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FDP Forum / Amp Mods, Repairs, and Projects / Diode Matrix Rectifier Question
(This message was last edited by picturevalve at 08:21 AM, Jul 25th, 2010)
(This message was last edited by Bubbalou at 09:26 AM, Jul 27th, 2010)
FDP Forum / Amp Mods, Repairs, and Projects / Diode Matrix Rectifier Question
Crackerhead
Elkhart, InJul 24th, 2010 06:50 PM Edit Profile Print Topic Search
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I'm building a Weber 6H50 Hiwatt type amp. To compare rectos, I built a diode matrix. It's 4 1N5408s in series per side. I measured the straight voltage out of the power tranny and it's 360 volts AC. It rectifies down to 328 volts DC. Is there THAT much voltage drop per diode? I was thinking my B+ would be over 400 volts. Also, I thought that HWs were supposed to be a "Cleaner" amp. Hence, I'm thinking that High B+ equals more headroom.
Any thoughts on this?
picturevalve
Wales. U.K.Jul 25th, 2010 05:23 AM Edit Profile Print Topic Search
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Is that 328v with or without a smoothing capacitor?
ECS-3
Contributing Member
*****
USA / VirginiaJul 25th, 2010 06:28 AM Edit Profile Print Topic Search
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Make sure you have the meter set to AC for the transformer measurement and then DC for the rectifier output.
360 AC RMS should rectify out to around 500 DC.
There is something wrong with your measurements.
The forward voltage drop for 1N5408 is 1.2V
Crackerhead
Elkhart, InJul 25th, 2010 07:08 AM Edit Profile Print Topic Search
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No smoothing cap. I'll check it again, ECS-3. I'm using a Greenlee meter set to DC for measuring the output. I didn't think those diodes would drop THAT much voltage.....Thanks for the response!
picturevalve
Wales. U.K.Jul 25th, 2010 07:48 AM Edit Profile Print Topic Search
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If you're measuring without a smoothing cap to hold the peak voltage then your readings are going to be lower, by how much depends on the type of meter you're using.
Billm
Contributing Member
******
New Jersey, USA
Hey! What exit?Jul 25th, 2010 08:11 AM Edit Profile Print Topic Search
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That's one of the best explanations of AC measurement that I've seen. Good link.
picturevalve
Wales. U.K.Jul 25th, 2010 08:39 AM Edit Profile Print Topic Search
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It doesn't quite address the full wave rectifier question except where it shows the waveform seen by AC “average responding” meter - which is the output waveform of a full wave circuit.
360v ac gives 509v out of the bridge less diode drop(16 x 1.2v =19.2v) gives 490v. Average meter reading =490 x 0.7 = 343v. Not too far away from what you're getting, depending on your meter. Let us know what you get when you put that 500+v cap on the output.
Crackerhead
Elkhart, InJul 25th, 2010 09:30 AM Edit Profile Print Topic Search
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Will let you know, PV! Mr.Stoopid was reading the voltage straight to ground and pulling out hair.......Thanks, everyone!
picturevalve
Wales. U.K.Jul 25th, 2010 10:49 AM Edit Profile Print Topic Search
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Another useful link below gives your dc output without a cap. as ~325v, if you ignore the diode drops.
ECS-3
Contributing Member
*****
USA / VirginiaJul 25th, 2010 05:47 PM Edit Profile Print Topic Search
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I"m not sure why you would want to measure the DC output without filter caps, since you are going to need the caps in a practical power supply anyway. May as well hook them up and then measure the smoothed out voltage, which should be close the peak DC number I listed (with no load). Under load the DC voltage will drop down a bit and AC ripple with increase some.
Crackerhead
Elkhart, InJul 25th, 2010 07:34 PM Edit Profile Print Topic Search
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I was just wanting to compare the voltage of the Diode Recto to the voltage of the supplied Weber Copper Cap Recto. I thought I would use the diode rectifier in place of the copper cap, since Hiwatts were solid state rectified.....
Crackerhead
Elkhart, InJul 25th, 2010 07:38 PM Edit Profile Print Topic Search
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Last post didn't make sense upon review. I realize the Copper Cap IS solid state, but it does have a sag resistor, too......
Bubbalou
Contributing Member
*********
USA
THE LOW END OF UPPER TEJASJul 27th, 2010 09:25 AM Edit Profile Print Topic Search
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"Last post didn't make sense upon review. I realize the Copper Cap IS solid state, but it does have a sag resistor, too......"
You may already know this, but there will not be any from the Weber Copper Cap if there is no load.
Crackerhead
Elkhart, InJul 27th, 2010 03:17 PM Edit Profile Print Topic Search
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Roger that, Bubbalou. I was thinking down the line to when the amp was operational. I considered putting the SS and copper cap rectos on a DPDT switch to have the option of more tonal variation. There's a BUNCH of room in the chassis for this....
Bubbalou
Contributing Member
*********
USA
THE LOW END OF UPPER TEJASJul 27th, 2010 03:58 PM Edit Profile Print Topic Search
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"I considered putting the SS and copper cap rectos on a DPDT switch to have the option of more tonal variation."
Interesting idea!
good luck
Crackerhead
Elkhart, InJul 28th, 2010 08:55 AM Edit Profile Print Topic Search
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Just as a sidenote, Bubbalou. I also use the two different High Voltage taps on the power tranny, too. Put them on a DPDT switch and presto! Variable B+ without hassle and without lowering the heater voltage! Probably helps tube life and my 6V6s love it when I put them in a circuit designed for 6L6s. My Tweed Super clone rocks with 6V6s......
Bubbalou
Contributing Member
*********
USA
THE LOW END OF UPPER TEJASJul 28th, 2010 10:45 AM Edit Profile Print Topic Search
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Crackerhead, on the DPDT switch for the high voltage taps, I suggest you put a .022-.047mfd non polorized 600 volt cap such as an orange drop to reduce the arcing across the switch contacts when they open. I did this on the standby switch on an old Fender Super Reverb. Connected it right across the two posts of the switch.
Crackerhead
Elkhart, InJul 29th, 2010 06:33 AM Edit Profile Print Topic Search
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Thanks for the tip, Bubbalou! After thinking about it, wouldn't I need four caps? One for each leg going to the center lugs on the switch?
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