Re: Connecting QRP-PA-2008 to the Sierra
- Hi Joe:
Well, I'll be happy with 5W on all bands if I can get it. Anything beyond that is a bonus.
I like your idea of an external enclosure to start with. I want to test the amp before drilling holes (for the MOSFET heat sinking) in the Sierra. Perhaps I can put it in a small Bud box.
I'll keep you posted.
--- In firstname.lastname@example.org, joe living <jliving2001@...> wrote:
> Interesting, Rob. I've heard good things about the QRP Projects amplifier.
> I did some experimenting with my Sierra a few years back trying to make it into a 10 watt rig. I had trouble trying to fit a 10 watt amplifier into an all band QRP rig designed for 2 watts. All sorts of feedback problems arose causing instability on some bands but not others. I'd recommend not trying to fit the amplifier inside the Sierra enclosure at first, but to build the amp in its own separate enclosure using shielded cable for the input and output. I am not an engineering expert, just an amateur, so take what I say with a grain of salt. It might be nice to hear what others have to say about trying to make the Sierra into an all band 10 watt rig. My experience taught me that it is not an easy task.
> Joe KH6/W3GW
- Thanks Dave; all good info and I'm glad to know I got the schematic right!
I had considered changing R14 (Drive pot) to a panel-mounted 500 Ohm pot attached to the rear panel. Your suggestion and the info on DF2OK's site has pointed me towards the leaving R14 in place and adding a pot on the PA input; I've got a 500 (vs 470) Ohm pot I can use.
I also have some 2N5109s for the driver.
--- In email@example.com, Dave G3VGR <dave.g3vgr@...> wrote:
> I have the original DL-QRP-PA in my Sierra. (picture at
> Your schematic is correct, however a popular change was to use a 470 ohm
> potentiometer across the input of the PA to vary the power.
> The pot is mounted on the rear panel
> See DF2OK's website for more info
> The page is in German, but Google does a good translation.
> I didn't get much drive from the 2N2222A on the highest bands, so
> changed it for a 2N5109
> 73, Dave G3VGR
- 1 of 1 Photo(s)
This may be slightly OT but related.
My Sierra was suffering from the dreaded "Low Output Syndrome" and I had tried several mods to beef it up. Finally I decided to try the DLQRP 2008 amplifier so that I would have 5 w rather than 400mw on 20 m.
This amp requires both a fixed and keyed 8v. The keyed 8v is available as +8 tx off of the collector of Q4. My measurements of this showed that the voltage was only 4 v on keydown. I think this limits the drive out of buffer Q5 but I'm not sure why I'm getting 4v rather than 8v.
As an experiment I replaced Q4 (2n4126) with another PNP I had in the junk box, a 2n3906. I reasoned that since it was functioning as a switch the hfe difference shouldn't matter. But now the collector voltage is only 2 volts!
I need some advice. Do I need to get another 2n4126 or might the problem be elsewhere?