So I’m alive with sneakers on indoors. Sweden is like in Japan. You don’t wear shoes indoors except if there is a party and you have the nice ones on.
I think it was a good try.
B+1 = 466 VDC
B+2 = 465 VDC
B+3 = 462 VDC
No tubes inside. To high? Won’t the voltage drop when the tubes are in place?
Will go with the tubes now.Yes... as long as the heaters are hot and the tubes are installed you should see a lot lower. The problem is when starting cold. I'd go ahead and install all the tubes.
There are ways to avoid bringing the full 465V onto the caps. We might be able to install what is known as a "bleeder" resistor in the power supply. This might load down the power supply just enough to keep it below 450V even when cold or no tubes installed. Another option would be a standby switch to keep HT off the caps until the heaters are warmed up. Or possibly a well placed Zener diode that drops 20V.
Still alive. Just got Amp curfew from my wife for tonight. She’s on call tomorrow so a lot of time to search for problems then.And connect the speaker.
I was hoping your mains voltage was like 230v instead of 240v and that would keep you below 450V. Once you get this going, you should consider upgrading to 500V caps.
Thanks for still giving guidance. Will do readings and check for bad solder joints tomorrow. Will then update the chart. The hum was quite profound.Don’t worry about caps losing voltage after shutdown. That is to be expected because the tubes continue to conduct even after you turn off the switch. The fact that they held voltage with no tubes means you don’t have a short. Also the fact that your voltage is too high would indicate no short. Progress!
So… B+1 is staying up near 428 even with all tubes installed?
It is time to take some voltage readings on those power tubes. Fill out your chart with voltages for the power tubes. All voltages measured to chassis please. Remember to measure heater voltage (pins 2 and 7) to chassis in AC mode on your DMM.
Thanks for positive input. “Measuring across each side”?With the tubes hot they will continue to draw current from the capacitors when the power is turned off and drain them.
If you could, a voltage chart on the tube pins will help in troubleshooting now. First measurement of concern is the cathode resistor on the output tubes. We want to figure out how much current they are drawing from the power supply.
With the voltage and resistances we will do some Ohm's law.
430V - 366V = 64V 70V / 5600 ohms = 10.4 mA
366V - 260V = 106V 106V / 22000 ohms = 4.8 mA
So this tells us you have about 1mA per triode/pentode, looks about right. Subtract 10.4 mA - 4.8mA = 5.6mA going to the screens, which looks reasonable. So on first power up it seems you have a running amp.
To figure out more we can use the pin voltages. Also before you fire it up again, drain the power supply filter caps and then measure the resistance across the OT primary. Use your volt meter to make sure there is no voltage across the primary and then you are going to measure from the plate of one 6V6 to the first power supply node.Then do it for the other side. Then along with getting the voltages when the power is back on 'Carefully' measure the voltage across each side of the primary. We will use the voltage across the primary and the resistance of the primary to calculate the current through each tube. Also get the voltage drop across the sag resistor.
Not sure how much hum you have, but if you have a alligator clip jumper you could try shorting out pin 3 to pin 1 of a volume control to kill any signal coming from the preamp section. I will just leave that for now until we have the numbers. Your looking good so far.
B+1 and pin 3 of each tube.
I measured the resistance but the voltages readings created quite a noice. Not appreciated by tha family and dog who all was asleep before I powered it up with the speaker. Like the shielded wire made a difference… Have to do it tomorrow unfortunately. Not a fast process.B+1 and pin 3 of each tube.
That is why I suggested shorting out the pot to see if it is in the front end. Try (during the day) pulling the input tubes. If it still hums try the PI tube.I measured the resistance but the voltages readings created quite a noice. Not appreciated by tha family and dog who all was asleep before I powered it up with the speaker. Like the shielded wire made a difference… Have to do it tomorrow unfortunately. Not a fast process.
V1 pin7 resistance value is dependent on the preamp switch position.
Ohm/Current Pin 1 100K to B+3
0K to ground
0K to ground
O.L to ground
O.L to ground
Pin 2 32K to ground
49 to ground
218K to B+3 107,7vdc 50 to ground
50 to ground 3,17vac Pin 3 814 to ground
0K to ground
4,68k to ground 3,1mvdc 5,3K to B+2/ 156ohm to b+1
5,3K to B+2/
150o to b+1
Pin 4 49 to ground
4,7M to ground
417K to ground 0vdc 464 to B+2
464 to B+2
Pin 5 49 to ground
0K to ground
238K to B+3 108vdc 230K to ground
226K to ground 225mvdc Pin 6 100K to B+3
0,99M to B+3 29,6vdc 0,98K to ground 1,07vdc N/A
Pin 7 1M/32K to ground
0 vdc hum
49,5 to ground
49 to ground 3,16vac 49 to ground
49 to ground 3,17vac Pin 8 814 to ground
100K to B+3
49,5 to ground
270 to ground 24,9vdc 270 to ground 21vdc Pin 9 49 to ground
N/A N/A N/A N/A
volume at 20%. Voltage readings after fixing 270R sag resistor to CT.
There might be a problem there. When measuring HT CT to chassis R=0 ohm.Yes, you should be awake, alert, not drunk, not angry, and very patient when working with voltages that can kill you. It’s good to be a little scared.
I didn’t check your preamp tubes, but your power tubes looked reasonable given the voltages you have. It doesn’t seem like our sag resistor (10W) is doing much sagging though.
Turn off amp, unplug, confirm caps are discharged (did you know they can build some charge back up even after discharged?). Measure resistance for the HT center tap (where it connects to the 270R / 10W) to chassis. Make sure it reads 270.
It would be nice to take a voltage reading there, but it’s not going to be accurate because the current there is not nice and smooth.
There might be a problem there. When measuring HT CT to chassis R=0 ohm.
I measured the 270R leg (that attach to CT eyelet on board) connection to ground and there is continuity. I measured CT/270R connection to R17/R18 connection (wire connection under board) and continuity there.
I still have the R17 and R18 in those positions according to @printer2 layout. But have the connection under according to your layout.
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