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Drake L7PS transformer resistance checks




 
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Author Topic: Drake L7PS transformer resistance checks  (Read 143 times)
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W6MQI
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« on: March 22, 2020, 06:58:19 PM »

Did some resistance checks on the main L7PS power supply transformer the primary seem low to me. The primary is reading .2 ohms between all tap points, and the secondary is reading 5 ohms. Do these readings seem okay? Picked up the amp at a SK estate sale for next to nothing, and  its been sitting for about a year or so at my place not real sure of its history. I did a recap, new diodes, and equalizing resistors before adding power to the power supply. Upon adding power the supply was putting out its rated voltage in both CW, and SSB positions, only problem is in SSB position the power supply wants to jump out of its skin heavy humming (Buzzing) doesn't sound right at all. I did try tuning up in CW position the amp was putting out about 500-600 watts switching to SSB I saw no difference in output I forgot to monitor the grid current when I did this to see if grid current change or not. So I guess my main question is what should I see for resistance on the transformer primary, and sec?


Dave
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WBear2GCR
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Brrrr- it's cold in the shack! Fire up the BIG RIG


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« Reply #1 on: March 22, 2020, 11:41:46 PM »


I do not know what the DCR should be.

However, I'd look at the current draw off the mains.
The current draw off the secondary.

Do you know the PS is wired correctly?
I think I'd not have changed anything until I tried it stock... a variac
is a friend for this.

Do you know the tube(s) are in good shape??

What's the plate current meter show in CW and in SSB?
Does the plate dip properly?
What does the manual say for plate current?

What's the B+ voltage in the different positions?
Under load??

Can you put together a resistive high power dummy load
for the PS only?

Are you running off a 240vac mains line?

Just some ideas...

                       _-_-
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_-_- bear WB2GCR                   http://www.bearlabs.com
W6MQI
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« Reply #2 on: March 23, 2020, 12:05:52 AM »

Well somehow I seemed to have fixed my problem decided to rebuild the power supply one more time copying the Harbach design. Well for what ever reason things are working right now (two fingers crossed).  Sorta think there may have been a bad solder joint some where in either the capacitor bank or diode strings in the original build who knows anyway it works now.    Hate it when I fix something and I don't know how I fixed it.

73, Dave
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