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Got a Chubster 40 blowing the F1 fuse in for repair. First line of sight was making sure it is not a shorted power tube or bridge rectifier. I am certain it is not the rectifier diodes as they are checking out good and not shorted/open. Turned on the amp via 100 watt light bulb limiter and variac. The light shines brighter and brighter as I bring amp up to line voltage, this happens with or without tubes installed. Also the light bulb limiter shines bright whether or not amp is in standby. Measured AC at power switch(pilot light is built into the switch and does not light at all) and it is 16VAC at 120VAC line voltage. Checked B+ voltage after rectifier and it measured about 40-45vDC at 120VAC line on variac. Would the bulb limiter with a 100watt bulb cause my voltages to be this low? I am thinking no...
I also am looking through GeoFex website on power transformer testing. I have tried to measure resistance on my meter from each primary wire to chassis ground/transformer bolts. I am having trouble measuring any readable resistance from either primary wire to chassis ground. I have one meter that goes up to 2000M and I was able to briefly read about 60M resistance before it goes to OL. I am a bit confused on how to perform the resistance tests on the primary windings so far. I did measure 4.45M each side on the secondary B+ windings to ground and on another meter it was 3.6M each side. To me I am not satisfied with any tests I have done yet. This is the first time I have had to troubleshoot a PT and as most will say it last on the list of failures typically speaking. I have checked continuity in the amp's AC wiring all the way from power plug to primary wires and it is good.
I guess I am going to have to remove the primary wires from the switch to try resistance measurements better?? Also, with primary disconnected I need to check for 120VAC on the switch too to make double sure it is not something from the switch backwards towards wall voltage. What sort of advice can anyone lend to my current situation? So far I am taking it a little slow to make sure I cover all my bases. Thanks.
Oh yeah I forgot to mention that when I opened the amp up there was cage nut that had fallen loose in the amp. I am guessing that the cage nut could have shorted out something that might have caused a problem.
I also am looking through GeoFex website on power transformer testing. I have tried to measure resistance on my meter from each primary wire to chassis ground/transformer bolts. I am having trouble measuring any readable resistance from either primary wire to chassis ground. I have one meter that goes up to 2000M and I was able to briefly read about 60M resistance before it goes to OL. I am a bit confused on how to perform the resistance tests on the primary windings so far. I did measure 4.45M each side on the secondary B+ windings to ground and on another meter it was 3.6M each side. To me I am not satisfied with any tests I have done yet. This is the first time I have had to troubleshoot a PT and as most will say it last on the list of failures typically speaking. I have checked continuity in the amp's AC wiring all the way from power plug to primary wires and it is good.
I guess I am going to have to remove the primary wires from the switch to try resistance measurements better?? Also, with primary disconnected I need to check for 120VAC on the switch too to make double sure it is not something from the switch backwards towards wall voltage. What sort of advice can anyone lend to my current situation? So far I am taking it a little slow to make sure I cover all my bases. Thanks.
Oh yeah I forgot to mention that when I opened the amp up there was cage nut that had fallen loose in the amp. I am guessing that the cage nut could have shorted out something that might have caused a problem.
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