I mounted the BD139 with the flying leads soldered to the legs on the original build.
On this rebuild, I wanted to solder the legs of the BD139 to the helper board and use a 3 pin connector assembly for the flying leads. I assume the 3 pin connector would be soldered into the bottom 3 holes on the helper board.
I have carefully spread the legs of the BD139 and dry mounted to the helper board. Looks like it should work OK.
My real question was:
Do you mount the emitter of the BD139 to the right side of the helper board or the left side of the helper board? Or does it not matter as long as you make the proper connection on the FH9 amp pcb?
Thanks,
MM
On this rebuild, I wanted to solder the legs of the BD139 to the helper board and use a 3 pin connector assembly for the flying leads. I assume the 3 pin connector would be soldered into the bottom 3 holes on the helper board.
I have carefully spread the legs of the BD139 and dry mounted to the helper board. Looks like it should work OK.
My real question was:
Do you mount the emitter of the BD139 to the right side of the helper board or the left side of the helper board? Or does it not matter as long as you make the proper connection on the FH9 amp pcb?
Thanks,
MM
Does not matter as long as it’s correct. Note that the helper board may need a jumper as it was set up to have a surface mount resistor on the gate (pin 1).
Hi X,
Thanks for the help. I am going to solder wire onto the legs of the transistor. Decided using the helper board in this application is not worth it.
Is it advisable to solder full length on the legs, or, can the legs be shortened for easier soldering. Often wondered about this.
MM
Thanks for the help. I am going to solder wire onto the legs of the transistor. Decided using the helper board in this application is not worth it.
Is it advisable to solder full length on the legs, or, can the legs be shortened for easier soldering. Often wondered about this.
MM
Hi, Kokanee!
When I soldered my BD-139 transistors to the leads, i soldered about 1/2 " of wire to each leg & covered the joints with some heat shrink tubing without shortening the pins.
There's no rule that says you can't trim them however. Just make shure there's a solid connection on each leg.
Hope this helps.
Jim
When I soldered my BD-139 transistors to the leads, i soldered about 1/2 " of wire to each leg & covered the joints with some heat shrink tubing without shortening the pins.
There's no rule that says you can't trim them however. Just make shure there's a solid connection on each leg.
Hope this helps.
Jim
Thanks for your note Legis. That’s exactly what I also do. Shrink tubing is important here to prevent short and to give strain relief.
Thanks guys, that is what I did also. Putting things back together, but have to take a break for a couple of days. I will be posting a dry fit pic to see if good to go for power up next week.
MM
MM
Current limiting bulb tester
I may or may not have a parasitic or a soft short in my amp. I didn't notice this before because my shop lights are super bright but after the initial flash of the bulb as the psu caps charge up the light continues to glow ever so slightly. Does the fh9hvx draw enough current at idle to cause this? There is no load connected at the moment meaning no speaker or dummy load.
I had to turn the overhead lights off to see this.
Supply voltages are the same on both channels.
Any suggestions on where to check for any current drain?
Jim
I may or may not have a parasitic or a soft short in my amp. I didn't notice this before because my shop lights are super bright but after the initial flash of the bulb as the psu caps charge up the light continues to glow ever so slightly. Does the fh9hvx draw enough current at idle to cause this? There is no load connected at the moment meaning no speaker or dummy load.
I had to turn the overhead lights off to see this.
Supply voltages are the same on both channels.
Any suggestions on where to check for any current drain?
Jim
It depends on where your bias current trimpot is set. Use a voltmeter across the 0.22R 5w KOA BPR resistor. If your trimpot is far off, it might be running higher than 120mA (the recommended current). If off, adjust for about 26mV across the 0.22R resistor.
Having a slight glow on your DBT also depends on size of your bulb, 60w probably yes, 150w probably no
Coincidentally those wattages were the bulbs I tried as I was fresh out of 100w incandescents.
I have a 150w clear bulb and it was even harder to see. After I wake up enough, I'll recheck the voltages across the test points without the DBT
in the loop.
I have a 150w clear bulb and it was even harder to see. After I wake up enough, I'll recheck the voltages across the test points without the DBT
in the loop.
Bias setting question
When setting the bias, what should the status of the inputs be and should I have the dummy load on the outputs?
Also should the voltage across the .22 ohm resistors remain fairly constant with the inputs shorted?
When setting the bias, what should the status of the inputs be and should I have the dummy load on the outputs?
Also should the voltage across the .22 ohm resistors remain fairly constant with the inputs shorted?
Ideally you should short the input and no load on the output.
The voltage should be relatively stable unless you are adjusting the pot, but will vary some with temperature as the outputs heat up. Set it to 15mV and let it sit for 10-15 mins and see what it does, that will give you some room if it starts to run away thermally.
If all good for 20-30 mins then go up to 25mV and watch for the same amount of time before walking away.
The voltage should be relatively stable unless you are adjusting the pot, but will vary some with temperature as the outputs heat up. Set it to 15mV and let it sit for 10-15 mins and see what it does, that will give you some room if it starts to run away thermally.
If all good for 20-30 mins then go up to 25mV and watch for the same amount of time before walking away.
Thanks Bullitstang.
Assuming the votage remains relatively stable, what can I expect it to do when an input voltage voltage from a signal generator is applied & the input voltage is increased?
Assuming the votage remains relatively stable, what can I expect it to do when an input voltage voltage from a signal generator is applied & the input voltage is increased?
If you increase the input signal (AC) the output if connected to a load will increase. The DC bias current doesn’t change. Go ahead and connect an inexpensive test speaker and listen for first sound.
X,
I slowly raised the bias voltage to 26 mv and let the amp idle for 30 minutes or so and rechecked it and it had fallen to 22mv.
Using an Akitika signal generator and dummy loads, the bias voltage climbed dramatically as I increased the input. I put it on my scope and turned it up until it started to clip. Dialed it back
To a pure sine wave & the bias had climbed to 800mv! Both channel outputs were equal and I measured the output. It was about 78v pk-pk just before clipping. Shut it down at this point.
I didn't try the speakers. What's going on with the bias?
I slowly raised the bias voltage to 26 mv and let the amp idle for 30 minutes or so and rechecked it and it had fallen to 22mv.
Using an Akitika signal generator and dummy loads, the bias voltage climbed dramatically as I increased the input. I put it on my scope and turned it up until it started to clip. Dialed it back
To a pure sine wave & the bias had climbed to 800mv! Both channel outputs were equal and I measured the output. It was about 78v pk-pk just before clipping. Shut it down at this point.
I didn't try the speakers. What's going on with the bias?
I think that’s normal operation - you were putting out 78vpp so that would be 95w into 8ohms. The DC component of the bias current increased but was part of a large 78v AC signal. I wouldn’t worry about it unless the heatsink was excessively hot when playing music at normal levels. If you run the amp at 95w continuously, the heatsink will be hot like a Class A amp.
If i correct understand you have something not clear.
Bias is current that It flows constantly through the output devices WHEN no input signal is present.
Last edited:
Ahhhh...see? You can teach an old dog new tricks! Thanks guys!
I'll try the speaker test later today hopefully.
Jim
I'll try the speaker test later today hopefully.
Jim