02-01-2015, 10:53 PM
Thought I’d provide an update on the status of the Model 14B distorted audio problem reported earlier (see below).
Based on the great advice I got here, tubes were tested and several were replaced as needed. The audio transformer was also checked and proved to be OK. Tube pin voltages were below spec in some cases by about 20% so I suspected that some original resistors had gone high. New resistors were installed but the distorted audio persisted.
My local mentor stopped by yesterday to have a look for himself. He examined the speaker, pressed down on the cone and said he could hear the cone rubbing on the voice coil. Though he described what he was hearing and expressed confidence that the problem had been found, I could not hear what he was describing. After he left I also examined the speaker but, instead of pressing down evenly on the cone, I applied outward pressure to the side of the cone where the stain and dried crud was present. BINGO! The distortion disappeared.
Photos of the speaker are available at the bottom of this page: http://k9uw.weebly.com/current-and-future-projects.html
This discovery creates a new question. Is there a way to fix this problem without resorting to a re-coning? I do have a good source for re-coning if that is the best approach.
Some day I hope to have the experience to be helpful to others on this forum but, for now, I’m here to capture your advice. Thank you, in advance, for your suggestions!
Based on the great advice I got here, tubes were tested and several were replaced as needed. The audio transformer was also checked and proved to be OK. Tube pin voltages were below spec in some cases by about 20% so I suspected that some original resistors had gone high. New resistors were installed but the distorted audio persisted.
My local mentor stopped by yesterday to have a look for himself. He examined the speaker, pressed down on the cone and said he could hear the cone rubbing on the voice coil. Though he described what he was hearing and expressed confidence that the problem had been found, I could not hear what he was describing. After he left I also examined the speaker but, instead of pressing down evenly on the cone, I applied outward pressure to the side of the cone where the stain and dried crud was present. BINGO! The distortion disappeared.
Photos of the speaker are available at the bottom of this page: http://k9uw.weebly.com/current-and-future-projects.html
This discovery creates a new question. Is there a way to fix this problem without resorting to a re-coning? I do have a good source for re-coning if that is the best approach.
Some day I hope to have the experience to be helpful to others on this forum but, for now, I’m here to capture your advice. Thank you, in advance, for your suggestions!
Mike, K9UW
Amherst, WI
