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2x 4D32 transmitter




 
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Author Topic: 2x 4D32 transmitter  (Read 783 times)
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W4RFM
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« on: June 12, 2020, 03:55:53 PM »

Here I go again. Health has improved, and so it is back to the work bench.  I lost my diagram of an 80 or 80/40 meter 2 tube 4d32 transmitter.  As I remember it was very similar to an HT-20 but with two tubes in the output.  Just picked up a 2x 807 mod transformer, should make a nice set up. I appreciate all the input, but bare in mind, I will build it with 2x 807 modulators (I have the schematic and the parts) and 2x 4D32's in the RF.  Thanks everyone.
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WBear2GCR
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« Reply #1 on: June 13, 2020, 06:55:51 PM »


Not sure exactly, but iirc, a 4D32 is about equal to 2 x 6146.
So, in something like a DX-100, again iirc, and some other rigs, I think a
Viking, a pair of 807s is used to modulate a single 4D32, or in the DX-100
a pair of 6146s...

The 807s might be a bit short on the "ooomph"?

One might consider a pair of 4D32s, or maybe a pair of stout sweep tubes?

                      _-_-
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W4RFM
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« Reply #2 on: June 14, 2020, 02:23:00 PM »

Bear I see your point, and appreciate your input. I am looking to get maybe 150 watts of 95% modulated A M out to the wire.  Two 807's "should produce up to 120 watts running B.T.T.W.,so getting a steady 75 watts might be a mite easier.... in a study of broadcast TX designs, I see that Gates, Collins etc, just paralleled the two tubes and summed the outputs to the output network, thereby doubling the ability of the final stage to handle additional current and generate the desired amount of R F. I will go that route till it blows up or melts down. Smiley
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WBear2GCR
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« Reply #3 on: June 16, 2020, 09:38:57 AM »


Switch to sweep tubes, or 811a?

Might be much easier.
My Val-I-Ain't is easily modulated to over 100% positive by a pair of 6DQ5s,
driving 3 x 6146B.

The 6DQ5 is hardly the most strapping of all the sweep tubes...
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w4bfs
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« Reply #4 on: June 20, 2020, 09:22:35 AM »


.....The 6DQ5 is hardly the most strapping of all the sweep tubes...


interesting that you brought that up

6DQ5 rated at 24 Watts plate dissipation but physical plate size suggests a higher value esp for sylvanias and possibly others

at least 30W maybe more without sharply decreasing tube life ...

now a cb leanyer is another matter  Cry
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« Reply #5 on: June 21, 2020, 05:05:03 PM »

My souped up Viking 1(aka Viking Bud) runs a 4CX250B. With the plate variac at full scrot it'll do 150 watt carrier easy. The 807s are running in AB2 with 750VDC on the plate and 300 on the screens. Been doing that since 1973 with just one 807 crapout. 95% is also easily done. See the attach data sheet I refered to when setting it up. Note the power output of 120 watts. More than enuf!


* 807 AB2.png (177.05 KB, 729x727 - viewed 30 times.)
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WBear2GCR
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« Reply #6 on: June 22, 2020, 01:59:09 PM »


.....The 6DQ5 is hardly the most strapping of all the sweep tubes...


interesting that you brought that up

6DQ5 rated at 24 Watts plate dissipation but physical plate size suggests a higher value esp for sylvanias and possibly others

at least 30W maybe more without sharply decreasing tube life ...

now a cb leanyer is another matter  Cry

In modulator service, my expectation is that a pair will outperform 2 x 6146, 2 x EL34/6CA7, 2 x 807,
2x 6L6GT,  2 x 6550... the larger sweep tubes will do more snot. It's different than CCS with a carrier
at RF... The key is the peak current available from sweep tubes is "HUGE" (dunno if you get those
TV car ads where you are? I get the impression that guy is all over the country...)

