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Author Topic: Firing up the KW Transmitter.. Need help with operating guidlines.  (Read 33444 times)
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W2XR
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« Reply #50 on: May 08, 2009, 03:03:53 PM »

Pulled the mod transformer out.  Its shorted from OUTPUT to Ground. More on the left side then the right side. Its not a dead short but it shows resistance. The input side is fine. The mod deck is fine also. 

Looks like I need a 600 watt Mod transformer if anyone has any ideas on where to get one.

Clark

How about floating the mod transformer above ground and take great care to never, ever touch that critter when the HV is on?

73,

Bruce
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Real transmitters are homebrewed with a ratchet wrench, and you have to stand up to tune them!

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ke7trp
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« Reply #51 on: May 08, 2009, 03:12:38 PM »

we discussed this already.  It might work.  I was waitint to see if I could get a replacement before we try that.

Clark
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KD6VXI
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« Reply #52 on: May 08, 2009, 05:37:52 PM »

Pulled the mod transformer out.  Its shorted from OUTPUT to Ground. More on the left side then the right side. Its not a dead short but it shows resistance. The input side is fine. The mod deck is fine also. 

Looks like I need a 600 watt Mod transformer if anyone has any ideas on where to get one.

Clark

Oh stopit!

Run down to the local grocery store.

Purchase teflon cutting board.

Mount mod iron on cutting board.

FLOAT mod iron from case to ground in said fashion.

Fire up new 4 kilowatt PEP transmitter errr....

375 watt AM transmitter Smiley

--Shane
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kc2ifr
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« Reply #53 on: May 08, 2009, 05:52:12 PM »

OR........
Check with Gary about rewinding the transformer........
http://tubes_tubes_tubes.tripod.com/tubestubestubes/
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kc6mcw
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« Reply #54 on: May 08, 2009, 06:39:46 PM »

Yes! You must isolate the isotope. ..I agree with Shane.
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kc2ifr
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« Reply #55 on: May 08, 2009, 06:45:25 PM »

I guess isolating the transformer will work but obviously its on its way out. Could last a long time or could fail completely soon.
I am of the opinion if it cant work as designed............replace it.
Band aids dont make reliable equipment.
Its nice to run equipment that u dont have to make excuses for.

Bill
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ke7trp
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« Reply #56 on: May 08, 2009, 07:13:12 PM »

I can try wood later tonight.. But thats not going to be a long term solution.  I found three options right now. One is a peter dahl.  Decent prices. Should fit.

Clark
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N3DRB The Derb
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« Reply #57 on: May 08, 2009, 07:36:14 PM »

Clark,

its normal for one side to have more resistance than the other side. the ohmage will increase because you have more turns of wire as you approach the outside of the winding(s). that alone is not a sure fire indication of a bad transformer.

you need that thing to be hi - pot tested  to verify for sure. I have a Freed hi-pot tester but I dont know if it works or not. I need to look inside it first and repair/replace any weirdness. maybe after I inspect it and verify ok operation I can send it to you for a test.

 

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Gito
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« Reply #58 on: May 08, 2009, 07:45:33 PM »

Hi Clark

It must be a short between Primary and secondary winding(not a dead short) Called it R1,there's also a short between the output to Ground called R2.
The B + oil capacitor is charged by the HV  trough R 1 and then it bleeds the Capacitor trough R2 ,showing as 500 ma plate current,the oil capacistor is charged to R2 divided by R1+R2 ,

When you hooked the B+ The current flows directly through R2 and the meter is pegged

R1 and R2 is actually Carbon tracks  when the Mod. Transformer is damaged.

 maybe It shows high resistance or no resistance when you measured it  with an Ohm meter.
 But when you apply High voltage it is a different story.

Regards

Gito
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ke7trp
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« Reply #59 on: May 09, 2009, 12:30:03 AM »

Short lived.... 

We placed a wooden plate under the transformer and extended the wires.. Fired it up and the short was gone. HV was 2000, Screen 250.  Grid 15MA, Mod current 80MA Mod voltage 2600.

I applied Drive from a Johnson ranger and peaked the Plate tune and then plate load. The Plate current meter read just off the peg. I think the plate Current meter is faulty. It never read more then 50MA and I had lots of power out. Great.. Increased the drive and retuned power was up. Applied a small amount of audio with my voice (from ranger) and heard my voice inside the Transmitter. Left it keyed for a minute.. No trouble.. Stable voltages and power out on Bird meter.

