland]

Desolder the red/white pair from the tube sockets/terminal strips, then swap them (Left to right).

[mpent]

C4S problem solved. Swapped out transistor and blown LED. Thanks everyone!