BIG problems

[Gepetto]

The output transistors are On Semi as well albeit 15024s, they should be better than the Delco`s in any case.
So there is nothing more that I can do until they get here?
I`m glad things are starting to take shape thanks again guys.

Mike
ON Semi is the Motorola legacy. Some number of years ago Moto spun off their discrete and integrated semiconductor business and that was the birth of ON.

Moto always made the best and most reliable bipolar power semiconductors on the planet.

 

[Michael F]

Did you check that the bias adjusts properly now that you have things settled down?

Is that safe to do? Should I put the 410s in first?

 

[Michael F]

Mike
ON Semi is the Motorola legacy. Some number of years ago Moto spun off their discrete and integrated semiconductor business and that was the birth of ON.

Moto always made the best and most reliable bipolar power semiconductors on the planet.

Please tell me they are not made in PRC

 

[laatsch55]

Is that safe to do? Should I put the 410s in first?

Does that mean you DIDN"T have any in when you were testing and de-bugging?

 

[laatsch55]

410's in place of theMJ's, gotcha...

 

[Gepetto]

Is that safe to do? Should I put the 410s in first?

Sure now that you have them Mike. Wasn't sure that you hadn't done that step already.

 

[Gepetto]

RCA410s in next then check the offset and bias.

 

[Gepetto]

Please tell me they are not made in PRC

Some in Mexico, some in Malaysia, some in China.

 

[laatsch55]

We lost 'im Joe.....Youngins....can't keep up.

 

[laatsch55]

Mike, apologize, the board didn't go out today, work was way early and I was late before I ever woke up.

 

[Michael F]

New measurements

Installed new Q`s 1,2,3,4 today. Put amp on DBT, brought up variac to 120, bulb stayed dim but LED board didn't light up anymore (rail voltage only +40 0 -40)Offset was about .020 on both channels.
Passed the bulb test so I took it out of circuit and brought variac up to 120, LED board lights up and offsets drop to around .010.

Next was to put in RCA 410s to replace the MJ`s. Once again, bulb dims but no LEDs.
DBT out of circuit, board lights up, offset L .09, R .05.

Tried biasing but could not get acceptable values:

( where < = R20 turned fully towards power supply, ^= halfway, >= R20 turned fully towards I/O connectors )


Left channel R38 ranged from .875 < .675 ^ .575>
Left R39 range was similar .887, .675, .595 respectively

Right channel R38 .753, .553, .480
R39 ..731, .537, .478

Amp sat idle (on)for 15 or so minutes prior to first measurement and turned off and discharged in between measurements.

What do you have to say about that?

 

[Gepetto]

Installed new Q`s 1,2,3,4 today. Put amp on DBT, brought up variac to 120, bulb stayed dim but LED board didn't light up anymore (rail voltage only +40 0 -40)Offset was about .020 on both channels.
Passed the bulb test so I took it out of circuit and brought variac up to 120, LED board lights up and offsets drop to around .010.

Next was to put in RCA 410s to replace the MJ`s. Once again, bulb dims but no LEDs.
DBT out of circuit, board lights up, offset L .09, R .05.

Tried biasing but could not get acceptable values:

( where < = R20 turned fully towards power supply, ^= halfway, >= R20 turned fully towards I/O connectors )


Left channel R38 ranged from .875 < .675 ^ .575>
Left R39 range was similar .887, .675, .595 respectively

Right channel R38 .753, .553, .480
R39 ..731, .537, .478

Amp sat idle (on)for 15 or so minutes prior to first measurement and turned off and discharged in between measurements.

What do you have to say about that?

It appears that the bias circuit is operational.

What did you replace the original Q6 2N3403s with? It looks like the gain (beta or Hfe) of your replacements is not sufficient to get into proper range. On one channel change out R19 from the original 470 ohms to 1K ohms and try again.

 

[Gepetto]

It appears that the bias circuit is operational.

What did you replace the original Q6 2N3403s with? It looks like the gain (beta or Hfe) of your replacements is not sufficient to get into proper range. On one channel change out R19 from the original 470 ohms to 1K ohms and try again.

You should really be using a very high gain transistor like a 2N5088 for the bias application.

 

[Michael F]

It appears that the bias circuit is operational.

What did you replace the original Q6 2N3403s with? It looks like the gain (beta or Hfe) of your replacements is not sufficient to get into proper range. On one channel change out R19 from the original 470 ohms to 1K ohms and try again.

Hi Joe, Q6 is a 2N3415. I still have the originals. As for R19, I`ll have to hunt down a 1K.
Any point in putting the original Q6 back in?

 

[Michael F]

Mike, apologize, the board didn't go out today, work was way early and I was late before I ever woke up.

No worries Lee, I had a similar day..

 

[laatsch55]

If the resistor change doesn't do it, yes. No gain , no work. That's the one thing newbs like me had to get through our heads, a tranny can check good and still noit work. And when your major troubleshooting clue is a shorted or open tranny, ya get lost.

 

[Gepetto]

Hi Joe, Q6 is a 2N3415. I still have the originals. As for R19, I`ll have to hunt down a 1K.
Any point in putting the original Q6 back in?

2N5088 has 2X the minimum Hfe that the 2N3415 has.

2N3415 is a general purpose transistor. 5088 is a high gain amplifier transistor

 

[Michael F]

Replaced R19 with a 1K, no real change

 

[Michael F]

2N5088 has 2X the minimum Hfe that the 2N3415 has.

2N3415 is a general purpose transistor. 5088 is a high gain amplifier transistor

I`m beginning to think I wasted a lot of money on that EBay kit

 

[Gepetto]

I`m beginning to think I wasted a lot of money on that EBay kit

Did you solder the leads on the 2N3415 in the correct order? They are not the same as most TO-92 transistors are.

When looking at the transistor flat with leads pointing down on both transistors is E-C-B. E= Black Wire, B= Brown Wire, C= Red Wire

If they are mis-wired, you will not get the desired bias effect.