My point exactly!!!! I'm still suspicious of that bridge...

Ok Dave, Here is the PS and the 807 plans. I can pick up a nice clear
tone on 80M on a near by set! Here is the schematics.
Gary

If one of the 1N4007s shorted, it probably would take out the power transformer or at least half of the secondary. It's not really possible to have an "open" 1N4007 under most conditions. The power transformer doesn't have enough VA to cook a 1N4007 and get the chip to separate.

A shorted diode would also probably kill the electrolytics.

I am still puzzling....

Rich

If the bridge was failing, he wouldn't have nearly 700 volts unkeyed at the plate.
I agree that the PIV rating is questionable.

Pete

Hi Gary. Nice job on the transmitter. I'm wondering how reliable your meter readings are, where your measurement points are, and what you're using to measure to output power. Remember that with those 40K resistors shunting the filter caps, you're drawing 35ma just from them and it doesn't seem to be effecting the output voltage all that much. You may want to take a look at how much voltage you're dropping across that 8 henry choke - some of the receiving types has a lot of wire resistance.

What seems to bother me the most is the 3 volt drop in filament voltage. If the filament voltage decreases that much, you wouldn't be heating the cathode(s) for very long and you should see a rapid drop off in output as well as plate current. Do you observe the filament brightness decrease when you push the key? All of the symptons seem to indicate a resistance in the primary of the transformer that's reducing the primary voltage, which would cause the filament A/C and high voltage A/C to be cut in half. Do you have the power supply plugged into a variac or something that might change the primary voltage under load?

arnie

The 40K's are drawing only abt 9 mA key up.... The xmtr portion is pretty straight-forward with the exception of the lack of a metering circuit for grid drive. Think of the key as turning on a static-load for the pwr sply. My sense is that there's a problem with the pwr sply - the B+ side.... The key to the problem is the measured 6.3 Vac fil voltage collapsing key-down. It's almost like the xfmr is looking at a near short-circuit condition at key-down. If you can hear the osc, then the amplitude must decrease as the xmtr is keyed as the fil voltage goes to 3 Vac.. It would be interesting to see what would happen if you were to borrow the B+ from an ext sply. Completely remove the bridge connections, tie B+ 1 and 2 together and connect to an external 400 Vdc and see what happens key down...
Dave - WA6VVL

Ok guys, Just took some more voltage readings
807 plate 673 vdc key up...409vdc key down.
6AG7 plate 277vdc key up....163 vdc key down
The filiments are 7.0vac key up and 6.51 vac key down,
so the filiments aren't dropping as first stated.
With the set on for 10 min. the xsfmr is cold..
I plan on Monday re-checking all my wireing and soldering joints.
All readings are with my Fluke 87 And the panel meter still reads
100ma key down..
Thanks to all for your help, I still think a bigger transformer may help.
Gary

Gary

When you tune your Plate and Load capacitors, can you get a dip in the plate current?

Rich

Hi Rich, I'm glad you brought that up, No I don't see any dip. In fact
I don't see any changes at all when I turn any of the tuning capacitors.
I find this very strange, However with the 80m Xtal i'm using it's right
on frequency...Yes I'm puzzeled too!!!
Gary

Hi Gary,
I wouldn't change that xfmr until you get the xmtr working.
And, you should, much sooner than later, double the number of 1N4007's in your bridge.
With a light bulb as a load, set the LOAD cap to max (fully meshed), and adjust TUNE for max brilliance in the bulb. Max brilliance is approximately where the dip s/b seen on the meter. Then adjust the grid drive to max the brilliance of the bulb. Many xmtrs of this design use an untuned 6AG7 stage to drive the 807, so even if the grid drive isn't optimum to start, it still s/b providing drive to the 807.
If none of this works as I've described above, the xmtr, or at least the 807 portion, isn't working..
The fact that you can hear the xtal freq says the 6AG7 stage is working..
Dave - WA6VVL

I notice you are using receiver tuning caps for both plate and load. The mica trimmers on these were probably never intended for high RF voltages.

Is that speaker in the background part of your circuit?

Rich

Is the little blue capacitor C10 or C12?

Both need to be rated for high voltage.

Rich

I blew up the photo of the top view of the chassis, and it may be an optical illusion, but it looks like the coupling cap C12, is connected to the frame of the PLATE cap C14???
Dave - WA6VVL

That's where I was going....

Rich

OMG..I think you are right Dave And Rich, the speaker is for my code
pratice oscillator..Not part of the xmtr. I just unplug it and use it for the
xmtr
Dave I'll check that c-12 right now...Good work guys
I'll let you know how I make out.
Thanks, Gary

Yessss!! That was it..I had c-12 going to gnd. instead of the stator
She is putting out about 25W and the Xfmr stays nice and cool!
I am still loosing a little key voltage key down but nothing like it was.
The ma meter reads about 40ma. key down.
Thanks again guys, I would be lost without you..
Gary

Hi Gary,
Congratulations!!!
40 mA key-down sounds a little low, all things considered. Is that with both the GRID and LOAD adjusted for max brilliance?? It might be higher with a real 50 ohm load instead of the light bulb??
Don't forget my recommendation of doubling up on the 1N4007's in the bridge. One per leg just isn't enough.
Dave - WA6VVL

Thanks Dave, I think I will add them extra doides this weekend.
I noticed something though, I checked the voltage on the plate of
the 807 and got 665vdc key up, but with key down the Fluke 87
would not read the voltage, like there was an over load.. The
meter would make a beep beep noise, I put the Tripplet analog
on DC volts and it read about 1080VDC. Whats going one here?
My friend who has been my ELMER for the past nine months said
I am putting out a nice clear and strong signal..He lives about 6
miles away. He is an old retired signal corps radio man. He can
do CW at 30WPM like crazy. I have had my tech. ticket about
3 months now and am having one heck of a time copying CW
at 5WPM But for being 68 years old, I'm still trying
But once again, thanks to all for the GREAT help.
Gary

The meter is picking up RF which it doesn't like.

One of the sad side effects of Digital Meters.... they pick up RF and it confuses the readings.

I was running 170 VDC (rectified 120V line) on my 180 KHz. induction heater. I put a DMM across the DC buss and when it was not tuned to resonance, the meter would go up toward 1000V and then read "overload."

Try reading the DC voltage across the choke bypass cap C10. Maybe the cap will give you some RF filtering. Keep the test leads well away from the 807 and tank circuit.

Rich