#1
I am currently in the market for a 70's Twin Reverb and have some thoughts/questions about running the amp with an external cab (yep, my back hurts already). Right out the gate, there's no "safe" way to run a non-ultralinear TR using a cabinet without swapping out the internal speakers. I always match impedances, but I'm wondering if I can get away with a mismatch at least for a little while.

The cabinet I plan on using is an 8 ohm closed-back 2x12; two 16 ohm speakers in parallel. If I plug this into a non-UL TR, the total load becomes 2.67 ohms. People talk about Fender amps being okay running 2 ohm loads, so I can only imagine that 2.67 ohms would be a slightly better mismatch. What exactly is the effect of running the amp with this kind of load? Would this be an okay idea?

I checked the schematic for this era of TRs and the external speaker jack is marked "4 or 8 ohms," but there's no reference to the internal speakers or total load of the amp. This would leave me to believe that TRs can handle 2 and 2.67 ohm loads. Perhaps someone could clarify this?

If I take the same cabinet and plug it into a ultralinear TR, the speaker jacks are in parallel so I would end up with a 12 ohm load. When plugging a cabinet into the extension speaker jack, the 8 ohm tap on the OT becomes active, making this a 50% upward mismatch. People say Fender amps can handle a 100% upward mismatch, so this mismatch seems like it would be fairly safe. With this situation, however, I can eventually change the speakers in my cab to make it 4 ohms and then I have no worries. For the time being, would a 50% mismatch be reasonably safe? I'm leaning towards this option because it would make playing with or without a cabinet much simpler.

In these situations I realize that the external speakers will be receiving half the power of the internal speakers, but the efficiency of the speakers and closed-back cabinet could make up for the loss of power.

Another idea I had for the non-UL TR was to re-wire the internal speakers for 16 ohm and then use my cabinet to get a 5.33 ohm load. However, now the internal speakers are receiving half of the power of the external speakers and the cabinet would definitely appear louder. I've read that the difference between 5.33 and 4 ohms is negligible, but I imagine that the difference in volume will be quite noticeable.

Am I missing any other possible configurations that would be better? Thanks.
Fender '72 Telecaster Deluxe RI
Schecter C-1 Artist II
1978 Music Man HD130
+ a bunch of neat pedals

screamy emo band
#2
1st question: A Twin is already loud as hell with an open back, stage filling design. Why would you want to make it louder by adding more speakers?

If it were mine and I wanted to do this, I would replace the internal speakers so that each cab presented an 8 ohm load. This will always be safe and not risk cooking that expensive OT. You might be ok at 2 ohm but it is a grand science experiment with very real downsides.

I gigged for 30 years with a 64 Super Reverb 45w and it was just always too loud for the stage wide open. Always, so I dragged around baffles and attenuators to avoid getting kicked out of LA clubs.... Again.

Often, less is more.
"Your sound is in your hands as much as anything. It's the way you pick, and the way you hold the guitar, more than it is the amp or the guitar you use." -- Stevie Ray Vaughan

"Anybody can play. The note is only 20 percent. The attitude of the motherfucker who plays it is 80 percent." -- Miles Davis

Guthrie on tone: https://www.youtube.com/watch?v=zmohdG9lLqY
Last edited by Cajundaddy at Mar 22, 2016,
#3
@Cajundaddy
I don't plan on using the cab to make the amp louder, but rather to fill more space and add more depth. I play in a two-piece band and aim to create a wall of sound to make up for the lack of second guitar and bass. I also don't plan on using it all the time.

I've thought about replacing the internal speakers to reflect an 8 ohm load and then with the 8 ohm cab, I'd get 4 ohms. My only issue with that configuration is that I would always need to use the cab to run the amp properly.

Basement punk bands in Minneapolis sure like to get loud though.
Fender '72 Telecaster Deluxe RI
Schecter C-1 Artist II
1978 Music Man HD130
+ a bunch of neat pedals

screamy emo band
Last edited by nick.culliton at Mar 22, 2016,
#4
Quote by nick.culliton
@Cajundaddy
I don't plan on using the cab to make the amp louder, but rather to fill more space and add more depth. I play in a two-piece band and aim to create a wall of sound to make up for the lack of second guitar and bass. I also don't plan on using it all the time.

