Melos Sha Gold

[ManUtd]

Hi There!
I got one of these with a fault.
It powers up "normally",but no light in tubes.
This fault has suddenly occured after playing well for a long time.
Anyone got hold of some scematics or knows were to find it?

Regards,
ManUtd

 

[anatech]

Hi ManUtd,
If the heaters aren't lighting it should not be too difficult to troubleshoot. If you find a blown fuse, check any rectifiers in the heater circuit if they exist first before replacing the fuse. I am not familiar with this amp, just general advice.

-Chris

 

[ManUtd]

Hi ManUtd,
If the heaters aren't lighting it should not be too difficult to troubleshoot. If you find a blown fuse, check any rectifiers in the heater circuit if they exist first before replacing the fuse. I am not familiar with this amp, just general advice.

-Chris

Hi Chris!
Thanks for Your help,unfortunately heaters are lightening.
I think i do need schematics to figure out more.

Reg,
ManUtd

 

[anatech]

Hi ManUtd,
Okay, I misunderstood you completely. What exactly is happening (or not)?

-Chris

 

[ManUtd]

Hi ManUtd,
Okay, I misunderstood you completely. What exactly is happening (or not)?

-Chris

Well,amplifier turns on and led in front starts blinking(Normal).
Blinking is indicating "warm up" in approx. 3minutes.
But blinking do not stop and i can hardly see that Tubes are on(light).I have measured 90V input to Tubes.
The 4 leds located at 2N6045 are on.
There is 2 transistors on Heatsink with no value on it.(I mean text on them are scraped off).

Regards,
ManUtd

 

[anatech]

Hi ManUtd,

There is 2 transistors on Heatsink with no value on it.(I mean text on them are scraped off).

They may be three terminal regulators. No biggie.

So you are saying it never comes out of warm up? Check the ripple on the heater supply. If it's too large (cap going, going, well kinda gone now) the timer circuit will be constantly reset.

Do you have an oscilloscope and meter available to you?

-Chris

 

[ManUtd]

Hi ManUtd,

They may be three terminal regulators. No biggie.

So you are saying it never comes out of warm up? Check the ripple on the heater supply. If it's too large (cap going, going, well kinda gone now) the timer circuit will be constantly reset.

Do you have an oscilloscope and meter available to you?

-Chris

Hi Again,
I had to sleep(fresh up my mind).
Yes I got a scope and Multimeter(Fluke).
Do You know what voltage shall be read on ECC88 pins(I mean typically) i think the 90V measured is normal.
Soon I will have Scematic also,thanks to this forum.


Reg,
ManUtd.

 

[ManUtd]

Hi Again,
I had to sleep(fresh up my mind).
Yes I got a scope and Multimeter(Fluke).
Do You know what voltage shall be read on ECC88 pins(I mean typically) i think the 90V measured is normal.
Soon I will have Scematic also,thanks to this forum.


Reg,
ManUtd.

Download Scematics Here:
http://www.eserviceinfo.com/download.php?fileid=21578

Hopefully it works too!

 

[anatech]

Hi ManUtd,
Thanks for the link. I can't make out the exact component values but now I have a good idea what it "looks" like.

Use your 'scope and look at the plate (set for 50V/div, AC coupling, and reduce to show signal - be nice to the Y amp ) Then look at the gate of the 2SK68A followed by the source.

The grid voltage of the 6922 is undefined, but you want to see the cathode more positive. The tail current can be figured out by measuring across the 68 ohm resistor on the source of the 2SK107.

Let me know what you get.

-Chris

 

[ManUtd]

Hi ManUtd,
Thanks for the link. I can't make out the exact component values but now I have a good idea what it "looks" like.

Use your 'scope and look at the plate (set for 50V/div, AC coupling, and reduce to show signal - be nice to the Y amp ) Then look at the gate of the 2SK68A followed by the source.

The grid voltage of the 6922 is undefined, but you want to see the cathode more positive. The tail current can be figured out by measuring across the 68 ohm resistor on the source of the 2SK107.

Let me know what you get.

-Chris

Everything seems to happen to me right now.

I tried to start my old Scope from Philips but it is only beeping in it, no signal in screen.
Before that i measured 60mVDC across 68Ohm resistor.
Measured with no signal and after 3minutes warm up.

 

[anatech]

Hi ManUtd,
When it rains ....

Okay, so measure the plates, grids and cathode connection to start.

-Chris

 

[ManUtd]

Hi ManUtd,
When it rains ....

Okay, so measure the plates, grids and cathode connection to start.

-Chris

I Have measured this results (DC) directly on Tube.All are measured after 1 Minute On-time.Pin 1 =Rising to 90V and drops down to 75,5V.Pin 2 Rising to 125mV (hmmm!).Pin 3 0,75V
Between Pin 4 and 5 i got 2,9V.Pin 6 Rising up to 92V and drops down to 86V.Pin 7 135mV (hmmm!).
Pin 8 0,76V.

What about pin 2 and 7 are these normal? Could it be leakage in a capacitor?

Reg,
ManUtd.

 

[anatech]

Hi ManUtd,
Pins 2 and 7 are not referenced to ground. So this could be perfectly normal for this unit.

I looked at the current source reading and want you to reconfirm for me. I calculated a cathode current of 0.88 mA for both sections. That is current starved. The first section is running with a grid voltage of -0.625V and the second section is -0.625V wrt the cathodes. A very low value that supports the low cathode current observaton. There may be a problem here.

-Chris