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Author Topic: Johnson Viking Adventurer HV filter caps?  (Read 45517 times)
N2EY
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« Reply #60 on: October 14, 2011, 01:34:50 PM »

A 20 Ohm shunt would double that, allowing the meter to read 120mA of plate current at full scale?

No! Just the opposite! 20 ohms will make it read full scale on about 30 mA!

Think about it conceptually....

The purpose of the shunt is to allow some of the current to go through it, rather than through the meter.

If we have a 10 mA meter, and we want it to read 200 mA full-scale, then we need a resistor that will divert 190 mA through itself and leave 10 mA for the meter.

Such a resistor will be smaller than 10 ohms, not larger.

Doesn't need to be 10 watts, either. 1/2 watt is plenty, the power dissipated in the meter circuit is tiny.

73 de Jim, N2EY
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N2EY
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« Reply #61 on: October 14, 2011, 01:36:22 PM »

20 ohms had no luck, then checked the meters internal resistance (disconnected) 3 OHMS!!! I shoulda checked that first, as you guys recommended.

Should I just completely change out the meter? I have a Radioshack 0-1mA meter with an internal resistance of 80 ohms. That might work better.


I would keep the original meter and just change the 10 ohm shunt to something smaller. What small resistors do you have available?

73 de Jim, N2EY
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KC2VDM
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« Reply #62 on: October 14, 2011, 01:45:41 PM »

ohh, okay, I got confused on the formula. I'll try it and get back to you. I'm  using 1/2 watt resistors  in the meter circuit.

I've got plenty of small value resistors.

-Alex

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N2EY
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« Reply #63 on: October 14, 2011, 02:03:55 PM »

Just to toss it out there, I did find some 25 Ohm, 10 watters. I'll see how one of them would work later.

What would you use them for?

The 807 screen resistor should be 20,000 ohms, not 25 ohms.

73 de Jim, N2EY
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W8JI
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« Reply #64 on: October 14, 2011, 02:09:07 PM »

20 ohms had no luck, then checked the meters internal resistance (disconnected) 3 OHMS!!! I shoulda checked that first, as you guys recommended.

Should I just completely change out the meter? I have a Radioshack 0-1mA meter with an internal resistance of 80 ohms. That might work better.

-Alex

Alex,

Your life is needlessly being complicated and not for a better meter performance!! I'm betting you have a standard common 50 mV movement in your new meter, and it is intended to be 10 mA five ohm. It COULD be a 30 mV, which would be 3 ohms, but they are rare. The next common step is a 25 mV, which would be 2.5 ohm movement in your new meter.

In two minutes you could have added one resistor and been done and just used the original shunts. Not only that, the meter would work more reliably with the one resistor fix.

The original 10 mA meter was scaled to be 200 ma at FS. We know the plate shunt resistor was 10 ohms. The meter resistance was  obviously 2/.01 = 200 ohms.

If you just stuck a ~200 resistor in series with the 10 mA meter you have, everything would work with original values.

If you have a 180 ohm resistor and a 10-20 ohm resistor connect them in series with the meter you have and you are done. You can just use the original shunts, and with the higher voltage on the meter it will actually be more reliable. If you just have a 180, use it. It will be close enough until you find something better.

73 Tom
 
« Last Edit: October 14, 2011, 02:10:43 PM by W8JI » Logged
KC2VDM
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« Reply #65 on: October 14, 2011, 02:18:51 PM »

1: yes just realized I had the wrong value for the screen resistor.

2: I was about to ask about putting one in series!

-Alex
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KC2VDM
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« Reply #66 on: October 14, 2011, 02:48:53 PM »

FINALLY!!!!!!! THE MYSTERY IS SOLVED! Grin

Added a 180 ohm resistor in series ( and put the original resistor back) and now the final plate current for 25 watts out is 3mA (as indicated by the meter)!


Thank you guys for all your help! I'm overjoyed that this thing is finally running! Now I can stop pulling my hair out about this rig!

