Hoffman Amplifiers Tube Amplifier Forum

Amp Stuff => Tube Amp Building - Tweaks - Repairs => Topic started by: Rubrburnr on July 26, 2015, 07:12:45 pm

Title: Princeton (5F2A) Build Question
Post by: Rubrburnr on July 26, 2015, 07:12:45 pm

Hey!  I want to do a 5F2A build to replicate a Feder Princeton and have a couple of questions.  Is the 5F2A Hoffman kit a 15watt kit?  I know I need a 10", however I don't know if I need a 4ohm or an 8ohm speaker.  Ok, final question (for now), how easy would it be to add and Aux. Input (3.5mm) into the chassis? I would prefer to play an mp3 without using an adaptor.... 

Thanks in advance!!

Title: Re: Princeton (5F2A) Build Question
Post by: Fresh_Start on July 27, 2015, 06:08:08 am

5 watts, not 15

Chassis has two input jacks, so you could use one for 3.5 mm. However, it would be simpler to follow Hoffman's docs and use 2 1/4" jacks and a converter. With something plugged into both jacks, they are effectively both "Hi" and there's some resistance between the two inputs for isolation.

Hoffman sells two "Champ" output transformers: 771 and "NOS 771". The first has both 4 ohm and 8 ohm taps, but is bigger and will have more bass and headroom. The second only has a 4 ohm tap and will sound more like a tweed Princeton.


Good luck,
Chip

Title: Re: Princeton (5F2A) Build Question
Post by: Rubrburnr on July 27, 2015, 10:03:42 am

Thank you for the reply Fresh_Start!  As you can tell I am extremely new to all of this.  Ok, so if I were to building a 15watt amp for a 10" speaker, which kit should I be looking at?

Title: Re: Princeton (5F2A) Build Question
Post by: sluckey on July 27, 2015, 11:31:04 am

If you like Fender tweeds then a 5E3 would work.

Title: Re: Princeton (5F2A) Build Question
Post by: Rubrburnr on July 27, 2015, 02:01:51 pm

Excellent!!  I do like Fender!  I originally wanted to build the 5E3 but I was afraid I would sacrifice sound quality pushing it through a 10" speaker.   What ohm will the speaker be needed for the 5E3?

Title: Re: Princeton (5F2A) Build Question
Post by: sluckey on July 27, 2015, 03:01:23 pm

Depends on the OT you put in it.

Title: Re: Princeton (5F2A) Build Question
Post by: Rubrburnr on July 27, 2015, 04:17:59 pm

What if I were to put the Mojo768sp in it?  I am definitely open to suggestions...

Title: Re: Princeton (5F2A) Build Question
Post by: sluckey on July 27, 2015, 05:16:30 pm

Quote from: Rubrburnr on July 27, 2015, 04:17:59 pm

What if I were to put the Mojo768sp in it?  I am definitely open to suggestions...

I'm not familiar with Mojo transformer numbers. Don't they list the specs?

Title: Re: Princeton (5F2A) Build Question
Post by: Rubrburnr on July 27, 2015, 05:25:59 pm

Quote from: sluckey on July 27, 2015, 05:16:30 pm

Quote from: Rubrburnr on July 27, 2015, 04:17:59 pm

What if I were to put the Mojo768sp in it?  I am definitely open to suggestions...

I'm not familiar with Mojo transformer numbers. Don't they list the specs?

Sure do...
 Part#      Mounting       Height       Length        Width   Watts   Primary   Sec.            Weight
Mojo768sp PDF   3 1/8"   2 1/4"   2 3/4"   2 1/4"   25         8000        4-8-16          1 lb 7 oz

http://el34world.com/Transformers/files/MOJO768sp.pdf (http://el34world.com/Transformers/files/MOJO768sp.pdf)

Title: Re: Princeton (5F2A) Build Question
Post by: sluckey on July 27, 2015, 05:28:14 pm

Looks like you have several choices for speaker impedance.

Title: Re: Princeton (5F2A) Build Question
Post by: Rubrburnr on July 28, 2015, 06:41:49 pm

Thanks for your help!!  I'm sure I'll be back with many more questions...