I've thought about replacing the internal speakers to reflect an 8 ohm load and then with the 8 ohm cab, I'd get 4 ohms. My only issue with that configuration is that I would always need to use the cab to run the amp properly.

Basement punk bands in Minneapolis sure like to get loud though.



If you only run the amp at low volumes, 2.67 ohm will not likely be a problem since we are not talking about much current. Running at full tilt 2.67 ohm will generate some heat in your OT putting it at risk. I don't like burning down a good amp so I would not do it. A Twin will run just fine at 4 or 8 ohm with no noticeable difference in tone or loudness. Still damn loud.

Honestly, a DRRI or HRD and an SM57 into the PA would probably accomplish the same goal without all the moving and storage.
"Your sound is in your hands as much as anything. It's the way you pick, and the way you hold the guitar, more than it is the amp or the guitar you use." -- Stevie Ray Vaughan

"Anybody can play. The note is only 20 percent. The attitude of the motherfucker who plays it is 80 percent." -- Miles Davis

Guthrie on tone: https://www.youtube.com/watch?v=zmohdG9lLqY
Last edited by Cajundaddy at Mar 22, 2016,
#6
Just my 2 cents. I had a Twin for many years in the 70's and it was probably the best all round amp I ever owned. It was killer loud but also next to my fiancé's Ampeg SVT it has to be one of the heaviest amps ever made. To make it worse, I had the nerve (stupidity?) to put in a set of JBL speakers. I can't imagine needing another cabinet. Good luck. (Also going down to 2 ohms sounds a little scary to me. One accidental short and........)
Yes I am guitarded also, nice to meet you.
#7
Hey all, thank you for the insight! I do not plan on running a TR with a 2 ohm load. With my 8 ohm cab, the load would be 2.67 ohms. Also, my band rarely plays at venues that mic amplifiers.
Fender '72 Telecaster Deluxe RI
Schecter C-1 Artist II
1978 Music Man HD130
+ a bunch of neat pedals

screamy emo band
#8
Quote by Cajundaddy
If you only run the amp at low volumes, 2.67 ohm will not likely be a problem since we are not talking about much current. Running at full tilt 2.67 ohm will generate some heat in your OT putting it at risk. I don't like burning down a good amp so I would not do it. A Twin will run just fine at 4 or 8 ohm with no noticeable difference in tone or loudness. Still damn loud.

Honestly, a DRRI or HRD and an SM57 into the PA would probably accomplish the same goal without all the moving and storage.


Updated for relevance and accuracy.
"Your sound is in your hands as much as anything. It's the way you pick, and the way you hold the guitar, more than it is the amp or the guitar you use." -- Stevie Ray Vaughan

"Anybody can play. The note is only 20 percent. The attitude of the motherfucker who plays it is 80 percent." -- Miles Davis

Guthrie on tone: https://www.youtube.com/watch?v=zmohdG9lLqY
#9
Quote by nick.culliton
@Cajundaddy
I don't plan on using the cab to make the amp louder, but rather to fill more space and add more depth. I play in a two-piece band and aim to create a wall of sound to make up for the lack of second guitar and bass. I also don't plan on using it all the time.

I've thought about replacing the internal speakers to reflect an 8 ohm load and then with the 8 ohm cab, I'd get 4 ohms. My only issue with that configuration is that I would always need to use the cab to run the amp properly.

Basement punk bands in Minneapolis sure like to get loud though.


If you want a more dynamic, simulated second guitar sound, you should run a second different amp altogether. Running a speaker cabinet is really not going to do much, especially for the audience.
#10
Quote by Cajundaddy
Updated for relevance and accuracy.


“Ignorance more frequently begets confidence than does knowledge.”
Charles Darwin
#11
I canned the Twin Reverb idea and got myself a '78 Music Man HD130. It's a little smaller and lighter than my Bassman 100. Plus switchable impedance makes my life much easier.
Fender '72 Telecaster Deluxe RI
Schecter C-1 Artist II
1978 Music Man HD130
+ a bunch of neat pedals

screamy emo band