DC Heaters for V1 & V2

[big_teee]

Hi All:
I Started the OP.
So In Conclusion, the Diagram I posted needs what?
Does it stand as is, or do one sets of 100 ohm resistors need to go?
Would it work as well without the bridge and one set of 100 ohm resistors, and just apply elevated voltage to the Heaters?
So what Can I take away from this thread? I'm getting ready to build my next HyGainer!
Thanks again for all Your discussion.
Terry

[defaced]

Would it work as well without the bridge and one set of 100 ohm resistors, and just apply elevated voltage to the Heaters?

This is where I would start (it has worked for me with builds that had more gain than a 2204). Engineer's Perspective #23: don't solve a problem you don't yet have.

[trobbins]

I would suggest not using the proposed circuit, but backtrack as to what your present problem is. All you have indicated is that you want to 'tame' an amp. Was there a problem in the first place, or are you just trying to identify the best way to make a new amp work?

[jmaf]

Hi All:
I Started the OP.
So In Conclusion, the Diagram I posted needs what?
Does it stand as is, or do one sets of 100 ohm resistors need to go?
Would it work as well without the bridge and one set of 100 ohm resistors, and just apply elevated voltage to the Heaters?
So what Can I take away from this thread? I'm getting ready to build my next HyGainer!
Thanks again for all Your discussion.
Terry

My 2 cents: just elevate the good ol AC, without rectifying. Save yourself the trouble. If you use the 12 V pins 4 and 5 you'll use half the current = less noise. Also, by using pins 4 and 5 you don't need to surround the socket pins with heater wires. If you use pin 9 you necessarily cross one of the grid leads' path.

[vibrovox7reverb]

How does one float the filaments on a fixed bias amp? I've read this link

The Valve Wizard

but I'm still confused on what the HT+ is....if I could figure it out then I'm sure I could apply it, but I need to know what that is first.

[trobbins]

HT+ is any DC voltage rail in the amp that is higher in voltage than the level you want to apply to the heaters. Eg. HT+ could be the 250VDC level used for the input preamp tubes, or could be the 500V used for the output stage.

[big_teee]

HT+ is any DC voltage rail in the amp that is higher in voltage than the level you want to apply to the heaters. Eg. HT+ could be the 250VDC level used for the input preamp tubes, or could be the 500V used for the output stage.

Can you please persue that further?
If You used the 250v at the V1 B+ Rail.
Then What?
Would it have to be Dropped down Further to the 50-70 Volts Level.
Please Elaborate as Much as Possible.
Thanks,
Terry

[trobbins]

Read Merlin's excellent description and google voltage divider.

But I suggest there is no need to go in to a new technical area if you have no technical substantiation for starters for needing to travel that path.

Ciao, Tim

[Chuck H]

Hmmm... Really? I think you misunderstood why the Q was asked. The obvious has already been taken into account. If you can't elaborate, well, then you can't. Otherwise you should.

[big_teee]

Read Merlin's excellent description and google voltage divider.

But I suggest there is no need to go in to a new technical area if you have no technical substantiation for starters for needing to travel that path.

Ciao, Tim

No Problem, Thanks for Your help!
Terry

[trobbins]

Hmmm, maybe I did. Let's check.

big_teee were you able to understand the description on Merlins webpage relating to using a HT+ to generate a DC elevation level? Are you able to work out component values for a voltage divider?

[R.G.]

Voltage divider from B+. They can be high value resistors, all you need is the voltage.

HT+ is probably "High Tension positive", or the main positive power supply.

[soundguruman]

Saw this on another site, and I nabbed it. lol
No one knew who the author was and no one had tried the circuit.
I'm looking for a way to tame the front end of a cranked up Marshall 2204.
Will this work and be suitable for a 2-(V1,V2) 12AX7 Circuit.
[ATTACH=CONFIG]15588
Thanks in advance,
Terry

Well, you should have DC heaters in a high gain amp, but things like bulk metal foil resistors, high grade capacitors like silver mica, humbucking pickups, etc...etc...will help also.
You can check the McIntosh schematics for the most lowest noise DC heater circuits...
But one obvious thing comes to mind, most designs are converting an existing AC heater winding, to a DC circuit.
It is really better to have a bit more current, like a dedicated transformer for the heaters DC. The reason for this is that the voltage inevitably is dropped, below 6.3 volts DC.
And, the emission of the cathode is shortened by reduced heater voltage, also shortening the life of the preamp tube.
But you are for sure on the right track to lower 60 cycle noise in a high gain amp.

[okgb]

Let me know if I should start another thread , but I have a hum problem with a friend's Japanese soldano sp 77
Separating the psu and preamps grounds reduced the hum by 50% [ all one pcb ] but there is still some higher frequency hum left
which is regardless of preamp gain , but becomes more obvious with master vol settings , even with the last of 4 tubes left in
you can hear it once master pot reaches the 1/2 way mark then gets worse as it gets higher .
the filaments are a.c. heated and just centre tapped to ground , so
I wondering if anyone can suggest an " easy " circuit to convert to d.c. ?
not sure how much it may help so straight forward would be appreciated , tia

[Chuck H]

What is "higher frequency hum"? Is that 120Hz as opposed to 60Hz? Keep pulling tubes. Pull the first tube. Is the hum still there? Pull the second tube... Continue until the hum stops. Once you've isolated it to a tube you should try another tube in that socket. Way too many current production preamp tubes are noisy right out of the box these days. Current tubes are also reported to handle cathode followers with less grace. Soldano designs use a lot of high cathode reistances and cathode follower circuits. Perhaps a DC elevated filament center tap would be sufficient. That would be much easier than DC heaters. Nothing to lose by trying it.