I have searched and read pretty much everything on diyAudio regarding 12B4 preamps & now my head is spinning!
I would like to build one but am looking for schematics for both the pre & a good PSU to match (I'm a bit partial to tube rectifiers but can be easily convinced). Many of the earlier posts no longer have the attachments so I'm sorta flapping in the breeze here. It seems as if fdegrove & arnoldc are on to something but some information seems to be missing.
Any help for this pseudo-newbie would be much appreciated.
Thanks in advance.
I would like to build one but am looking for schematics for both the pre & a good PSU to match (I'm a bit partial to tube rectifiers but can be easily convinced). Many of the earlier posts no longer have the attachments so I'm sorta flapping in the breeze here. It seems as if fdegrove & arnoldc are on to something but some information seems to be missing.
Any help for this pseudo-newbie would be much appreciated.
Thanks in advance.
One grid, two pins brought out for use. Best practice is a CC grid stopper at EACH pin, right at the pin. Your input will then connect to both resistors, on the other end of the resistor.
Here are the inevitable questions -
1) what is the value of the resistor after the 9H choke in the psu?
2) what are the resistor power ratings (want to check my math) and ANY type preferences?
3) the closest I could get to a 9H choke was the Hammond P-T193M at 10H/300mA, I see no reason why this expensive little puppy should not work?
4) AC heaters?
5) you like the Mundorf cap $70 more than the Solen 🙂 ?
Thanks again.
1) what is the value of the resistor after the 9H choke in the psu?
2) what are the resistor power ratings (want to check my math) and ANY type preferences?
3) the closest I could get to a 9H choke was the Hammond P-T193M at 10H/300mA, I see no reason why this expensive little puppy should not work?
4) AC heaters?
5) you like the Mundorf cap $70 more than the Solen 🙂 ?
Thanks again.
Yes, it's my design. The schematic drawing was made by Erick Bates, AKA Buzz, from a narrative I provided. The parts values and styles shown reflect Buzz's "pile" and strong predeliction for "boutique" items. I'm CHEAP and look for good performance at modest expense.
The critical current in mA. for proper choke I/P filter operation is approx. V/L. It works out that 1K Ohm of resistance is used for each Henry in the 1st inductor. So, a 9 KOhm resistor is appropriate with 9 H. and a 10 KOhm bleeder is appropriate with 10 H.
AC heaters should be fine, as they are biased off B+. If hum levels are unacceptable, switching to DC heater power is easy enough.
If an "oiler" is to be used as the O/P coupler, I'd look for Soviet surplus. Mundorf is good, but oh that price. No, I would not use Solen or any other SCR (France) made MPP. You can get GE 40L3501s and 470 nF. film and foil bypasses from Jim McShane for very little money.
A Hammond 193M is certainly massive enough for 1st inductor service in this design. You might get away with a Hammond 193JP, as the potting should muffle "singing". This PSU filter is pseudo-choke I/P. The "fudge" factor cap. takes some strain off the 1st inductor.
A 5 W. rated part provides a nice margin of safety, in the bleeder position. A 1 W. part is fine for the 500 Ω cathode bias resistor. All the other resistors can be 1/2 W. Carbon composition please, in the grid stopper positions. Except for the stoppers, low noise Vishay-Dale RN65 metal film parts get my nod.
IMO, the popular 10M45S is not up to snuff, for this job. Use a good cascode design for CCSes.
The critical current in mA. for proper choke I/P filter operation is approx. V/L. It works out that 1K Ohm of resistance is used for each Henry in the 1st inductor. So, a 9 KOhm resistor is appropriate with 9 H. and a 10 KOhm bleeder is appropriate with 10 H.
AC heaters should be fine, as they are biased off B+. If hum levels are unacceptable, switching to DC heater power is easy enough.
If an "oiler" is to be used as the O/P coupler, I'd look for Soviet surplus. Mundorf is good, but oh that price. No, I would not use Solen or any other SCR (France) made MPP. You can get GE 40L3501s and 470 nF. film and foil bypasses from Jim McShane for very little money.
A Hammond 193M is certainly massive enough for 1st inductor service in this design. You might get away with a Hammond 193JP, as the potting should muffle "singing". This PSU filter is pseudo-choke I/P. The "fudge" factor cap. takes some strain off the 1st inductor.
A 5 W. rated part provides a nice margin of safety, in the bleeder position. A 1 W. part is fine for the 500 Ω cathode bias resistor. All the other resistors can be 1/2 W. Carbon composition please, in the grid stopper positions. Except for the stoppers, low noise Vishay-Dale RN65 metal film parts get my nod.
IMO, the popular 10M45S is not up to snuff, for this job. Use a good cascode design for CCSes.
Hi guys,
Very interesting tube here🙂
Please, can you say to me if these 12B4 are even slightly microphonic?
What brands are suggested ?
Thanks ,
Paolo
Very interesting tube here🙂
Please, can you say to me if these 12B4 are even slightly microphonic?
What brands are suggested ?
Thanks ,
Paolo
You asked the question I was too scared to! I looked through every reference I had but couldn't find it.
It is a constant current source or CCS. A quick search will bring up more information than you could ever want.
Ok. This is so simple I'm going to make it.
Questions though... 47nF... how many uF is that? What kind of cap?
The Resistors, what voltage should they be good for where not indicated?
The xformer... how many volts at how many amps on the 120VAC and 12VAC secs?
Sorry I'm a bit thick when it comes to this stuff.
Questions though... 47nF... how many uF is that? What kind of cap?
The Resistors, what voltage should they be good for where not indicated?
The xformer... how many volts at how many amps on the 120VAC and 12VAC secs?
Sorry I'm a bit thick when it comes to this stuff.
Thanks tweeker...No resistor will see more than 200V in that amplifier, wattage is the only rating of concern here.
The inexpensive O/P coupling cap. setup is a 5 μF. GE 40L3501 MPP bypassed by a 470 nF. film and foil part. 470 nF. = 0.47 μF.
Jim McShane has the GE MPPs and some of the now NOS Panasonic ECQ-P(U)s. Other candidates for the film and foil bypass are a Dayton from Parts Express and a 716P series Orange Drop.
The diodes in the B+ bridge are 600 PIV Schottkys. Church mice are noisier. 😀
Jim McShane has the GE MPPs and some of the now NOS Panasonic ECQ-P(U)s. Other candidates for the film and foil bypass are a Dayton from Parts Express and a 716P series Orange Drop.
The diodes in the B+ bridge are 600 PIV Schottkys. Church mice are noisier. 😀
Eli Duttman said:
Besides the fact that these sound terrible, I've had them fail as a dead short at reasonably low voltages. For a cheap cap, go with the 716.