Applied a bit more audio and BAM the Fuses blew. 

With new fuses the unit powers up fine. If you flip the HV on now the Fuses blow instantly. 

The mod transformer must have really shorted out this time. 

The good news is that I have located a peter W dahl 1000 watt unit that will fit and a Thermodor 600 watt unit that will fit. I need to decide which to buy now. I think with the new iron, The transmitter will work.  At least we saw power out!

I can smell the Mod trans burning inside..  I know now it is the problem.

Clark
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N3DRB The Derb
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« Reply #60 on: May 09, 2009, 01:21:49 AM »

yeh, if you can smell it, it's done. removes all doubt for me.

you should investigate the rf deck now to see if here are any surprises at full bore. get a handle on tuning quickly, etc. If there are any surprises there you wanna catch em now before you introduce the new mod iron.

Just curious, what was the old iron? Depending on frequency response power level and such it may very well be a good idea to have it rewound. Big mod iron is pricey. You'll never lose on such a deal. Demand for big mod iron is too high.
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ke7trp
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« Reply #61 on: May 09, 2009, 01:31:41 AM »

YEah.. I have been through the RF Deck.  Aside from no parasitic resistors being isntalled, It looks pretty good. It tuned smooth and I have it resonant on 3870 now.  I have no idea if the 4-400s are good or not. I have two spares so thats not a problem.

The MOd deck needs the new transformer and it also has 4 old Orange Sprague electrolytic caps that need replacing. Might as well do that when I install the new transformer.

I also want to pull the Lower deck out and inspect the underside.  The 872s are out and solid stated already as is the other Rectifier tubes.  I think I need to eventualy go through the bleeders. There are 330 watts of bleeder on the HV supply and 240 watts on the modulator deck. To me that seems like overkill. Just burning up with heat.

I am pretty sure that with a new mod transformer this will come to life. I had real stable voltages.  ROCK solid 2000 on the HV with the variac at 40%. Rock solid Screen at 250 to 300 with the variac down at 30%.

Just need to decide which iron to get for it. Prob just get the PWD unit and be done with it.  I just want to get it up and running for a week. Then, I can decide if its worth it to tear it down to upgrade it.

Clark
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ke7trp
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« Reply #62 on: May 09, 2009, 01:38:25 AM »

Here are some pics of the mod trans on the left. The Right one is the big Mod power transformer for the 810s. Its 2600V out.


* DSCF3366.JPG (176.61 KB, 1296x972 - viewed 491 times.)
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N3DRB The Derb
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« Reply #63 on: May 09, 2009, 01:53:56 AM »

thats some beefy iron. The mod iron looks sorta sad, with it's plate leads hanging down in defeat.  Sad  from the tags looks like the power unit is a Chicago Standard. they're hard to hurt. good stuff.
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N3DRB The Derb
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« Reply #64 on: May 09, 2009, 02:04:01 AM »

Quote
There are 330 watts of bleeder on the HV supply and 240 watts on the modulator deck. To me that seems like overkill. Just burning up with heat.

there's formulas for figuring out how much bleeder you need for a given voltage, current, etc to ensure he best possible regulation for the supply. 330 watts does sound like a lot tho. Possible some of that is being used for screen dropping, or some other legit purpose not just bleeding.
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ke7trp
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« Reply #65 on: May 09, 2009, 02:12:51 AM »

It is a large Chicago trans.  2350-0-2350.  Probably big enough to run the entire box.. which has been suggested.

The Big bleeders dont run anything else. I have the full schematics. The Screen supply is 100% seperate.. Good and bad..

Why there are so much bleeder is anyones guess.  The previous owner realized this and purchased new bleeders and did the math and included that math on a sheet for me.

Clark

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Gito
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« Reply #66 on: May 09, 2009, 05:29:18 AM »

Clark.

The voltage of a power supply soars up to 1.4 of the RMS voltage of the transformer voltage ,without load
when you rectified a 2000 v RMS you got 2800 v DC,
so to make the output more stable ,it uses Resistance Bleeder as a constant load,
So when You load/tune the Transmitter lightly or heavily .The plate voltage is relatively constant,
They used high wattage bleeder to do it ,
but as I know they used 3 0r 4 times the wattage they actually   need,
if you need a 100 kilo ohm  75 watt resistor ( by calculating the wattage need) ,They used a 100 kilo ohm 300 watt rating. maybe for safety reason.

The power that is used by the Bleeder actually is only 100 watt.

Regards

Gito
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