My Ceriatone OTS started blowing mains fuses a couple of weeks back so I brought it home from the rehearsal studio and got it on the bench yesterday.
Rigged up a light bulb limiter as I was running out of fuses (2a slo blow) I've put a 60 w bulb in the line, it glows brightly when I flip the power switch ( I have tried a 100w bulb and being a clear one it started smoking internally so I swapped back, my wife will be furious if I kill one of the 100watters, they are getting difficult to find now!). So I proceeded to disconnect all the primaries to make sure there was nothing wrong with the various amp circuits. I have lifted all the earths to the secondaries too. I am left with the 240v primary, the 0v primary and the earth connection still connected that is all and still the bulb lights up brightly. I have also swapped the 240v primary for the 220v primary , still the same.
I have measured the resistances of the primaries and the 0-240v reads 7R2 and all the others read logically, nothing seems completely shorted. OC from all of them to earth.
I cannot see how this can be anything other than a transformer problem fuses blow within 1 second without the limiter, other than if the Carling mains switch was somehow dumping AC to earth through the body , but that would trip my RCD I would think (it is quite sensitive) .
Comments
"Take these three items, some WD-40, a vise grip, and a roll of duct tape. Any man worth his salt can fix almost any problem with this stuff alone." - Walt Kowalski
"Only two things are infinite - the universe, and human stupidity. And I'm not sure about the universe." - Albert Einstein
Thanks, I couldn't understand why it would pull so much current if it was still reading logically. Nik did suggest 7R2 wasn't far off standard.
"Take these three items, some WD-40, a vise grip, and a roll of duct tape. Any man worth his salt can fix almost any problem with this stuff alone." - Walt Kowalski
"Only two things are infinite - the universe, and human stupidity. And I'm not sure about the universe." - Albert Einstein
"Take these three items, some WD-40, a vise grip, and a roll of duct tape. Any man worth his salt can fix almost any problem with this stuff alone." - Walt Kowalski
"Only two things are infinite - the universe, and human stupidity. And I'm not sure about the universe." - Albert Einstein
http://www.inmadout.com/download/pdf/TA34M50.pdf
https://www.edcorusa.com/xpwr173
My Ceriatone original has a 6v tap rather than a 5v , and the relays are run off this. I'm guessing that the 1v drop won't be significant. Its going through a a dedicated rectifier and a 7812 voltage regulator. A 100v bias tap rather than 60 will just be a resistor swap?
WOndering if there's any mileage in swapping the OT at the same time for something better? Not considering Mercury BTW.
Rift Amplification
Brackley, Northamptonshire
www.riftamps.co.uk
The Edcor option appears to have a German retailer?
https://www.don-audio.com/Edcor-XPWR173-Power-transformer
The acid test for any mains traff regardless of purpose is the primary magnetizing current. This is remarkably constant for all transformers of around 100VA and even larger and smaller ones at 70-80mA iirc. Best way I find to measure mains current is a 1 Ohm 10W in the neutral circuit and clip DVM across that.
This is of course with no secondary loads and mains at 240ish volts. The MC rises very sharply as you exceed about 260V!
OPTs can be checked for a shorted turn by feeding heater volts into the speaker winding. Bit of maths will tell you what the anode to anode voltage SHOULD be, watch pinkies!
By association, if of an experimental bent, you can use a low voltage secondary mains traff as an OPT if it has a 115-115 primary.
Dave.
Still trying to figure out the correct spec. I know the voltages but not the required current draw.
Not an exact spec, 320-0-320 instead of 345-0-345, and no spare filament tap to run the relays. So had to get a 266JB6 filament transformer to run them, Just room to squeeze it in next to the the PT.
Now a question for anyone who might know. I need to create an artificial centre tap for the heater circuit since the PT does not have one. Does anyone know where you can get 100R 1W 1% resistors without paying an arm and a leg in postage. Mouser have them, but under £33 its £12 postage!! I will get some 3W metal film R's at the same time as I might have to adjust the dropping string due to the lower HT, but still not 33 quids worth! Unless anyone has some good ideas for what I might usefully need and buy from Mouser?
"Take these three items, some WD-40, a vise grip, and a roll of duct tape. Any man worth his salt can fix almost any problem with this stuff alone." - Walt Kowalski
"Only two things are infinite - the universe, and human stupidity. And I'm not sure about the universe." - Albert Einstein
"Take these three items, some WD-40, a vise grip, and a roll of duct tape. Any man worth his salt can fix almost any problem with this stuff alone." - Walt Kowalski
"Only two things are infinite - the universe, and human stupidity. And I'm not sure about the universe." - Albert Einstein