It was brand new when I built the amp, and it worked for a few days just fine.
Also I am pretty sure I tested it somewhere along the journey of this thread... it has been months since I had the will to even look at this project.
OK, maybe this will narrow things down a bit, and maybe it is just me being a dumb-****.
I just re-ran this test but made one change - I disconnected the green transformer wires (filament?) from the T1-GRN terminals on the board.
The reading is now 80.6 K ohms.
Logic tells me that since this is much closer to the correct reading (75 K ohms, as described by George) then the short (causing the 212 ohm reading) has something to do with these green wires.
Am I even close to correct?
Last edited:
A short between the HV winding and the filament winding inside the transformer, or outside?
No need to guess.
What's the resistance between the two windings?
It should be 'no connection' aka infinite resistance if the transformer is disconnected from the circuit.
Are the transformer wires soldered into the circuit board or attached via screw terminal blocks? If via terminals, it would only take a minute to disconnect and test the transformer independent of the circuit board.
No need to guess.
What's the resistance between the two windings?
It should be 'no connection' aka infinite resistance if the transformer is disconnected from the circuit.
Are the transformer wires soldered into the circuit board or attached via screw terminal blocks? If via terminals, it would only take a minute to disconnect and test the transformer independent of the circuit board.
Screw terminals.
I just tested resistance between the windings (red and green) all possible combinations thereof. All infinite resistance.
I actually performed the same test somewhere on some page of this thread, months ago.
I just tested resistance between the yellow (5v rectifier filament winding) and the green (6.3v filament winding).
All combinations of yellow and green measure 0.3-0.4 ohms.
I don't know enough to determine whether that is an issue, but my gut tells me that should be infinite resistance, too.
All combinations of yellow and green measure 0.3-0.4 ohms.
I don't know enough to determine whether that is an issue, but my gut tells me that should be infinite resistance, too.
Last edited:
I know nothing about how this circuit works, so I'd be blindly following that guidance to remove components and then I wouldn't have a clue what the results meant or how to proceed from there. So I would have a board with missing components and be more confused.
As I said early on - any idiot can build this amp, but I am proof that not any idiot can fix it.
I am seriously contemplating pulling the board out and sending it to George for testing - if that offer is still on the table. I've been going in circles on this bloody thing for months.
What really grinds my gears is that the bloody thing worked perfectly for days, so I built it right to begin with.
Last edited:
My gut is telling me that it is a power transformer issue. More specifically, a heat-induced short.
This would explain why the amp powers on normally and the B+ rises normally and levels out normally, and then after another minute or so, when the transformer begins to warm even slightly, bam! expansion triggers a short and current dumps through C3, heating it up and making my dim bulb tester glow brightly.
But I don't know a damned thing about any of this. I am relying solely on intuition.
My question now is; what other problem could cause the exact same normal start-up and then subsequent failure?
This would explain why the amp powers on normally and the B+ rises normally and levels out normally, and then after another minute or so, when the transformer begins to warm even slightly, bam! expansion triggers a short and current dumps through C3, heating it up and making my dim bulb tester glow brightly.
But I don't know a damned thing about any of this. I am relying solely on intuition.
My question now is; what other problem could cause the exact same normal start-up and then subsequent failure?
Last edited:
In a previous post George ask you to lift one end of R4 and retry the bulb tester. This would cutoff B+ from C3 and determine if the problem was coming from elsewhere such as through the 6.3v heater cable. Maybe you already tried this?
I suggested removal of the whole heater elevation circuit as that better isolates the potential problem. Once operating I would then measure ac and dc voltage from the 6.3v heater to ground (on 1000v scale). Should not read any voltage. If you have a voltage then it is coming through your transformer (or less likely though a fault in the board). Do this fast since if you have high voltage on your heaters the tubes will not like it.
Could also just measure resistance of 6.3v heater to ground once C3, R3 and R4 removed (amp off) but will not tell you as much (but is much safer). Should be open circuit.
Not an expert so take the above advice with a grain of salt; although I would not hesitate to test my amp in this way (I have an SSE). And yes your board will be missing a few components for now but hopefully you will have an answer.
I just tested resistance between the yellow (5v rectifier filament winding) and the green (6.3v filament winding).
All combinations of yellow and green measure 0.3-0.4 ohms.
If you can get a reading other than infinity with one meter lead on a green wire, and one meter lead on a yellow wire, then you have found the problem!
These windings MUST be insulated from each other both inside and outside the transformer. Continuity here WILL cause exactly the problem discussed here, an exploded C3, by dumping full B+ onto a low voltage cap.
With the green leads disconnected from the board there should be an infinite resistance between them and ANYTHING else in the amp.
All combinations of yellow and green measure 0.3-0.4 ohms.
If you can get a reading other than infinity with one meter lead on a green wire, and one meter lead on a yellow wire, then you have found the problem!
These windings MUST be insulated from each other both inside and outside the transformer. Continuity here WILL cause exactly the problem discussed here, an exploded C3, by dumping full B+ onto a low voltage cap.
With the green leads disconnected from the board there should be an infinite resistance between them and ANYTHING else in the amp.
Thanks George.
I just double-checked this. To be very specific
- green #1 to yellow #1 = 0.3 ohms
- green #1 to yellow #2 = 0.4 ohms (but then drops to 0.3 ohms eventually)
- green #2 to yellow #1 = 0.3 ohms
- green #2 to yellow #2 = 0.3 ohms
So my power transformer is toast? I guess I need to try to make a warranty claim at this point. This aught to be fun.
Thing is, they will likely just want to send a replacement and I don't think I want another Hammond in my amp.
I just double-checked this. To be very specific
- green #1 to yellow #1 = 0.3 ohms
- green #1 to yellow #2 = 0.4 ohms (but then drops to 0.3 ohms eventually)
- green #2 to yellow #1 = 0.3 ohms
- green #2 to yellow #2 = 0.3 ohms
So my power transformer is toast? I guess I need to try to make a warranty claim at this point. This aught to be fun.
Thing is, they will likely just want to send a replacement and I don't think I want another Hammond in my amp.
Page 19, post #187, I tested this green to yellow continuity based on George's advice. At the time, I reported "infinite resistance".
There are two possibilities; 1) I may have had my multi-meter range set too high and misinterpreted the 0.00 as infinite, or 2) This is a compound problem and I subsequently fried my power transformer during testing.
There are two possibilities; 1) I may have had my multi-meter range set too high and misinterpreted the 0.00 as infinite, or 2) This is a compound problem and I subsequently fried my power transformer during testing.
- Status
- This old topic is closed. If you want to reopen this topic, contact a moderator using the "Report Post" button.