Thanks Win. Yes, just like you describe.
I'm familiar with how to set the bias but since the pcb is tightly in place there's nowhere to clip the testers. I'm considering soldering little wire nubs in place to clip on to so I can test from underneath.
The repair man had said that he had done the check out and biasing but that now seems really doubtful.
I'm familiar with how to set the bias but since the pcb is tightly in place there's nowhere to clip the testers. I'm considering soldering little wire nubs in place to clip on to so I can test from underneath.
The repair man had said that he had done the check out and biasing but that now seems really doubtful.
OK, red plating is the problem, then?
Just to further clarify, it is one of the 300B red plating, and when you swap the left and right tubes, the problem does not follow the tube?
If it is the 300B, you need to check, and then attempt, to set the plate current to a safe value. I don't own any 300B's, so I don't know what the correct value is for your amp. The good side measurement may or may not be correct. Perhaps someone running 300B's can give some useful information here.
Unfortunately, a blown MOSFET on that side, depending on the mode of failure, can also cause this problem. The way your luck is going ......
Check and attempt to set the current first.
If it is a 5842 orange / red plating, then the 10M45 on that side has likely failed.
Win W5JAG
Just to further clarify, it is one of the 300B red plating, and when you swap the left and right tubes, the problem does not follow the tube?
If it is the 300B, you need to check, and then attempt, to set the plate current to a safe value. I don't own any 300B's, so I don't know what the correct value is for your amp. The good side measurement may or may not be correct. Perhaps someone running 300B's can give some useful information here.
Unfortunately, a blown MOSFET on that side, depending on the mode of failure, can also cause this problem. The way your luck is going ......
Check and attempt to set the current first.
If it is a 5842 orange / red plating, then the 10M45 on that side has likely failed.
Win W5JAG
I'll add that to the list then thanks.
(Good thing my lady is out of town this weekend.)
There we go!
Win et al,
Thanks for all the help.
I realized I was way out of my depths having never built anything like this so I just dove in and ordered a board from George and built out that out from scratch. For a hands on guy like me it was a great learning experience and seems to have gotten everything working (check out and biasing went well) and sounding good so far (touch wood). 3am now so listening quietly.
Will get a better idea how everything really sounds later tomorrow and how everything holds up in the coming days.
Thanks again.
Deniz
Win et al,
Thanks for all the help.
I realized I was way out of my depths having never built anything like this so I just dove in and ordered a board from George and built out that out from scratch. For a hands on guy like me it was a great learning experience and seems to have gotten everything working (check out and biasing went well) and sounding good so far (touch wood). 3am now so listening quietly.
Will get a better idea how everything really sounds later tomorrow and how everything holds up in the coming days.
Thanks again.
Deniz
Meters are reading right. 385 volts at B+ (R30) and 50 ma at R18 and R29.
The bass however distorts on really bass heavy tracks (Tosca "Pearl In" https://www.youtube.com/watch?v=mNk9cbJqtjs ((first track)) ).
Also there's a very intermittent static sound that happens every few tracks but that's just around for 1 to 3 seconds.
The bass however distorts on really bass heavy tracks (Tosca "Pearl In" https://www.youtube.com/watch?v=mNk9cbJqtjs ((first track)) ).
Also there's a very intermittent static sound that happens every few tracks but that's just around for 1 to 3 seconds.
Well things didn't last long.
The intermittent static was coming from the right channel but on the last track of a Dexter Gordon CD the left channel went erratic. First some static / crackling and popping. I watched the meters closely and the meter at R29 overloaded then read numbers as high as 167. I quickly shut it down.
2 hours later I swapped in a known good rectifier (a Mullard GZ34) and same thing happened. This time with a steady and audible 50hz hum that wasn't affected by changing the volume.
I'm a bit short on patience at this point so I'll wait before doing any more test but what should I be looking for? Oscillation? Grounding issue?
The board is new as are all it's components and I've triple checked all of the connections. 6.3 volt secondary is soldered in and is secure, sockets are new and securely soldered in. Voltages all read right during check out and biasing. 5842's are new as are the 2 different GZ34's I've tried. Other than some bass distortion, things ran well for about an hour.
Gavin had this working for quite a while before I bought it. Is there something that might have broken or loosened in shipping it from England (besides the mosfets) that could be causing these problems??
The one and only thing I've reused from Gavin's board are the risers / extensions for the 5842's that bring them up high enough to clear the enclosure. I guess I'll pull those just to see but that seems too simple and they're in there very firmly.
The intermittent static was coming from the right channel but on the last track of a Dexter Gordon CD the left channel went erratic. First some static / crackling and popping. I watched the meters closely and the meter at R29 overloaded then read numbers as high as 167. I quickly shut it down.
2 hours later I swapped in a known good rectifier (a Mullard GZ34) and same thing happened. This time with a steady and audible 50hz hum that wasn't affected by changing the volume.
I'm a bit short on patience at this point so I'll wait before doing any more test but what should I be looking for? Oscillation? Grounding issue?
