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Creamman

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Jun 17, 2019
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Hi Rock Soderstrom,

you wanted to know which power supply I am using: Hammond 370EX.

I use the 5AR4 tube in the power supply which is mounted outside the housing, just like the Hammond.

Looking for grounding problems I noticed that the B + somehow collapses as soon as the power supply is loaded, which ultimately results in a loss of 50V, so that B + is only 233V?

While looking for my mistake I noticed that I installed LM317T.
LM317HV would be correct according to the circuit diagram.

I ordered some and hope they fix my 100 Hz hum.

Thank you for your help, I get back as soon as the new voltage regulator is soldered.
 

Creamman

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Jun 17, 2019
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So..... I installed the new voltage regulator. Checked all groundings again, all soldering points and all components.

Unfortunately none of this helped !!!!
I noticed that the hum only appears after the heating process is completed. I also noticed that this humming can be heard without a loudspeaker, directly from the electronics ...
But so far I could not hear from which component it comes from. ?? But it is most noticeable near the power supply board.
 

scott2000

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So..... I installed the new voltage regulator. Checked all groundings again, all soldering points and all components.

Unfortunately none of this helped !!!!
I noticed that the hum only appears after the heating process is completed. I also noticed that this humming can be heard without a loudspeaker, directly from the electronics ...
But so far I could not hear from which component it comes from. ?? But it is most noticeable near the power supply board.
Can't recall the frequency of the noise addressed but this thread went in to some rabbit holes. Maybe you can get some more ideas from there??. His final solution is mentioned in the last post.

 

rock soderstrom

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I also noticed that this humming can be heard without a loudspeaker, directly from the electronics ...
But so far I could not hear from which component it comes from. ?? But it is most noticeable near the power supply board.
If you can hear the buzz without speakers, it is probably mechanical hum. Most of the time it is the mains transformer that starts humming. However, other components can also cause it.

Let's start with the power transformer. Can you feel the vibrations of the transformer with your hand? If yes, the hum can have several reasons. Which transformer do you use?(Its a Hammond 370EX). Is it sufficiently dimensioned? Some transformers tend to hum at high load or overload. Some just do it for no obvious reason...What happens when you mechanically disconnect the transformer from the case? Do you have another transformer to test?

As scott mentioned above, here is a user with a similar problem and his solution.


If it's not the transformer, try to locate the source of the vibration. Are you using a choke? Check if it vibrates. Have you changed the rectifier tube? Are all capacitors polarized correctly? Note the errata in the documentation.
The Drip PSU board gives the possibility to use diodes instead of tube rectifiers. You have to choose one, either tube or diodes, not both at the same time.
 
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rock soderstrom

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I took a look at the data sheet of the Hammond 370EX. It can deliver 4 amps at 6.3 volts AC. Your LA2A needs about 3,3A of heating current (the 5V/ 3A in AC for the rectifier tube will be added), in DC(!) for the Drip Opto 7. From my point of view the power transformer is overloaded.

The Valvewizard writes the following about it:

"Another important thing to be aware of is that rectifying AC to DC in this way introduces a power-factor loss of about 0.5, which loads down the transformer more. In other words, to supply a heater with 300mA of DC the transformer actually has to deliver about 600mA of AC, So be careful not to overload the transformer."

Can you still touch the power transformer after a while?
What happens if you unplug V3 and V4 on both channels to relieve the heating winding. Less buzz?

 

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Creamman

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The humming comes from the power supply. It's not getting warm at all.
I swapped the rectifier tube for the diodes. No success.
I disconnected the entire secondary side of the 370 Ex. Transformer still hums.
I reconnected everything, disconnected the Travo from the case, removed V3 and V4 from the motherboard and switched it on. Now the transformer literally began to dance, with a very loud mechanical hum. I don't use a choke, just a resistor.

I will now start to search for a new Transformer.
 

rock soderstrom

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I disconnected the entire secondary side of the 370 Ex. Transformer still hums.

If the transformer is humming without any load, there are only two possibilities:

1. the primary wiring is wrong. How is the transformer connected at the moment?

2. the transformer is defective.
 

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