I've gone through this and tested (70% or higher where 67% is green range) all the tubes (four - 6BM8, two 12AX7, and new J&J 6CA4 rectifier tube) and replaced any that were not in the green on my BK 667 tester. Replaced 10 caps, and 3 of the 4 front slide switches, cleaned all pots and function switches, new power cord grommet, and new speaker jumpers. All controls work - bass and treble for each channel are working smoothly.
Loudness and rumble filter are audible and working. Only tested 8 ohm speaker terminals.The only flaw is the missing knob cap. I've played this for several weeks with no issues. It is a well made (Japan) unit. The item "Olson AM-214 Stereo Integrated Tube Amplifier 6BM8/ECL82 Serviced & Working" is in sale since Sunday, January 6, 2019. This item is in the category "Consumer Electronics\Vintage Electronics\Vintage Audio & Video\Vintage Amplifiers & Tube Amps". The seller is "jamxii" and is located in Cary, Illinois. This item can be shipped to United States, Canada, United Kingdom, Denmark, Romania, Slovakia, Bulgaria, Czech republic, Finland, Hungary, Latvia, Lithuania, Malta, Estonia, Australia, Greece, Portugal, Cyprus, Slovenia, Japan, China, Sweden, South Korea, Indonesia, Taiwan, South africa, Thailand, Belgium, France, Hong Kong, Ireland, Netherlands, Poland, Spain, Italy, Germany, Austria, Bahamas, Israel, Mexico, New Zealand, Philippines, Singapore, Switzerland, Norway, Saudi arabia, Ukraine, United arab emirates, Qatar, Kuwait, Bahrain, Croatia, Malaysia, Brazil, Chile, Colombia, Costa rica, Panama, Trinidad and tobago, Guatemala, Honduras, Jamaica, Grenada, Barbados, Bangladesh, Bermuda, Bolivia, Ecuador, Egypt, Guadeloupe, Iceland, Jordan, Sri lanka, Luxembourg, Macao, Martinique, Maldives, Peru, Pakistan, Reunion, Viet nam, Uruguay.