Bias points

[Valvehead]

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

[Valvehead]

something like this i guess

2pc 4mm Binding Post Banana Jack Socket Panel Mount for Multimeter Test Probe | eBay

[Shadrock2]

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

[Valvehead]

perfect ! thanks

[pdf64]

Consider just fitting a stereo jack socket, 1/4" or even 1/8".

[Mick Bailey]

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

[nosaj]

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

[pdf64]

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!

[nosaj]

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

[pdf64]

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.

[nosaj]

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

[pdf64]

A plate connection may be handy for electrostatic headphones!

[Enzo]

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.

[Mick Bailey]

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.

[Enzo]

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.