Have you tried the transformer completely unloaded with basically no current draw?
Every amp I own has a noisy transformer, be it toroidal or EI. I think the mains in my house is poor so I’ve put my name down on a group buy here for a couple of DC filter PCBs. (Does the same job as Eli’s schematic above)
Every amp I own has a noisy transformer, be it toroidal or EI. I think the mains in my house is poor so I’ve put my name down on a group buy here for a couple of DC filter PCBs. (Does the same job as Eli’s schematic above)
What happens when mounting bolts unintended connect laminations? There would be a short in the eddy currents and the iron magnetic field changes too.
It can - and yet has - been shown that the flux densitiy next to the corners of rectangular cores is negligible. Hence the question of isolating the mounting screws or not is of minor importance.
Best regards!
Best regards!
eddy currents are but a small percentage of the hysteresis loses....so here the quality of the core materials matter a lot, M6/z11 are best to use for OPT...for Power rm18,m24 seems okey...for low cost traffos, H50/m58 are commonly used..
power traffo losses increases with weight as suppliers of cores give them at watts lost per kg of core..
power traffo losses increases with weight as suppliers of cores give them at watts lost per kg of core..
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diynewb83, may i ask what your ambient temperature is? a 43*C temperature rise seems not so bad if your ambient is at 30*C like here in Manila.....
Ambient is room temp, around 21ºC.
Unfortunately, I only have a couple of free hours a week to play with this. My current readings are calculated from the voltage drops across the decoupling resistors in the PSU, plus the unbypassed resistors on the KT88 cathodes. In the next couple days I'm going to have to start desoldering some parts and getting more accurate current readings, starting way back at the coil. Hopefully something will pop up.
I also forgot to mention another missing part of the schematic, the heater secondary has an artificial center tap to ground using two 100ohms, but this should only add about 32mA to the load.
Interesting. I don't have any dimmers on that particular circuit. I'm struggling to think of what else may have an SCR in it.
It never had occurred to me that there may be DC on the line. My substation is only about 500m down the road from me. What would potential sources for it be? What's a good way to measure it? The only way I can think of is zero'ing out my scope with DC coupling and seeing if the wave is riding on something.
I built a lowpass RC using a 10uF and 200k and plugged it in. Over time it fluctuated between 5mV-9mV. With a DCR of ~1.36 ohms on the primary, it is unlikely that this is the problem, although this was a good thing to check!
Lol all these exotic solutions. In reality the transformer could use some more varnish or shellac or epoxy or whatever they coat the windings with now.
Once I definitively prove that I'm not on the path to something failing here, my favorite exotic solution (and likely what I'll do) is jamming a popsicle stick in the core lol
In reality were talking about a real cheap unit, designed to the max. output for maximum profit for this company. Today those transformers are being made in asia, because its even more cheap. Buy something better designed, with better core lamms and bigger core which doesn't work on the edge of its data, something individual, coated with more varnish and the problem dissappears. If you buy cheap, problems occur.
This started me thinking. How would you even have a dc component along with the ac? It would have to show up as an offset.
Most led lights have a half wave rectifier in them. This is usually creates noise on the power line. IF you are on the same circuit with a bunch of LED lights lots of NOISE!
From what I've read around, it's not really a DC offset, more of a wave imbalance caused by half-wave rectified devices in your house(I guess things like hair dryers, laser printers, LEDs, etc. can do that, although I'm not privy as to exactly why[LEDs are obvious]).
One side of the sine gets loaded down more than the other, and this manifests itself as a DC offset.
22ºC temperature rise, that is not so bad, some transformer insulations are rated for 100ºC temp rise...the nylon bobbins and even paper ones can take that heat without melting or burning...
here is the thing, hold the hot traffo with both hands and count the seconds that you can withstand the heat...that will tell you how really hot the thing is...
give us a load schedule of your power amp, meaning total filament power in watts and plate power in watts, add the two to get the total wattage load of the power traffo...
then give us the spec or model number of your power traffo....
we need to be able to compare the two to make informed opinions, as it stands now, all comments are mere speculations..
then give us the spec or model number of your power traffo....
we need to be able to compare the two to make informed opinions, as it stands now, all comments are mere speculations..
Since all the tubes are cathode biased and I haven't had time to unsolder anything yet, I've basically calculated much of this. To give an example, I measured 400V between the plate and cathode of the KT88. Then I measured 24V across the un-bypassed cathode resistor(500 ohms) to get 48mA, assuming cathode current and plate current are roughly the same. 400V*48mA = 19.2W. Let me know if this methodology is flawed.
The 12AU7 is coming out to 874mW. The 12AX7 is coming out to 235mW.
This is stereo so everything * 2. At idle the total plate power is coming out to roughly 41W.
For the heaters, for the 4 tubes and the artificial center tap to ground, I'm coming up with just short of 4.5A, so about 28W rounding up.
The 5V is unused, as I am using diodes for rectification.
My transformer is the 274BX. I'll link the spec list here in case I'm reading something incorrectly:
https://www.hammfg.com/electronics/transformers/classic/200.pdf
VA = 198
Secondary = 750V C.T. @ 201mA
Filament 6.3V @ 6A
so by the looks of it, yours is a mechanical problem, to be solved by mechanical methods..
notice that single ended tube amps are Class A and power is constant whether playing music or simply turned on...
70w/198va is a mere, 35% utilization, but with all things tube single ended, they try to overbuild things and for the simple reason of heat....
you can even get a power traffo 6*70 or 420 watts and that would have been valid.....
i am not saying you should, but i mean you could if you have deeper wallets...
notice that single ended tube amps are Class A and power is constant whether playing music or simply turned on...
70w/198va is a mere, 35% utilization, but with all things tube single ended, they try to overbuild things and for the simple reason of heat....
you can even get a power traffo 6*70 or 420 watts and that would have been valid.....
i am not saying you should, but i mean you could if you have deeper wallets...