5f2a head First Build. Hooking up dual 4 and 8 ohm outputs

[gymrat1964]

My OT has a 4 and 8 ohm tap. I want to hook up two jacks, one for each, so that I have a choice of plugging into either cabinet. The problem that I see is the feedback connection goes to the positive terminal on the output jack. If i connect to both I will essentially be shorting out the 4 and 8 ohm taps. My thought is putting in a 2 way switch that will send the feedback connection to either the 4 or 8 ohm jack, whichever is being used. Is this the best solution?

[Enzo]

Don't make it more complex than it needs to be. The feedback is designed for the circuit as is. The voltage of the one tap. It doesn't matter if you use a different tap for the speaker.

SO wire the thing up stock, then all you need do is mount a second jack, and wire it to the unused tap on the transformer.

[Tom Phillips]

My OT has a 4 and 8 ohm tap. I want to hook up two jacks, one for each, so that I have a choice of plugging into either cabinet. The problem that I see is the feedback connection goes to the positive terminal on the output jack. If i connect to both I will essentially be shorting out the 4 and 8 ohm taps. My thought is putting in a 2 way switch that will send the feedback connection to either the 4 or 8 ohm jack, whichever is being used. Is this the best solution?

Good news. You can just connect the feedback line to one tap and it will work properly even when you connect the speaker to the other tap. For the Princeton 5F2-A circuit you should connect the feedback to the 8 Ohm tap. This applies if you use a switch to select taps or two separate jacks. Keep in mind that, if you use separate jacks, then you cannot use shorting jacks as Fender often did on the main speaker output on many amps because the unused jack would short the output of the amp.

Edit: Simulpost with Enzo

[Chuck H]

My OT has a 4 and 8 ohm tap. I want to hook up two jacks, one for each, so that I have a choice of plugging into either cabinet.

But not both. With that arrangement you could plug a 4 ohm cabinet into the 4 ohm jack (8 ohm jack unused) or an 8 ohm cabinet into the 8 ohm jack (4 ohm jack unused). You should not plug an 8 ohm cabinet into the 8 ohm jack AND a 4 ohm cabinet into the 4 ohm jack. Well, you could do it, but I believe it's the same as any parallel cabinet situation. You would be halving your load. If you're going to use one cabinet or the other how much easier (and less prone to mistaken hookups) is it to use an impedance switch and choose 4 ohm or 8 ohm at the switch? Mesa did a thing for awhile where they had multiple jacks for the OT secondaries. Confused everyone, It was cumbersome.

And I'll back Enzo and Tom. The feedback loop connects to only one secondary. If there IS only one secondary then it can be connected to the output jack. This was the case with the 5f2a. Since your amp will have impedance choices you'll want to connect the feedback loop to a single impedance tap instead of the output jack. This is because the feedback loop needs to supply a fixed voltage to a circuit, prior to the output tube and speaker relationship, that operates at a fixed voltage regardless of speaker impedance.

[gymrat1964]

Awesome, thank you all for your input. I will be using only one at a time. Appreciate the help!

[Dave H]

You should not plug an 8 ohm cabinet into the 8 ohm jack AND a 4 ohm cabinet into the 4 ohm jack.

But you could plug a 16 ohm cabinet into the 8 ohm jack AND a 8 ohm cabinet into the 4 ohm jack

[Chuck H]

But you could plug a 16 ohm cabinet into the 8 ohm jack AND a 8 ohm cabinet into the 4 ohm jack

True! But that was the problem with the Mesa arrangement. They had (I think) an 8 ohm jack and two 4 ohm jacks. The instructions were (I think) to plug an 8 ohm cabinet into the 8 ohm jack, a 4 ohm cabinet into a four ohm jack or two 8's into both four ohm jacks. Just silly IMHO. Why not just have parallel output jacks on the amp connected to an impedance switch and let the player figure out parallel loads at the cabinets instead of at the amp? "Switch says the amp wants this load" is simpler than two 8 ohm cabinets into the jacks labeled 4 ohms.

[Enzo]

Any way you print it on the amp, there will always be a large percentage of the amp users who don't get it.

We print "two jacks wired in parallel", and think it explains something. But to them it does not.

I think the average user sees an ohms number and goes no further. "Oh, two jacks that say 4 ohms, I guess I can plug two 4 ohm speakers into the amp then."

[Chuck H]

I think the average user sees an ohms number and goes no further. "Oh, two jacks that say 4 ohms, I guess I can plug two 4 ohm speakers into the amp then."

Exactly! The Mesa thing actually implies "Plug two four ohm cabinets in here". Which is stupid. I do think more users would at least pause to think, or seek what they don't know if there's an impedance switch and two jacks. But I could be wrong. And yep, users are going to get it wrong for time immemorial. Anyway, I'm a proponent of the switch.

[Enzo]

On the other hand, one more thing to fail...

We do have people write in asking if their speaker says 4/16 ohms and their amp says 4/8/16, should they set it to 4 and run two cables?

[mikepukmel]

On the other hand, one more thing to fail...

We do have people write in asking if their speaker says 4/16 ohms and their amp says 4/8/16, should they set it to 4 and run two cables?

Two 8 ohm cables or two 16 ohm cables? That's where I got lost. And I could NEVER find where the ohms are written on the cable.