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Old 17th June 2009, 10:22 PM   #1
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Default no choke and transformers ratings

Hello there,
If one removes the choke from the power supply(for a resistor instead), do the mains transformer ratings need to have at least "full swing" current capability (i mean when Vg=0 for all tubes on maximum modulation)
in my case
2x2A3@2,5k >> 200-230 mA
2x6SL7@100k >> about 5-6 mA only
My mains is rated 200mA... will removing choke cause stress to it ?

The sound i have is almost perfect on gentle playing (timbre, speed, depth, musicality, very strong dynamics...the real thing between my speakers) but UNBEARABLE on peaks
I was on 6SN7+2A3 before, so far from full swing and no stress but musically frustrating. Going finally back to 6SL7 was a therorical non-sense but a perfect musical match, whatever the 5 i have i use, BUT the peaking stress.

Thanks in advance
eric
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Old 17th June 2009, 11:12 PM   #2
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i just tried to put the choke back (my amp has only screw connectors inside )...
The sound just went flat, gray, ...loosing all the magic i had achieved.
Or is it the choke that is wrong : hammond 193g 10H 150mA ?
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Old 18th June 2009, 02:43 PM   #3
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Can you post a schematic?
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Old 18th June 2009, 02:51 PM   #4
kheper is offline kheper  United States
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You should take voltage measurements of the B+ with and without the choke. 102 DCR for the 193g is high but not high enough to choke out all of the loveliness of triodes.
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Old 18th June 2009, 05:11 PM   #5
ChrisA is offline ChrisA  United States
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Default Re: no choke and transformers ratings

Quote:
Originally posted by mahleriana
[B]Hello there,
If one removes the choke from the power supply(for a resistor instead), do the mains transformer ratings need to have at least "full swing" current capability (i mean when Vg=0 for all tubes on maximum modulation)]
I think when you swap a resistor for a choke, [I}to get the same level of filtering[/I] the resistance of the resistor would need to be a lot more than the DC resistance of the choke. The effect of this is that you can get more power out through the transformer by using a choke. But the answer to your question depends on the exact values of the parts used. You have to look at the impedance of the whole filter network, not of the parts. The real reason chokes are used is because an engineer figured he could get more milliwats per dollar because the cost of the choke was offset by saving in the PT and filter cap. With lower voltage supplies the economics is reversed. No magic in chokes, just economics.

I think you can abuse the design a little and not design for the peaks at full volume. I think this is what gives tubes their "sound" -- when pushed they distort but in a "musical way" that sounds good. On the other hand solid state amps must never, ever clip. It depends on your goals. Is this an audiophile class amp where the goal is for the owner to "feel good" about the parts inside or a guitar amp where distortion is a design goal? Or do you just want to play music?
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Old 18th June 2009, 08:35 PM   #6
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Here is my schematics

I designed it only for Hifi, not for guitar.
When swapping from choke to resistor, B+ follows quite normally, no hints of weird things.

The noname CC plate resistor create a little stress i guess (steel end caps) but though i have bought a whole bunch of kiwame, mills, holco, allen bradley, etc, it is the only 100k i have right know (new resistors order in process)

I changed my 2.5k OPT to 5k (hammond again), the stress was hugely reduced.
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Old 18th June 2009, 08:38 PM   #7
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to be complete, going 2.5k to 5k, the stress was hugely reduced, but musicality was affected negatively (less punch, leaner tone)
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