-Alex
KC2VDM
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W8JI
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« Reply #67 on: October 14, 2011, 03:04:56 PM »

FINALLY!!!!!!! THE MYSTERY IS SOLVED! Grin

Added a 180 ohm resistor in series ( and put the original resistor back) and now the final plate current for 25 watts out is 3mA (as indicated by the meter)!


Your meter is roughly about 25 mA per every 1 mA indicated, so you have about 75 mA on the plate.
You should have about 500 V HV. That's 37.5 watts input (about) and with 25 watts out for about 67 % efficiency.

Good work. Have fun.
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KC2VDM
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« Reply #68 on: October 14, 2011, 03:31:41 PM »

Hey, I couldn't have done it without everyones help. Actually, I can push 45-50w out if it tune it right, but that's stressing the 807 a bit.

-Alex
KC2VDM
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N4NYY
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« Reply #69 on: October 14, 2011, 04:13:38 PM »

Wait. The thing ain't working right until it dims the house lights when you key !
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KC2VDM
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« Reply #70 on: October 14, 2011, 04:22:59 PM »

HIHI, I have the HA-14 for that department!
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N2EY
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Posts: 5085




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« Reply #71 on: October 15, 2011, 09:24:49 AM »

FINALLY!!!!!!! THE MYSTERY IS SOLVED! Grin

Added a 180 ohm resistor in series ( and put the original resistor back) and now the final plate current for 25 watts out is 3mA (as indicated by the meter)!

Excellent! Great to hear you found the solution. As usual, W8JI gave good, *practical* advice.

I still suggest you check the accuracy of that meter/resistor combo by temporarily putting it in series with a meter of known accuracy, a battery and a limiting resistor. That way, you *know* where the 110 mA point is.

While it may be possible to get more than 50 watts into the Adventurer final, IMHO it's not a good idea. While the 807 will do 75 watts input at 750 volts B+ and still be within ratings, the Adventurer power supply will be working over ratings at that level. 807s are cheap and easy to find compared to the Adventurer power transformer and filter choke.

btw, the manual shows the stock fuse as 2 amp.

---

The Adventurer was my 2nd non-homebrew transmitter. I traded a DX-20 for it, and IMHO I got the better deal. It had a number of odd quirks, which I fixed by disassembling and rebuilding it per the kit instructions.

That was 40+ years ago, though, when the parts were a lot more available and Adventurers were pretty common for $25-30 used.

For some reason lost to memory I converted that Adventurer to use a 1625 by adding a small heater transformer and changing the socket. IIRC I did it because I had lots of 1625s and no spare 807s. (How things change!) More than a decade and several owners later I bought it bacl at a hamfest, still using a 1625. Unconverted it and sold it - now I wonder why.

73 de Jim, N2EY

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KC2VDM
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Posts: 145




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« Reply #72 on: October 15, 2011, 12:45:17 PM »

That's amazing you bought your own rig back years later! I don't mean to keep dragging this thread on (beating the dead horse maybe?), but wanted to say that it works as it should in the ham bands (I'd be dumbstruck if it didn't). My 7.114 Xtal came today, and it works! look for me around there in a few months!
Right now all I can say (fluently) is "VVV KC2VDM TEST SK"

-Alex
KC2VDM
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G3RZP
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« Reply #73 on: October 16, 2011, 03:03:44 AM »

US made 807s were near indestructable. I ran one for a long time on 40 CW with 1750 on the plate, 500 on the screen and around negative 200 on the grid. Driven by a 6L6, it ran about 120mA plate current, and I got very close to 150 watts out. A very short duty cycle of course, which got the efficiency up.

UK ones weren't so good for some reason.
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W0OPW
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« Reply #74 on: October 22, 2011, 06:31:59 PM »

Jim-my replacement manual shows the fuse as 5 amp, but penciled out and 2 written in. I wonder if they might have realized there was a problem after I had my transformer hand delivered from Waseca( by big mucky-muck by the name of Magnuson). Cost me $15 too. Not sure what his function was. The date was around July of 1958. It might be interesting to see if others have different values for the fuse. I can still smell that burning insulation.
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