Hi, I am not sure when things went wrong but my SE with 45s now sounds very fuzzy. I decided to try a higher voltage than the 275v that it was running with a GZ34S rectifier. So I put in a diode rectifier but the B+ was then 330v so I went back to the GZ34S rectifier. It now sounds very fuzzy. What is strange is the B+ is up at 312V - it seems to have bumped up by 40V. Also the bias isn't very steady, and sometimes one bias goes to 0 while the other doubles. I didn't see any smoke and a quick check of the components didn't reveal anything fried. Any suggestions as to where I should look? Thanks! Henry
If this is an original TSE, not a TSE-II it's possible that the extra B+ blew a mosfet, but that usually kills all sound.
Before possibly frying a 45 tube, I would pull them out.
Next measure the voltage on the grid pins while turning the bias pot for that tube. You should have a negative voltage that varies from somewhere around -20 volts to about -100 volts.
Before possibly frying a 45 tube, I would pull them out.
Next measure the voltage on the grid pins while turning the bias pot for that tube. You should have a negative voltage that varies from somewhere around -20 volts to about -100 volts.
With the tubes out the B+ is running at 330 on the pins of the 45s and the 5842s. When I turn the bias pots, the grid pins on both 45s run from -21 to -113v. The caps that see B+ (C4 and C5) are rated 450v so I think they are OK. I attach a pic of my board purchased in 2014. Thanks for any advice!
Hi,
it is still not working. I put in a maida reg so that I can control the B+ and set it to 280. The amp checks out without the 45s in. The bias is good and the 5842s grid can be set to 175v. It is stable.
Once I put in the 45s the B+ drops to 230v and the output current is about 135mV. The grid adjusts from -20 to -112v and doesn't have much effect on the current. Over a couple of minutes the current slowly goes up while the 5842 plate voltage goes down, so I didn't leave it on for long.
Does any of this info suggest it is the 2SK2700 or 10M45? Could it be that I fried the 45's?
Thanks!!!
Henry
it is still not working. I put in a maida reg so that I can control the B+ and set it to 280. The amp checks out without the 45s in. The bias is good and the 5842s grid can be set to 175v. It is stable.
Once I put in the 45s the B+ drops to 230v and the output current is about 135mV. The grid adjusts from -20 to -112v and doesn't have much effect on the current. Over a couple of minutes the current slowly goes up while the 5842 plate voltage goes down, so I didn't leave it on for long.
Does any of this info suggest it is the 2SK2700 or 10M45? Could it be that I fried the 45's?
Thanks!!!
Henry
I replaced the 2SK2700s (with FDPF5N50NZ) and 10M45s and everything tested out (B+ = 280, Bias =-200, grid pins -110 to -20, the output current 28mA). It sounded great. Turned off after 5min tried it again later and it is blown again! When I put in my 45s, the current across the 45s (R18) is back up to 135mA on one tube and 0 on the other, there is a hum and B+ drops from 280 to 240. I don't think there is any sound now - but I didn't leave it on to really test. The 45 with 135mA got hot fast.
Any advice?
Any advice?
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More observations on one channel not working:
- I tried swapping the the tubes and it is not tube dependent. When I remove the tube from the defective channel, the otherside goes from 0 up to 27mA - and sound plays through that channel well.
- I measured grid voltage with both tubes in and they are the same.
- I swapped the OPTs and the bad channel stays the same
- the 10R resisters (R18 and 29) on each channel measure fine.
- I tried swapping the the tubes and it is not tube dependent. When I remove the tube from the defective channel, the otherside goes from 0 up to 27mA - and sound plays through that channel well.
- I measured grid voltage with both tubes in and they are the same.
- I swapped the OPTs and the bad channel stays the same
- the 10R resisters (R18 and 29) on each channel measure fine.
I haven't been able to get it running yet. Every time I replace the mosfets (STF3LN80K5s) it runs for about 5 min but the sound is very muffled. Then the B+ drops from 280 to 240 and the current across R18 goes from 27 to over 100mA while R29 goes to 0.
I tried replacing the CLC regulation of B+ with a maida regulator. That was stable, but there was quite a lot of hum. Should I just give up?
I tried replacing the CLC regulation of B+ with a maida regulator. That was stable, but there was quite a lot of hum. Should I just give up?
This does not make sense to me either. Are you measuring the grid voltage right at the tube pin? The fact that this current does not change much when you vary the voltage points to a bad or possibly an oscillating tube. 45's do not often oscillate.
Does the bias current / voltages hold steady if the 5842's are removed? 5842's DO have a tendency to oscillate, especially if the input wiring was changed during the modifications.
The only thing else that comes to mind is the 100 ohm resistor in series with the grid pin (R33 and R34). Replace them as one could have been damaged and it breaks down with current flow. I have also seen a bad R5 do strange things, but this results in a bias voltage that changes a lot.
It's possible that one of the solder pads for the mosfet leads got messed up during the change of parts. Verify continuity from the part lead to the associated circuitry on the board. If the drain lead lost contact to B+ the source (45 grid) voltage could wander under load. Verify continuity with an ohm meter on an unpowered board from the middle lead on the mosfet to the BPLUS - DRV_B+ jumper.
Is the filament voltage steady at 2.5 volts?
Thanks for the advice!! I am going to replace all the bias resistors and the grid stoppers next week. I did measure voltage right on the pins. I haven't looked at removing the 5842's - I will try. The heater voltage is steady at 2.5V. I am thinking it might be a lifted pad or a bad joint so I will check over again when I am replacing parts. I am tempted to move the mosfets off the board and put them on the enclosure so I can monitor the heat. I hope it is not the tubes, I put my spares in and they did the same thing. Cheers!
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