Ampeg B2R with hf oscillation - diyAudio
Go Back   Home > Forums > Amplifiers > Solid State
Home Forums Rules Articles diyAudio Store Gallery Wiki Blogs Register Donations FAQ Calendar Search Today's Posts Mark Forums Read

Solid State Talk all about solid state amplification.

Please consider donating to help us continue to serve you.

Ads on/off / Custom Title / More PMs / More album space / Advanced printing & mass image saving
Thread Tools Search this Thread
Old 11th June 2014, 11:41 PM   #1
diyAudio Member
Join Date: Jan 2013
Location: Oregon
Default Ampeg B2R with hf oscillation

Howdy folks. I'm a bit of a solid state noob and I'm working on an Ampeg B2R that I got in non-working condition. The output relay was triggered, so I jumped it out of the circuit. I get a very high-pitched oscillation through the speaker. The oscillation is present with or without the preamp board connected. The preamp out works just fine into another amp, but the power amp is goin nuts.

I read a 150vac ripple on the +60 rail, a 32vac ripple on the +16 rail, and both negative rails are clean. DC voltages are within 10% of spec and are stable. The o-scope shows very high frequency interference on the + rails, can't determine the frequency exactly but there's plenty going on above the audible range. I read a 10mv dc offset on the output, and between 20-30mv across R37, R39, R41, R47, R48, and R50.

It's obvious to me that something is kicking back hf interference of some magnitude into the positive rail, but beyond that I am stumped. Can anybody help me out? Schematic attached.
Attached Files
File Type: pdf 2546d1212338958-ampeg-b2.pdf (438.4 KB, 28 views)
  Reply With Quote
Old 12th June 2014, 12:59 AM   #2
diyAudio Member
Join Date: Jan 2013
Location: Oregon
To make matters more confusing, it all of a sudden started working. I will assume that one of the solder connections that I re-flowed or one of the jumpers that I jostled has solved it. The ripple is still there(possibly from the fan motor?) but the amp functions flawlessly. Bad ground cnxn perhaps...

I don't like mystery problems and mystery solutions because I never actually know if I've fixed it or not. I didn't learn much either. Still haven't put the relay back into the circuit. Won't get back to it until later tonight.

  Reply With Quote


Hide this!Advertise here!
Thread Tools Search this Thread
Search this Thread:

Advanced Search

Posting Rules
You may not post new threads
You may not post replies
You may not post attachments
You may not edit your posts

BB code is On
Smilies are On
[IMG] code is On
HTML code is Off
Trackbacks are Off
Pingbacks are Off
Refbacks are Off

Similar Threads
Thread Thread Starter Forum Replies Last Post
HF Oscillation Heat-Up Spk's Magnet!? Zekk Tubes / Valves 5 7th July 2013 11:51 PM
HF oscillation bursts at low ( < 40Hz) frequencies bigwill Tubes / Valves 18 18th June 2012 09:08 AM
HF oscillation with no load, but only on one channel. bigwill Tubes / Valves 66 20th August 2011 07:50 PM
Cure for HF oscillation on positive cycles only RichardJones Pass Labs 4 27th June 2002 12:20 AM

New To Site? Need Help?

All times are GMT. The time now is 11:14 PM.

vBulletin Optimisation provided by vB Optimise (Pro) - vBulletin Mods & Addons Copyright © 2017 DragonByte Technologies Ltd.
Copyright 1999-2017 diyAudio

Content Relevant URLs by vBSEO 3.3.2