Audionics help

lpd · 5th March 2007, 12:40 AM

Ok I have an Audionics BA150 that has a problem. At start up there is an audible hum present. This is at warm up of which I thought there wasn't any b+ voltage present. Here is a schematic of the amp....

Any ideas?Schematic

SY · 5th March 2007, 03:29 AM

Does the hum go away with warmup? Do the various DC voltages come up to normal values?

lpd · 5th March 2007, 04:29 AM

Hum does not go away with warm up. It does get a little lower but not much. As for voltages I'm not sure I just tested tubes, sockets ect.

SY · 5th March 2007, 11:01 AM

The power supply electrolytic caps are also well past their use-by date. I'd replace them (they were Mallory CGS, if memory serves). Check also that all grounds are tight and not affected by corrosion.

This was a very cool amp with innovative design. I'm glad to see that there's still a few around.

lpd · 5th March 2007, 04:13 PM

I will double check all grounds ect. Also the bias led's are supposed to flicker as the bias is adjusted. Mine are a solid light which according to the manual indicates tube or circuit failure. The signal sounds fine and the tubes appear to operate within their specs, I'll check voltages tonight.

SY · 5th March 2007, 05:03 PM

Definitely check the idle current. If it's acting the way you describe, the autobias circuit may have failed, or possibly the emitter follower screen drivers, more likely the former.

5th March 2007, 12:40 AM	#1
lpd diyAudio Member Join Date: Nov 2003 Location: BC	Audionics help Ok I have an Audionics BA150 that has a problem. At start up there is an audible hum present. This is at warm up of which I thought there wasn't any b+ voltage present. Here is a schematic of the amp.... Any ideas?Schematic

5th March 2007, 03:29 AM	#2
SY diyAudio Moderator Join Date: Oct 2002 Location: Austin, TX Blog Entries: 1	Does the hum go away with warmup? Do the various DC voltages come up to normal values? __________________ “Listening to records is like ****ing a picture of Brigitte Bardot.” - Sergiu Celibidache

5th March 2007, 11:01 AM	#4
SY diyAudio Moderator Join Date: Oct 2002 Location: Austin, TX Blog Entries: 1	The power supply electrolytic caps are also well past their use-by date. I'd replace them (they were Mallory CGS, if memory serves). Check also that all grounds are tight and not affected by corrosion. This was a very cool amp with innovative design. I'm glad to see that there's still a few around. __________________ “Listening to records is like ****ing a picture of Brigitte Bardot.” - Sergiu Celibidache

5th March 2007, 05:03 PM	#6
SY diyAudio Moderator Join Date: Oct 2002 Location: Austin, TX Blog Entries: 1	Definitely check the idle current. If it's acting the way you describe, the autobias circuit may have failed, or possibly the emitter follower screen drivers, more likely the former. __________________ “Listening to records is like ****ing a picture of Brigitte Bardot.” - Sergiu Celibidache

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5th March 2007, 04:29 AM	#3
lpd diyAudio Member Join Date: Nov 2003 Location: BC	Hum does not go away with warm up. It does get a little lower but not much. As for voltages I'm not sure I just tested tubes, sockets ect.

5th March 2007, 04:13 PM	#5
lpd diyAudio Member Join Date: Nov 2003 Location: BC	I will double check all grounds ect. Also the bias led's are supposed to flicker as the bias is adjusted. Mine are a solid light which according to the manual indicates tube or circuit failure. The signal sounds fine and the tubes appear to operate within their specs, I'll check voltages tonight.

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