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Post subject: 1965 Bassman cap job and mods
Posted: Fri Dec 02, 2011 10:11 am
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Hi All,

I have a 65 Bassman that I did a cap job on and noticed some mods that were done and wanted to find out why they were done.
I think the power transformer was replaced with one made in 1972. I guess that's when the mods were done. The first two filter caps don't look original.

Any comments are greatly appreciated.

These are pics of the amp when I got it.
The first pic is a sticker. Are there techs that leave these things when they work on stuff or probably just be the initials of a person that owned it?
The second and third are of added mod stuff....added resistors and blue wire mod.
http://s1214.photobucket.com/albums/cc491/debeall/1965%20Bassman_the%20way%20it%20was%20when%20I%20got%20it/

Here is the amp after the cap job....
http://s1214.photobucket.com/albums/cc491/debeall/1965%20Bassman_after%20cap%20job/

I plan on replacing some of the resisters. I'm just doing one step at a time.
What are some of the more important resisters to replace?

The amp sounds great, by the way.

Thank you very much for any advice.


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Post subject: Re: 1965 Bassman cap job and mods
Posted: Fri Dec 02, 2011 10:49 am
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If the amp "sounds great", why replace anything?

IF IT AIN'T BROKE, DON'T "FIX" IT.

JMOOC......

Arjay

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"Here's why reliability is job one: A great sounding amp that breaks down goes from being a favorite piece of gear to a useless piece of crap in less time than it takes to read this sentence." -- BRUCE ZINKY


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Post subject: Re: 1965 Bassman cap job and mods
Posted: Sat Dec 03, 2011 3:26 am
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You must remove those four resistor on pilot light socket . This is an "artificial " center tap for heater. You use these resistor only if your power transformer do not have a center tap.

You have this center tap ; green- yellow wire. Remove the four resistors


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Post subject: Re: 1965 Bassman cap job and mods
Posted: Sun Dec 04, 2011 3:14 am
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The right layout and schematic is from AA165 version D-FE

The blue wire is usefull but it's not the original yellow clothe wire like you have on other 6L6.

Also the red-yellow wire from the power transformer go to what it look a zener diode ( with hole in chassis ) this is used to lower the power transformer voltage.

Don't forget to replace the original 2 prog AC wire for a modern 3 prong.

You do a very nice job on capacitors. Nice amp.


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Post subject: Re: 1965 Bassman cap job and mods
Posted: Mon Dec 05, 2011 1:43 pm
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Retroverbial, the original caps were forming bubbles on the + side so thought it would be best to replace them. I'm kinda going by the tag you have on your posts.

I also installed a 3 prong ac cable.

I just wanted some input on getting it in good reliable gigging condition. I don't want it to give me trouble at the gig.

You guys are a lot of help. Thanks so much for everyone's advice.


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Post subject: Re: 1965 Bassman cap job and mods
Posted: Mon Dec 05, 2011 2:01 pm
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Buble on one side of the capacitor; yes replace it.
I do a mistake when I write the amp model , it is a AB 165


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Post subject: Re: 1965 Bassman cap job and mods
Posted: Mon Dec 05, 2011 2:41 pm
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debeall wrote:
Retroverbial, the original caps were forming bubbles on the + side so thought it would be best to replace them. I'm kinda going by the tag you have on your posts.

I also installed a 3 prong ac cable.

I just wanted some input on getting it in good reliable gigging condition. I don't want it to give me trouble at the gig.

You guys are a lot of help. Thanks so much for everyone's advice.


I understand now -- and I concur.

Those of us who gig have all the issues we need already without having to worry about the reliability of our gear. You made the right call.

Rawk on!

8)

Arjay

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"Here's why reliability is job one: A great sounding amp that breaks down goes from being a favorite piece of gear to a useless piece of crap in less time than it takes to read this sentence." -- BRUCE ZINKY


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Post subject: Re: 1965 Bassman cap job and mods
Posted: Tue Dec 06, 2011 12:05 am
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Retroverbial wrote:
debeall wrote:
Retroverbial, the original caps were forming bubbles on the + side so thought it would be best to replace them. I'm kinda going by the tag you have on your posts.

I also installed a 3 prong ac cable.

I just wanted some input on getting it in good reliable gigging condition. I don't want it to give me trouble at the gig.

You guys are a lot of help. Thanks so much for everyone's advice.


I understand now -- and I concur.

Those of us who gig have all the issues we need already without having to worry about the reliability of our gear. You made the right call.

