More tests

[N4LTA]

Set it up at about 32 watts out - measured pretty closely

130 mA in at 363 volts  -

Screen voltage dropped to 235 volts on one tube about 242 on the other at 130 mA  - Looks in the ballpark

Screen current is about 5.5 mA per tube roughly  -  right where it ought to be

The grid voltage was -75 volts and I could drive it no lower even doubling the 1 watt drive to 2 watts - I was shooting for -80 volts
In looking in an old handbook, it mentioned that with screen grids, fixed bias could not cutoff the tube in a protective bias situation if the screen was fed with a dropping resistor - only with fixed screen voltage. It suggested using all grid leak and a clamp tube for protecting. This amp cuts off pretty well with -125 volts and no drive and only pulls 5 mA anode current with drive off and the -68 volt supply. The screen voltage rises to near the anode voltage so little current is flowing. -  Not sure whether I have screwed  up or not.


Grid current was a  low - about  4.7 ma and should be 7 mA - not getting the drive for some reason.

Looking at the grid tank on the scope showed about 90 volts - 180 VOLTS PK TO PK at 1 watt drive - no change in the tank voltage voltage at 2 watts - it just stops  - and it is a nice sine wave in the tank - so maybe the 100 pf coupling cap is doing all she can - I would have expected the tank to be distorted by the grid current??

I should have but didn't look directly at the grid.
  
Assuming plate current was 130 - screen current - say 11 mA - then plate current is 119mA

Plate input is - .119 x 363  = 43.2 watts

Output was 32 watts  -  so plate efficiency is  32/43.2 = 74%  or pretty good.

Should be able to drive it a little more ? - but doubling the drive made no difference - maybe increasing the grid leak a little more ?

Or am I likely there? I still feel like I should get a little more drive and get the grid current up to specs.


Pat
N4LTA

[KM1H]

No comments until you get all the little things on the list fixed.  Too many ass-umptions for now.

[KC2ZFA]

Also, look here: http://www.qsl.net/kb7rgg/radio/807/807specs.html

Class C Modulated Amplifier (CCS)
Plate Voltage ................................. 325 Volts
Grid No. 2 Voltage ............................ 250 Volts
Grid No. 2 Dropping Resistor .................. 12.5K Ohms
Grid No. 1 Voltage ............................ -75 Volts
Peak Grid No. 1 Voltage ....................... 95 Volts
Grid No. 1 Current ............................ 3.5 Ma.
Plate Current (Zero Signal) ................... 80 Ma.
Grid No. 2 Current (Zero Signal) .............. 6 Ma.
Driving Power ................................. 0.3 Watts
Power Output (approx) ......................... 17 Watts
Beer consumption .............................. .010 pints/watt

[N4LTA]

Yes - I used that spec. during the design

Carl - There ain't much on the list to fix.

The screens are in spec, the plate effiiency is very good.

Only thing is the control grid current and I am going to re-wire it tonight and see if I can get it up to 7 mA.

The grid tank staying a nice clean sine wave puzzles me - I would have thought the grid AC current pulses would have distorted it?

If the grid circuit wont load any more - I am going to call it done

Pat

[N4LTA]

Wired the grid circuit like yall told me it ought to be and for the most part I am satisfied.

I can drive it to 160 Ma and I get 39 watts out into a dummy load  - pretty decent signal but it could use another L section. I don't think that is anything usual.

On the dummy load - it tunes nicely and the load cap (tripple 365pF variable) tunes up about 1/2 meshed.

I put it on my dipole which is pretty near flat and the load cap peaks a good bit unmeshed  - just barely in - I know the dipole is probabaly not 50 ohms but there is near no reflection on the Bird. I would have thought the pi net would have had more range than that.

Nothing unstable - It takes more drive than it should - but I think my turns ratio on the grid tank is too high 14:1 I probably need to add a couple turns and see if I can get the input SWR down.

Tell me I am done?  Almost got 40 watts out! I am using one NOS Sylvania from the 80s and one war horse from the 40s. It might make 40 with two nos tubes?


Comments Please!
Pat

[The Slab Bacon]

Comments Please!
Pat

Yea, now build the modulator! ! !   

[N4LTA]

Heck,

I am going fishin and let it rest this weekend. The end of the world coming has messed up all the offshore fish and they think it is May. They are killing the Dolphin, Wahoo and Blackfin Tuna off SC. I need to go down there and put an end to it - If I go out it will go back to normal.

Pat

[The Slab Bacon]

Heck,

I am going fishin and let it rest this weekend. The end of the world coming has messed up all the offshore fish and they think it is May. They are killing the Dolphin, Wahoo and Blackfin Tuna off SC. I need to go down there and put an end to it - If I go out it will go back to normal.

Pat

"Even a bad day of fishin beats a good day at work"   

[KM1H]

Yeah, you done boy   Dont beat it to death for perfection.

Go do some fishin.

Carl

[N4LTA]

Sunday morning back home  - sunburned face - drove 460 miles in 30 hour period, yesterday took a nice 180 mile boat ride on a 25 foot center console boat (in total comfort)- on the Atlantic ocean - started out at 4:00 am near Charleston SC and went out 75 miles and then south past Savannah, Ga. Spent $404 on gas, $50 on bait, paid a kid $140 to mate for us. Ate sardines and vienna sausages and drank beer.

An excellent adventure for three 60 year old plus grown men.

Did exactly as I predicted. Changed the entire SE coast fishing prognosis single handedly


But it sounds like the transmitter is finished.


Pat
N4LTA