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Old 20th August 2013, 02:52 PM   #3221
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I have a lot of hum today...)
I measured the Rods reg Raw AC ripple is around 20-40mV,
the filament has less then 0.01mV AC ripple. I assume this is not the source of hum.
When I put my hand on one of the caps for raw filament filtering the hum changes but its not less, also when I touch the heatsinks the hum changes a bit..
Now to my B+, I am using the RGN504 followed 0.5uF + 50H choke + 5uF + 50H choke + 10uF. The AC ripple at the end of B+ is 20mV. I guess this could be the source of hum.
The psu togeter whit raw filament is on one board and the amp is separate board,
around 30-50cm from it...
Had some one similar problems?

The 26 is also very sensitive to touch, very microphonic!!!
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Old 20th August 2013, 03:03 PM   #3222
iko is offline iko  Canada
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Check your grounding scheme. Show a schematic, showing your actual connections.
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Old 20th August 2013, 03:30 PM   #3223
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Quote:
Originally Posted by DIYspaceW View Post
I have a lot of hum today...)
I measured the Rods reg Raw AC ripple is around 20-40mV,
the filament has less then 0.01mV AC ripple. I assume this is not the source of hum.
When I put my hand on one of the caps for raw filament filtering the hum changes but its not less, also when I touch the heatsinks the hum changes a bit..
Now to my B+, I am using the RGN504 followed 0.5uF + 50H choke + 5uF + 50H choke + 10uF. The AC ripple at the end of B+ is 20mV. I guess this could be the source of hum.
The psu togeter whit raw filament is on one board and the amp is separate board,
around 30-50cm from it...
Had some one similar problems?

The 26 is also very sensitive to touch, very microphonic!!!
no the 26 is very silent with good DC regulator like the coleman ( i had a 102DB speaker) but you probably need more cap filter i also had a separate CLCLC filter on mine but the last two C are 30uf and 60uf MKP .
i'm sure it will helps
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Old 20th August 2013, 05:32 PM   #3224
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I see...Will have to draw the schematic down to paper...
Primary I assume it needs to be some sort of ground loop...

I used star ground...All the connections are made to one point...
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Old 23rd August 2013, 01:06 AM   #3225
tcqanh is offline tcqanh  Viet Nam
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Quote:
Originally Posted by Rod Coleman View Post
Hi - Please use the circuit shown in the PDF document ANdht01.

The problem here: the rectifier and capacitors must not be grounded at any point - this will cause the cathode-bias to be (near) zero.

The correct circuit is shown in the PDF.

If you like, you can add extra chokes (CMC and differential), but please check that the total dc resistance adds up to about the same as the examples in the PDFs.

You can add extra high frequency caps, to try them out.
Hi Rod,

I have few filament boards for previous plan of pre-tube phono many years ago. This is Salas' design. I intend to use them for DHT and connect 2 tubes 26 in series like DHTrob's way.

D17 will be non using.

How do you think about this ?
Attached Images
File Type: png Filament circuit for DHT- Draft version.PNG (22.2 KB, 469 views)

Last edited by tcqanh; 23rd August 2013 at 01:10 AM.
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Old 23rd August 2013, 08:49 AM   #3226
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There are all kinds of filament regs that work, that's not a problem. But Rod's is a step up because it's been carefully designed through several iterations to be a level higher than "just working". It depends how important you think the filaments are. If you're using filament bias, you would probably take the view that they are critically important. If not, it's up to you really. Rod has put down the marker.
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Old 23rd August 2013, 10:38 AM   #3227
dhtrob is offline dhtrob  Netherlands
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Quote:
I have few filament boards for previous plan of pre-tube phono many years ago. This is Salas' design. I intend to use them for DHT and connect 2 tubes 26 in series like DHTrob's way.
Not being Rod, I would like to mention that if you are using one filament voltage for both '26's in series, center connected to ground, this design will be quiet enough.. Using Rod's filament supply will result in better performance though..
If using filament bias, this design will be noisy (hissing noise from speakers).
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Old 24th August 2013, 08:20 AM   #3228
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Quote:
Originally Posted by tcqanh View Post
Hi Rod,

I have few filament boards for previous plan of pre-tube phono many years ago. This is Salas' design. I intend to use them for DHT and connect 2 tubes 26 in series like DHTrob's way.

D17 will be non using.

How do you think about this ?
Hi, I think the earlier one you posted with current-control - will be easier to make point-to-point, and current control will be better,.

But watch out for noise [and degraded sound from intermodulated noise, etc]
as Andy and Rob mention.
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Old 28th September 2013, 11:10 AM   #3229
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I replaced the AZ1 but was faulty/broken because B+ only arrived to 85V aprox. I used the old AZ1 and now I have B+ OK but filament heaters measures 1,130V & 1,340V aprox. the issue is that I don't have sound in both channels, I use the attached schematic, TIA for help.
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Old 28th September 2013, 11:22 AM   #3230
dhtrob is offline dhtrob  Netherlands
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Hi Merlin,

Schematic looks okay. Even at 1.2V the 26 should be alive.
I take it that al other voltages measure as in de schematic? (Voltage cathode, 5 volt drop over the Lundahl? 0D3 are lit?)
If so: Did you wire the Lundahl correctly?
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