The AM Forum

From http://amfone.net/Amforum/index.php?topic=11808.0 (http://amfone.net/Amforum/index.php?topic=11808.0)




I have not yet taking the time to bug Frank yet.  I just have not have the time to dedicate to tracking this down yet.  So for now have just been getting by with what I can get.

I was hoping for at least 50W.  I think the manual says 100W.  I have another watt meter to check against the one I got the 25W reading, which I will do first.

I also have to double check the tune-up procedure.  It seems to imply that I should get up to 150mA plate current, which should be about 100W in at 675VDC, but I don't get near that.

I seem to get more current when I turn the loading up according to what the procedure tells me to do and it's easier to dip the plate current (even easier to dip it watching the scope, no lag), but the total watts out is better when the loading is backed off to nothing.

I think it is more likely that I am doing something wrong than something wrong with the rig itself.

Huh?? Why is it posted 3 times?? Just trying to get my attention??

Dave, keep in mind that the 100w rating is the DC input to the final.
DC input X plate efficiency = RF outpoot! Typically those rigs will do somewhere between 45-65 watts out depending on your plate voltage and the condx of the 6DQ5 final tube.

Here are a couple of thoughts:

1. Proper tune up= turn load cap to lowest setting, adjust plate tune for the dip at resonance. Then increase load to desired plate current level. Afta setting the load control, recheck plate tune for "dip". It may take a few times going back and forth between tune and load to get the max outpoot. Also check the grid drive and make sure that it is still where it should be. If the neutralization is off a bit you will have to retweek the grid drive after adjusting the fina plate.

2. I know that you are running that thing off of a battery. First check and see what the input voltage to the powa supply is under load. Dont forget that the "nominal" 12v rating of an automotive electrical system is actually 13.8-14.2v. If your battery voltage is sagging under transmit, a few voltz in the input side can make a big difference in the voltage on the HV outpoot side. IIRC (but I could be wrong) that thing had no trouble making somewhere around 50w on my 120v supply.

3. How are you checking the outpoot?? Keep in mind that most, if not all wattmeterz are calibrated to be accurate only into a 50 ohm resistive load. If you are checking the outpoot into a bad antenner without a tuna, the readings will be erroneus at best. try tuning it into a good 50 ohm dummy load and see what you are getting.

4 if all else fails give me a land line to discuss it furtha.

                                                    the Slab Bacon

Power Input= plate current(amps) X plate voltage (V)
= .15 amps X 675 v
= 101 watts
Consider roughly 60% efficiency =~ 63 watts out

Note sure what you mean.  I broke this topic out of the last one, to not derail someone else's thread, but not sure why you say posted 3 times?

Your first post here appeared 3 times. I took the other two away.

That is basically what I did (peak grid, dip plate, increase load, dip plate).  The fact that I get slightly more power out with the load all the way backed off makes me suspect your second suggestion below.


Good point, I will check this.


That's what I am checking it into.
The chain is like this: (tx)==>(mod scope tap)==>(power/swr meter)==>(dummy load)
(Now that I look at it I should probably put the the power/swr meter closest to the tx to get the most accurate reading, but I doubt it matters much.  And is certainly of no consequence to this discussion.)


Will do.  As always, thank you.

Thank you.

I probably used the back button, where I should know I should not.

Errrr, I hate when that happens!!