开云体育

ctrl + shift + ? for shortcuts
© 2025 Groups.io
  1. Ham-Amplifiers
  2. Topics

Plate modulated GG triodes

 

Recently a friend and I have been playing around with plate modulating GG Triodes in class C.? ?Just for fun.? ?My rig is a 450TH modulated by a pair of 100TH tubes.? His rig is a single 3-400Z modulated by a pair of 3-400Z tubes.? He is getting 600 watts carrier fully modulated.??

This is a tricky thing to get to work correctly but can be done. The trick was to place a choke and resistor in the grid line to self-modulate the grid. bingo. 100 percent modulated carrier.?

We noticed the 8877 3cx1500 actually has this mode listed on the PDF.? They specify grounded Grid Class C plate modulated, cathode driven configuration.??

It also states that you must modulate the Driver to 83 percent and plate modulate the rig to the rest required.? ?This is because the Drive power is never modulated.

Anyone ever try this?? I might try it for fun.? Probably wont use an 8877.?

I wonder what the purpose of this config was.? What was the advantage? They could get 1000 watts AM carrier fully modulated from a single 8877 in this config which is amazing. Maybe it never caught on?

I am simply going use my ranger to modulate the Cathode to 83 percent. Then tap off the ranger's modulators to drive the outboard modulates in phase through a transformer.? I will need to adjust the audio to the outboard modulators to get it working.??

C
 

开云体育

?

Gents,

?

For those experimenting with Plate Modulation I need to ask

about the power supplies and the modulation transformer(s).

?

Especially with 3-400’s as modulators.

?

The filament supply must be stout, there as well.

?

Please describe?

?

Hal Mandel

W4HBM

?
 

It is best to run a separate Power supply for the modulators.? You can run the RF deck and Modulator deck off the same supply of course.? The reason is that you can run higher voltage on the modulator and get more ratio to modulate the final.? Example, The Modulator is at 3000 volts and the RF final is at 2500 volts.? You wont need as much ratio on the modulation transformer. This way higher positive peaks can be had.

You just need a standard Filiment transformer.? You do need a strong filiment choke on the final Tho.? A standard 15 amp will get warm.

Attached is a schematic.

GG-Plate-mod.jpg

 

开云体育

?

Dear Clark,

?

Thanks for posting the reply to a previous post regarding the power supplies

for plate modulation.

?

The schematic you included shows a grid reactor with a value of 20 henries.

?

Wow.

?

In this day and age finding the bits and pieces to put together a set

will probably require much time and investment. Gone are the days

of surplus treasures, I’m afraid.

?

Even approaching the fabrication of a viable transformer to run a couple of

gallons on HF is not so easy as it once was. PWD, then Hammond, then

Harbach... They may have the specs on file, but who can come up with a

tape-wound Hypersil and vacuum seal it like they used to in Texas?

?

Anyway, thanks. Good luck on your build.

?

Hal

W4HBM

?
 

开云体育

We build this kind of thing out of junk we have laying around.? It's out there is you ask and look for it.??


C

On Aug 24, 2023 10:57 AM, "HaL Mandel via groups.io" <hmandel@...> wrote:

?

Dear Clark,

?

Thanks for posting the reply to a previous post regarding the power supplies

for plate modulation.

?

The schematic you included shows a grid reactor with a value of 20 henries.

?

Wow.

?

In this day and age finding the bits and pieces to put together a set

will probably require much time and investment. Gone are the days

of surplus treasures, I’m afraid.

?

Even approaching the fabrication of a viable transformer to run a couple of

gallons on HF is not so easy as it once was. PWD, then Hammond, then

Harbach... They may have the specs on file, but who can come up with a

tape-wound Hypersil and vacuum seal it like they used to in Texas?

?

Anyway, thanks. Good luck on your build.

?

Hal

W4HBM

?
 

Just curious, the feed through power of a G-G Amp might be ~ 2 to 5% of the power output when the tube has a high Mu. For a low Mu tube, that could be upwards of 20%. The self modulated control grid adds a new to me concept that I never have seen before. I presume the Plate Modulated GG triode is run class C?

