Most DVMs won't read AC on top of a DC source, they give an AC reading that may be misleading.
The best way, I find, is to measure for ripple on a DC supply with an oscilloscope. Use a high voltage X100 probe if reading more than 100volts.
The best way, I find, is to measure for ripple on a DC supply with an oscilloscope. Use a high voltage X100 probe if reading more than 100volts.
First thing to check would be the 47uF power supply capacitor, also the 220uF following.
Is this a new build, or has the hum recently started?
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WHAT is B+ value?
15V ripple can go from horrendous to insignificant relative to V+ ... which you don´t even hint at. 🙂
15V ripple can go from horrendous to insignificant relative to V+ ... which you don´t even hint at. 🙂
I ended up rewiring the amp because I thought the hum might be heater related being it's 60hz but it didn't help anything.
280v it would be higher but I am using a transformer that steps my voltage down to 105v. It has a 110v power supply in the amp. I'm waiting on the bucking transformer to deal with that.
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This 120Hz ripple may be about normal on the input capacitor, but it should be gone after the following LC filter.
If the ripple on the 47uF is only 60Hz, one of the rectifiers could be bad or have a poor connection. In this case,
the B+ would usually be much lower than normal.
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I think the B+ is fine. The amp sounds very good other than the hum. if it was 120hz I'd suspect that but it's definitely 60hz. The hum is quite low if it's hooked up to 87db speakers but on my cornwalls....
If the hum is really 60Hz, it could be magnetic coupling from the power transformer.
Also the 120VAC power switch and wiring is close to one of the output transformers.
Is the hum stronger in one channel than the other?
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I hope not. I'm hoping it's the heaters going to the 2a3 being it's direct heated. I was thinking it's in the output tubes because it doesn't change with volume. I'm going to rectify one side and see what that does. Just waiting on some parts.
The same in both speakers. I have new tubes on the way. Best to eliminate that first. These are cheap tubes.
Oh I see what your saying. That's the choke under the power switch, the outputs are in the back on the other side of the can cap.
Thanks.
Doesn´t look like much, it´s only 5% ripple, and that at a high consumption rate (Class A amp), besides "Single ended amps Hum" because there is not self canceling as in a PP amp.
So not "bad"|(aas in nothing broken) but of course you may try to lower that even further.
Doesn´t look like much, it´s only 5% ripple, and that at a high consumption rate (Class A amp), besides "Single ended amps Hum" because there is not self canceling as in a PP amp.
So not "bad"|(aas in nothing broken) but of course you may try to lower that even further.