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    Building, troubleshooting and testing of these amplifiers should only be
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    the safety precautions around high voltages.

EL84 in triode

have monoblocks 4x EL84 in triode - driven by 2x ecc81 -

The EL84 are on 430v and amp gets hot

Have to replace the trafo so have to decide new anode voltage on the EL84 ...
neg grid voltage a.o.

Virtual Valve Museum has a EL84 on max anode 300V and max anode 550V la=0

The anode of the EL84 (7) is with a 91ohm connected to the grid g2

If the new anode voltage is f.e. 330v does the 91ohm be lowered as well...

Not looking for power cause speakers are 94dB .. ...any hints .....
 
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disco

Member
2006-04-17 6:27 pm
Holland
Max, you better look for an established design if you want to build your own amp. Without the necessary knowledge one can't design an amplifier. If you want to experiment and learn while doing so, start simple with an EL84 and ECC81. Read a good book (the ancient stuf is not so practical), Bruce Rosenblit wrote a nice primer. Have fun!
 
give it a try anyway..

Anode load resistance 150k ( 75k and 75K 460uF + 460uF in series

Cathode bias -22 v - should be - 24

cannot be more specific cause got the amp ....and discovered was too hot before in my hands

brown spots on trafo and board..it is a 220v design

when on variac decrease voltage sounds much much better .....but extra current comes in sooner or later so replace the trafo seems best options....but need to give the specs for another trafo of course

what about http://www.diyaudio.com/forums/tubes-valves/185823-unexpectedly-good-el84-amp.html

anode on 330v ...

And cathode voltages ....120 mV now variac on 180v) 250-275mV when on 220v (bias pot regulatable)
 
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Anode load resistance 150k ( 75k and 75K 460uF + 460uF in series

I mean the output transformer primary impedance. This is important to know if you are trying to figure out what operating point you want your | | EL84 wired triode. Either way you need to get the anode/screen voltage down.



What's is the cathode resistor values? Are the cathode resistors shared?

If you can draw up a quick schematic it would be advisable or at the very least give us some decent pictures to see what we are dealing with here.
 
do not want to change but get the anode voltage down from 430 to around 330v

We need to know what we are working with before just dumping voltage into heat. This would include all primary and secondary taps on power transformer and the rectifier and filter network. Either trace it out and draw up a schematic or at the very least take a picture most of us can figure it out by that. Without this we are relying on crystal balls.

Once you get your voltage down then you can figure out the best bias condition for you.
 
I mean the output transformer primary impedance. This is important to know if you are trying to figure out what operating point you want your | | EL84 wired triode. Either way you need to get the anode/screen voltage down.

Thanks yes should be down....output transformer difficult to measure get 0.5 ohm to .....fluke keeps running ...so how to measure accurately../


What's is the cathode resistor values? Are the cathode resistors shared?

Cathode resistors are 10ohm paralled with a 100uf elco

If you can draw up a quick schematic it would be advisable or at the very least give us some decent pictures to see what we are dealing with here

i get the pictures here ...cannot get a schematic yet
 
We need to know what we are working with before just dumping voltage into heat. This would include all primary and secondary taps on power transformer and the rectifier and filter network. Either trace it out and draw up a schematic or at the very least take a picture most of us can figure it out by that. Without this we are relying on crystal balls.

primary side of trafo from left to right
1:150v
2: 60v <> 5:60v these 2 are connected
3: 13v
4: 13v

6: 65v

secundary side follows (have to be careful ...not my own and been much too hot.... it is a tiny triode 25 old manley cannot find schematics anywhere)
 

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secundairy side - left to right

1 and 3 feeding rectifiers anode 430v

(2 non active)

primary 3 and 4 feed rectifiers for neg bias see above

4 travels to pin 4 of all El84 .. heather

and 6 to pin 4 of 1ste ecc81 ..heather

5: earth
 

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