MI60 Clone

Come talk about our DIY amp project...in english !
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vitriol82
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Re : MI60 Clone

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Hello,

To help you , we need to know every steps of your actions.
Some questions are without answers:

1- What about the heater voltage without and with tubes?
2- Have you done the good bias system?
3- What are the specifications of the output transformer? If this one is too light, the current bias can increase alone by thermal effect.
4- Can you do a voltage check up for each tube :
For préamp tube : Va , Vk and Vg1
For power tube: Va , Vk, Gg1 and Vg2
For power supply: secondary HT (ac), A+, B+, C+

Do one check without tubes and an other one with the tubes

Last question, what kind of chocke do you have used? (16H/50 mA must be used)

If modifications have been done instead the original schematic, please post your schem.
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theleftfoot
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Re : MI60 Clone

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hey, will do it...but befor i start, can you say me wich is the good bias system?

i use a Hammond Drossel 159M (Inductance: 15 H, DC Current: 100 mA, Resistance: 256 Ohm, Max. DC: 500 V)

more to follow

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vitriol82
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Re : MI60 Clone

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Seeing the layout you have choosen, the schematic of the bias system is this one:

http://gilles.thebault.free.fr/MI60/MI60bias.gif

This one must be may be adapted to your bias secondary, I don't know what is the diffrence of voltage beetwen the twice PT.
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theleftfoot
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Re : MI60 Clone

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why? i have a bias winding on this trafo? i don't understand?

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vitriol82
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Re : MI60 Clone

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Because on the schematic , you are on the HV winding, not on a bias winding
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theleftfoot
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Re : MI60 Clone

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hey guys,

i'm back....with good news!

THE WORKS!

changed the bias, the trace, the choke possison, star ground and of course the tubes....

and it works like a charme! no buzz quiet like a baby!

but one problem....is damm sillent! when i put the gain and the MV on 10 it sounds normal bedroom....

whats worng? did i need a resistor on the in input to ground?

thanks for the advice

raffa

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bilbo_moria
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Re: Re : MI60 Clone

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theleftfoot a écrit : but one problem....is damm sillent! when i put the gain and the MV on 10 it sounds normal bedroom....
:?: I don't understand what you mean, could you please explain ? What's wrong ? No sound ? Loud hum ?

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theleftfoot
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Re : MI60 Clone

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its very silent, quiet! i have to turn the MV all way up to hear something....

what kind of problem cant this be?

raffa

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bilbo_moria
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Re: Re : MI60 Clone

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Hi,

Where is placed your MV ? Just before C7 or post PI.

Do you have another preamp you could "plug" just before C7 (after having unplugged the MV) to test the PI and amp part ? I you have not a preamp, maybe one or two powerful stompboxes (OD, distorsion, booster).

Could you please measure all voltages as suggested by Vitriol and post here ?
vitriol82 a écrit :Hello,
To help you , we need to know every steps of your actions.
Some questions are without answers:

1- What about the heater voltage without and with tubes?
...
4- Can you do a voltage check up for each tube :
For préamp tube : Va , Vk and Vg1
For power tube: Va , Vk, Gg1 and Vg2
For power supply: secondary HT (ac), A+, B+, C+

Do one check without tubes and an other one with the tubes

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theleftfoot
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Re : MI60 Clone

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hey guys...i found the error! i forgot the connection pin3 to pin8 on V2!

--> now the amp works... :P

but one issue left me in misery...when i put 2 new el34 in the amp, bias on -45V...the bias current goes up to 200ma and the tubes buzz and i have to shutdown the amp....

when i put my practice tubes, that i use to test the amp...everything works good! -45V on 37mA!

i don't understand that? whats wrong here?

raffa

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charpy
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Re : MI60 Clone

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mabe one of your new tube is bad... this can happen sometime.

mabe your old tubes are almost dead and the bias point is set very his with those tube and you have to reduce the bias voltage for the new tubes (-50 or -60V)

anyway you must always adjust the bias when you change the tubes on a fixed bias amp (=grid biased amp).

but this is not neccesay for cathode biased amp

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theleftfoot
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Re : MI60 Clone

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okay, had time on the weekend...

when i remove the Phase Inverter Tube....the amp works....i can adjust the bias...with all diffrent tubes...it seems okay, but since i connect the Pin3 and Pin8, withhin i resolve the loudness (volume) problem, the bias goes up to 120 ma with the PI tube in....and the poweramp tubes buzz...

i controlled the Phase inverter circuit is okay....where is the error?

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charpy
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Re : MI60 Clone

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maybe a leakage on a coupling cap....

have you measured the voltage of the power tube's grid when the problem happen?

or mabe there is a supersonic oscillation.

can you make a tension chart for the PI and the output section, with the PI tube and without

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theleftfoot
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Re : MI60 Clone

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okay here are tensions with the working tubes...

V1
pin
1. 191.5
2. 0.026
3. 2.45
6. 281
8. 2.3

V2
pin
1. 332
2. 42.7
3. 73.5
6. 314
7. 45.3
8. 73.5

V3
pin
3. 499
4. 492
5. -43.5
6. 496

V4
pin
3. 499
4. 492
5. -43.5
6. 496

For power supply: secondary HT

A -> 499V, B -> 495V, C -> 438V

choke: hammind 15H

tubes; EH el34

...and i saw that i use only 400V coupling caps...ups

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vitriol82
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Re : MI60 Clone

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I find the HV a bit too high of 50V in general

I don't understand for V3 and V4 how you can find a voltage in pin 6, because this pin is not connected inside the tubes 8O

And the pin 1 (g3) must be connected to pin 8 (catode)

Yes the coupling caps must be 630V, may be change them and test again.
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