Hi. I recently changed out all capacitors in my dynaco st-35. All was working great afterwards. Then suddenly a receive scratching clicking type noise in one channel. I take out all tubes and it is silent. I have changed the tubes out but the same problem.
I then notice after about 3-4mins smoke coming from #5 eyelet on the circuit board. Could this be too much voltage on this point.
What should i replace to solve.
Many thanks. Regards. Martin
I then notice after about 3-4mins smoke coming from #5 eyelet on the circuit board. Could this be too much voltage on this point.
What should i replace to solve.
Many thanks. Regards. Martin
Check the solder at the islet. That one is the filament to either v1 or v4. Carries about 300 ma. Resolder and keep an eye on it during power up. Also look for solder bridges on the board that might be shorting out traces.
Make sure you washed the rosin off of the circuit board when you mounted new parts on it.
You need Isopropyl Alcohol and Q tips, or similar to clean the rosin off.
You need Isopropyl Alcohol and Q tips, or similar to clean the rosin off.
Are there any resistors I should change that might be causing it to get warm like this?
Not so likely to be an R or C. A new tube can certainly be bad.
But, swap the tube with its mate (of the same pair). Is the same tube still bad?
But, swap the tube with its mate (of the same pair). Is the same tube still bad?
Or does it point to a bad transformer? Tubes have been changed. I will take it to a technician. Was looking forward to solving it though. Seems beyond my knowledge. No idea how to fault find these things.
Won't be a transformer, such problems are very rare if the amplifier is properly fused.
Generally, to check for a tube problem without other test equipment, you would swap the tubes between channels.
If the same tube is bad, replace it. If the same socket has the problem, look further.
If the problem started after the capacitor changes, check all of your work carefully.
Sometimes people forget to clip excess lead length, etc.
Generally, to check for a tube problem without other test equipment, you would swap the tubes between channels.
If the same tube is bad, replace it. If the same socket has the problem, look further.
If the problem started after the capacitor changes, check all of your work carefully.
Sometimes people forget to clip excess lead length, etc.
Where in sweden do you live ? I am in gothenburg and can fix your st-35
Don't give up!
The service engineers if the old days were not all tube gurus, but they had a methodology for homing in on the most common issues.
They had service diagrams with expected voltages at lots of points in the circuit, and sometimes resistances to ground from each valve pin.
If it is safe for you, methodically measure the voltage to ground on each valve pin and report here. That will highlight the vicinity of the issue.
From an IT perspective, the most likely cause of an issue is the last change, so, a pound to a penny, it is likely linked to the cap change you did, directly or indirectly.
Try to keep one hand behind your back when measuring the voltages. I use some insulation tube over the tip of the probe to minimise chance of shorting when getting to obscured pins.
The service engineers if the old days were not all tube gurus, but they had a methodology for homing in on the most common issues.
They had service diagrams with expected voltages at lots of points in the circuit, and sometimes resistances to ground from each valve pin.
If it is safe for you, methodically measure the voltage to ground on each valve pin and report here. That will highlight the vicinity of the issue.
From an IT perspective, the most likely cause of an issue is the last change, so, a pound to a penny, it is likely linked to the cap change you did, directly or indirectly.
Try to keep one hand behind your back when measuring the voltages. I use some insulation tube over the tip of the probe to minimise chance of shorting when getting to obscured pins.
I'm in Lund. But I just did a silly thing and used kontact PRF and had a bit of a wire melt down. I had fixed the problem as it was the tubes that were sparking it seems. I now need to trim the power transformer wire and reattach and replace 2 other wires. What is the grade and type of wire that is used. It's solid core with a black sleeve. Live and learn. Won't be doing that again.
Managed to fix it. Put new sleeves on all melted wires and resoldered.
The initial problem seems to have come from corrosion in the pin housings.
All working and happy 🙂
Before and after pic
The initial problem seems to have come from corrosion in the pin housings.
All working and happy 🙂
Before and after pic
The scratching noise is back. Going to change the socket. Strange. Or can a capacitor do this too?
The solder joints in general don't look very good, including the original ones on the pcb.
Dyna's wave soldering was not very good.
Dyna's wave soldering was not very good.
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Use 63/37 if you have it, but avoid adding a lot of solder. Just a little, no large blobs.
Do make certain that all of the eyelets are soldered to the traces as well as to the wires.
It would be rare for tube sockets or capacitors to cause that kind of noise.
However, if you still have the original "black cat" capacitors, those should be replaced
(with similar values) to prevent leakage.
Do make certain that all of the eyelets are soldered to the traces as well as to the wires.
It would be rare for tube sockets or capacitors to cause that kind of noise.
However, if you still have the original "black cat" capacitors, those should be replaced
(with similar values) to prevent leakage.
I'm up and running again. No pops and scratches. Redid all the joints. See how long it lasts. Thabks for all comments