wiring 8 and 4 ohm tap

[pjd3]

Hi,
My OT has taps for 8 and 4 ohm. Its not the wiring itself I'm questioning but, the type of jack they are terminating to.
Is it a good idea to use a switched jack for say, the 8 ohm tap so that its not completely open if the amp gets turned on accidentally with no speaker plugged In?

I've heard through the years that what a tube amp hates is not having any speaker load when on. Of course, I need to wonder if being shorted is any worse or better.

If either are not a good idea then I'll just wire up a two connector speaker jack for the 8 ohm for now, wire up the 4 ohm later. I've only used one 8 ohm speaker for years now.

Thank you!
Phil D

[pjd3]

After some google searching the subject, it seems many feel having the shorting jack although not ideal is better than risking an open output.

If thats the case then I would just use the shorting jack for the 8 ohm speaker out and just wire the normal jack as normal for the 4 ohm tap.

Seem reasonable?

Phil D

[sluckey]

If thats the case then I would just use the shorting jack for the 8 ohm speaker out and just wire the normal jack as normal for the 4 ohm tap.

Think about that for a minute. Let's say you have nothing plugged into the 8Ω jack but you do have a speaker plugged into the 4Ω jack. But you're getting no (or very little) sound. That's because you have the entire OT secondary shorted out.

To safely do this you can use a single shorting jack and an impedance selector switch. Or... you can do it the way Sunn did using a 12A switching for the 8Ω jack and a 13A transfer jack for the 4Ω jack. Wire the 12A switch terminal to the ground terminal as usual. Connect the 12A tip to the 13A tip. Connect the 8Ω secondary lead to the NC terminal of the 13A and connect the 4Ω secondary lead to the 13A NO terminal.

Refer to these links...
https://www.tubesandmore.com/products/j ... er-circuit
http://sluckeyamps.com/sunn/sunn_sceptre_1971.pdf

I have found the 13A jack to be fussy about making a good connection after some time. I don't trust it. I rewired the speaker jacks in my Sunn.

[pjd3]

I see what you are saying. My plan was based on the "over-confidence" that I would only be using the 8 ohm speaker tap - but, that could change, or, I plug into the wrong jack.

The impedance selector switch sounds like the way to go. And I could even only use the 8 ohm tap for now until I hook up the 4 ohm. More steps but would insure safely to the amp.

Thank you Sluckey,

Phil d

[pompeiisneaks]

We...

More than likely the gas lid solenoid is not working..make sure it has power to the solenoid and that the pin for releasing the gas lid is not stuck.How do yu get fuel into it.?

John

415 816-0746

What in the hell are you talking about? Are you a spam account trying to get a few comments in so you can start posting more garbage? Solenoids and fuel in TUBE AMPS? Yeah I'm going to block this account.

~Phil

[Tony Bones]

If you'd ever had a sticky gas lid release pin then you wouldn't be so glib.

[pompeiisneaks]

If you'd ever had a sticky gas lid release pin then you wouldn't be so glib.

[Charlie Wilson]

Fly back voltage is what usually kills an output transformer. If the voltage on the secondary has no where to go(open) it builds up until it goes back the other way and tears through the primary in voltages over 1k. Shorting jack should prevent this, I say should, this is why Fender used a shorting jack. If you are only using the 8 ohm tap, just wire the 8 ohm and tape off the 4 ohm. If you want to use two 8 ohm speakers in parallel and have an extension speaker, then wire both.
CW

[Bill Moore]

I did the switching jack for 4, and 8 ohm options on my DR build. The shorting jack in the "main", and with a plug in the "aux" jack it switches to 4 ohm. If necessary to run a 4 ohm load with one speaker, just plug a dummy plug in to switch impedance. I figure, I'm more likely to use 2 8 ohm speakers, when I use it with an extension anyway.