KitsAndParts.Com Forum

Ikers wrote:

Am I reading this right...the 5 watt CW amp is available as a kit?   Frank

Yes...while supplies last.
I'm working to secure more of the 2SC5739 RF transistors for future kits.
-Diz

I am understanding that the 5 watt amp takes 1 milliwatt input, which is the same as 0 dB.  What circuit will drive the amp for 40 meters?

OK Diz. I just built a Michigan Mighty Mite for 40 meters.  The link is      http://www.metaphoria.us/hamradio/Michi … _mite.html
Where on the oscillator can I tap? and what dB pad attenuator (and circuit) would I use to tame that to 0 dB and still get a 50 ohm signal to put into the kitsandparts 5 watt amp?  I don't think you mean I should tap the actual output of this transmitter that goes to the antenna?  I don't have the equipment to measure these types of signals.  I also just got a Johnson Transceiver Tester at a yard sale.  If it works it takes a crystal and has a signal generator output.  This unit is for CB radios, in particular.  It only claims to be a signal generator at CB radio frequencies, so it probably won't work on 40 meter crystals.  Does anyone know if this produces an input for the amp to use?  I'm a technician (but Extra Class Ham), not an engineer. 
  BTW-Diz, I love this amp.  Assembly is going fb.

Last edited by ae4gm (2011-09-06 11:23:33)

If you have a 30 mw output from your transmitter and you want to pad down to 1 mw:
db = 10 * (log P1/P2)
db = 10 * (log 30)
db = 10 * 1.48
you need a 14.7 (or 15)db pad with inputs and outputs of 50 ohms.
You can plug those values into a matching Pi Attenuator Calculator (one of many on the web) and you have your attenuator. Pick the most common value resistors as close to calculations as you can find and you should be in business.

Tom, ak2b

ae4gm...you may consider changing the emitter resistor from 27 ohms to something higher.
Play with it until you reduce the RF output to about 1 mW...that should also clean up the oscillator and reduce chirping etc. - Diz

Is this a complete kit and how does one buy it?

I am new here.  I am interested in something that will increase the level coming from
my HP8656B sig gen.   I want to use the sig gen as a VFO for my Ameco AC-1.
I can only get +17dBm (1.58 volts) and I need somewhere in the range of 5-10 volts
to get me the same output I get with a xtal.

I was thinking about the 5 watt amp which is really more than I need but if its a complete kit
and depending on the price it might something to play with.

Any help would be appreciated.

Thanks
Ken
N1KK

I'm trying to wind T2 binocular on the 5 watt amp.  It says to strip and tin the wires that bend back over the magnet.  Does this mean that the tinned wires actually touch the magnet or does it mean just the tips of the wires are tinned where they go into the board?

I made a yahoo group page to be able to put a drawing by Steve Smith of the T2 windings on the 5 watt amp.  If anyone sees errors on this group please say something so I can correct it.
The link is     http://groups.yahoo.com/group/kitsandpa … kit/files/

Last edited by ae4gm (2011-10-10 14:29:54)

BD139-16 replacement for 2SC5739

http://kitsandparts.com will be stocking the BD139 transistor and will be available for shipping on Nov 30 2011.
We will be using this transistor in future 5 watt class C amplifiers.

Ok, I need some advice...

I thought everything was working, but the 5 watt amplifier seems to be going into oscillation. It puts out lots of power, and match looks perfect into a dummy load, but it sounds terrible on a monitor receiver..with wideband noise everywhere. When I try to load into a real antenna, the SWR is terrible no matter what I do with my antenna tuner. Would it be correct to assume that I can't get a match because the amp is really outputting broadband garbage, rather than power on a single frequency?

In my rig configuration, I am using the N3ZI DDS, along with the N#ZI receiver, home built buffer, and right now just some relays to switch the antenna, RF to the buffer  and the DDS RIT line. The buffer for the VFO is built on perfboard and stacked on top of the amp module. The amp then goes to a low pass filter bank, where each of the low pass boards arestacked on top of each other using brass standoffs, and switched in or out using seperate input/output relays.

If I skip the lowpass filters and take the amp straight to a coax fed, matched 20M vertical, sometimes the oscillation goes away, and I get a good match. If I try 40M without the filter into the doublet, fed with ladder line, I cant get a match no matter what I do with the transmatch.

Also, when using the dummy load, the low pass filters have very little effect on output power (eg...still lots of power coming out on 20M even with the 80M low pass in line)

Questions:

- How important is shielding?
- should the amp, and/or the buffer be in it's own box, or outboard from the rest of the transciever?
- IS perfoard a poor way to build the buffer?

This is really the first project of this magnitude I have tried from scratch, although I have built lots of kits. The DDS, receiver seem to work well, and the buffer is definately amplifying. I expect the amp is OK too, and I just have too much RF floating around, but any advice would be great. I plan to take the amp and buffer only to work tomorrow and try using a proper signal generator and spectrum analyzer

To Bseres. I think you need to partially pull out the main chip (with power off) on the N3ZI DDS VFO (socket) and push it back in, reseating the pins.  Mine does this sometimes with loads of power showing and no usable output.  Once the chip is pushed in, it aways works fine.

Since the amplifier is working ok the next step is to find out what is coming out of the buffer and at what level when driven by the DDS VFO. Assuming the buffer is working as advertised I see no reason to change it. If you have a scope, put a 50 ohm dummy load on the scope input and see if you can adjust the output of the buffer to around 600mv p-p (~0dBm).

Tom, ak2b