Hoffman Amplifiers Tube Amplifier Forum

Amp Stuff => Tube Amp Building - Tweaks - Repairs => Topic started by: mresistor on July 03, 2018, 01:32:37 pm

Title: '66 bassman physically vibrating
Post by: mresistor on July 03, 2018, 01:32:37 pm
Ok  I've got a 66 bassman in for cutting out twice - once during each of two live performances.  I played it and left it on for a couple of hours and it sounded great to me, even up around 8 or so on the vol.  The power tube sockets looked awful and one was just worn out. So I replaced them with two new porcelain sockets. While removing the old sockets I ran across plenty of questionable wirie connections and solder joints. One of the sockets had been replaced previously.  Installed 1 ohm resistors while there.  One 12AX7 V3 had a very weak side. Replaced it.


The thing that is causing me a little concern is that when I turn this amp on, I can feel buzzing vibration, like a vibrator, while holding the switch. And I can hear some hum. When it is on I can feel the vibration touching the chassis. My DR, SR and PR do not do this but they aren't 52 years old either.  So I was searching on the internet and found one person saying that if an amp with solid state rectification was physically vibrating that the problem is a bad diode in the rectifier. Was he talking about a full wave bridge?


Any thoughts on this?


I could surely replace both strings of diodes in the rectifier with a couple of 1N5408s I have on hand but I don't want to take everything apart unnecessarily. 
Title: Re: '66 bassman physically vibrating
Post by: mresistor on July 03, 2018, 01:42:03 pm
After reading through this thread  http://www.ampgarage.com/forum/viewtopic.php?t=17505  I checked all the PT bolt nuts for tightness and found one loose , tightened it and the vibration decreased.


Not near as noticeable now..   
Title: Re: '66 bassman physically vibrating
Post by: p2pAmps on July 03, 2018, 01:43:15 pm
Quote from: mresistor on July 03, 2018, 01:42:03 pm
After reading through this thread  http://www.ampgarage.com/forum/viewtopic.php?t=17505  I checked all the PT bolt nuts for tightness and found one loose , tightened it and the vibration decreased.


Not near as noticeable now..   

Thats exactly why I stopped grounding anything to tranny bolts...
Title: Re: '66 bassman physically vibrating
Post by: dude on July 03, 2018, 02:20:00 pm
What would cause PT nuts to loosen?  Naturally, one tightens then pretty snug, especially a head with no speaker to vibrate...? I always use a good star washer on a PT star ground. Never felt a vibration from a PT but I guess for a one in a hundred chance, don't use the PT nuts.


Just read that article, good to know that iron can cause vibration, guess it doesn't take that much to drill a small hole away from iron.


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