Heathkit HW-101 Power Output
I have a refurbished HW-101 which I enjoy a great deal. Periodically I want to operate it when connected to my Attic Dipole Antenna, thru my MFJ 949E. In doing this I would like to reduce the output since I don't want 100 watts at the antenna close to my living quarters! The HW-101 manual does not address how to properly operate the rig at reduced power. Therefore, which control(s) should I use to properly reduce the HW-101's output to say 35 or 50 watts. Should it be the Driver/Preselector or Final or Mic./CW controls. Tnx & 73, Ken-KG4LLQ
I would guess it is the "Final" controls, but it would be that "tab" lever below the knob. I believe this is what adjusted the antenna loading. Can you adjust this to decrease the loading, then adjust the knob to re-resonate (dip plate current)?
The best way to do this is to reduce the mic gain.
If you detune the radio that can cause problems because of the reduced efficiency and mismatch between the driver and the PA and between the PA and the tuner.
On HF the power isn't as much of an issue as if you were running 100W on six or two meters and above.
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Look at the front panel. There is a control marked "mic. / CW level". Turn it fully counter-clockwise and then slowly turn it clockwise until the desired power level is reached!
There is no need to "detune" the unit. Just tune the transceiver as normal and then reduce the power with the level control!
Glen, Thanks. I thought that is what should be done but I wanted to check first.
Best 73, KEN
Reducing the CW level control to lower output power will only work in CW mode. To reduce output power use the external ALC phono jack on rear panel and connect a 200k ohm pot and 9 volt battery to provide a variable negative voltage to control the output level. The adjustable negative voltage comes off the pot wiper. The current is in ua range so the battery lasts a long time. You can operate down to QRP levels in this manner. Just load up normally and then dial power down to whatever level you want with the pot. You can find the circuit on the internet. Terry K9TW
Forgot to mention you need a switch to turn off battery so you dont drain it down or you can obtain the -9 volts from a wall-wart transformer in lieu of a battery. Easy to forget to disconnect the battery and drain it down.
Would it work like my amp? If I take one tube out, then the amp will only work at half power? I tried that once and it did !
Maybe take a tube out of the 101 and it will only give 50 watts...? I never tried that with my old radios so I'm not sure it will work, but you can try it. Then if it does, then you can tune normally and have everything at a normal setting and have better modulation instead of just turning the mic gain down and have significantly less modulation.
Only one problem...... You might have to neutralize the radio. But maybe not because I don't know if the Heath 101 has a grounded grid or not. My Kenwoods do not and have to be neutralized. See if your radio has to be neutralized or not if you change tubes. If they don't then my idea should work.
Last edited by W0UZR; 09-25-2011 at 01:56 PM.
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The filaments are in series so pulling one tube kills filament voltage for the other. Also, one tube means a different plate impedance and now the tank capacitor will tune the pi-network to resonance at a different location than the approx amount of plate mesh that is indicated on front panel of the rig. Very simple to have any output level you want by applying varying negative voltage to the alc line. This simple method does not require you to remove the covers of the rig.
When the audio gain control on SSB is reduced the transmitter WILL put out less power! Try it! In fact in any SSB transmitter when the microphone gain is turned fully clockwise there will be no power output at all (for all practical purposes) unless there is a "hum" present. There is always the suppressed carrier but in the HW-101 that should be at least 40 dB down (hopefully a lot more) and that is a fixed amount no matter what the ALC voltage is.
Also, you don't have to use an external battery. Just turn the ALC control in the unit so that the meter reads below zero.
An experiment that you can make on any of your SSB transmitters is to put a tone on the microphone input (use a two-tone oscillator if you want to - this simulates voice), turn down the microphone audio control completely, key the transmitter, watch the wattmeter, and then slowly increase the microphone gain. You will definitely see the power increase as the microphone control is increased. The power will increase until it reaches the level at which the transmitter put out when in the tune position.
The transmitter should be tuned at full power to assure linearity. Then, when the audio gain is reduced less power will be put out and the transmitted signal will still be "clean".