help with 551s

[fosgatefan]

Well I got them ordered and I made sure everything was correct.

I wont be able to install the parts until next week because I'm going out of town on Wednesday and I still need to get the aluminum bar. I called Menards and they only have about an 1/8 of an inch thick. I looked on granger and found 3/8 x 3/8 and I think ill just go with that.

 

[Perry Babin]

Try Lowes and Home Depot. They have aluminum stock. 1/4" thick will work. 1/8" will also but it won't look very good because it will bend when you tighten the screws.

 

[fosgatefan]

I just replaced the 2A transistor with MMBTA56 and it still draws to much current. I dont know what to check next

The thickest aluminum I could find at lowes was 1/4" so if I get the amp working ill just use that.

 

[Perry Babin]

What is the gate voltage for the power supply FETs (no B+ applied, only ground and remote)?

 

[fosgatefan]

3.3v for all of the gates

 

[fosgatefan]

with 9.4v from the power supply

 

[Perry Babin]

How much current is it drawing?

If you leave it powered up for a few seconds, which components begin to get hot first?

 

[fosgatefan]

It draws about 1amp at 7v and TC20 seams to be getting the hottest

 

[fosgatefan]

I just measured it out of the circuit and It is shorted from the drain to the source, so I am going to try another one.

 

[Perry Babin]

When you replaced the rectifiers, are you sure you installed them in the correct locations?

 

[fosgatefan]

Im pretty sure I did, TC18 is MUR1620ctg and TC8 is MUR1620CTRG. I did find that TC20 was ok.

 

[Perry Babin]

The schematic doesn't have TC8, 18 or 20 so I don't know if you have them in the correct locations.

The center leg of the CTG rectifier should go to the positive terminal of the rail caps. The center leg of the CTRG rectifier should go to the negative leg of the rail capacitors.

 

[fosgatefan]

Would you happen to have a schematic.

 

[Perry Babin]

Yes but it's very poor quality. email me if you want it.

babin_perry@yahoo.com

 

[fosgatefan]

what else do you think I could try. I am almost 100% positive these are in the correct location.

 

[Perry Babin]

You can use your ohm meter and be precisely 100% sure.

 

[fosgatefan]

Ok my measurements are .2ohms (Short) when I measure ctrg between negative and the middle of the caps and ctg also measures a short between the positive and the middle, and a few of them measure higher resistance which is probably normal.

 

[Perry Babin]

Do you read a short from the center legs of the rectifiers to the chassis ground terminal?

 

[fosgatefan]

No I measured 458ohms and 411ohms

 

[Perry Babin]

I'll need photos to help any more with this amp.

babin_perry@yahoo.com