Basically, you can't measure Vdc at the 807's plate key down - it's "HOT" RF and may even fry a DMM. The easiest place is your plate meter - either terminal will do. Anything above the RFC L2 s/b "off-limits" measurement-wise.

Regarding CW, it's not easy for everyone, even those that try hard. CW has always been my favorite mode, but operating lately has not been a priority, CW or otherwise. Even though I truly enjoyed CW, I didn't get good at it until I studied for my Extra in '92. Now, I'm certainly rusty, but still better than pre-'92. Just keep plugging away at it and don't get discouraged.

Dave - WA6VVL

Not a good idea to read plate voltage on the 807 while transmitting. Not sure about digital meters but you can burn out the meter on a VOM reading this RF voltage. Actually the meter movement can be burned out with only one meter lead connected.

Hi Norm,
At 4 MHz, the stray cap in the instrument is enough to take out the DMM's LSI chip or the movement in an analog multimeter. DMM's or analog multimeters aren't designed for that kind of RF overload, so it's an absolute crapshoot if they will survive.
Dave - WA6VVL

Most of the tube TV's you will find these days are AC/DC and no transformer. The old AC TV's would run B+ of 300-350V at 250ma or more and with a FWB or doubler you could safely get the same current using CW.

Carl

Hi Carl,
Yes, those "old" TV's (now ancient by today's standards) had great pwr xfmrs. During my high school days in the early 60's, we used to cannabilize them like crazy as those junk TV's were plentiful. That's why the 6DQ6 was my tube of choice for xmtrs (a la Heath DX-20). A large % of those xfmrs had the rect tube mounted on the pwr xfmr's end bell... Boy, those were fun days to be a ham...
I think we bought our 1st RCA color TV in '65, and there was no pwr xfmr in that set as I recall...
Dave - WA6VVL

Hi

Don't overlook older microwave oven transformers. They are wound 1 turn per volt. Too much output for an 807 but not hard to rewind.

Dave did you have your license since early 1960's? Mine is WA6VGE.

Hi Norm,
Yes, my first call was WA6LXW in late '59 or early '60. I got married in '65 and let my license lapse and picked up my present call in '73. So there's an eight year "gap" in my ham career..
Dave - WA6VVL

A great idea, but the transformer will be nearly as large as the present transmitter! Good ballast in a wind storm.

DO NOT attempt to use an MOT (microwave oven transformer) without rewinding for a lower voltage. Not only would it fry the transmitter, it might fry the operator, too.

Seems like newer microwave ovens have gone switch-mode to save weight and cost. A pity.... just more RFI for those of us who listen to AM and shortwave.

Rich

(First licensed as KN9VLQ in 1960.)

Regarding Gary's pwr xfmr..... At the end-of-the-day, he may not experience the increase in output pwr that he expects with a larger xfmr and all the work that goes into replacing it. Many yrs ago, I built a very similar 6AG7/6L6 rig and was disappointed by its low output power - and it wasn't pwr supply related. This resulted in a several week research project that looked at B+ voltages on the 6AG7 vs drive vs B+ voltages on the 6L6 vs output pwr. That resulted in an article "Notes On The 6AG7/6L6" published in the Jul.'93 Electric Radio. The bottom-line is that Gary will never see max output pwr out of his 807 running his 6AG7 on the lower 273 Vdc B+ voltage. Reference the Heath AT-1 which operates the 6AG7 at the SAME B+ as the 6L6 which maximizes the output pwr using these two tubes. Heath got it "right". I still have one 6AG7/6L6 HB rig in my collection and the 6AG7 runs off a regulated 150 Vdc. The output pwr is puny compared to the AT-1, but I've never changed its design..
Dave - WA6VVL

I agree about maxing the power output.

If the present transformer has enough core, it won't make much difference. Since the 5 V filament winding is not used, that helps keep the HV winding "up." Also, if the 6V filament windings are not used at full rated current, that's more flux available for the HV winding. I may not be using the correct terms, but a transformer is rated to supply a certain amount of power. If it isn't being used by the heater circuits, it's available for HV, assuming that the HV winding has large enough wire... which shouldn't be a problem at 100 to 150 mA.

The difference in signal strength between 25 watts and 50 watts isn't going to be significant; especially on CW. I retired my Heath SB200 about 25 yrs. ago. The neighbors didn't think I needed to run a KW and they were right.

Rich

Hi Rich,
I agree with your assessment.... Gary has already demonstrated that the 807 can sit there with 100 mA plate current. That would be sufficient if he could actually load up the xmtr to that plate current with the existing drive from the 6AG7. I'm again reminded of the pipsqueak pwr xfmr (similar in size to Gary's) in the Conar 400, and it does quite well.... All things considered, that xfmr is probably OK.....
Dave - WA6VVL

From what I can see, Gary's transmitter is doing about what it's supposed to be doing. I took a look at the Viking Adventurer, my first commercially made transmitter back in the 60s. 6AG7 feeding an 807. Rated for 50 watts input and would average 20 to 25 watts output. The manual shows B+ going from 650V key up to 450V key down. Not well regulated but typical for transmitters then.