If the feed through power is low, the limitation to downward modulation will be minimal. A high Mu tube needs a bit of a kick in the pants to get to plate current saturation, where the peak grid-cathode swing is way positive, and drawing significant grid current. A low Mu tube might reach the same saturation plate current at zero bias where there is no grid current, but a much larger swing in voltage grid to cathode.

I run a Gonset GSB-201 with 4 Russian 811A's (high Mu) for AM. On AM I use 12v bias, which at 1500v B+, the tubes idle at the edge of cutoff. For SSB I use -4.5v with an idle current at about 60ma.
On AM, old texts from the 1930's call this class BC amplification. What is the result?

* very clean (AM)
* gain drops from 10 db to about 7 db (takes more drive)
* resting carrier efficiency changes from around 30% to about 38%
* I can achieve 800w PEP from a 150-175 watt carrier that has a drive that has asymmetrical modulation. With normal mode (-4.5v bias), the drive is reduced (more gain), efficiency drops, and max PEP output drops to around 600 watts PEP
* With Class BC, the output modulation percentage is about 5% higher than the modulation percentage of the driver stage.

So, If I biased my Amp class C (maybe 24v bias), added a grid choke (20H), and plate modulated the 811A plates, then what would happen?

Jim
Wd5JKO
 

开云体育

Jim, that sound about right.? Years ago I ran a Ranger and a Thunderbolt amp.? This combo is very inefficient.? ?In AM mode they ran the pair of 4-400 with 350 MA if idle current. Then, they had your drive the amp up to 10 to 15 ma of grid current. You ended up with nuclear hot tubes, 300watts and no peaks.? No matter how you loaded it, It would never show any peak power.

One day I decided to switch the T bolt in to Class C.? It has that mode for CW.? Then, I drove the ranger into it.? It took twice the drive but the ranger could do that easily with the padder removed.??

I ended up with a cool running amp, 1200 pep from a 300 watt carrier.? I checked it both ways on my Spec AN and found 1 db of difference. ALL of the heat was gone.??

I am unsure what would happen if you added the choke.? It might be worth a try.

We tried many different methods.? Including applying audio to the grid via a transformer.?

The way Gates handled this was to have a separate winding on the mod trans. This winding modulated the Driver tube.? This way the drive power is modulated.

What I want to try and will soon, is to modulate the drive on a plate modulated rig.?

In the case of my friends rig, There is 60 watts not modulated as drive for the 500 ish watt of carrier unless you come up with a way to modulate it, That 60 watts just sits there on the scope
C


From: [email protected] <[email protected]> on behalf of Jim Candela via groups.io <jcandela@...>
Sent: Saturday, September 23, 2023 7:32 AM
To: [email protected] <[email protected]>
Subject: Re: [ham-amplifiers] Plate modulated GG triodes
?
Just curious, the feed through power of a G-G Amp might be ~ 2 to 5% of the power output when the tube has a high Mu. For a low Mu tube, that could be upwards of 20%. The self modulated control grid adds a new to me concept that I never have seen before. I presume the Plate Modulated GG triode is run class C?

If the feed through power is low, the limitation to downward modulation will be minimal. A high Mu tube needs a bit of a kick in the pants to get to plate current saturation, where the peak grid-cathode swing is way positive, and drawing significant grid current. A low Mu tube might reach the same saturation plate current at zero bias where there is no grid current, but a much larger swing in voltage grid to cathode.

I run a Gonset GSB-201 with 4 Russian 811A's (high Mu) for AM. On AM I use 12v bias, which at 1500v B+, the tubes idle at the edge of cutoff. For SSB I use -4.5v with an idle current at about 60ma.
On AM, old texts from the 1930's call this class BC amplification. What is the result?

* very clean (AM)
* gain drops from 10 db to about 7 db (takes more drive)
* resting carrier efficiency changes from around 30% to about 38%
* I can achieve 800w PEP from a 150-175 watt carrier that has a drive that has asymmetrical modulation. With normal mode (-4.5v bias), the drive is reduced (more gain), efficiency drops, and max PEP output drops to around 600 watts PEP
* With Class BC, the output modulation percentage is about 5% higher than the modulation percentage of the driver stage.

So, If I biased my Amp class C (maybe 24v bias), added a grid choke (20H), and plate modulated the 811A plates, then what would happen?

Jim
Wd5JKO

1 - 7 of 7