PRRI external speaker

I'm considering an extension cab but this section in the manual confuses me. The internal and external speaker jacks are side by side and the plate indicates a total 8 ohm load. I understand two 16 ohm speakers in parallel would calculate to 8 ohms, but does this also mean I can't use just the external speaker jack with a single 8 ohm speaker? Thanks

EXTERNAL SPEAKER—Plug-in connection for an external
speaker. This jack is wired in parallel with the INTERNAL
SPEAKER JACK {M} and affects the speaker impedance load.
Use 8Ω minimum total. To use the external speaker output, first
disconnect the internal speaker. Then connect a 16Ω speaker
load (minimum) to the internal speaker jack and another 16Ω
speaker load (minimum) the external speaker jack.

The Fender documentation always states 8ohm total load but there's plenty of folks that run Fender amps with an 8 ohm extension speaker plus the internal speaker connected. They can handle a 4ohm total load.

Adding an 8ohm cab should not be a problem.

Thanks!

fowlermike wrote: "but does this also mean I can't use just the external speaker jack with a single 8 ohm speaker?"

I know that you had one question answered, ad I know that you posted the manual's passages that are pertinent to this...but the statement I quoted above makes me want to say this..... Do not plug a speaker into the extension jack only. You must have a speaker in the main or internal speaker jack before you can use the external speaker jack.

Also, I agree with the posts above that FEnder amps in the past have been very tolerant of mismatches..especially to the lower side....50% of the recommendation. However, your manual states explicitly that one should not do this. That is not to say that the amp won't tolerate the mismatch, but the manual tells you not to do this. Vintage FEnder manuals did not makes this type of statement. Ex: Here is a direct quote from a manual for the 1973 "Super Reverb and Pro REverb Amplifiers'' as it states on the front. The rear panel functions section for the extension speaker jack reads: "PRovides a connection to an extension speaker enclosure."

With your amp, I would say.... You pays your money and you take your risks.

FWIW< all amps perform best with a load matched to the OT's requirement.

So, I guess what were saying is that if we want to use the ext. spkr with the internal speaker, we should load a 4 ohm speaker in the cab, and a 4 ohm ext. spkr so there is no mismatch?

As I read it you would install a 16 ohm speaker to the internal jack and another 16 ohm speaker to the external jack to create a total 8 ohm load

The PRRI the transformer will work just fine with another 8 ohm cabinet plugged in, but it pushes it a little harder. I'm not super technical, but I know that the transformer is like a vintage one that doesn't drop to 4 ohms when it sees another 8ohm cab plugged in.

Because of that I changed mine to the Heyboer TO22 sold by Allen Amps (http://www.allenamps.com/parts.php#transformers). It's beefier and allows you to have the external 8 ohm speaker drop it down to 4 ohms.

I noticed a big difference in clarity when I did this and used the amp for a while with an external 2x12 cab along with the internal speaker.

So, I guess what were saying is that if we want to use the ext. spkr with the internal speaker, we should load a 4 ohm speaker in the cab, and a 4 ohm ext. spkr so there is no mismatch?

No, I am thinking that that OT might tolerate a mismatch at 4 ohms.....two 8 ohm loads in parallel. However, the manual explicitly says not to run less than an 8 ohm load...in total. That means...run a single 8 ohm load...whether as the internal speaker or an external 8 ohm load plugged into the main speaker jack with the internal speaker disconnected or as two 16 ohm loads in parallel through both of the speaker out jacks.
That OT definitely does not want to see a 2 ohm load that would result from the two 4ohm loads in parallel suggested by MisterMullens.

Thanks Wally, I think you got to the heart of my question which I probably didn't articulate. As a newb I'm reading that manual to say I need to run internal and external together but I believe I can just run the external as long as I keep an 8 ohm load, be it one 8 ohm speaker or two 16 ohm

fowlermike54, here is another way of ooking at it....
1)You can run the internal speaker..8 ohms...by itself out of the Main Speaker jack.
2)You can run an external sepaker cab/load of 8 ohms instead of hte in-cab speaker by unpluggin g the internal speaker form the Main Spkr jack and plugging that external 8 ohm load into the Main Spkr jack. IN otehr words, with only one speaker load,
3)ACcording to the strict reading of the manual; if you want to run two speaker loads, you should run two 16 ohm loads for a total load of 8 ohms.

That is what your manual says, Those of us who have had/do have vinatge Dr's are very comfortable running two 8 ohm loads for a total load of 4 ohms...b.ecause FEnder provided for it and it has been done for ages. There are also folks with vintage FEnders who have run a 100% larger load with no ill-effects. Your manual says that your amp should not be treated that way. I am not going to argue with Fender because they built the amp. At any rate, a tube amp sounds best with a matched load on it. That load for your amp is 8 ohms....no matter how you get there, adn there should ALWAYS be a load plugged into the Main Spkr jack.