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
Or right. Whatever you do to that circuit it will remain mediocre. Not sure if even adding a pound of silver will help.
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.
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
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
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?
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?
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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.
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.
A friend of mine wanted an all tubed monobloc version and we reach to that:kstagger said:
http://www.dissident-audio.com/AutoIndex/index.php?dir=SE_300B/KISS/&file=SE300B-Eric.pdf
Since Western Electric showed the way, you may use a pentode to drive a 300B without being finger pointed as heretic.
Yves.
I agree with Yves. Pentode driver is the fastest way to make a good 300B amplifier!
You can use many pentodes. If you have none in your junk box, buy some JJ EL84 for a low price. Use a high voltage supply [500 - 550V unloaded] and LCLC filtering. Use a resistor divider to get VG2=150V, and anode resistor. 12 .. 15K
Pentode drivers give much more articulate sound than 6SN7 cascade, and gets you closer to the music - but the power supply must be cleaner.
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OK,
I have switched gears a little...I tried the CCDA, then the SRPP, and ultimately I settled on something very close to the JE Labs 300b and/or the below schematic. I am using the 6SN7 driver and the gain seems ample but distortion comes on before I would like. I am thinking of trying a MOSFET follower. It does drive/play loudly but not as much as my MOSKIDO or the EL84PP. There is something, however, about that sweet SE sound...
I have switched gears a little...I tried the CCDA, then the SRPP, and ultimately I settled on something very close to the JE Labs 300b and/or the below schematic. I am using the 6SN7 driver and the gain seems ample but distortion comes on before I would like. I am thinking of trying a MOSFET follower. It does drive/play loudly but not as much as my MOSKIDO or the EL84PP. There is something, however, about that sweet SE sound...
An externally hosted image should be here but it was not working when we last tested it.
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Hi Nick
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.
Actually analog_sa's input is very meaningful. Pls check Pete's study High-Gm driver pentode test data here he also showed cascoded drivers behavior. In fact I also started with cascoded type drivers for 300b many many years back and moved into pentode driver, single 417, trioded 7788/d3a or no tube driver at all.
Regards
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.
Actually analog_sa's input is very meaningful. Pls check Pete's study High-Gm driver pentode test data here he also showed cascoded drivers behavior. In fact I also started with cascoded type drivers for 300b many many years back and moved into pentode driver, single 417, trioded 7788/d3a or no tube driver at all.
Regards
? The Reichert schematic isn't a cascode, it's for cascaded triodes. Are you knocking cascodes or multiple stages?
Update...
I implemented the above schematic for the most part. I have abandoned powerdrive for now since I could not get it to work - must need to tweak a bunch of resistors to get it to work.
HOWEVER...today I plopped in a 5AR4 for rectification and added another 10uF for the first cap which kicked the B+ up to about 450...I must say that this amp will keep up with the EL84PP amp...or pretty close anyways...300b's are running about 80mA
While I'm sure there would be a benefit...I no longer feel a STRONG desire to get powerdrive working...this amp...so far...is that good...
I implemented the above schematic for the most part. I have abandoned powerdrive for now since I could not get it to work - must need to tweak a bunch of resistors to get it to work.
HOWEVER...today I plopped in a 5AR4 for rectification and added another 10uF for the first cap which kicked the B+ up to about 450...I must say that this amp will keep up with the EL84PP amp...or pretty close anyways...300b's are running about 80mA
While I'm sure there would be a benefit...I no longer feel a STRONG desire to get powerdrive working...this amp...so far...is that good...
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Looks like 200K (or perhaps 280K) to me, the grid choke is not a bad idea as long as you understand what is going to happen to the infrasonic response. Need to significantly increase the value of the coupling cap, and sometimes a little R [somewhere from 0 - 50K] in series with the choke will help reduce the Q of the resulting LF resonance.
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Nice looking amp btw.. I've been running 300B SE amps in various incarnations for about 10yrs.. Working on a GM70 amp now..
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