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SSE low output 1 Channel

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Looking for a little help troubleshooting my SSE. Got it up and running about 6 weeks ago, just yesterday noticed low output and distortion from one channel. Initially it would go back to functioning correctly, but now is quieter in its output. I swapped out the pre-amp and power tubes, but not the rectifier, no change. Opened the amp up, visually checked for loose connection and bad solder joints, did big see anything. In short, one channel good, the other still playing at low output. Any ideas of where to start troubleshooting greatly appreciated. Thanks!
 
First of all I'm no expert. But I had a similar problem.
I found that I'd wired up one output transformer incorrectly. One channel was fine and the other was weak and distorted. I noticed that the two output transformers were not wired up in an identical fashion...changed the wiring and the problem disappeared. About a month later the tube that powered the incorrectly wired transformer gave out....
 
Have you swapped sources to make sure the problem is not in the source, as opposed to the amp?

A bad cathode bypass capacitor can cause a reduction in gain, but might or might not also cause an increase in distortion.

Might want to post some good quality pictures of the amp - eyes on is easier.

Win W5JAG
 
Yes, I checked the input sources, everything seems to be good there. Measured the resistance on the bias resistors, they seem well within tolerances. Attached is a few photos, any help is much appreciated. Thanks in advance.

Edit: misunderstood Win and checked resistance on bias resistors, not bypass caps. Any way to check caps with a multimeter?
 

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It’s hard to see, but the jumper is there-I soldered that terminal onto the board backwards...the amp ran great for about six weeks till this issue started.

I just followed one of George’s basic designs, didn’t tweak anything. It is mated to a pair of Seas MTM’s from a DIY kit, extremely happy with how it sounds.
 
Did you try to drill out the PCB holes to fit fat coupling cap leads? If so you probably drilled out the circuit plating that goes through the hole connecting the top layer to the bottom. If so, you need to solder the cap wires on both the top and bottom side to complete the path.

If not its fairly easy to figure out which stage is bad. Measure the DC voltage across the cathode resistors in the output stage (white 560 ohm). It should be somewhere around 40 volts. One channel with zero or over 50 volts indicates a problem in the output stage.

Measure the voltage on the end of the coupling caps connected to the 12AT7 plates (towards the bottom on your pictures). It should be around 200 to 300 volts, something near zero, or over 400 volts indicates a problem in the driver stage.
 
Thanks George, I’ll take some measurements tonight and let you know what I find.

Did not have to drill out the holes for the coupling caps, so don’t think that is the problem. Opened it up yesterday and rechecked wiring diagram and the board for bad solder joints, and now not getting any sound out of the right channel...let the troubleshooting begin!
 
Ok, took measurements on the coupling caps, both measured right around 230V. The cathode resistors measured at 32V each. Any ideas where to go from here? As I noted in my last post, after checking and tightening the wire connections I have now lost all sound out of the right channel. Thanks in advance for your help.
 
measured right around 230V. The cathode resistors measured at 32V

This means that all of the tubes are conducting DC as they should. Something is preventing the flow of AC (signal).

The usual culprits in this case are the connectors where they pass through the metal chassis. It is also possible that the sharp edges of the chassis has cut into one of the OPT wires where they pass through the chassis.

The easiest way to test the input connections is to measure resistance with an ohm meter. Measure the resistance at the jacks on the rear panel. There should be 100K to 250K from input to ground, depending on what value you used for R11 and R21. You can also try swapping the channels at the green terminals for the board input. If the dead channel plays, and the good one dies, the problem is in the wiring. It's hard to see in the picture, but you may need to touch up the solder on those small resistors at the input. R12 doesn't look right, but that could be the picture.

You can try to compare resistance readings of the speaker jacks, but the OPT has less than one ohm of resistance in its secondary so most meters can't tell if there is a short. The usual test is to unsolder the wires from the jacks and connect the OPT directly to a speaker with clip leads.
 
Well, I feel a little ridiculous, but am relieved to have the amp working again. Swapped inputs around on the board, no change. Went to swap the output wires from transformers on the speaker terminals and noticed that one of the bolts had come loose on the terminal, problem solved! Thanks for your help, I made this a lot more difficult than it needed to be!
 
I made this a lot more difficult than it needed to be!

Look at as a learning experience for all of us.....when something complex doesn't work, test, the easy stuff (the DC) thereby ruling out a lot, then divide up and conquer what's left.

If this hadn't delivered any results, we would have stolen signal from the good channel to feed the dead channel starting at the coupling caps....that eliminates half the amp......little by little there would be nothing left to check.
 
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