The board is new as are all it's components and I've triple checked all of the connections. 6.3 volt secondary is soldered in and is secure, sockets are new and securely soldered in. Voltages all read right during check out and biasing. 5842's are new as are the 2 different GZ34's I've tried. Other than some bass distortion, things ran well for about an hour.
Gavin had this working for quite a while before I bought it. Is there something that might have broken or loosened in shipping it from England (besides the mosfets) that could be causing these problems??
The one and only thing I've reused from Gavin's board are the risers / extensions for the 5842's that bring them up high enough to clear the enclosure. I guess I'll pull those just to see but that seems too simple and they're in there very firmly.
My first WAG is you have lost a MOSFET on the side that wants to pull 167 ma. I would first pull the tube on that side so you don't toast it, and then check the voltage at the grid to make sure you have the right bias voltage, and that the coupling cap is not leaking.
FYI only: intermittent static and the persistent hum could also be a filter cap that was failing ( intermittent static; bass distortion) and has now failed completely ( steady 100 Hz hum unaffected by volume ).
I had similar symptoms when I was troubleshooting bad filter caps in my TSE modified to use 801A/SV-811A.
Win W5JAG
You don't want to turn the amp back on before finding out what caused the problem. You will risk further damage.
I've been busy so I'm stepping back until I have time to go through everything again step by step.
I'll just throw this out there though. A friend was over the other night. He's a sound engineer that sets up for shows all over Germany. He looked at my breaker box and like many old homes in Germany, there isn't a dedicated ground / earth. The breaker box simply has a jumper cable from what would be the ground cable in the apartment to the neutral line that comes into the building. He says in these situations simply flipping the plug around the other way often cleans up problems. Obviously, I'm already running amps (solid state) and turntables alreadyalreabut without rpoblems but I'm considering every possibility at this point.
I'll just throw this out there though. A friend was over the other night. He's a sound engineer that sets up for shows all over Germany. He looked at my breaker box and like many old homes in Germany, there isn't a dedicated ground / earth. The breaker box simply has a jumper cable from what would be the ground cable in the apartment to the neutral line that comes into the building. He says in these situations simply flipping the plug around the other way often cleans up problems. Obviously, I'm already running amps (solid state) and turntables alreadyalreabut without rpoblems but I'm considering every possibility at this point.
I doubt that is your problem.
I have read / heard that on the older unpolarized AC/DC type of stuff, flipping the plug can alleviate hum and some other performance issues, however, I have never seen it make any difference on any of my stuff.
I have seen older homes around here that still have knob and tube electric wiring. I would expect it is still fairly common, given the high cost of rewiring older structures.
I don't know much about Germany ( took the language, but my hick southern accent is apparently incompatible - my instructor finally told me I didn't belong in higher education. In fairness to her, I also had an english teacher tell me the same thing
) but our local building dept makes it needlessly hard to bring older structures up to modern electric service, in my opinion. I had a situation where I was rewiring a building I have, and replaced an existing panel with a modern one, and ran into all kinds of trouble because one would have to reach across a counter, in excess of some arbitrary distance, to access the panel. The demand was to move it to the opposite side of the wall, where it would be next to a sink in a bathroom. Reason eventually prevailed, but it took a while. There are a lot of rundown buildings around here because of this type of nonsense.
Win W5JAG
I have read / heard that on the older unpolarized AC/DC type of stuff, flipping the plug can alleviate hum and some other performance issues, however, I have never seen it make any difference on any of my stuff.
I have seen older homes around here that still have knob and tube electric wiring. I would expect it is still fairly common, given the high cost of rewiring older structures.
I don't know much about Germany ( took the language, but my hick southern accent is apparently incompatible - my instructor finally told me I didn't belong in higher education. In fairness to her, I also had an english teacher tell me the same thing
) but our local building dept makes it needlessly hard to bring older structures up to modern electric service, in my opinion. I had a situation where I was rewiring a building I have, and replaced an existing panel with a modern one, and ran into all kinds of trouble because one would have to reach across a counter, in excess of some arbitrary distance, to access the panel. The demand was to move it to the opposite side of the wall, where it would be next to a sink in a bathroom. Reason eventually prevailed, but it took a while. There are a lot of rundown buildings around here because of this type of nonsense.Win W5JAG
I've finally gotten back around to checking things out again tonight.
Readings with just the rectifier in read;
B - 261
B+ 415
and the filament at only 5.5
B- seems low and B+ maybe a little high. I can't find or remember what the exact numbers are supposed to be though so if someone could please enlighten me it'd be very much appreciated.
Before I moved on to anything else I noticed sparks across Q2 (and flipped the switch on the power strip immediately) so definitely a problem with the mosfet there. Looking with a flash light and magnifying glass the solder joints look clean with clean space across them. So am I right to think that I'm exceeding the voltage the mosfets can handle (drain-source voltage)?
While I'm at this, does anyone using connection pads (wire to board mounts), have a part number for them? I'm having a very hard time getting the right ones and I'd love to be able to pull the board without desoldering all the wires). (I've got the present board set up so I can test from underneath).
Dinner is cold so I'll get back to this as soon as I'm sure of the next step. Which at this point I presume is lower the voltage the mosfets see and / or using higher rated ones.
