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Post subject: loose tubes on Fender Bassman 50
Posted: Mon May 14, 2012 9:37 am
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I have a Fender Bass 50 Amplifier which i inherited from my late wife, but she always had problems with one or both of the tubes falling, which caused overheating of the other tube, and ultimately bursting of the tubes, or kicking out the slow blow fuse. Now that I own the amp I would like to solve the problem of the loose tubes. I have checked the metal retainers which grab on the base of the tubes and seem to be doing their job. I took the amp to a music store last year and they suggested purchasing "tube retainers", but the store went out of business and now that its opened up again, they are taking a different view that I should not use tube retainers. Any advise will help

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Post subject: Re: loose tubes on Fender Bassman 50
Posted: Mon May 14, 2012 10:08 am
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You may need to retension the tube sockets. Though if the bear trap retainers are holding tight (Did you try squeezing them together to tighten them?), I'm not sure how the tubes could be falling out. I would suggest taking the amp to a qualified amp tech for a thorough checkup.

Note: I have not had the need to retension any of the sockets in my amps, so someone here who has done it can probably give you a better description of what is involved than I could.

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Post subject: Re: loose tubes on Fender Bassman 50
Posted: Mon May 14, 2012 1:44 pm
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If contact inside tube's socket are loose , say the one feed the negative voltage for the bias , you can have a bias to hot and burn the tube. Or intermittent contact could stess the tube with on off voltage.......

I do retensionnig lots of these olds socket 's contacts.

How to .

Fender amp's contact look like a "C " if you look them from the side you plug the tube in. You have to close them a little bit, each side of the "C".

Be careful, lethal voltage there , you have to discharche filter capacitor before. Amp unplug for sure. You need to use a tool with some kind of needle end to go between the "bakelite" ( tube side ) and each end of the "C" to close it little bit.

I hope my explanation are clear ? Don't forget ; lethal voltage in tube amps .


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Post subject: Re: loose tubes on Fender Bassman 50
Posted: Mon May 14, 2012 1:53 pm
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I forgot to tell you , tube could look loose ( it move) on socket but this could be normal . I often see the "C" socket"s contact tight on tube's pins but loose IN their socket hole , This is normal and contacts are good between socket 's contact ans tube's pins. You can check that by looking inside the amp's chassis. --Lethal voltage --

All you need is to close the retainer spring.

But if you have problem with tube's life, you have to tingtened tube' s socket . Or better find a good tech , not the guy you see.


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Post subject: Re: loose tubes on Fender Bassman 50
Posted: Mon May 14, 2012 2:04 pm
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I will have to make a correction on my original post. The tubes are not so loose that they actually fall out, but when the amp is on for a period of time with speaker box connected, after a bit of playing vibration from the speaker box ultimately shakes the problem tube and you can hear a rising hum coming from the speaker and when you look behind the amp, one tube will be bright red whilst the other one is its normal yellow or white color. If I simply push the tubes upwards, (with a glove on of course) the problem ceases until next time. Also what is the method for discharging the tubes before handling them?


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Post subject: Re: loose tubes on Fender Bassman 50
Posted: Mon May 14, 2012 2:14 pm
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That is what I understand the first time .
This tubes have some "C" contact loose like I write . Bias voltage is disconnected and tube is red.

You have to retightened contacts


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Post subject: Re: loose tubes on Fender Bassman 50
Posted: Mon May 14, 2012 3:11 pm
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stratele52 wrote:
Fender amp's contact look like a "C " if you look them from the side you plug the tube in. You have to close them a little bit, each side of the "C".

Be careful, lethal voltage there , you have to discharche filter capacitor before. Amp unplug for sure. You need to use a tool with some kind of needle end to go between the "bakelite" ( tube side ) and each end of the "C" to close it little bit.


+1

I stole a dental chisel from Dr. Russ T. Plyers (my oral surgeon) and used my Dremel tool with a carbide sanding disc to re-shape the head more to my liking. Be especially carefully not to damage the socket's bakelite housing in any way. Otherwise and it may cause arcing issues when high voltage is applied.

HTH

Arjay

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Post subject: Re: loose tubes on Fender Bassman 50
Posted: Mon May 14, 2012 3:14 pm
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waynf wrote:
I will have to make a correction on my original post. The tubes are not so loose that they actually fall out, but when the amp is on for a period of time with speaker box connected, after a bit of playing vibration from the speaker box ultimately shakes the problem tube and you can hear a rising hum coming from the speaker and when you look behind the amp, one tube will be bright red whilst the other one is its normal yellow or white color. If I simply push the tubes upwards, (with a glove on of course) the problem ceases until next time. Also what is the method for discharging the tubes before handling them?


You definitely need to tighten the bear claw clamp and retension the sockets per stratele52's direction.

As far as draining the power supply caps, there are various methods ranging from touching a BIG screwdriver between the positive terminal of each power supply cap and ground (NOT recommended), and switching the standby switch off while strumming the guitar until the sound dies (also not recommended as you don't know for sure if the caps are fully drained). Most people rig up a tool with a large value resistor attached to clip leads (I forget the optimum value, but a couple hundred Kohm should work with a 2 watt resistor) that you connect to ground and the + terminal of each cap. I find that simply touching the black lead of a DVM to ground and the red lead to the + terminal of each power supply cap will drain the caps and you can watch the voltage drop to a safe level at the same time. That is how I drain the caps in my Bassman and BDRI. I can watch the voltage drop from 400+ VDC to about 20 VDC or less in a couple of minutes.

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Post subject: Re: loose tubes on Fender Bassman 50
Posted: Mon May 14, 2012 6:12 pm
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To add to the great advice so far, some pictures might help. I use a very small jewelers screwdriver as shown on the site, and that works well. Some sockets are a little different, but the same principle is involved.

http://billmaudio.com/wp/?page_id=171

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Post subject: Re: loose tubes on Fender Bassman 50
Posted: Mon May 14, 2012 8:44 pm
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shimmilou wrote:
To add to the great advice so far, some pictures might help. I use a very small jewelers screwdriver as shown on the site, and that works well. Some sockets are a little different, but the same principle is involved.

http://billmaudio.com/wp/?page_id=171


I stumbled on that earlier from another thread. You beat me to it. :D

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