300bSE journey under way

[cjkpkg]

The 300b has begun...attached is a pic of the basic layout and rough schematic. The PSU is still under development - each 300b will have its own filament xformer.

******* chassis must weigh 30lbs so far...at least...

looking forward to documenting this build...and a big shout out to this DIY community to make stuff like this possible!

Carl

[rman]

Cool

I like the constant current draw front end. Is that inspired by John Broskie?

Cheers.

[analog_sa]

Sufficient gain?

[THD+N]

Originally Posted by cjkpkg

The 300b has begun...attached is a pic of the basic layout and rough schematic. The PSU is still under development - each 300b will have its own filament xformer.

******* chassis must weigh 30lbs so far...at least...

looking forward to documenting this build...and a big shout out to this DIY community to make stuff like this possible!

Carl

Why not do the Reichert circuit? It is tried and true and you can't go wrong.
Flesh and Blood, The Reichert 300B By Herbert Reichert

[analog_sa]

Originally Posted by THD+N

It is tried and true and you can't go wrong.

Or right. Whatever you do to that circuit it will remain mediocre. Not sure if even adding a pound of silver will help.

[Yvesm]

Originally Posted by analog_sa

Sufficient gain?

No ! And by far !
Computed with an axe:
- 300b needs some 140V peak to peak in its grid.
- The only voltage gain stage (half 6SN7) will hardly exceed 10
- So 14V peak to peak (near 5V rms) will be necessary on input for full output power.

Yves.

[tomchr]

If you load the 6SN7 with a CCS, you'll get upward of 20 V/V gain in the common cathode stage. So to drive the 300B to 70 Vpeak you'd need 3.5 Vpeak (or 2.5 V RMS) on the input. I built a circuit that did that. It sounded really good. I used a source follower rather than a cathode follower for the driver stage, though.

An anode follower is another good option.

One question: How well does the circuit perform in a prototype setup? I'm assuming you built it on a peg board or something before you cut holes in the chassis...

~Tom

[cjkpkg]

honestly I have not breadboarded it up yet...I have seen so many 6sn7 front end designs around - most being anode followers though...JELabs, tmamps, diyaudioprojects.com etc...

The other thing that might be worth playing around with would be a 6sl7 up front with some minor tweaking of values...

Also I know Ill use the iron - James 6123 and allied 6k7vg. Since I have cut the holes for the iron and the tube sockets, I suppose I am stuck with octal unless I breadboard up a noval board and bolt it under the chassis.

I am assuming with some tweaking I will be happy with either a 6sn7 or 6sl7 front end. Thats the beauty of P2P right?

[kstagger]

diyhifisupply has a nifty 300B amp (designed by T. Loesch) that uses a pentode front end (EF86) driving a choke loaded 5687 cathode follower. That will really drive the 300B...

For my own 300B amp, I used the original "Legacy" 300B signal circuit and which has a SV83 as a driver. Results were excellent with a clean, snappy sound. Not soggy or "overly tubey" at all. Another option is the C3m or C3g.

[THD+N]

Originally Posted by analog_sa

Or right. Whatever you do to that circuit it will remain mediocre. Not sure if even adding a pound of silver will help.

I figured someone would post a useless reply...