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Old 4th January 2013, 12:00 PM   #1
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Default What is the difference between "rectifier tubes" and "power tubes"

hello everyone , before a month i start to learn about valve amplifiers...and i start to make a clone of 18 watt marshall...but i don't know very well about the tubes....so tell me please What is the difference between "rectifier tube (EZ81) " and " power tube (EL84) "??????????
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Old 4th January 2013, 12:32 PM   #2
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May you should read about vacuum tubes a little.
Try this first:

http://www.guitarstudio.tv/documents...Amplifiers.pdf
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Old 4th January 2013, 01:12 PM   #3
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artosalo thanks to share, very good link for a newbie like me.

Have a Happy New Year.
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Old 4th January 2013, 01:24 PM   #4
DF96 is offline DF96  England
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Quote:
Originally Posted by plig88
What is the difference between "rectifier tube (EZ81) " and " power tube (EL84)
Three grids. Find out what each grid does, and you will be well on the way to understanding valves.
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Old 4th January 2013, 01:48 PM   #5
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Sorry my ignorance all tube rectifiers don't have grids, right?
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Old 4th January 2013, 01:51 PM   #6
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Basically a Rectifier Tube will have no control grids. It will conduct fully in one direction and not in the other.

A Power Tube is just a high power amplifying valve. This will have one or more control grids which control the flow of current through the valve.

Vis-a-Vias. A Rectifier is either ON or OFF, An amplifier tube is partially ON or fully ON or OFF (basically being controlled by its grids)
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Old 4th January 2013, 01:56 PM   #7
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Thanks for the info, other question: one tube amplifier can be used as tube rectifier?
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Old 4th January 2013, 02:11 PM   #8
Tesla88 is offline Tesla88  Italy
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nice document artosalo
Anyway :
Tube rectifier is used to convert alternate current into direct current , the same work is performed by silicon rectifiers , so think about tube rectifier like a diode. Current can flow only in one dircetion , there are single wave rectifiers (1 anode 1 cathode) and full wave retifier (2 anode 1 cathode) , again some are direct rectifiers and heather is the cathode , indirect rectifiers have separate cathode and heaters.
EZ 81 is a indirect full wave rectifier. What you need to use this tube is a power transformer with a separate heater supply wiring for the EZ81 , don't use common wirng for rectifier and other tubes heaters .
Transformer must have a center tapped high voltage secondary , es 300 - 0 - 300 VAC
Center tap goes to GND and 300V goes to anodes of EZ81.On cathode you'll get positive voltage ..
Be careful with the smoothing capacitor value , silicon rectifier accept large capacitors , vacuum rectifiers need a capacitor with value in accordance with datasheet , for the EZ81 is about 50uF. If you exceed the value stated in the datasheet the tubes may arcing ... not a good thing !
http://www.drtube.com/datasheets/ez81-philips1970.pdf
If you want increase the value of smoothing cap you must use an inductor to limit current...

Power Tube function is give power to the speaker . Preamp tube amplify audio signal increasing voltage , power tubes amplify most in current . The power tube (EL84,EL34,6V6,6L6) and the class of operation (SE , PP , OTL ) determines the maximum output power.
Due tu the high impedance output of tubes (also power tubes) you need a transformer to couple plate impedance to speaker impedance . Quality of transformer is one of the most important factor on the global quality of a tube amplifier.
Since your would be a guitar amp , you don't need an high quality output transformer , an HiFi transformer is the worst thing you can put in a guitar amp. Jim Marshall started with using the worst transformer ever and this made the rock sound \m/

Be careful with tubes , high voltages inside a tube amp can kill in a Zap!

Apologies for my bad english...
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Old 4th January 2013, 02:35 PM   #9
yajnaS is offline yajnaS  India
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Quote:
Originally Posted by merlin el mago View Post
Thanks for the info, other question: one tube amplifier can be used as tube rectifier?
Tube rectifiers are designed for low voltage drop and high current (large plate, small gap), you cannot use an amplifier tube as a rectifier because the continuous current limit will be low and the voltage drop will be high.
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Old 4th January 2013, 02:38 PM   #10
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Hi!

In fact power tubes can and have been used as rectifiers. In that case the grid gets tied to the plate. Wether this is sensible is another question

Western Electric did this in some of their amps. 211s used as output triodes and also as rectifiers. I think the idea behind this was to reuse the 211s from the amplifier sockets for some more time as rectifiers. They also did this in a 205D amp. However there is no published data about the diode characteristics of triodes you need to characterize them yourself for rectifier use.

However I would not recommed this for a beginner

Thomas
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