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Author Topic: Low output on 6146 final  (Read 359 times)

WB8PFZ

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Low output on 6146 final
« on: December 10, 2022, 12:37:14 PM »

Would a bad coupling cap going from the plates to the output circuit cause low output? I have plenty of input current just not much output. Thanks Mike
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W0CKI

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Re: Low output on 6146 final
« Reply #1 on: December 10, 2022, 12:45:45 PM »

What does your HV read?
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WB8PFZ

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Re: Low output on 6146 final
« Reply #2 on: December 10, 2022, 02:10:29 PM »

940 no load.
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AC2EU

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Re: Low output on 6146 final
« Reply #3 on: December 10, 2022, 03:25:30 PM »

First, are you familiar with how to tune the finals ?

Check that you have the 50ma bias when you key up in SSB

Do you get any current reading when in tune mode?
What current do you get?
did you try the loading control?
did you try other bands?

WB8PFZ

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Re: Low output on 6146 final
« Reply #4 on: December 10, 2022, 03:38:41 PM »

Been tuning radios for 50 years.
40 mills idle current
loading control has very little adjusting
other bands the same
I tune up in cw mode.
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K0IZ

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Re: Low output on 6146 final
« Reply #5 on: December 10, 2022, 05:09:34 PM »

I assume you have tried a dummy load to eliminate problem with antenna.  If loading cap doesn't change much, that suggests to me that there is a problem with the load.  IE, no or minimum load.  So somewhere between the loading cap and the coax connector would be where I would look.  Relay?
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K2FW

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Re: Low output on 6146 final
« Reply #6 on: December 10, 2022, 05:10:57 PM »

Mike, have you tried another 6146?  Also, what transmitter are you using?
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AC2EU

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Re: Low output on 6146 final
« Reply #7 on: December 10, 2022, 05:11:13 PM »

Been tuning radios for 50 years.
40 mills idle current
loading control has very little adjusting
other bands the same
I tune up in cw mode.

Sorry,I don't know you so i had to ask about the tuning. There are newbies who think the old radios work just like the new ones, which causes problems for them and the radios.

It may be an open coupling cap or no/low screen voltage too as long as HV is there.
HV sag will ruin the output as well.

WB8PFZ

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Re: Low output on 6146 final
« Reply #8 on: December 10, 2022, 07:08:46 PM »

Makes me like my 930 even more :)
Thanks all
Collins 32S3 transmitter
radio run into a dummy load with a flat SWR
tested both 6146's to be good
will check or replace coupling cap
there is no HV meter on the radio  the power supply was rebuilt when I purchased it
I will check the screen voltage at the tube sockets. there is a resistor in series in the screen supply line, will check that
Someone redid the power supply connector and loaded some of the pins with excess solder, had a tough time getting the mating connector on. Would like to replace both connectors in the future, not an easy task.
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WB8PFZ

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Re: Low output on 6146 final
« Reply #9 on: December 10, 2022, 07:17:54 PM »

I have proper screen voltage.
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N8NK

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Re: Low output on 6146 final
« Reply #10 on: December 10, 2022, 10:39:26 PM »

It may seem ridiculous, but the suppressors at the plates can open to DC/HF whilst still presenting a high R in series to the output PI network. I've seen it once. I'd at least take 10 secs with a meter and check 'em. And I'd check from the plate connector to the far side of the suppressors as well. Why not? Ya never know for sure 'till ya check.
Chuck N8NK
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ZS5WC

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Re: Low output on 6146 final
« Reply #11 on: December 10, 2022, 10:54:00 PM »

 :)Not a slipped coupler from band switch to PA compartment?. Sounds like its out of tune.
Also the RX / TX change over relay could be in need of replacing.

Thanks,
William, ZS4L / ZS5WC
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WB8PFZ

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Re: Low output on 6146 final
« Reply #12 on: December 11, 2022, 05:35:16 AM »

Checked one of the suppressors and it checked 50 ohms on the money. As far as the band switch that would be a night mare to figure out. I guess anything is possible but that looks pretty well engineered.
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WB8PFZ

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Re: Low output on 6146 final
« Reply #13 on: December 11, 2022, 05:40:28 AM »

The load control has little effect on the power output but at the most output the cap is at it's lowest capacitance ( fully unmeshed) Maybe a clue?
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WB8PFZ

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Re: Low output on 6146 final
« Reply #14 on: December 11, 2022, 05:49:43 AM »

I put it back together and it works. Not sure what was the issue but it seems to be working. Taking the wife shopping will do some more checks later. 80 and 40 look good at 100 watts or more out. Thanks all. Mike
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