Yet another 12B4 line stage, or is the 12B4 better than the Grounded Grid.....

[Zen Mod]

Will it ever all be in just one chassis? Doubtful since I'm always trying something new in the very little spare time I have these days.

Mark

where you'll put chokes in it ?

 

[jasonb84]

Has anyone run this tube at class A with a plate of 150V/34mA as per the datasheet? Or is it felt that 120V/~24-28mA sounds best.

Regarding the plate choke and single OD3. Zen's schematic redraw has a 100+uf cap to ground, followed by 1k67/10W into the two OD3. These draw 30mA, they are in series so am I correct in thinking a single will also draw 30mA leaving the difference to go to the plate? Is there any need for voltage dropping resistors at all, ie could the PS be directly connected to the regulator if the supply voltage is low enough?

Is it now established that a good sounding way to go is to load up the PS with lots of iron, feed the single gas regulator and then use a plate choke to drop the last bit of voltage down to the plate? A choke rated at anything above 60mA will work but what does the inductance rating effect? If I'm given the DCR of the choke then I could work my way backwards to the supply.

 

[Zen Mod]

Has anyone run this tube at class A with a plate of 150V/34mA as per the datasheet? Or is it felt that 120V/~24-28mA sounds best.

hehe
I dunno;
I didn't play with 12B4 at all (you can't count at least 10 another similar and non similar toobz in my WOT prototype )

Regarding the plate choke and single OD3. Zen's schematic redraw has a 100+uf cap to ground, followed by 1k67/10W into the two OD3. These draw 30mA, they are in series so am I correct in thinking a single will also draw 30mA leaving the difference to go to the plate? Is there any need for voltage dropping resistors at all, ie could the PS be directly connected to the regulator if the supply voltage is low enough?

and question is?

Is it now established that a good sounding way to go is to load up the PS with lots of iron, feed the single gas regulator and then use a plate choke to drop the last bit of voltage down to the plate? A choke rated at anything above 60mA will work but what does the inductance rating effect? If I'm given the DCR of the choke then I could work my way backwards to the supply.

ok
I'll stop joking

if you use choke as anode load-nice starting point for anode voltage is in ballpark of 150 V;
assuming that your choke will not have more than ,say, 10V of voltage drop across it-you can freely discount that voltage drop in entire situation;anyway-toobz are made in some range of characteristics and you'll hardly find exactly replicated ones from manufacturer's data.

use power xformer,rectifier and smoothing mechanismus whatever you like,put resistor and gas toob ,no cap cross gas toob (for start) ,calculate that series resistor for sum current of say 55 to 60 mA ,put choke on top of anode ,cap on anode and listen
after that you can measure exact voltages,try to change few bits and bobs to make exact voltages,and you probably will not hear any change if you are in range of 10% of estimated values;


that's not RIAA EQ ;topology is more important than ohm or two here and there;
one possible element for improvement can be CCS instead series resistor (preceding gass regulator toob)
try it on breathboard first

you ca always buy few pcbs from P10 or Geek

 

[Geek]

What point for "best sound" is sooooo subjective

From the curves, a 150V @ 24-28mA has great linearity.

 

[Zen Mod]

Is there any need for voltage dropping resistors at all, ie could the PS be directly connected to the regulator if the supply voltage is low enough?

think again;

voltage drop across this resistor is ,in fact, voltage range for regulation ;
no surplus,no regulation

 

[jasonb84]

Thank you Zen for all the clarification. Now to source some parts and start building.

What is the range in henries that would be suitable for the anode choke?

 

[Mark A. Gulbrandsen]

$17,000! I hope it comes with K-Y!!!

Hey, mine is bult from the best parts available and theirs is not even built with ceramic/silver Tektronix terminal strips nor does it have the best available remote controled attenuator built into it. Ha... not only should it come with a gallon of K-Y but also with a 44 magnum to finish your self off after you discover on this thread that you can build it even better for less than 200 bucks!

Mark

 

[jasonb84]

To pose the question again in case no one picked up on it. I count 1 274B rectifier, 2 12B4A's, 4 OD3 regualtors but I still can't figure out the pair in front. They look to be a similar shape to the OD3 but emit a typical orange glow rather than the unique purple.
Anyone know what they are?

