Good afternoon,
Like the title says, list one channel on my SSE after about 6 years of steady use. It would get quiet and fuzzy on occasion once in awhile, but barely puts out any sound now(have to put ear to speaker to hear anything).
For fun I opened it up and swapped all the wiring on to the output transformers to see if that was the issue, but after switching the wiring to OT’s same channel was still out. Are there any specific areas I should be looking at when I open it up and start testing with the multimeter? Thanks in advance!
Alex
Like the title says, list one channel on my SSE after about 6 years of steady use. It would get quiet and fuzzy on occasion once in awhile, but barely puts out any sound now(have to put ear to speaker to hear anything).
For fun I opened it up and swapped all the wiring on to the output transformers to see if that was the issue, but after switching the wiring to OT’s same channel was still out. Are there any specific areas I should be looking at when I open it up and start testing with the multimeter? Thanks in advance!
Alex
I had a problem with my SSE which was on one channel, so that stopped me thinking the 12AT7 could be the culprit. I still haven't completed the faultfinding, but swapping the 12AT7 appears to be the solution. The other issues I have had have all come back to my assembly with the PCB connectors. Ideally in the future I will find a source of plugs and sockets that can be soldered and then use soldered wires in the boards, with the plugs to allow disassembly. They do seem to loosen over time.
Thanks for the replies, much appreciated. The 12AT7 plate voltage on pin 1 was 224V, pin 6 207V. The cathode voltages both read right around 1.9V. Also did some basic continuity testing to make sure the connections were good throughout. I don’t see anything obvious when looking at the amp, but clearly something isn’t right😬.
Thanks-Alex
Thanks-Alex
Yeah, went through it again checking voltages to see if anything was off between the two channels, haven’t found anything yet. I don’t have the function on the multi meter to test capacitance, so maybe I’ll need to pick up a new one. Not truly understanding how this amp works, I’m just looking for discrepancies at this point. If one of the MOSFET failed would that be detectable by checking voltage?
Thanks-Alex
Thanks-Alex
A mosfet device can fail two ways, shorted (most common) or open (rare but happens sometimes). Either failure mode will cause a pretty drastic change in the plate voltage on the corresponding section of the 12AT7 tube. Your voltages are reasonable for a working tube and mosfet. A shorted mosfet will raise the plate voltage into the mid 300 volt range. The affected channel will continue to play music which will usually be relatively undistorted but be much lower in volume, maybe 1/4 of normal, but clearly audible. An open mosfet will kill the affected channel completely and result in a plate voltage of zero. I have never seen an open mosfet in an SSE. Shorted mosfets are also quite rare in the SSE, and usually caused by a bad 12AT7 tube or loose heat sink resulting in an obviously overheated mosfet.
As stated, the screw terminals tend to loosen (actually the wires crush) over time. Tighten the screws in all of them. The SSE amp generates a good deal of heat, as does any SE amp. I have seen perfectly good solder joints become brittle and intermittent in 10 years of use, especially if the amp was subject to vibration (mine sat on one of the speakers).
Any of the diodes in an SSE (2 in the pre 2011 board and 4 in the newer board) will affect both channels equally if they are bad.
Measure the voltage across the cathode resistors R17 and R27. They should be within a few volts of each other. If not power the amp off, wait a few minutes and measure the resistance of R17, R27, R18, and R28. The large resistors R17 and R27 get pretty hot which can cause premature failure and brittle solder joints. R18 and R28 have been known to fail in amps that see clipping often, especially with EL34 tubes. I have blasted a few by using an SSE for a guitar amp.
Other users have seen "boutique" coupling caps fail after a few years of use causing a dead, weak, or distorted channel. Jupiter caps come to mind, but there have been others. I have not seen a coupling cap fail but I use relatively cheap caps.
As stated, the screw terminals tend to loosen (actually the wires crush) over time. Tighten the screws in all of them. The SSE amp generates a good deal of heat, as does any SE amp. I have seen perfectly good solder joints become brittle and intermittent in 10 years of use, especially if the amp was subject to vibration (mine sat on one of the speakers).
Any of the diodes in an SSE (2 in the pre 2011 board and 4 in the newer board) will affect both channels equally if they are bad.
Measure the voltage across the cathode resistors R17 and R27. They should be within a few volts of each other. If not power the amp off, wait a few minutes and measure the resistance of R17, R27, R18, and R28. The large resistors R17 and R27 get pretty hot which can cause premature failure and brittle solder joints. R18 and R28 have been known to fail in amps that see clipping often, especially with EL34 tubes. I have blasted a few by using an SSE for a guitar amp.
Other users have seen "boutique" coupling caps fail after a few years of use causing a dead, weak, or distorted channel. Jupiter caps come to mind, but there have been others. I have not seen a coupling cap fail but I use relatively cheap caps.
Awesome, thanks for the help with this, really appreciate it. This helps to narrow down what could be causing the problem.
Yes, I used Auricaps for the coupling capacitors, so those are a possibility.
Just need an evening to sit down and dig through it a little more. It’s been down for a few months, the back up amp I’m using just isn’t the same!
Alex
Yes, I used Auricaps for the coupling capacitors, so those are a possibility.
Just need an evening to sit down and dig through it a little more. It’s been down for a few months, the back up amp I’m using just isn’t the same!
Alex
Good afternoon
Finally had a minute to take a look at the amp today. Here’s what was measured:
R17 519 ohms 42.5 V
R27 526 ohms 43.0 V
R 18 98 ohms 443 V
R 28 99 ohms 442 V
I’m going to check all the wire connections again and check the solder joints on the potentiometer. Any other ideas would be appreciated, thanks!
Alex
Finally had a minute to take a look at the amp today. Here’s what was measured:
R17 519 ohms 42.5 V
R27 526 ohms 43.0 V
R 18 98 ohms 443 V
R 28 99 ohms 442 V
I’m going to check all the wire connections again and check the solder joints on the potentiometer. Any other ideas would be appreciated, thanks!
Alex