Measuring the hum applied to the heaters is more complex.
The reason is that it can be applied in 2 ways:
1) Common mode: That's where the same signal is applied to both terminals.
Measure between either terminal and ground.
2) [I can't think of the term
]Non common mode : Where the signal is applied across the heater terminals. Measure across the terminals.
The reason is that it can be applied in 2 ways:
1) Common mode: That's where the same signal is applied to both terminals.
Measure between either terminal and ground.
2) [I can't think of the term
]Non common mode : Where the signal is applied across the heater terminals. Measure across the terminals.Shorting the grid doesn't seem to make much difference: about one mV less.
I tried both methods of measuring AC on the heaters before: Measuring across the heater terminals gave 170 mV and between plus and chassis ground gave 85 mV in stand by mode.
I used star grounding with separate stars (not connected to chassis) for the different stages.
I tried both methods of measuring AC on the heaters before: Measuring across the heater terminals gave 170 mV and between plus and chassis ground gave 85 mV in stand by mode.
I used star grounding with separate stars (not connected to chassis) for the different stages.
Next trick
Let's try to eliminate the heaters from suspicion:
Fit a switch in (or get ready to cut the wire of) one of the 300b's heater windings on the transformer.
Once the amp is running, break the circuit, and listen (in the 1-2 seconds it continues to run) to check whether the hum stops.
85mV of common mode signal would be of the right order to be your problem. However the judgement is clouded by possible measurement inaccuracies and my ignorance of your amp's construction.
Please try my suggestion in the first paragraph anyway.
If you can switch both wires, it would be better.
The measurements in standby are not useful.
Let's try to eliminate the heaters from suspicion:
Fit a switch in (or get ready to cut the wire of) one of the 300b's heater windings on the transformer.
Once the amp is running, break the circuit, and listen (in the 1-2 seconds it continues to run) to check whether the hum stops.
85mV of common mode signal would be of the right order to be your problem. However the judgement is clouded by possible measurement inaccuracies and my ignorance of your amp's construction.
Please try my suggestion in the first paragraph anyway.
If you can switch both wires, it would be better.
The measurements in standby are not useful.
Heater as the source of the problem is eliminated. You are right, it should have stopped at the instance of the cut.
With the 0.33 uF still disconnected, try pulling the AZ1 out.
If you have a 5U4 or 5R4 around, try it instead of the 83.
If this doesn't help then there is not much more than the wiring left. Try moving around wires carrying AC.
With the 0.33 uF still disconnected, try pulling the AZ1 out.
If you have a 5U4 or 5R4 around, try it instead of the 83.
If this doesn't help then there is not much more than the wiring left. Try moving around wires carrying AC.
Unless the cap is a superconductor, I think there will be a (small) AC voltageOriginally posted by Jax
And I respectfully agree and disagree at the same time
The capacitor is shorting the AC component to ground which it is supposed to do.
But 92V on a 100V capacitor is way too close to my liking. I want 20-25% headroom. A 160V should do.
But I agree 160V is fine - but in the caps I normally use the next step from 100V is 200V, so that's the voltage I use...
Best regards,
Mikkel C. Simonsen
All Right, I did some experimenting with the OPT.
What I noticed was, when my hands come near the amp, the hum level rises, which is as expected. However, when I put my hands on the casing of the OPT the hum level drops to 3 mV. I then lifted the OPT out of the chassis and rotated the thing 90 degrees in both directions. No difference in hum level though.
Martin
What I noticed was, when my hands come near the amp, the hum level rises, which is as expected. However, when I put my hands on the casing of the OPT the hum level drops to 3 mV. I then lifted the OPT out of the chassis and rotated the thing 90 degrees in both directions. No difference in hum level though.
Martin
Hi John,
No, the amp is not earthed. That would mean listening to music in the kitchen which is the only place in my house that has earthed outlets. The amp is made of a wooden frame and a chromed copper plate. see picture. pretty crowded in there as you can see.
Martin
No, the amp is not earthed. That would mean listening to music in the kitchen which is the only place in my house that has earthed outlets. The amp is made of a wooden frame and a chromed copper plate. see picture. pretty crowded in there as you can see.
