Switchable biasing Bob85 style

[DIRTYWHITEBOY]

Regulation is great,further testing required

 

[Crusher]

Looks good. Curious is that made for just a 2 transistor module or is it adaptable later for more? I see that it only has 1 pot so I am assuming this is just for 2pill. Did you use a 723 or a series regulator? Can't really tell, looks like it may be hiding behind relay. Very neat & tidy shop area by the way.

 

[DIRTYWHITEBOY]

Crusher it should carry a 4 pill no problem and possibly more.the bias circuit uses a 723 reg. and the pass transistor for the circuit mounts on the amp heatsink.ive load tested it to over 1 amp at .62 volts with regulation.

 

[NorthStar]

I like the Professional boards bob uses.

 

[bob85]

crusher, the ideal setup is one board per pair of transistors but the board should be capable of higher output with a few parts changes,
212's load regulation from 100ma to over 1 amp is 7mv,
heres a better view

 

[DIRTYWHITEBOY]

Load testing is complete, regulation is 2mv at 1 amp.Installation and rf testing is next.

 

[mackmobile43]

Load testing is complete, regulation is 2mv at 1 amp.Installation and rf testing is next.

I have mine set at 250mv idle current and .640v and it seems to have a nice smooth sound on sidebands and the thermal tracking diode mounted in close proximity to the transistors does an excellent job of regulating the voltage as the temperatures rise.

Disclaimer: This amp is the first amp I ever built about 3 years ago and has seen many,many,many changes as you can see by the empty solder blobs on the board but has been a reliable test bed for all.

 

[mackmobile43]

So today I plotted the power levels of my 2/2879 amp in AB and C classes in 1 watt increments from 1 watt to 14 watts carrier without mic gain on and no audio input.

The meter used is a Bird 43 terminated into a model 82A Bird dummyload.

In AB the power requirements and outputs are: 250ma draw for the board with .645 volt output and load regulation is 2mv with a rise of 7ma from cold to hot on the transistors so the thremal tracking sensitivity is quite good and that's adjustable in varying the value of the load sharing resistor but at the 7 watt 10ohm value installed it's very good for intial tests.

Here are the radio input watts/amp output watts from the RCI-2950dx in AM mode into the homebrew 2/2879 amp with 3 windings on the input transfromer and 3 windings on the output transformer which I will get around to changing to 4 in and 3 out in the next series of test.

Radio......Amp AB.......AMP C
1...........29.............17
2...........65.............45
3...........102............80
4...........122............100
5...........160............125
6...........180............148
7...........199............179
8...........209............196
9...........240............209
10.........245............228
11.........260............242
12.........265............260
13.........280............262
14.........280............275

 

[mackmobile43]

I ran another wattage output plot after changing the wraps, I changed the input wraps to 2 in to 4 out and could not get the input swr down when leaving the output wraps at 4 out so I put put the input back to 3 wraps and the output down to 2 wraps and found a nice compromise the the input and output match at 1.1:1.

Here are the wattage again produce in 1 watt increment increase from 1 watt to 14 watts from the RCI-2950DX.

Radio......Amp AB.......AMP C
1.....22....................10
2.....47....................38
3.....68....................59
4.....99....................79
5.....122..................99
6.....165..................120
7.....188..................165
8.....199..................170
9.....218..................182
10...235..................200
11...245..................220
12...260..................237
13...280..................242
14...280..................242

 

[NorthStar]

Damn good numbers

 

[BOOTY MONSTER]

that doesnt exactly support folks saying 2879's will do more watts in class C because of the more efficent class c design .

of course i could be missing something . i was called a moron in another forum the other day . lol , maybe they are right ?

 

[mackmobile43]

that doesnt exactly support folks saying 2879's will do more watts in class C because of the more efficent class c design .

of course i could be missing something . i was called a moron in another forum the other day . lol , maybe they are right ?

The purpose of this thread is not to dispute the efficiency of the 2sc2879 but merely to show that a bias circuit will create as much or more wattage with less drive input, granted the power consumption may be more for a given drive level but what you sacrifice there is more than compensated for in audio quality in every mode of tx.

 

[mackmobile43]

that doesnt exactly support folks saying 2879's will do more watts in class C because of the more efficent class c design .

of course i could be missing something . i was called a moron in another forum the other day . lol , maybe they are right ?

Oh, did I mention this board is switchable? when using a separate switch to power the board it will switch the input choke back to Class-c operation when not powered.............

 

[dudmuck]

might be better to use dBm

    in      AB out            C out
    dBm     dBm (gain)        dBm (gain)
 1w=30......43.4(13.4)........40.0(10.0)
 2w=33......46.7(13.7)........45.8(12.8)
 3w=34.7....48.3(13.6)........47.7(13.0)
 4w=36......50.0(14.0)........48.9(12.9)
 5w=37......50.9(13.9)........50.0(13.0)
 6w=37.8....52.2(14.4)........50.8(13.0)
 7w=38.5....52.7(14.2)........52.2(13.7)
 8w=39......53.0(14.0)........52.3(13.3)
 9w=39.5....53.4(13.9)........52.6(13.1)
10w=40......53.7(13.7)........53.0(13.0)
11w=40.4....53.9(13.5)........53.4(13.0)
12w=40.8....54.2(13.4)........53.7(12.9)
13w=41.1....54.5(13.4)........53.8(12.7)
14w=41.5....54.5(13.0)........53.8(12.3)

 

[mackmobile43]

might be better to use dBm

    in      AB out            C out
    dBm     dBm (gain)        dBm (gain)
 1w=30......43.4(13.4)........40.0(10.0)
 2w=33......46.7(13.7)........45.8(12.8)
 3w=34.7....48.3(13.6)........47.7(13.0)
 4w=36......50.0(14.0)........48.9(12.9)
 5w=37......50.9(13.9)........50.0(13.0)
 6w=37.8....52.2(14.4)........50.8(13.0)
 7w=38.5....52.7(14.2)........52.2(13.7)
 8w=39......53.0(14.0)........52.3(13.3)
 9w=39.5....53.4(13.9)........52.6(13.1)
10w=40......53.7(13.7)........53.0(13.0)
11w=40.4....53.9(13.5)........53.4(13.0)
12w=40.8....54.2(13.4)........53.7(12.9)
13w=41.1....54.5(13.4)........53.8(12.7)
14w=41.5....54.5(13.0)........53.8(12.3)

I was absent the day the professor showed this