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  • Bias points

    I want to add some external bias test points to my Marshall ....what is the correct technical term for these red and black "sockets" so i can order some ?
    maybe Mouser has some

  • #2
    something like this i guess

    2pc 4mm Binding Post Banana Jack Socket Panel Mount for Multimeter Test Probe | eBay
    Last edited by Valvehead; 01-23-2016, 04:49 AM.

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    • #3
      They are call "Tip Jacks"
      https://www.tubesandmore.com/products/S-H260

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      • #4
        perfect ! thanks

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        • #5
          Consider just fitting a stereo jack socket, 1/4" or even 1/8".
          My band:- http://www.youtube.com/user/RedwingBand

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          • #6
            If you wish to go down the banana socket route, you can get insulated chassis-mount versions in 2mm - good for meter probes.

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            • #7
              Originally posted by pdf64 View Post
              Consider just fitting a stereo jack socket, 1/4" or even 1/8".
              That would be just great when someone hooks up something they shouldn't
              nosaj
              soldering stuff that's broken, breaking stuff that works, Yeah!

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              • #8
                Originally posted by nosaj View Post
                That would be just great when someone hooks up something they shouldn't
                I was assuming that the test points would be connected to the power tube cathodes and 0V; if so I can't envisage anything too bad happening.

                But I guess the test points may be to the plates and OT CT!
                My band:- http://www.youtube.com/user/RedwingBand

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                • #9
                  Originally posted by pdf64 View Post
                  I was assuming that the test points would be connected to the power tube cathodes and 0V; if so I can't envisage anything too bad happening.

                  But I guess the test points may be to the plates and OT CT!
                  Yea it's just a headphone jack, go ahead plug in
                  soldering stuff that's broken, breaking stuff that works, Yeah!

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                  • #10
                    Originally posted by nosaj View Post
                    Yea it's just a headphone jack, go ahead plug in
                    If the test points are to 1 ohm cathode-to-0V resistors, then the sound wouldn't be much use, but I can't see that harm / damage would be likely?
                    I suppose that a user may think that if it was a headphone output, then a dummy load had been switched in, and so fail to load the amp output.
                    But various sockets live on the back panel of amps; it's the duty of the designer to label them, and the user to read and hopefully understand them.

                    For other types of test point, eg plate, it wouldn't be a good idea to put exposed high voltage sockets on the back panel, eg a guitar string may find its way in there.
                    My band:- http://www.youtube.com/user/RedwingBand

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                    • #11
                      Originally posted by pdf64 View Post
                      If the test points are to 1 ohm cathode-to-0V resistors, then the sound wouldn't be much use, but I can't see that harm / damage would be likely?
                      I suppose that a user may think that if it was a headphone output, then a dummy load had been switched in, and so fail to load the amp output.
                      But various sockets live on the back panel of amps; it's the duty of the designer to label them, and the user to read and hopefully understand them.

                      For other types of test point, eg plate, it wouldn't be a good idea to put exposed high voltage sockets on the back panel, eg a guitar string may find its way in there.
                      I guess I should have put more thought in my typing.. I was thinking when you mention plate and Ot coupled with a pair of headphones for some electroshock therapy. Just evil thoughts
                      nosaj
                      soldering stuff that's broken, breaking stuff that works, Yeah!

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                      • #12
                        A plate connection may be handy for electrostatic headphones!
                        My band:- http://www.youtube.com/user/RedwingBand

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                        • #13
                          Even when they are clearly labeled, people plug their connections in wrong. It h=may only have a small voltage on it, but if someone plugs their speaker in there insyead of the output jacks, PFFFFT, OT is history.
                          Education is what you're left with after you have forgotten what you have learned.

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                          • #14
                            I had a Sessionette 75 for repair where the owner had connected the extension speaker socket to the main speaker output of a Silverface Twin Reverb, and the inputs of both amps to a splitter box. This was done to see if he could get any more volume/better tone from the Sessionette. The Twin was fine, the Sessionette certainly wasn't.

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                            • #15
                              Never give the customer a chance to do it wrong, because he always will. Tip jacks pretty much will not take anything other than probe tips, unless you unbend a paper clip and stuff it in there. Using a common audio connector is just an invitation for some other thing to be connected there.


                              if you have been in the service biz long, I am sure you have encountered things that run on wall warts, and someone plugged the wrong one in. "Aren't they all the same?"

                              Even manufacturers do not always get this. A long time ago, we sold little MIDI thru boxes. Just a small thing with a bunch of MIDI ports. it ran on a DC wall wart. Someone plugged a reverse polarity wart into it, and blew it out. I had an appropriate wart, but I called the company to ask what is likely to blow up on reverse supply voltage in them. The guy was adamant we only use their proper wall wart. I told him I understood that, but customers can and do plug the wrong ones in. I was amazed they had no idea this might happen. I eventually figured it all out on my own, and made the customer happy. Sold a new wall wart in the process.
                              Education is what you're left with after you have forgotten what you have learned.

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