Rawk on!

8)

Arjay

Yep,I try to keep my amps in gigging shape,but I always take spare tubes and stuff and hope that an amp doesn't go down at a show.
Between me and my son,we always have at least one spare amp and could plug straight into the PA mixer in a pinch....you never know what can happen.
Last Fri. night I gigged with my '60 Super,at 51 years old,the amp was older than most of the people there who were listening,a true testament to Leo's designs. :D


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Post subject: Re: 1965 Bassman cap job and mods
Posted: Tue Dec 06, 2011 12:29 am
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Rebelsoul wrote:
Last Fri. night I gigged with my '60 Super,at 51 years old,the amp was older than most of the people there who were listening,a true testament to Leo's designs. :D


+1

And twenty-five years hence, the grandkids will still be rocking out our amps.

8)

Arjay

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"Here's why reliability is job one: A great sounding amp that breaks down goes from being a favorite piece of gear to a useless piece of crap in less time than it takes to read this sentence." -- BRUCE ZINKY


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Post subject: Re: 1965 Bassman cap job and mods
Posted: Tue Dec 06, 2011 7:58 pm
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Exactly! :D


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Post subject: Re: 1965 Bassman cap job and mods
Posted: Fri Dec 09, 2011 6:14 pm
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I have another problem, guys.

It would be a lot easier for me to record the problem and post a video or sound bite of it but maybe someone can relate to what I'm trying to relay here.

When I got the amp I knew I was going to do a cap job on it so I turned it on and played through it for a few minutes. I thought...nice breakup!!!...and just banged away on it not really paying attention to detail.

Now after the cap job, when I turn the amp on, everything's fine. Nice and quiet. But when I play my guitar, there is a distorted "farting, raspberry" sound playing along with the note. It's more noticeable on single notes played on the low E and A strings, The sound cuts out before the note fades out. I can play the note soft and it's fine, but when I add a little force to the note or turn the volume up a little more, it's there. It changes frequency with the frequency of the note. It sounds like I have a Tube Screamer playing along with me.

It's not the speaker. It's not a fret buzzing. It's not the tubes. It happens on both channels.

Also, the tone controls don't seem to do a whole lot. They work but not to the extreme you would expect. Overall volume seems squashed the more you turn it up.

I read somewhere that what I'm hearing might be the power tubes trying to deal with a voltage problem.

I checked voltages and here is what I have:

Filament voltage
v6 is 6.83v
v1 is 6.78v........... all others read in between.

Plate voltage is 510v .............does that seem like a lot to you?

v1 pin 1 is 231v
pin 3 is 1.85v
pin 6 is 245v
pin 8 is 1.9v

v2 pin 6 is 292v
pin 8 is 2.34v

v3 pin 1 is 225v
pin 3 is 1.86v
pin 6 is 280v
pin 8 is 2.36v

v4 pin 1 is 326v ...........schematic says 220v
pin 6 is 323v ...........schematic says 205v
pin 8 is 135v ...........schematic says 95v

Bias voltage
v5 pin 5 is -48.2v
v6 pin 5 is -47.8v

Don't know what this is but:
v5 pin 3 is 511v ...........schematic says 420v
v5 pin 4 is 373v "

v6 pin 3 is 511v "
v6 pin 4 is 373v "

Bias cap reads 62v

Is any of this in the ballpark of what it's supposed to be?

I hope that what's wrong just jumps right out at ya.


Thanks!


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Post subject: Re: 1965 Bassman cap job and mods
Posted: Sat Dec 10, 2011 3:26 am
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On your first post you said "....the amp sound great by the way"
After, you replace some resistors and do a capacitor job and now it sound bad !!!!!!
What happenend ? You do some mistake ? Check your work . What kind of capacitor you use ? Good Sprague or F& T or cheap asian import ?

____________________________________________________________________________
There seems to be too much voltage difference on the legs 3 and 4 of your 6L6. It is not normal to me.

And 510 volts on pin 3 shows a supply voltage too high or too cold bias.
Can you install resistors 1 ohm, 1 / 2 watt on the legs 8 of 6L6 and measure the voltage across the terminals of these resistors? This would be the bias current of the lamp. Needed to learn more and fix your problem.

Remember that, as I mentioned earlier, there is a Zener diode installed on a wire of your power transformer to lower the voltage. So there is already a problem of voltage at the base. Maybe this is insufficient and should zener down even more?
But the amp sound good first time with this mod .


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