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Hum in homemade amp
Hum in homemade amp
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Old 31st December 2017, 05:56 PM   #11
Antanas990112 is offline Antanas990112
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Quote:
Originally Posted by MelB View Post
Sounds like it is about the time it takes for the 6SN7 to warm up. The 300B and GZ37 will warm up right away. Is the 6SN7 somehow involved in biasing the 300B??
Hi,
I removed 6SN7 and left only GZ37 and 300B XLS (V4), but nothing has changed. The same 30-second hum and the mild vibrational sound of two main torroidal transformers which are placed underneath the cover. Both transformers are closely aligned. Maybe they interact there somehow?
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Old 31st December 2017, 06:15 PM   #12
Antanas990112 is offline Antanas990112
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Default Hum in homemade amp

Quote:
Originally Posted by PRR View Post
If it was a naked filament rectifier, the "best" connection is to the center of the filament or filament winding. Should be about 2V less 100/120Hz buzz. But I once goaded someone into measuring this and we could not squint a for-sure difference.

If this is a heater-cathode rectifier, the B+ should come off the cathode pin.

This, either way, is not his warm-up hum.

If a POWER tube's bias supply comes up slower than the B+, there can be a big overload on the power supply until things all come together.

Yes, small resistors to monitor current, or just monitoring for unexpected voltage sag, will give good clues.

EDIT- monitor 300b grid at start-up. I suspect there is a +20V jump as the 6SN7's several caps come to final voltage.
Hi,
I realised recommendation of Jac van de Walle: the 5V heater for the GZ37 alsready seems to have a center tap, you should use it to connect the output to. So where the 200mA fuse is. That gives less ripple at the first capacitor, 4uF in the schematic.
The current through the diode in the center tab of 450V~ are in the first 30 seconds is about 105 mA ( I was expecting to be about 200mA )
I tried to turn on an amplifier without 6SN7, but the same problem persists. After about 30 seconds, the hum grows and then it disappears.
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Old 31st December 2017, 08:25 PM   #13
hpeter is offline hpeter  Slovakia
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buzz at beginning smells like high spike consumption, until everything stabilises..
you can unplug 300b, and listen for magnetic feedback between irons. -it should be dead quiet

i use toroid 12H+1mF, with good results.
you should add some uF foil caps, it clears up the amp sound.
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Old 31st December 2017, 10:08 PM   #14
Antanas990112 is offline Antanas990112
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Default hum in homemade amp

Quote:
Originally Posted by hpeter View Post
buzz at beginning smells like high spike consumption, until everything stabilises..
you can unplug 300b, and listen for magnetic feedback between irons. -it should be dead quiet

i use toroid 12H+1mF, with good results.
you should add some uF foil caps, it clears up the amp sound.
old
Hi,
I would like to have dead silence, but I hear a weak, constant vibration. Such sounds were spread by old, poorly tightened transformers. These new toroidal transformers did not triggered any sound until I inserted them into one cover and put epoxy on them. I will try to turn them on separately. Maybe they somehow interact with each other?
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Old 1st January 2018, 10:49 AM   #15
Antanas990112 is offline Antanas990112
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[QUOTE=Antanas990112;5293874]old
Hi,
It's interesting that when only the 300B is removed, the vibrational sound from the toroidal transformer remains, and it's natural that there is no any hum.
But after removing only the GZ37, there is any noise from the toroidal transformer, but it remains constant hum, even larger than with all the tubes. What causes it if there is no HV ???
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Old 1st January 2018, 03:25 PM   #16
Antanas990112 is offline Antanas990112
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Quote:
Originally Posted by Antanas990112 View Post
When I turn on my amplifier after a few seconds appears an increasing hum and a vibrating sound from the power transformer (there are two main toroidal transformers inside one cover). After 20-30 seconds everything disappears and the amplifier works normally without any extraneous sounds. Those first 30 seconds make me feel bad. Where to look for a problem?
Kindly Antanas
Attachment 653787

Attachment 653791

Attachment 653792

Attachment 653794
I do not understand what's going on: under one cover there are two Amplimo 7N1476 transformers. They are somehow self-guiding with each other. If I connect ~ 220V to only one of them I get standard voltages in secondary windings (450V-0-450V), but also I get voltages in non-connected transformers' secondary winding (about 300V-0-500V. ??? Why???). I also found a sufficiently high voltage between the midpoint of connected transformer and the secondary terminals of disconnected transformer.
If I connecting their primary windings in parallel, in secondary windings of both transformers I get more or less the correct voltages, but also unwanted sounds mentioned above for the first 30 seconds.
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Old 2nd January 2018, 04:29 PM   #17
soulmerchant is offline soulmerchant  Switzerland
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Hi Antanas

Maybe those two Amplimio transformers are back-to-back. Its hard to tell without knowing all the details. Is it safe to assume that you did not actually build it yourself?

If you did not build it, then I would advise contacting the original builder. If this is not possible, I think the only thing to do is trace the schematic yourself by scratch...

BTW, looking at the schematic, as well as EML 300B plate curves the quoted voltages and millamps don't seem to make sense to me...

Ian
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Old 2nd January 2018, 07:55 PM   #18
Antanas990112 is offline Antanas990112
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Hi,
Unfortunately, it was my mistake. It's me put them into the cover with epoxy resin. Now it's a desperate thing to distinguish them. I did not think that they could interact with each other in this way. Maybe I needed to separate them with a metal plate ??? it's too late now. I see only one way - it's replace them with new ones (400 Eur ��) and how to avoid a similar destiny....in the future??
Kindly, Antanas
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Old 2nd January 2018, 11:21 PM   #19
soulmerchant is offline soulmerchant  Switzerland
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Dear Antanas,

Maybe it is possible to cut through the epoxy? Sorry I can't help you more.

Even with a Mu-Metal shield, it is not a good idea to closely stack torroidal transformers...
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