Ext. Speaker Output Jack

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Ext. Speaker Output Jack

Postby JemBoswell on Sun Apr 23, 2017 2:35 am

Hello,
I'm working on a 64 Fender Bassman. At the request of the owner, I have taken the extension speaker jack out of the circuit in order to use the extension jack hole for another purpose.

However, now I am not getting any output.... the main output jack is not working. There is a yellow wire that comes from a hole in the chassis (from the Output Transformer?) and this yellow wire


did go to the extension speaker as well. The other two lugs of the main output jack are wired together. There is a black wire that did come from from a hole in the chassis (the output transformer?) and went to the extension speaker jack but I taped that wire off and the yellow wire that went from the main jack to the ext. jack is also taped off.

Might be something else altogether since all I did was unscrew the extension jack and tape it up really good...so nothing was cut and we can restore it to original at any time.
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Re: Ext. Speaker Output Jack

Postby JemBoswell on Sun Apr 23, 2017 3:29 am

Continued from last post...Getting no output - amp was working fine before we removed the extension speaker jack. All we did was tape it up.
Now I am getting a high pitched squeal coming from the amp (not the speaker)...very weird. Guess I'll have to go through a check list.
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Re: Ext. Speaker Output Jack

Postby stratele52 on Sun Apr 23, 2017 9:13 am

JemBoswell wrote:Continued from last post...Getting no output - amp was working fine before we removed the extension speaker jack. All we did was tape it up.
Now I am getting a high pitched squeal coming from the amp (not the speaker)...very weird. Guess I'll have to go through a check list.


Squeal; look at the 820 ohms negative feedback resistor wich is not connected at the speaker output jack at it should be.

Do you have the layout ? Sure not, look at it an follow it; you have to switch 2 wires from external jack to internal jack.


The black wire go to internal jack ground lug.
The other wire ( yellow for you, green on my layout ) go to positive lug of the internal jack with the wire coming from the 820 ohms Neg Feed Resistor

http://el34world.com/charts/Schematics/ ... layout.pdf
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Re: Ext. Speaker Output Jack

Postby stratele52 on Sun Apr 23, 2017 11:45 am

Internal output speaker jack as it should be with your black and yellow wires.
Resistor show is on the eyelet board of your amp.
Don't forget the bare wire as a jumper.


Image
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Re: Ext. Speaker Output Jack

Postby Dean Jr. on Mon Apr 24, 2017 9:33 pm

Good post and and pictorial example ^^^^^^^^
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Re: Ext. Speaker Output Jack

Postby JemBoswell on Sat Apr 29, 2017 7:48 pm

OK, thanks everyone...here is what I did. I kept the external jack wired in exactly as it was but I had removed it from the chassis and wrapped it in electrical tape. The reason for this was I wanted to be able to restore the amp to it's original condition if need be. After thinking about it, I realized the main output jack is grounded to the chassis so I figured the external jack also had to be. So, I simply unwrapped the jack and connected a wire to the ground part of the jack (the part that touches the chassis and the ground or negative of the output cable) to a lug on the chassis. It worked! If I decide to remove that external jack altogether, I will follow your advice above. Thanks!

Regarding the squeal, that is not happening now. So, false alarm. Nevertheless, I replaced the "pre-amp" tubes as follows. I put JJ ECC83-S tubes in except for the socket nearest to the "Power Tubes". In that socket, I put a JJ ECC81.

The diagram on the inside of the cabinet says I should replace all 4 preamp tubes with "7025" tubes. Based on some research, I determined that the JJ ECC83S is the closest modern tube (that is affordable) to the 7025. I put the JJ ECC81 tube in that other socket because something in my memory told me that a 12AT7 works better in that socket. I think I got that idea from a later model Bassman (AA270) schematic.

I now plan to replace many of the capacitors. The capacitors under the "dog house" look modern and fairly new...those are the big filter caps. I've had this amp since 1987 or thereabouts...and I may have had it serviced by a professional at some point. The ones underneath, inside on the board, some of them are very old looking and say "molded" on the body. There are 2 witch are .25 mfd 400VDC, 3 which are .10 mfd, 400Vdc and one that is in the Ground Switch circuit which is a .047 mF 600 Volts. Note: the original "2 prong" cable was replaced with a grounded, 3 prong cable so I'm thinking that ground switch is obsolete. Nevertheless, I was told that this capacitor sort of acts as a safety somehow and if it goes bad, other bad things may happen.
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Re: Ext. Speaker Output Jack

Postby Dean Jr. on Sat Apr 29, 2017 8:03 pm

Well, alright then on the ext spkr jack.
Those caps you list above are tone caps in the preamp, correct. Unless those are bad or a person wants to change them to different values or thinks different caps will yield a different sonic, those do not need to be changed. That .25mfd/400v probably reads .022mfd and that would be the midrange tone cap in the Normal channel, iirc. The .1mfds, are the bass
tone caps---2X and one midrange in the Bass ch, perhaps. There are coupling caps in that circuit that should be similar to these you pint out. IF not, then they have been changed. Pictures help a lot.
There are some electroytic bypass caps on the board that you will find linked to pins 3 and 8 on those 12A-7 tubes. Some don't change those during a 'recap', some do...I usually do. There is at least one if not two electrolytic bias caps which should be changed during the recap.
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Re: Ext. Speaker Output Jack

Postby Gasstationman on Sat Apr 29, 2017 10:31 pm

Is it a 6G6-B or 6G6-C Bassman?
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Re: Ext. Speaker Output Jack

Postby drewleslie on Sun Apr 30, 2017 12:14 pm

Yep Anders ... if its 6G6 era circuitry it will have two 0.25 uF tone caps in bass channel.
How can you tell the difference between a chemist and a plumber? Ask them to pronounce 'unionized'.
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Re: Ext. Speaker Output Jack

Postby Gasstationman on Sun Apr 30, 2017 8:07 pm

drewleslie wrote:Yep Anders ... if its 6G6 era circuitry it will have two 0.25 uF tone caps in bass channel.

I was thinking the same thing.

A big cleanup and fix all issues can be a good thing to do before modding. You never regret a good job when it's done.
Good luck.
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