Martin
Attachments
Martin,
Very pretty, I must say! All those AE chokes and transformers too
Are all metal cases grounded? Check each in turn with a test lead.
Please do try it with an earth temporarily. If it makes a difference, you might try swapping the live and neutral connections to the mains transformer.
I'm a bit stumped at the moment (tiredness doesn't help). I'll sleep on it, and I'll post some thoughts tomorrow.
Very pretty, I must say! All those AE chokes and transformers too
Where are your hands going near? If it's the chassis, I would hope no change.
Are all metal cases grounded? Check each in turn with a test lead.
Please do try it with an earth temporarily. If it makes a difference, you might try swapping the live and neutral connections to the mains transformer.
I'm a bit stumped at the moment (tiredness doesn't help). I'll sleep on it, and I'll post some thoughts tomorrow.
A fresh start
I have removed all posts that are not relevant to solving the hum problem and moved them to texas. Some contained recrimination and baiting. Hopefully others will now post to this thread.
Since I have posted as a member as well as moderator, please contact another moderator if you feel my action is other than ethical
I have removed all posts that are not relevant to solving the hum problem and moved them to texas. Some contained recrimination and baiting. Hopefully others will now post to this thread.
Since I have posted as a member as well as moderator, please contact another moderator if you feel my action is other than ethical
Yes, I know, he is a great guy but I have pestered him so much in the past that I thought I'd try the forum. However, things are looking up. I made like a construction worker today and rewired my living room, including earth, of course. The result : 2,4 mV. I still think it could be less, though.
I found the source of the distorted hum in the other monobloc : 10 V DC on the 300B heater ! I still haven't figured out what causes it though.
I first thought one of the 10000 uF caps had died, but they seem to be ok, as far as I can measure them ( connect to an ohmmeter and see if the resistance rises to infinite, probably not the most reliable method) The trannie delivers a nice 5,3 V to the schottkies.
I found the source of the distorted hum in the other monobloc : 10 V DC on the 300B heater ! I still haven't figured out what causes it though.
I first thought one of the 10000 uF caps had died, but they seem to be ok, as far as I can measure them ( connect to an ohmmeter and see if the resistance rises to infinite, probably not the most reliable method) The trannie delivers a nice 5,3 V to the schottkies.
Martin,
Hey, well done with the earth system You are right, the hum could be lower. Please check that all the component cases are connected to ground, as I mentioned previously.
You should be able to find the difference between the monoblocks by A/B comparison with a meter. Look especially for wiring and component marking differences.
Is the 5.3v on-load, or off-load?
If the 10v on the heaters is real you should have noticed the valve glow very bright! It will suffer damage after a short period
Hey, well done with the earth system
You are right, the hum could be lower. Please check that all the component cases are connected to ground, as I mentioned previously.You should be able to find the difference between the monoblocks by A/B comparison with a meter. Look especially for wiring and component marking differences.
Is the 5.3v on-load, or off-load?
If the 10v on the heaters is real you should have noticed the valve glow very bright! It will suffer damage after a short period
Hi John,
Excuse my ignorance, I don't know what you mean. Do you mean with a tube in the socket, as a load ? In that case no. But I did run it for a minute with the tube before I found out. I hope by god that the KR300BXLS hasn't suffered. Especially since they almost doubled the prices. So I can't really compare the two monoblocs untill I find out what causes the high voltage.
I've checked the trannie casings but they are all connected to earth. My powertrannie is isolated from the chassis by rubber grommets, but it has two shields which are both earthed.
Excuse my ignorance, I don't know what you mean. Do you mean with a tube in the socket, as a load ? In that case no. But I did run it for a minute with the tube before I found out. I hope by god that the KR300BXLS hasn't suffered. Especially since they almost doubled the prices. So I can't really compare the two monoblocs untill I find out what causes the high voltage.
I've checked the trannie casings but they are all connected to earth. My powertrannie is isolated from the chassis by rubber grommets, but it has two shields which are both earthed.
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