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Posted: Tue Sep 14, 2010 2:00 pm
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You're fully right: http://media.photobucket.com/image/fron ... DC0015.jpg you see it is inside the chassis.

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Posted: Tue Sep 14, 2010 2:08 pm
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I can get a new tank cheap enough. Is there any method of finding if the tank is defective without replacing it?


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Posted: Tue Sep 14, 2010 2:16 pm
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I never test it but it should work:
1. Connect the output of CD player to a 1K pot (2 external connections)
2. The middle connection and the ground connected on the RCA input of the tank.
3. Ajusting gently the pot and the amp reverb you should hear Jimmy Hendrix in a cathedral !

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Posted: Tue Sep 14, 2010 2:27 pm
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Jimi Hendrix? That's my man! I will see if I can find something that will work. What do you think about the power supply shutting down after 2-3 minutes.


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Posted: Tue Sep 14, 2010 2:57 pm
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I don't see a protection in this amp schematic.

There is a LED (LD2) locaded A8 on the schematic that indicate if the AC supply is OK; Let me know if this LED turn off also during the amp shut down;

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Posted: Tue Sep 14, 2010 3:26 pm
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Yes it is just as if you unplugged it from the electricity. The led goes out and after a few minutes it all comes back on ready to rock. I have to leave now but will check back later. Thank you!


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Posted: Wed Sep 15, 2010 10:14 am
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I beleive that it could be the NTC (TH1) located in A6.

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Posted: Wed Sep 15, 2010 12:06 pm
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Thank you. I will try to test it. http://www.ohmcheck.com/thermistor.htm

Normal (cool) reading of 6.0 ohms. When heated it dropped to 2.1 before it got to hot for my hands. I am a rookie in electronics (as you know). Does this mean that the resistance is decreasing or increasing. My understanding is that I want the resistance to increase when heat is applied.


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Posted: Wed Sep 15, 2010 12:40 pm
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In fact the coefficient is Negative (NTC), meaning that the resistance decreases with temperature.
It a soft start: at switch on the 6 Ohms limits the current after a couple of second the resistance has decreased allowing more current. The amp start slowly avoiding "pops" and components stresses, instability also.

I think for test, you can shortcut the NTC.

Rookie, what does it mean?

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Posted: Wed Sep 15, 2010 12:43 pm
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Rookie is like a a professional sports player in his first year. He is learning. How do I shortcut? Do I bridge the two connections on the circuit board? Also I wonder if the board is getting too hot? What do you think would cause the board to overheat? I am thinking that if I by-pass the PTC something on the circuit board could overheat.


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Posted: Wed Sep 15, 2010 1:39 pm
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A small strap beween the 2 pins.

Before what you can do is to play with the amp and when it shutdown try to cool down the NTC with a small fan.

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Posted: Wed Sep 15, 2010 2:09 pm
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I removed the NTC and used a small strap between the 2 pins. It was sounding soooo good (except for the reverb) and then it shut down, without the NTC. What do you think is causing it to get so hot? The aluminum bar that holds the transistors was too hot too touch. After 2-3 minutes it had power again. It sounded like something clicked over near the tube area when it powered back on.


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Posted: Wed Sep 15, 2010 2:52 pm
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You're right, there is a protect on this amp: TS1 located on the second page A6 (schematic) and C6 (layout); This "bilame" cut the AC supply at 195°C.

A7--> SA3 (phase or neutral) is connected to TS1A and connected to fuse-CTN ...

Then you still have an overheating issue with the power stage.

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Posted: Wed Sep 15, 2010 2:55 pm
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De-solder again Q12/Q14 and let me know the sound and heating.

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Posted: Wed Sep 15, 2010 2:56 pm
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I tried it again and blew a fuse. It must be due to my bad soldering. I will check everything again. Do you have any ideas? I am learning so much and the amp sounds so good. I just got a used Les Paul Special that I will not get to play until Christmas, so I cannot afford a new amp. But I am looking at the Blues Jr. when I do get the cash.


Last edited by treblot on Wed Sep 15, 2010 3:09 pm, edited 1 time in total.

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