# 12" speaker replacement in a SF Princeton Reverb



## greco (Jul 15, 2007)

I am awaiting a new 12" Weber AlNiCo speaker for my SF Princeton Reverb.

When I stared to take out the 12" speaker presently in the amp, I noticed that the output transformer is virtually touching the speaker basket. As we all know, these amps were originally made for 10" speaker...so a 12" speaker is a bit of a tight fit.

If the new Weber speaker will not fit because of the OT, would the best solution be to move the OT slightly towards the rear of the amp by drilling new mounting holes...or...could I angle the OT slightly by only drilling one new mounting hole? Or any other possible approaches?

It is my understanding that the transformers are supposed to have the laminates (if this is the correct word) at 90 degrees to each other and, therefore, I wondered if only a slight change of angle would cause any real problems.

I know that this is a "worrying about a problem before knowing it exists" type of question, but I just want to be prepared. Somehow, knowing my luck, I suspect that the problem will exist. 

Thanks

Dave


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## Geek (Jun 5, 2007)

Hi,

If you mean mounting two transformers close at 90 degrees, yes, this is best. But in space-cramped situations, I have used 45 degreees quite successfully.

Cheers!


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## greco (Jul 15, 2007)

Geek said:


> Hi,
> 
> If you mean mounting two transformers close at 90 degrees, yes, this is best. But in space-cramped situations, I have used 45 degreees quite successfully.
> 
> Cheers!


Hi Gregg:

Thanks for the response. The transformers aren't that close...at a guess, I 'd estimate 6" to 8' distance between them.

Not wishing to wear out this topic...but is ANY angle between 90 and 45 degress OK... or is 45 degrees the very best choice based on some electronics theory? I think even 20 to 30 degrees angulation will give me the extra room I need.

I was able to find a another Weber 12A150 @ 8 ohms from a forum member (close to Kitchener) and I couldn't resist. I can't believe how huge the tone is from these speakers.


Cheers

Dave


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## torndownunit (May 14, 2006)

Dave,

If you are a member at the TDPRI forums you might want to look for info around there. putting a new baffle with a 12" speaker in a PR is a pretty common mod, and I know plenty of people over there have done it. I can't recall anyone mentioning problems with the speakers fitting.


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## greco (Jul 15, 2007)

torndownunit said:


> Dave,
> 
> If you are a member at the TDPRI forums you might want to look for info around there. putting a new baffle with a 12" speaker in a PR is a pretty common mod, and I know plenty of people over there have done it. I can't recall anyone mentioning problems with the speakers fitting.


Hi torndownunit:

Thanks for the info. 

I measured the angle of the basket on the present speaker and compared it to my Weber to see if I could get a better idea about the possible fit/problem. The difference is that the Weber has a small 90 degree rise from the attachment ring of the speaker before the angle of the basket starts. However, the good thing is that the Weber has much larger openings in the basket than my existing speaker.

I'm too lazy to take my existing Weber out of the extension cab and try and fit it into the Princeton (the logical approach) just to see if I really do have a problem or not. 

Cheers

Dave


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## Geek (Jun 5, 2007)

Hi Dave,



greco said:


> The transformers aren't that close...at a guess, I 'd estimate 6" to 8' distance between them.


Ah, no worries then mate! :smile:




> Not wishing to wear out this topic...but is ANY angle between 90 and 45 degress OK... or is 45 degrees the very best choice based on some electronics theory? I think even 20 to 30 degrees angulation will give me the extra room I need.


If they are right next to each other (for future ref, since that isn't your problem now), no. You're pretty much stuck. UNLESS, you have enough room right underneath to mount the other on the bottom of the chassis and at 90 degrees. This trick works with non Z-mount transformers only though.




> I can't believe how huge the tone is from these speakers.


Pretty wicked, aren't they! 

A fella just recently donated to the guitar amp cause a hatchback-full of vintage AlNiCo and ceramic speakers for guitar and bass. Vintage Jensen, CTS, Rola, etc. and there was four out of maybe 25 that came close to the Weber in tone.

Cheers!


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## greco (Jul 15, 2007)

Thanks Gregg..much appreciated

The hatchback full of speakers sounds (pun is intended) like it was exciting. Must have been fun testing all of them.

Cheers


Dave


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## Geek (Jun 5, 2007)

Hi Dave,



greco said:


> Must have been fun testing all of them.


It was, to the chagrin of the wife 

Cheers!


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## greco (Jul 15, 2007)

greco said:


> I am awaiting a new 12" Weber AlNiCo speaker for my SF Princeton Reverb.
> 
> When I stared to take out the 12" speaker presently in the amp, I noticed that the output transformer is virtually touching the speaker basket. As we all know, these amps were originally made for 10" speaker...so a 12" speaker is a bit of a tight fit.
> 
> ...


I finally put the Weber into the SF Princeton Reverb. What a job!! I had to remove the grille cloth (with frame..of course) and back off the mounting bolts for the speaker through the baffle. The speaker is a VERY close fit to the trannie. 

However...it is all back together now and sounds GREAT !!

These Princeton Reverbs are such fantastic little amps.

Cheers

Dave


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## Geek (Jun 5, 2007)

Awesome! :banana:


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## Wild Bill (May 3, 2006)

greco said:


> I finally put the Weber into the SF Princeton Reverb. What a job!! I had to remove the grille cloth (with frame..of course) and back off the mounting bolts for the speaker through the baffle. The speaker is a VERY close fit to the trannie.
> 
> However...it is all back together now and sounds GREAT !!
> 
> ...


Glad to hear it worked out ok for you!

I first learned about transformer coupling from one of the better engineers at Traynor/Yorkville Sound named Gene. Hum coupling CAN occur at better than 6"-8"! ? Especially with some "cheaper" transformers.

Hifi designs tend to be more "fussy" about hum than guitar amps. We just wail louder! Many high end hifi engineers would wire up the output transformer without drilling any holes for mounting, initially heeding the "90 deg" rule. Then they would patch a pair of headphones on to the output of the OT and fire up the amp circuit, with no signal applied. They were listening ONLY for hum! Then they would slowly rotate the transformer a few degrees to either side of that arbitrary 90 deg mark.

You don't even need to completely power the circuit! You can power only the PT primary to allow it to generate any hum field and leave the tubes out. Any hum from the PT only will be picked up in the OT and heard in the headphones.

It seems that due to factors in trannie winding it often turns out that things aren't exactly true to 90 degrees. As you slowly rotate the trannie while listening to the hum in the headphones you can clearly hear the "null" dip in hum level. THEN you mark and drill the holes!

I've always been grateful to Gene for the tip. I've used it to good advantage many times.

:food-smiley-004:


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## greco (Jul 15, 2007)

Wild Bill said:


> Glad to hear it worked out ok for you!
> 
> I first learned about transformer coupling from one of the better engineers at Traynor/Yorkville Sound named Gene. Hum coupling CAN occur at better than 6"-8"! ? Especially with some "cheaper" transformers.
> 
> ...


Thanks Wild Bill...your post was very interesting. From now on, if i ever see an amp with the trannies NOT at exactly 90 degrees to each other, I'll suspect that you might have worked on it, especially if it is sounding great. :food-smiley-004:

Peace

Dave


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