              _-_-bear

PS. a very interesting option might be a 2 x 4D32 modulator section!
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W4RFM
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« Reply #7 on: June 22, 2020, 03:36:29 PM »

All this input is great, but as I said in the beginning statement, I will build it with 2x 807's (I have the tubes and the mod iron) , and I will use 4d32's in the RF, (again I have the nos tubes). I do appreciate the comments and suggestions, but this is what I want to do. "the heart wants what the hearts wants", I have heard.
I do like the 2x 4D32 modulator however, if the impedance was close....hummmmm.
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K1JJ
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« Reply #8 on: June 22, 2020, 04:48:50 PM »

Hi Bob,

I just finished wiring up the RF tank for my single 4D32, 125 watts out,  plate modulated by a Hammond 1642SE xfmr  and 150 watt audio amp.  I'm really liking this rig so far! It will be functioning in a week or so at most.

** The plate impedance is about 2400 ohms.  On 160M it took about 4000 pF of C2 (the loading cap) and quite a bit of C1 to produce a match to 50 ohms. This is two 2000pF caps in parallel.  I used the MFJ-259B at the 50 ohm output with a 2500 ohm resistor across the tube pate to ground in simulation.

Now, you will be using two tubes which is about 1200 ohms plate impedance. Your tank C values will be very high, especially on 160M, so plan for it.  Get out the pi-net calculator on the web and start thinking of where the C will come from in your junkbox... :-)

The 4D32 is just one of those tubes that can put out the power using low plate volatage, thus the low impedance.

Yes, if your mod iron can take it without saturating, a pair of 4D32 modulators triode-connected would be a very robust lashup, good for an easy 200 watts of AM carrier.

As modulators, you might try experimenting by driving the screens with the grids grounded and then the grid and screens tied together and driven.  Look for best IMD and positive peaks as well as good audio waveforms.  Worst case you could always regulate the grids and screens and run them as standard pentodes, much like I do with my 4-1000A tetrode modulators. I don't know of anyone using 4D32s as triode-connected modulators, so you are plowing new ground.  But no reason why they can't work FB.  

Personally, I would be against using a pair of 807s to modulate a pair of 4D32s... not enuff reserve and headroom. If you are going to run a pair of 4D32s in the RF final, might as well feed them the raw meat they deserve.  A pair of anything driving the same tube pair is a great AM setup.  My two AM big rigs use that basic setup and have never lacked audio power to do 150% positive modulation if desired.

You will find that IMD and harmonic distortion comes up very quickly once you start drawing heavy grid current and generally hitting the modulators hard to match the carrier you are trying to modulate. Better to have the modulators loafing along.  Your band neighbors will appreciate it and your audio quality reports will be better.

Tom, k1JJ



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« Reply #9 on: June 22, 2020, 04:56:56 PM »

Duplicate error.
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« Reply #10 on: June 22, 2020, 08:00:22 PM »

I think my newest plan is to modulate a single 4D32, with the pair of 807's.  I am not trying to blast the band, 125-150 watts of RF will be just fine. It will operate only on 3880 /3885.
I have the Pi network numbers, and the parts on hand, using vacuum variable in both places, and a big honking coil. Just a couple of nets here in the south i want to check into. I have that 500 watt  Gates BC500K if I need more signal someday.

I would like to know how much plate voltage has been safely used on a single 4D32. Anyone? (I will be using two sep power supplied for the RF & the modulator, so dont panic. Smiley Smiley
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« Reply #11 on: June 22, 2020, 10:08:00 PM »

Hi Bob,

I  agree with your choice.  One single 4D32 would be a much better match for the 807s regarding RF impedance and audio power capacity. You will have plenty of headroom this way.

As far as HV, I ran four in parallel with my "Dual Quads"  PDM rig and had as much as 2200V on the final.   This was PDM series modulated, so it would be like running 1000V or so using conventional plate modulation.  I had only one flash-over in many months of operation.  The four were putting out 600 watts of carrier on AM with big audio. So that's why I am saying anything between 100-150 watts per tube is achievable.  125 watts out at 600V is probably a good conservative level.

The specs call for around 600-650V.  I have a Variac to adjust it between 0-800V and expect to run it at 550-650V.  This is because I am limited by my 75 watt Hammond transformer and 150 w amplifier plans. If I went much above 125 watts RF out or 700V, I wud simply run out of audio capacity.  Like you, I also have bigger rigs to choose from.

So in your case, try a single 4D32 final between 550-700V and see where the best modulation, match and overall performance lies with those 807s.

T
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« Reply #12 on: June 24, 2020, 11:59:47 AM »

That will be my plan going forward. Thank you Tom.
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