Thanks all.
Readings with just the rectifier in read;
B - 261
B+ 415
and the filament at only 5.5
B- seems low and B+ maybe a little high. I can't find or remember what the exact numbers are supposed to be though so if someone could please enlighten me it'd be very much appreciated.
Before I moved on to anything else I noticed sparks across Q2 (and flipped the switch on the power strip immediately) so definitely a problem with the mosfet there. Looking with a flash light and magnifying glass the solder joints look clean with clean space across them. So am I right to think that I'm exceeding the voltage the mosfets can handle (drain-source voltage)?
While I'm at this, does anyone using connection pads (wire to board mounts), have a part number for them? I'm having a very hard time getting the right ones and I'd love to be able to pull the board without desoldering all the wires). (I've got the present board set up so I can test from underneath).
Dinner is cold so I'll get back to this as soon as I'm sure of the next step. Which at this point I presume is lower the voltage the mosfets see and / or using higher rated ones.
Thanks all.
Those are close to what I get from my TSE with just rectifier tube in.
Since you mentioned spark, take out the rectifier tube and do the first step measurement (shown here) again and see if you get negative voltage from both B+ and B-. If you do, try the second step.
Thanks for the reply. I didn't post it, but I did in fact test without the rectifier tube in and got similar B- but got 0 for B+. Surprisingly B+ didn't budge.
Well. I got new mosfets in the mail today. They're 2SK3565QM-ND. The same that EvanC is using in his. Mondays are a day off for me so I dug in.
I pulled the pcb and checked everything. The large TC 100µF 450VDC Clarity Cap that's mounted off board in parallel with C5 tested fine (115µF). D4 and D5 checked fine too so I went as far as pulling C4, C5, C6, C9, C11 to get accurate measurements with a capacitor tester and those all checked out fine. Sick of pulling caps that looked fine and figuring it had to simply be the mosfets, I went ahead and replaced those.
I then went through the checkout and everything tested and adjusted what I think was well;
With no tubes in
B+ -1
B- 284
Filament supply 4.9 on each.
With rectifier in
B+ 400
B- 278
Filament still steady at 4.9 on each
Output tubes set to lowest negative voltage
Right channel -138
Left channel -141
Then with 5842's in (175VDC)
B+ 378
B- 188
I then added load with my test speakers, put test leads across R18 and R29, put the output tubes in, and powered on. I didn't get a chance to get a read on the output tube plate supply because as soon as I powered on I got a load hum with some crackle and the center pin of Q2 sparking.
Going back and testing the mosfets that I pulled in the first place, those turn out to have been ok!
I'm really just about at the end of my rope. I've tested everything that's been mentioned in this thread and can't find what is going on. With all the experience and expertise here I trust that somebody can point out something I'm missing.
I pulled the pcb and checked everything. The large TC 100µF 450VDC Clarity Cap that's mounted off board in parallel with C5 tested fine (115µF). D4 and D5 checked fine too so I went as far as pulling C4, C5, C6, C9, C11 to get accurate measurements with a capacitor tester and those all checked out fine. Sick of pulling caps that looked fine and figuring it had to simply be the mosfets, I went ahead and replaced those.
I then went through the checkout and everything tested and adjusted what I think was well;
With no tubes in
B+ -1
B- 284
Filament supply 4.9 on each.
With rectifier in
B+ 400
B- 278
Filament still steady at 4.9 on each
Output tubes set to lowest negative voltage
Right channel -138
Left channel -141
Then with 5842's in (175VDC)
B+ 378
B- 188
I then added load with my test speakers, put test leads across R18 and R29, put the output tubes in, and powered on. I didn't get a chance to get a read on the output tube plate supply because as soon as I powered on I got a load hum with some crackle and the center pin of Q2 sparking.
Going back and testing the mosfets that I pulled in the first place, those turn out to have been ok!
I'm really just about at the end of my rope. I've tested everything that's been mentioned in this thread and can't find what is going on. With all the experience and expertise here I trust that somebody can point out something I'm missing.
You have to troubleshoot methodically, otherwise you'll go nowhere. First, make 100% sure, you do not have bad solder connections, loose pins, cracked PCB, etc. A good procedure is:
1) check the PSU (power supply). That includes the heater supply, B+ and B- (both channels).
2) check the power amp. B+, B-, BIAS voltages.
If anything is out of specs, stop right there. Find the problem and fix it.
3) lastly check the preamp, if needed.
Sparks around the MOSFET indicate a bad connection around it or a short. I recommend to follow the step by step checkout procedure shown on the tubelab website. It might help you find the problem quickly:
Checkout | Tubelab
1) check the PSU (power supply). That includes the heater supply, B+ and B- (both channels).
2) check the power amp. B+, B-, BIAS voltages.
If anything is out of specs, stop right there. Find the problem and fix it.
3) lastly check the preamp, if needed.
Sparks around the MOSFET indicate a bad connection around it or a short. I recommend to follow the step by step checkout procedure shown on the tubelab website. It might help you find the problem quickly:
Checkout | Tubelab
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