So I have finished my Mainline 1.1 build but appear to have a final volt test issue. All resistance tests and the early volt test passed without issue. However, I am now getting wonky readings off the 6.3v pads. Initially I was getting 8v on the + and 1.4v on the -. I found a thread here with a similar issue that was resolved by clearing touching contacts on one of the socket pads; so I had a look those and found one spot where there could have possibly been cross contact (but not 100% clear there was - either way I adjusted it). When I put things back together my problem had reversed! Now I am getting upwards of 330v on the 6.3 pad. Resistance check and all other volt checks still pass. Pulled the tubes . . . same result.
Mainline final volt test fail
- Thread starter Tbar
- Start date
Can you post some build photos?
You should see about 50V on one of those terminals and 56V or so on the other. If you are seeing 330V, then you may have your black meter probe in the wrong spot, there may be a missing ground wire, or some unusual soldering problem exists. Definitely don't attempt to use this amp until this is resolved.
You should see about 50V on one of those terminals and 56V or so on the other. If you are seeing 330V, then you may have your black meter probe in the wrong spot, there may be a missing ground wire, or some unusual soldering problem exists. Definitely don't attempt to use this amp until this is resolved.
What do you measure on the power supply board where the black wire leaves (the - terminal)?
Be sure the amp is fully discharged, then pop the wires out of the +275V pads (both red wires and the black wire), then leave those poking up into the air. Recheck the voltages on the 6.3V pads, bearing in mind that you'll need to clamp your negative probe to that - terminal on the 275V pads on the power supply board. Soldering in a small piece of scrap temporarily is a reasonable method to make this easier and safer.
Can you unbolt the power supply board and show the bottom? Can you let me know what meter you're using?
Also you could end up with this situation if the zener diode on page 35 is missing or possibly if it's installed backwards it could blow on you, then you'd end up with high voltage on those heater terminals.
It would be worth inspecting that zener diode for damage (if it's blown, it should be pretty obviously cracked and there may be a burn mark on the board).
If this is what has happened, there is a workaround that's pretty easy, so you don't really have to worry about sourcing replacement parts.
It would be worth inspecting that zener diode for damage (if it's blown, it should be pretty obviously cracked and there may be a burn mark on the board).
If this is what has happened, there is a workaround that's pretty easy, so you don't really have to worry about sourcing replacement parts.
If you pot the board back and get your meter negative clamp back on the - terminal of the 275V pads, what DC voltages to you measure on each side of the little zener diode back there?
Well that diode isn't diode-ing anymore.
You can remove the 75K resistor from that board next to the zener diode, then replace the zener diode with a piece of wire, and your Mainline will work as intended. You'll see 6.3V and 0V on the 6.3V pads instead of the 50/56V, but that won't have any influence over the operation of your amplifier.
-PB
You can remove the 75K resistor from that board next to the zener diode, then replace the zener diode with a piece of wire, and your Mainline will work as intended. You'll see 6.3V and 0V on the 6.3V pads instead of the 50/56V, but that won't have any influence over the operation of your amplifier.
-PB
I honestly have no idea why your zener diode wasn't working properly. It could have been a simple soldering issue, though those things are so small that it's pretty tough to get a cold solder joint on them. These parts are only really on that board because they also go in the Eros 1.1, where we really need that 6.3V power supply biased up about 50V. In the Mainline, it works just as well to have it grounded, but we kept the instructions consistent between the two kits.
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