Issues with driverboard testing [resolved]

[ericoto]

Working on Kaiju all testing previously was fine after wiring driver tubes and installing cs4 boards all readings off, both sides A side LEDS not lighting, B light fine, voltages about 233-235 at IA and OA respectively. Initial reading at 36 and 46 fine at 175. Any help suggestions appreciated

[Paul Birkeland]

You will need to slip one wire out of one IA pad, then fire the amp up to see if the other IA pops up.  If it doesn't, then trade which IA wire is connected and which isn't, then recheck.  When you find which board is pulling down the high voltage rails, remove it and post more photos of the top and bottom.  Also post photos of the string of zener diodes mounted to the 5 lug terminal strip on that side of the amp.

-PB

[ericoto]

Well I tried it an neither side corrects, still reads low about 240V, noted that voltage at 14 is also down at about 240V  I have rechecked board construction and wiring no obvious errors, High voltage checked fine in preceeding tests

[Paul Birkeland]

The red wire from one of your plate chokes is not attached and soldered where it's supposed to be.  It's probably trying to short out the high voltage power supply to the chassis.  I would correct that mistake, then with the amp off, unplugged, and discharged, be sure that the DC resistance between the blue and red wires on each plate choke is still roughly the same.  If the plate choke on the offending side has dropped substantially in resistance, you will need to remove it and purchase a replacement.

[ericoto]

Thank you for getting back to me so quickly. I did recheck the choke connections, they appear to be in the right place 35L and 43L, I desoldered both and then resoldered. I still have the same issues, the voltages are low around 240 in both IA as well as OA. The resistance is to both chokes is also the same approximately 485 ohms Should anything else be attached at these points? Also I have 4 60 ohm resistors remaining I dont see where these ayyach. Thank you again for your help

[ericoto]

I was looking this over andhave found a problem this morning 1 of the diode's off the power transformer secondary appears loose, possibly a cold joint I did not have time to correct it but will try that when I get home this evening. Could that explain the problems?

[Paul Joppa]

Yes, that could explain the problem. The two diodes make up a voltage doubler, so if one of them is disconnected ...  :^)

[Paul Birkeland]

Thank you for getting back to me so quickly. I did recheck the choke connections, they appear to be in the right place 35L and 43L,

This is absolutely not correct, as this red wire isn't connected to anything and can short out the HV supply. 

[ericoto]

yes, I did note that previously and did correct that, since then I have resoldered on both sides.  I'll send you a picture of it when I get home.  I'll also resolder the diode to see if that helps. Are the resistances on the chokes okay?

[Paul Birkeland]

Yes, those are good resistances.  The remaining resistors will go on the amp as you wire in the remaining connections on the output transformers.

[ericoto]

Thank you for the help, all is good now, voltages fine and LED's lighting, suspect knocked off weak diode solder when looking for original cause which was the choke wiring.

[ericoto]

All assembled and working sounds fantastic wonderful depth and seperation.with BeePre see attached photo. I have the DC filament will build after listening for a while.

[ericoto]

I have listened for over one week and then went ahead with DC filament supplies. Tried soem 10UF Clarity caps which did improve sound slightly but too big with DC filament, with 300b tubes, my reading at B1 B4 And C1 C4 runs higher than expected at around 5.4 to 5.5 VDC. IS this OK? Our line current is often high over 124V, I am testing on bench will be used with a power conditioner when connected to system. Thanks

[Paul Birkeland]

What are the voltages between +Reg and -Reg on each side of the DC board? 

It could be that Psvane tubes draw a little less filament current, though that would be unexpected.  Depending on your meter, if you have on that has something like a 200V and 500V scale for DC, then 5.5V may actually be an OK reading (some meters just won't resolve low voltages all that well).

[ericoto]

Thank you for the quick response, I wasn't too worried but wanted to check to see if it had been an issue. I'll proceed.