The New 4D32 plate modulated project - "SummerBreeze"

[w9jsw]

Tom,

For your little rig idea, why not a triode? Less PS voltages to manage. Say perhaps an 809?

John

[K1JJ]

I finally got around to doing some final mods and tests on Summer Breeze, the single 4D32 plate modulated rig.  The 813 rig and GFZ audio driver took me away for a few days.

Anyway, I couldn't be happier about how well the 4D32 rig is performing.  In the design phase I couldn't decide whether to run one or two 4D32s plate modulated by the Hammond xfmr and 150 watt Dayton amp. I was getting about 135 watts out carrier max at 700 volts under load. I wasn't satisfied with the power level so I added in a 24V transformer in phase with the HV transformer primary. (Like a bucking transformer but the opposite)   It brought my HV up to 850V under load. I am able to load up to a max of 200 watts carrier out now.  At 850V X .270 mA = 230 watts input.  200w/230w= 86% efficiency. (I subtracted the screen current thru the cathode meter)    I know that efficiency sounds high, but that's what the Bird says into a dummy load with the swr near 1:1.    It's like a Viking Valiant on steroids.  So bottom line is that ONE, not two,  4D32s is a perfect match for the Hammond xfmr and audio amplifier.  Two tubes would bring the plate impedance down to 1200 ohms which would be a little low for the Hammond and require larger tank capacitor values. Right now the plate impedance is about 3100 ohms with one tube... FB!

The peak modulation voltage on the tube plate is probably approaching 2KV under heavy positive modulation. The Hammond  xfmr is rated at about 3500V. I'm glad I used overrated tank components now.  Even the PS filter caps are  rated 1200VDC total with eight caps in series/parallel. It all adds up fast when pushing the DC HV and modulation levels hard.

At 200 watts out I am able to modulate it very well with tones that go well over 100% positive peaks.  That's a little above the xfmr rating but the amplifier is within spec.  I will  back it off in real use somewhat, but am very pleased with the power a single 4D32 can put out.  The plate is dissipating about 35 watts with no color. Like a finely tuned grenade.... :-) It has a muffin fan so stays reasonably cool.  I always beat the crap out of my rigs in testing to find the weak parts and faulty designs -  and optimize it past the tube data sheets. After making it a super hero, I then back everything off to the tube rating  or less and it rarely breaks after that abuse.

At full power, I do see a slight bit of blue flash activity in the tube when I unkey, like a screen acting up. But this tube was abused for months in the PDM dual quads rig, so it may be already damaged. I have some more good tubes around once the testing is over.

The audio quality is probably the best of all my rigs. About 5 Hz to 20 KHz… unreal.  The audio is very simple and of high quality components.  Summer Breeze will fill a nice niche below the 813 rig.

It runs cool like its namesake suggests. The fil requirements are low, the plate efficiency high and the SS amplifier hardly breaks a sweat.  Not bad for approaching a quarter KW  rig.  

Next, I'm trying to come up with a simple 40-60 watt RF driver for the three AM rigs to take the strain off the FT-1000D.  The 4D32 is such a nice tube - I'm thinking of one in linear service. A single 813 is also a possibility since I could even borrow 850 V from Summer Breeze and run the 813 class C as a driver.

I'm about ready to put SB on the air soon.  I might take a few pics of the completed rig in its operating position.  Very quiet and about 10' away, so background noise is nil.

John, anything is possible for a tube choice at this point.

T

[N4LTA]

I think I will order a 1642SE for myself. I should have the shop back in 8 weeks or so and  I have  the 4D32s and power supply iron  on site. I am starting the wiring on the 807 60 watt modulator but cutting metal is a bear on the apartment table. Instead of series modulating the dual 4D32, the Hammond transformer looks like the best way to modulate. A small Crown class D amp should work well on this project. I had multiple audio amps destroyed in the fire and I can get a Crown amp as a replacement cost amp.

Pat
N4LTA

[K1JJ]

I think I will order a 1642SE for myself. I should have the shop back in 8 weeks or so and  I have  the 4D32s and power supply iron  on site. I am starting the wiring on the 807 60 watt modulator but cutting metal is a bear on the apartment table. Instead of series modulating the dual 4D32, the Hammond transformer looks like the best way to modulate. A small Crown class D amp should work well on this project. I had multiple audio amps destroyed in the fire and I can get a Crown amp as a replacement cost amp.

Pat
N4LTA

Pat -

I'll be curious how your pair of 4D32s work out with the Hammond.  I'll bet if you run 600-700V and load the finals so that you are doing 150- 175 watts out, it will be a clean setup with ample audio with the xfmr limitation.  IE, if you load it right and reduce the plate current, you can bring that plate impedance up towards the 3K area, just like my single tube.  

I played around with the amplifier taps and found the 8 ohm tap > 3100 ohms was the best in the bridged mode.

Right now I'm trying to decide on a small master linear tube to RF carrier drive these AM rigs.   Two 6146s, a single 4D32 or an 813 - decisions, decisions.  I like GG, but if I can put the linear in grid driven service, class C,  it will take only 1 to 2 watts at most to drive any one of these prospective tubes to 60 watts out - and the FT-1000D fan will never come on.

The FT-1000D passes a squarewave at 5 Hz with the modified balanced modulator. So it can also double as the station Pissweaker rig driving the little linear at 25 watts AM carrier or so.

T

[N4LTA]

I have a Hammond 284X  transformer rated at 1200 volts Ct with a couple of 6.3 volt heater windings and a 5 V 5 amp winding. It also has a 125 volt tap to bring down the voltage a few percent.

A  cap input filter would have about 825 volts peak and loaded should be in the range you are talking about. A couple of 500 volt snap in caps on my existing board should work fine.

Choke input would be about  540 volts and maybe a few more percent with the 115 volt tap. Maybe 570 volts. Much better voltage regulation. I have a 10H 300 mA choke in hand.

Two 220 - 470 uF or so will fit the board. Plenty of filtering.


Pat
N4LTA

[K1JJ]

I think I will order a 1642SE for myself. I should have the shop back in 8 weeks or so and  I have  the 4D32s and power supply iron  on site. I am starting the wiring on the 807 60 watt modulator but cutting metal is a bear on the apartment table. Instead of series modulating the dual 4D32, the Hammond transformer looks like the best way to modulate. A small Crown class D amp should work well on this project. I had multiple audio amps destroyed in the fire and I can get a Crown amp as a replacement cost amp.

Pat
N4LTA

Pat, did you ever build up a rig using the pair of 4D32s and the Hammond 1642SE?

T

[N4LTA]

I lost quite a few parts in the fire but the transformer survived. I have re-aquired most of the other parts. Might be interested in startig it again. I can't remember what the plate and screen voltage are for the 4D32. Might be interested in doing the 6146 version.

Pat