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

[Curly Woods]

Hi Zen,

Thats exactly what I intend on doing. We already tested one German built HV power supply aside from the gas toobes, gas toobes beat it hands down. There are alot of very good claims for the Wright Regulator and it is a very costly circuit to build and it is very parts specific for it to even work properly. I rummaged up the old Wright Regulator board group buy to see of any boards might still be available. One thing is for sure... The Wright Regulator is boreing compared to the wonderful glow those gas toobes give off!!! But nice glow doesn't correlate to good sound quality... I think even if the Wright Regulator does sound better I'm still going to have to keep those gas toobes lit up just for the romantic looks...

Can you say Wright Regulator 10 times really fast? Its pretty dififcult!

Mark

I absolutely agree about solid state regulation in a tube circuit. I just do not like the sound of them. I am building a pair of mono block tube amps where the driver stage is regulated with a shunt tubed circuit. I have high hopes that it will sing

 

[bequerel]

Cypher,
Rk is the same regardless of load type as far as I know.
Your calculations look OK to me.

 

[fdegrove]

Hi,

I absolutely agree about solid state regulation in a tube circuit. I just do not like the sound of them. I am building a pair of mono block tube amps where the driver stage is regulated with a shunt tubed circuit. I have high hopes that it will sing

Join the club and sing it will.

Cheers and see at that other thread,

 

[simonov]

Here are my thoughts on 12B4 preamp. Does the picture look right?

 

[Mark Allen]

You wouldn't be the first person that Bruce pissed off! There have been many others too. It's been a while since I've trolled this thread so I unfortunately can't say if there was a toobe rectification circuit posted or not. Another possibility you can consider and one to get even with Bruce is to get one of the Chinese grounded grid kits. I've built one and for the money it's not only quite decent but it will teach you gobs about audio and doing mods as it is very mod-able. Out of the box it sounds decent with the right toobes. I don't normally recommend ANY Chineese stuff to anyone however I've always felt that Bruce could do more good by showing a little more humbleness towards those that support him.

Getting back to the 12B4, there are SO MANY ways to go with the darn thing that it would be fairly easy to fill a book. If you really want to proceed down the 12B4 path you might want to haunt EBay for a used variable high voltage DC supply. I only paid 30 bucks for my Eico unit. It also helps to have a smaller say 0 to 24 vdc bench supply for filaments. With all the experimenting you'll be doing it is really the best route.

Mark

Mark

 

[coffeedj]

Here are my thoughts on 12B4 preamp. Does the picture look right?

You will have a hiss problem with this circuit. Go to my published design:
Amplifiers and select
"My Favorite Line Stage Amp" to see my recommended solution for this problem. You will note that the regulator is isolated through a small buffer resistor, and that final filtering for the 12B4 is done on the load side of the buffer.

For those of you who have been waiting for my 12B4 kit to come--it is finally here! This posted design is the final version, and I am doing a test build with one of the forum members for the first kit.

I'll be placing in up on Old Stock Audio for sale as a complete kit with custom case and options once the first 'kit' test is completed.

You can contact me if you are interested.

 

[Mark Allen]

You should have sent me the trial kit... I'd have had it built on a nice chassis in a couple of days and you'd already be selling them. Count me in for one of the kits. I once built a 15" Heathkit color tv over a three day weekend... And it worked fine on first power up...

Mark

 

[simonov]

2x60H is overkill. At that Rp (about 1k) one could go just fine with say 40H. No need to add excess capacitance (from the chokes) and limit your upper bandwidth. Same goes for the extra resistance(thus higher B+ required). With just one 60H choke u get F3 = 3Hz @ Rp = 1k.

For the record 40H choke gives F3=4Hz @ Rp = 1k.


Venci.

 

[coffeedj]

2x60H is overkill. At that Rp (about 1k) one could go just fine with say 40H. No need to add excess capacitance (from the chokes) and limit your upper bandwidth. Same goes for the extra resistance(thus higher B+ required). With just one 60H choke u get F3 = 3Hz @ Rp = 1k.

For the record 40H choke gives F3=4Hz @ Rp = 1k.


Venci.

What you say is true, but if you are trying to feed a subwoofer that goes to 15Hz, you need an F(-3dB) at about 1 Hz. But your point is good--I'm going to make the second choke an option. I did have a few people complain about the low freq. end not being low enough with a 60H choke, (my guess is for movies) which is why the second one was added. With two chokes it is flat to 20Hz.

BTW these chokes are custom made for me in Hong Kong and even in serial mode have an upper frequency cutoff way above 100KHz.

 

[coffeedj]

You should have sent me the trial kit... I'd have had it built on a nice chassis in a couple of days and you'd already be selling them. Count me in for one of the kits. I once built a 15" Heathkit color tv over a three day weekend... And it worked fine on first power up...

Mark

Send me an email at djc@oldstockaudio.com I'll reply as soon as the final kit is ready. Or if you want to do the chassis yourself--it is ready now.

 

[6L6]

Bump.

I'm breadboarding a 12B4 preamp and want this thread towards the top where it can be found easily.

 

[coffeedj]

Some thoughts

One point to note on the 12B4 power. It really helps drive the baseline noise floor to zero if you use a separate power supply. DC heaters are also a good idie.

 

[6L6]

The plan is CRCLC with a 20H choke and lots of capacitance.

I will try DC heaters as well. Thanks for the tip!

 

[vconsumer]

I have had a half-breadboarded, half-finished build of Eli Duttman's 12B4 amp in my system for the last few weeks. I built it on two chasses and converted to DC heaters. I am very pleased.

 

[jcdrisc]

Mark, here is my take on a 12B4 linestage.
Broskie's TUBECAD is well worth the money

 

[jazbo8]

I think there is an error in the Vmax out on your report, such large difference between the + and - swing suggests relatively high distortion.

 

[mach1]

That scenario would require approx 25v input: not a very likely condition to be encountered in reality. At normal input levels around 2v the swing would be confined to an area of the plate curves where the +ve and -ve negative excursions would be far closer.

 

[jazbo8]

We must have missed school that day, the whole thread is about using the 12B4 as a line amp...

 

[jcdrisc]

noisy gas tubes

I make again the firm assertion that ALL gas tube regulators are noisy, fdegrove.
Look at any Tek tube scope psu. Tek uses a 1M/100n filter before the grid of the error amp to get rid of all the hash. Why any amp designer uses them is beyond my comprehension. I enclose here a noise generator from Scroggie's book where an 85A1 is the noise source

 

[Mark Allen]

All of my 12B4 builds used stacked gas regulators and the noise floor was exceptionally low. Perhaps if this was a high gain circuit like a tape head or phono stage it would matter a lot. Not the case here. In fact my bench H-V supply is an old Eico tube supply and it is even exceptionally quiet, no,worse than a similar range H-V bench supply I have.

Mark