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Old 31st October 2007, 06:02 AM   #11
pchw is offline pchw  United States
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Hi Ron,

What kind of tube do you plan to use? You have the current set to 25ma which doesn't sound right. Since you are looking at 12.6V heaters, you probably have something like 12SN7 or 12A?7 or series/parallel connect of 6.3 tubes such as 6CG7 or 6922. Just one of these tube will draw much more than 25ma, and you need to multiply that by 4!!! Try 4700uF - 2ohm - 4700uF to see you can get close to 12-12.6V.
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Old 31st October 2007, 07:11 AM   #12
Stixx is offline Stixx  Germany
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Ron,

you're indeed way off with your heater schematic. Current draw for the heaters can be taken from the datasheets, but is usually in tenths of an ampere...like 0.3A or something.
Filtering caps have to be much larger since you are dealing with lower voltages (for the heaters).
So something along the lines in the pic attched should come closer...this is for two C3G tubes for my headamp, and actual values are very close!

good luck!
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Old 31st October 2007, 04:45 PM   #13
Renron is offline Renron  United States
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PCHW & STIXX,
Thank you both for your help and patience in teaching me!
Now that you both have pointed out where I was wrong it is easy to see. Such is the beauty of hindsite.
The Valve I will be using is ECC802s / 12au7. Heater currnet is 150mA @ 12.6V or 300mA @ 6.3V.
My Transformer puts out 5A @6.3 so current suppply is not a problem.
Modeling 150mA in PSUDII using STIXX schematic as a reference point (thank you) I compiled this circuit
Note: I did not take voltage drop across the Bridge into account, I'll measure it later and adjust resistor values as needed.

PSUDII is a little confusing because it states values of capacitors as mF------milli Farads, capacitor labels use the (m) to mean micro Farads. 18,000uF = 18mF in PSUDII, but looking to purchase a suitable capacitor 18mF = 18uF. This has confused me more than once.

Question: Because the heater PS capacitor is floated with 1/4 B+ Voltage but referenced to itself @~12.6V, what is the recommended voltage range?
20V? (12.6V +10% for safety) or
80V? (1/4B+ (+) 12.6V + 10% for safety)
I'm guessing 80V or 100V capacitor rating.


Thanks guys! I really appreciate the help
Ron
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File Type: jpg heater ps.jpg (91.3 KB, 235 views)
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Old 31st October 2007, 07:31 PM   #14
Stixx is offline Stixx  Germany
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Ron,

I'm no expert either but have modelled dozens in PSUDII and actually built two psu's with good results.

Quote:
My Transformer puts out 5A @6.3 so current suppply is not a problem
Don't you have other secondary taps on your transformer? With 5A you can include a tube rectifier...

Quote:
Note: I did not take voltage drop across the Bridge into account, I'll measure it later and adjust resistor values as needed.
I think voltage drop across a bridge rectfier is neglectable...the more important factor here is the resistance of the secondary winding. I didn't measure, but 2ohms may be on the high side which in turn will effect your resistor value.

Quote:
18,000uF = 18mF in PSUDII, but looking to purchase a suitable capacitor 18mF = 18uF.
mF is mega-Farad?? somehow unusual term...

I'd grab two 22000uF/25V since you are still heating your tubes with 6.3V and not 60V or something. I can't put the explanation in scientific terms (at a lack of words here being german ) but referencing the heaters to B+ of course doesn't change heater voltage.

best,
Oliver
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Old 31st October 2007, 08:52 PM   #15
Renron is offline Renron  United States
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Stixx,

Sehr Dank, My German is not good, sorry.
But Thank, Thank, Thank you.

In PSUDII the (m) for size of capacitors is milli, not Mega. see below,

I am having enough trouble understanding what I am doing without adding a rectifier valve too.
Obviously this is my first Preamp - electronics project.

Ich möchte ein Bier trinken mit Ihnen (from Google translate)

Ron
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Old 31st October 2007, 10:37 PM   #16
pchw is offline pchw  United States
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Hi Ron,

You mentioned that your trafo has 2 x 6.3V secondaries. So, the 5A rating is the sum of the 2, correct? Or, it is 5A each Either case, you will need to wire them in series to get 12.6V, so the current rating will be the same. 4 x 12AU7 in 12.6V only consume 0.6A total, you have plenty to spare. If you want reasonably good heater supply, use a LM317T to regulate the voltage, 0.6A is well below it's 1.5A limit. You will find plenty references here or in the web on how to use LM317T. If you don't want to get too complex for the time being, just use CRC where C=4700uF (as Oliver said, 25V rating is good enough) and R=3 or 4 ohms (5W). Later, you can upgrade the RC section to the LM317T circuitry. For 12AU7, connect the ground of the heater supply to 1/4 of the B+ should be good.
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Old 1st November 2007, 08:59 AM   #17
Stixx is offline Stixx  Germany
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Quote:
In PSUDII the (m) for size of capacitors is milli, not Mega. see below,
haha, true...it occurred to me a few minutes after I posted, but I couldn't edit my post anymore.

Quote:
Obviously this is my first Preamp - electronics project.
You'll get there, no doubt! Three years ago a schematic basically was some sort of egyptian artwork to me... I learned from reading, and more reading...

Quote:
ch möchte ein Bier trinken mit Ihnen (from Google translate)
Prost - - - - Cheers!!

Oliver
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Old 1st November 2007, 05:14 PM   #18
Renron is offline Renron  United States
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I must be learning!!!!

I let the magic smoke out of the Bridge rectifier yesterday

I looked at the transformer and it is (1) 6.3V CT...not (2) 6.3V secondaries... .....I must be learning......SOMETHING.....??

After I finished laughing, I figured out what I did and DOH! Newbie me, I twisted both legs of the CT 6.3 to the + of the bridge and ran the CT to the - side......and POOF! Pretty blue smoke , blew the fuse too! LOL .....I must be learning.

Oliver, Prost! Thanks for the words of encouragement!

I realize that my transformer has 6.3V CT, so unless I use a voltage doubler circuit I will have to use 6.3V for Heater Supply.
I know A/C is OK, but I'd prefer DC heaters.

Fred, Thanks for the suggestions with the LM317T, I'll go with that after the FW rectifier with CT.

Thanks Very much guys!

Ron
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Old 2nd November 2007, 02:34 AM   #19
pchw is offline pchw  United States
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Quote:
Originally posted by Renron
I must be learning!!!!

I let the magic smoke out of the Bridge rectifier yesterday

I looked at the transformer and it is (1) 6.3V CT...not (2) 6.3V secondaries... .....I must be learning......SOMETHING.....??

After I finished laughing, I figured out what I did and DOH! Newbie me, I twisted both legs of the CT 6.3 to the + of the bridge and ran the CT to the - side......and POOF! Pretty blue smoke , blew the fuse too! LOL .....I must be learning.

Oliver, Prost! Thanks for the words of encouragement!

I realize that my transformer has 6.3V CT, so unless I use a voltage doubler circuit I will have to use 6.3V for Heater Supply.
I know A/C is OK, but I'd prefer DC heaters.

Fred, Thanks for the suggestions with the LM317T, I'll go with that after the FW rectifier with CT.

Thanks Very much guys!

Ron
Hey, Ron, we all had those days No guts, no glory, right
When you twisted the two legs of the 6.3, you effectively shorted the secondary. Good that you had the fuse in place. Before you work on the doubler, measure the AC of the 2 legs just to make sure it is 6.3. Also, tape the CT to void accidentally shorting. You are not likely to use it.

Have fun!!
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