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Old 10th September 2008, 06:30 PM   #11
kevinkr is offline kevinkr  United States
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Quote:
Originally posted by milen007


Hi whitelabrat
sorry for newbie question, just a quick search but cant find the spec for 6AL5. mind sharing how it can do the job you suggested? thx in adv

6AL5 is only good for a few mA.

With 5AR4 or any other high current rectifier you will see no more than a couple of volts with your proposed load. You could get perhaps a 60 - 80vct transformer and use a 5AR4 might get you close to the voltage you need. (Final trim with the dcr of the choke) At these voltages that is a very rough estimate and could vary a lot from tube to tube and as a function of load current.
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Old 10th September 2008, 06:39 PM   #12
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kevin, can i parallel 2 of the 5ar4 to double it current? 250mAx2? is this workable? thx
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Old 11th September 2008, 08:36 AM   #13
sarrisk is offline sarrisk  Greece
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Quote:
Originally posted by kevinkr



You're not planning on using the 5AR4 to rectify 18V are you? Tube rectifiers are not a suitable choice for very low voltage high current supplies used in most solid state designs although I have heard of a few people attempting to do this with varying degrees of success.

Tube rectifiers all have much higher voltage drops at a given current than a solid state rectifier and generally much lower peak current and continuous current ratings as well. A 5AR4 has a maximum current rating of around 250mA and will drop at least 20V - 25V at this current level.

Hopefully I have misunderstood you.

Thats correct,
generally not suggested for this type of application. As I mentioned above, that it is a little bit different, i thought about EZ81 (6ca4). I draw 2 different cases and I think the second one is more suitable for you. see the attachment

note that for the first case choke=10H/200mA

regards
costas

PS sorry for the delay I was out of office yesterday
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File Type: jpg tube-psu-20v.jpg (34.4 KB, 434 views)
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Old 11th September 2008, 10:57 AM   #14
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Hi sarrisk

thanks alot for doing that. i got few questions,

can i dont use the 7824? as the application do not need to be regulated. or is it use to protect the tube rectifier?

i assume both application use the same tube right?

from duncan psud II, ISFM 1.8A and IFRM 0.5A. which one is the current rating?

sorry about these newbie questions. learning as much as i can.

for my application, i think the 1st setup will do the job. as i only need 150mA. how much voltage will be drop with that small current?

from psud II, EZ81 gives out the same DC voltage as the AC voltage in.

please correct me if im wrong. thx in adv
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Old 11th September 2008, 11:17 AM   #15
sarrisk is offline sarrisk  Greece
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Its ok to use the first schematic. I think you are going to take about 20Volts output.
I dont know about duncan psud II - post the link to take a look.
For the second schematic 7824 is for the initial regulation and EZ81 is for extra regulation (no interference at all because of the valve). I thought about this because you are going to power your dac.

cheers
costas

P.S.
1. Yes both apps use the same tube
2.These are only schematics. I didn't test them to give you the exactly voltage and current.
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Old 11th September 2008, 01:24 PM   #16
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hi sarrisk

Duncan's psu design at www.duncanamps.com/psud2/index.html

This program quite handy as it can simulate the output

What's the max current EZ81 can pass through? Some state 150mA. Some 250mA. Should I parallel the tube?
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Old 11th September 2008, 01:58 PM   #17
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k starting to get it.
I assume 5ar4 is to rectify high voltage which is why not suitable for 18v
PLs correct me if I'm wrong

Can someone suggest low voltage tube rec with higher current?
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Old 11th September 2008, 05:49 PM   #18
kevinkr is offline kevinkr  United States
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Quote:
Originally posted by milen007
k starting to get it.
I assume 5ar4 is to rectify high voltage which is why not suitable for 18v
PLs correct me if I'm wrong

Can someone suggest low voltage tube rec with higher current?

Tungar bulbs, but they are no longer made. High vacuum rectifiers are not designed for very low voltage operation at high currents.
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Old 11th September 2008, 06:17 PM   #19
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2x 6CM3 might get you close.... but, solid state diodes are the best bet for this app. Something as cheap as 1N4002 would do. pennies...

edit: with 6CD3 in psudii, a 36VCT tranny will only get you ~10VDC at 150mA load.... 'taint gonna cut it
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Old 11th September 2008, 11:37 PM   #20
JC951t is offline JC951t  Taiwan
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I once did a zen pre using parallel 6X4 but that was
at about 90 V. There was a diy dac article using a 6X4
rectifier with a drop resistor to power the 3 terminal
regulators.
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