DIY C3g F2a tube amp

I recently spend some time building a new F2a tube amp over the year-end holidays. 



It uses a siemens c3g tube as the driver tube and Siemens F2a as the power tube.  Separate B++ power supply for the c3g from the B+ supply for the F2a. Power irons are from Nicholas - Promethieus and OPT is from Hashimoto.  I have switch select for the c3g to be on a triode or pentode mode, and f2a in triode or ultralinear mode.

I have cloked-in about 25 hours of burn-in time.

Hi Mthoi,
  Looks great...! You've talking about it when I visited your place a couple of months back and now it's already up and running.

  Now..The million dollar question...How does it sound compared to your 845 and 300b?

Hi Vt4c,
That is a tough question.  I have since moved the f2a to replace the 300b in my living room Altec VOTT system. 

I can get four tube-op combiantions using switch select - c3g in triode/pentode, F2a in triode/ultralinar.  Each has its own sound character.

The F2a (in triode c3g/triode F2a - 8W, as compared to the c3o/300b) has better mid-bass and HF extensions, better PRAT and clearer mids.  It also drives the Altec 1505 horns better - removing some of the "honkiness". It also sounds less warm.

In C3g pentode/f2a Ultralinear mode (est. 12W) , it out-drives the 12at7/2A3/845 (18W) amp for speed, prat.  

Generally, I like the F2a for the overall clarity and mid-bass control. It makes the 300b sounds "slow".

Hi Mthoi,
   Thanks for your reply.

   From your description, it sounds like the F2A on the VOTT is better match compared to the 300B.

    You've not particularly mentioned about the bass of the F2A, is it good...I suspect it should?

Mthoi, 

Congrats that you have built something better.

Enjoy your new toy.

Cheah

Vt4c - I tried the set-up with the Tyler Acoustic/Jabo horns setup in my TV room. The bass is good and is comparable to the 845; perhaps not be as "deep", but the "speed" is better.  

Cheah - Tx.  A new toy to keep the idle hands busy over the year-end holidays.

I have since clocked about 35 hours and it is sounding better.  Played Santana last night and liked the speed; the kick drums and percussions are sharp and tight. The electric guitar sounds very good.

Mthoi, 

For 300b you may want to try Elrog version. They are just so different. Hard to discribe with words, until you listen to one.

Cheah

Hi Cheah,
I look forward to the opportunity to audition an Elrog 300b. I have been following Thomas Mayer's blogs on this tube also.
I have started an interest in
klangfilm amps, hence the f2a. I guess I am also going through a "flavour of the month" in diy.
Reg

Hello MTHOI,
Amazed at the speed of your amp building skills ! You can get one amp done in a few days .
I took a few months building a kit !
Let me know when you come to town .
Hi fi scene here  is quite active here  these days

kp

Greetings Dr KP,

Tx - some idle time during year end that prompted the quick build.

I would alert you in advance on the next trip to Kuching.  It would be an opportunity to catch up with all the Hi-Fi Kakis.

Best regards.