 

[jasonb84]

Forgot to add:
What is the expected life of these tubes in this particular circuit? Should we be stocking up on an extra pair or two?

 

[pengboon]

Ha... not only should it come with a gallon of K-Y but also with a 44 magnum to finish your self off after you discover on this thread that you can build it even better for less than 200 bucks!

Mark

Hahaha... I couldn't stop laughing when I read this !!!

Hey Mark, yours doesn't come with the orange glow toobs!!

 

[pengboon]

To pose the question again in case no one picked up on it. I count 1 274B rectifier, 2 12B4A's, 4 OD3 regualtors but I still can't figure out the pair in front. They look to be a similar shape to the OD3 but emit a typical orange glow rather than the unique purple.
Anyone know what they are?

My guess is a 0A3/VR75, since it looks octal.

 

[Mark A. Gulbrandsen]

Hey Mark, yours doesn't come with the orange glow toobs!!

Actually mine has 4 purple-pink glow toobs plus the two 12B4's. My rectification is also via toob but is contained in the DC bench supply which is seperate. Lets see.... the Stainless Steel top plate adds another $16.00 at Metal Supermarket to my already $200.00 price tag.....

Mark

 

[lt_texan]

transformer out ver

I made mine transformer out with switchable resistor/battery bias. I do like the battery bias best. Haven't seen much on others using Sowter output trannies. Is it cost? Quality? Bad return in this position?

Also, please help with some advice plese, should I have something across the transformer out, resistor and cap in series? This drives long cables to 2A3 monoblocks with 417A driver, input resistance is 1M (value of 417A's grid leak)

Thanks
Dan

 

[Mark A. Gulbrandsen]

So what is all the hoopla about using a tranny on a line stage that has this low of output impedance......? This line stage is pretty hard to beat in a transformerless state!

Mark

 

[Zen Mod]

So what is all the hoopla about using a tranny on a line stage that has this low of output impedance......? This line stage is pretty hard to beat in a transformerless state!

Mark

Mark
you still didn't tried choke loaded or parafeed or VOT with 12B4....
I remember that you also were sceptical - regarding few other things earlier

 

[Mark A. Gulbrandsen]

Choky,

My regulated DC supply does have choke feed.... then there's the gas regulators after that. My 12B4 is a trubute to Dr. Gizmo if you know who he is..... The last thing I'd want to do is stick a transformer in my line stage....

Mark

 

[Audio_idiot]

Hi guys,
I've been following this thread for a while and love the extream simplicity of it.

Hi Mark,
If you have not try anything other the R plate, have a go with the choke plate, it's much easier to implement then IT. I had some experiment with plate choke with many of my projects and they never fail to increase the gain and bandwidth.
Have a try and hear for yourself. Moreover, chokes can be comperatively economical experiment.

Cheers

 

[Zen Mod]

Choky,

My regulated DC supply does have choke feed.... then there's the gas regulators after that. My 12B4 is a trubute to Dr. Gizmo if you know who he is..... The last thing I'd want to do is stick a transformer in my line stage....

Mark

me:

you still didn't tried choke loaded or parafeed or VOT with 12B4

I know that you have choke feed.......
what I say is -try to get rid of resistor anode load
if you have luck,you will have another layer of dynamics and details
Gizmo was my brother
in his style - "don't tell me later that I didn't tell you that before"
Gizmo and ZM have one big common thing -we love our toyz

 

[Mark A. Gulbrandsen]

I have no problem trying a choke in there, thats a sensible thing to try. I also have not tried a solid state regulator at the plate either. Someone had reccomended the IXYS type....

Please reccomend a choke if you would.... No, I won't try an output tranny if you held a .357 to my head!

Mark

 

[lt_texan]

.... No, I won't try an output tranny if you held a .357 to my head!

Mark [/B]

sounds reasonable.

I used a Lundahl choke (LL1668) load on my 417A/2A3 monkey. I like it, but nothing ot compare it to, as this is the only way I built it.

Probably a good choice here.

Dan