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    pas filament supply question

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    rmk

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    Join date : 2020-11-18

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    Post by rmk on Wed Nov 18, 2020 9:55 pm

    Hello!

    I was going to replace the se and filter caps in a pas 3x with diodes, 3300 uf caps using a 4 terminal strip on the chasis stud.

    Is an additional dropping resistor usually needed?
    PeterCapo
    PeterCapo

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    Post by PeterCapo on Wed Nov 18, 2020 10:54 pm

    .


    Last edited by PeterCapo on Mon Nov 30, 2020 4:47 pm; edited 1 time in total
    peterh
    peterh

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    Post by peterh on Thu Nov 19, 2020 3:54 am

    rmk wrote:Hello!

    I was going to replace the se and filter caps in a pas 3x with diodes, 3300 uf caps using a 4 terminal strip on the chasis stud.

    Is an additional dropping resistor usually needed?

    No.
    Filament voltage is on the lower side anyway.
    PeterCapo
    PeterCapo

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    Post by PeterCapo on Thu Nov 19, 2020 9:36 am

    .


    Last edited by PeterCapo on Mon Nov 30, 2020 4:46 pm; edited 1 time in total
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    rmk

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    Post by rmk on Thu Nov 19, 2020 4:18 pm

    Its not clear to me what the voltages should be at a properly working SE. If its not too much trouble, what are the proper voltages at each of the numbered locations?


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    peterh
    peterh

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    Post by peterh on Thu Nov 19, 2020 5:32 pm

    I do not have the old rectifier.
    But according to the manual ( and that corresponds to my memory ) the filament is floating
    with the middle of the tubes in PC-6 connected to ground.
    The transformer gived 10.5 Volt AC, this is doubled and gives 22Volt DC approximate
    around ground. ( tube differences will shift this up and down around ground.)
    Note that the caps must be isolated from the chassies and from each other.
    PeterCapo
    PeterCapo

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    Post by PeterCapo on Thu Nov 19, 2020 6:01 pm

    .


    Last edited by PeterCapo on Mon Nov 30, 2020 4:47 pm; edited 1 time in total
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    rmk

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    Post by rmk on Sat Nov 21, 2020 1:25 pm

    unrelated question. i replaced the SE today. I noticed the AC wires to the power switch were ran topside. Shouldnt these be on the underside as a twisted pair? (see photo).

    pas filament supply question 20201112
    peterh
    peterh

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    Post by peterh on Sat Nov 21, 2020 2:39 pm

    rmk wrote:unrelated question. i replaced the SE today. I noticed the AC wires to the power switch were ran topside. Shouldnt these be on the underside as a twisted pair? (see photo).

    pas filament supply question 20201112
    Yes, they could induce hum at this position, they are very close to the signal(s)
    The manual puts them under and close to the side, twinned.
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    rmk

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    Post by rmk on Sat Nov 21, 2020 3:41 pm

    thx, i rerouted it to the underside, twisted along the side. fwiw, it didnt seem to cause hum.

    Hopefully the switch and the disc cap is good after reworking.
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    rmk

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    Post by rmk on Sat Nov 21, 2020 4:37 pm

    I took measurements at 117vac line voltage. After replacing the SE (and the can capacitor) the heaters are showing approx 12.1/11.06 vdc for each pair of tubes. Im assuming that is correct.

    The can capacitor numbers all seem good.

    The only concerning voltage reading was PIN 1 on the plate on each tube on PC6 showing approx 134 vdc (115 vdc is the reference). Is this normal? (Pin 1 on each tube of PC5 was ok at 170vdc).
    peterh
    peterh

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    Post by peterh on Sat Nov 21, 2020 4:51 pm

    rmk wrote:I took measurements at 117vac line voltage. After replacing the SE (and the can capacitor) the heaters are showing approx 12.1/11.06 vdc for each pair of tubes. Im assuming that is correct.

    The can capacitor numbers all seem good.

    The only concerning voltage reading was PIN 1 on the plate on each tube on PC6 showing approx 134 vdc (115 vdc is the reference). Is this normal? (Pin 1 on each tube of PC5 was ok at 170vdc).
    The voltages are ok.
    The 134Volt vs 115 Volt is due to spread in tube paramaters and not to
    be concered about. It could also be to a plate resistor getting bad, you could
    check the resistors in place, one connected to pin 1 and eyelet 16 should read
    150k, the other is 100k and connected between pin6 on the tube and eyelet 16
    ( eyley 16 and eyelet 1 are interconnected) If the resistors has drifted
    then replace with 1w film resistors. All done with power off and mains
    disconnected.


    Last edited by peterh on Sat Nov 21, 2020 4:54 pm; edited 1 time in total (Reason for editing : power off!)
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    rmk

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    Post by rmk on Sat Nov 21, 2020 5:28 pm

    thank you for the tip, those resistors did measure correctly. Have a nice day.
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    rmk

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    Post by rmk on Sun Nov 22, 2020 11:20 am

    I think the power switch is flakey. I was going to replace it and the .02 snubber. All I have on hand is a double pole switch and .01 safety cap and or a .01 film cap.

    Would that value work here?

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