Gary, congraduations on a really nice build - it looks great and seems to work pretty well. Watch out for the chirps. Let us know what frequency your crystal is on so we can listen for you.

arnie - W1GCI

Dave, I got a kick out of your latest ER article! You really seemed to enjoy beating your head against the wall or was it the iron? Those poor NC-270's dont deserve that much abuse

Carl

Hi Carl,
Your reply is a GIGGLE!!!! Yeah, I know.... Especially the NC-270!!! With my design background in xfmrs. my curiosity just got the better of me!! Your email remarks about the "new" NC-270 design team didn't help either. I just kept wondering what these guys were thinking??? Now that I'm very happily retired, I had more time to REALLY beat my head against the wall... Oh well, that's the last hurrah of my NC-270 "adventures" - I promise!!!
Dave - WA6VVL

Hi Guys, I have been really enjoying your discussions about my Xmtr
project. Thank goodness both meters Still seem to be operating alright
I never gave the RF a thought about damaging my meters. You guys are
great I want to thank Rich and Dave for there great advice.
Will the two diodes in series in the PS help any with the output?
Or is this just for keeping the PS safe against over load?
My ELMER stopped by and looked my rig over and was impressed
at the signal he received at his station which is about six miles away.
He said for a homebrew rig the tone was great. He also liked my dipole
antenna I constructed for 80M I got the plans online..It's a quarter wave
with two 45uh coils in between the two radiators, I'm getting a 1: 1.5 SW.
My code sending and receiving is awful, I haven't tried to make any contacts yet.
The only xtal I have is for 3.550mc. I am 67 years and have always loved Ham radio
I was an avid SWL all through High School... I have had my ticket for only 4 months now.
Just love restoring old radios. This was my third Xmtr. The first was the Hart 65 and the
Hart 25, both were from a 60's Popular Electronics. Both work the first time!!
I really feel dumb connecting that cap wrong on this last project. Good thing I posted a couple of pix!!
Thanks to all,
Gary

Hi Gary,
That IS a very nice looking xmtr based on the length of time you've been licensed... You did a GREAT job... I've seen far far worse from hams that have been licensed a lifetime!!!
The two 1N4007 diodes in series on each leg of the bridge provide a breakdown of 2 KV, and with the pwr xfmr you are using, that's what you need. If you left just one diode per leg, chances are pretty good sooner/later one of them would short because of the over-voltage.
I still think that pwr xfmr is good enough for now.
I would be interested to know just what the highest plate current is when fully-loaded.
Connecting C12 to the wrong place?? Welcome to the "club". Mostly, we've "all been there done that"...
Age here is also 67, but have been licensed since '60....
Have fun,
Dave - WA6VVL

Hi guys, Dave you asked what my meter reading would be if hooked to a 50 ohm
ant. Well it's 100ma.. I hate to sound dumb, but could you explain the "DIP" thing?
I think it means getting the max output from your rig...Right?
You said to set load to full mesh. Ok on my set, it's Plate, Load, and Grid. Which one would be tune? When making adjustments I did see the meter drop back, Then turning the
Grid knob the meter went up to 100ma. I think I got it right. Now, does this 100ma mean
that the Xmtr is putting out Max wattage?
By the way I haven't tried making any contacts... My Elmer says I'm putting out a nice
clear signal, but he only lives about six miles away. Wonder how far I am getting out on
80M at 3550. I have only tested in the early morning hours. At night that freq. is crowded.
And I don't want to make a fool out of myself or be a nusance to other Hams.
You guys sure have been a big help to me.
Gary

Hi Gary,

The added diodes to the bridge will only increases their PIV, their working voltage, and will keep the original single diodes from shorting sooner/later. You will notice no change in voltage or output.

With 50 ohms as a load, set the LOAD cap to max (fully meshed), and adjust PLATE for a pronounced dip in the meter. This dip indicates the resonance point of your pi-network. If you're monitoring output power, the output power should also increase at the dip. Then adjust the grid drive to max the meter reading. 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. Then slowly increase the LOAD adj (decreasing its capacitance) while continuing to dip the PLATE tuning. Keep going until you can just barely see the dip with the PLATE tuning. It's always a back 'n forth process. Your xmtr s/b tuned for max output at this point. If you're monitoring the output power, you may notice that max output power doesn't occur at exactly the dip, but it's very close. For now, use the dip.....

Dave - WA6VVL

Gary

You can peak up a meter reading when checking grid but plate current needs to dip. When measuring plate current there will be a dip. It should not be at end of your variable cap range. Each side of the dip current will be higher.

Most likely you hava an output coil with variable caps on each side of this coil. One adjusts amout of signal to the antenna. The other resonance. Adjusting one has an effect on the other. Best to check a Radio Amateur Handbook.

If your transmitter isn't in resonance an 807 plate may start glowing red with 100 ma current. You shouldn't see any red on 807 plates in operation.

You start with the loading control fully meshed. Tune the plate to resonance using the plate tuning capacitor.
You are at resonance when the plate current shows a dip as the plate tuning capacitor is tuned.

Maximum power output should coincide with a dip in the plate current reading.

Slowly increase the loading (open the load capacitor) while redipping the plate current using the plate tuning capacitor.

Stop when you reach the desired max. plate current and/or maximum power output.

If the dip in plate current does NOT coincide with the maximum power output, you may need to neutralize the 807.

Pete