¿ªÔÆÌåÓý
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 |
