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5F2-A odd rectified voltage Q

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  • #1

    5F2-A odd rectified voltage Q

    Hi folks. I just finished a 5F2-A with a SS rectifier. I get 260vac/ 311vac at each HV (PT's always read this 'lower voltage pair' of HVs at 311/ 262v). From the 2 tied in4007 diodes from each of these HVs to a central point.. I get only 262vdc (~580vac). I was expecting ~360vdc; I got 340vdc with this PT & a 5Y3GT at pin 8 before (albeit in a 5e3 circuit), & have 350vdc using a SS four diode rectifier in another amp with only 255vac/ 260vac at its HVs..

    Are there different versions of in4007 diodes? perhaps I got wrong type? I see there's an 'OC' marked below these in4007s; my other amp's having a squiggled arrow below.. its all terribly peculiar. Any help grateful, Captain.
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  • #2
    A 1N4007 is a 1N4007. There are no secret types.

    What filter cap are you feeding? Since your DC matches your AC, it sounds to me like it is unfiltered.
    Education is what you're left with after you have forgotten what you have learned.

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    • #3
      Hi Mr. Enzo, yes indeed its unfiltered- Im testing the rectifier voltages with just AC switch as 'step 1'. For filter caps I have 2 paralled 16ufs for the 1st cap, two single 16ufs for the others. I put in a different set of in4007s with same results, so those and solders/ contacts fine.. I cant remember what readings I should see with a SS rectifier! cant' find info either.. muppet!

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      • #4
        The only way for the raw pulsing DC coming out of the rectifier to charge up to peak is , well, to have something to charge - a filter cap. That is what the "filter" in filter cap means - it filters out the bumps of the raw DC.

        Add the filter cap, and your DC will become approximately your AC voltage times 1.414

        What color are the wires from the transformer? That voltage difference is not proper. Or is this one of those Ted Weber power transformers?

        And for the future, you might look into 20uf or 22uf at 500v caps instead of the 16ufs. COmpare prices. The amp will be just as happy with the slightly over rated part.
        Education is what you're left with after you have forgotten what you have learned.

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        • #5
          Originally posted by Enzo View Post
          What color are the wires from the transformer? That voltage difference is not proper. Or is this one of those Ted Weber power transformers?
          You're a very clever man Mr. Enzo. Anyway I tested DC at the filter caps flipping standby, expecting again 260v.. alas its at 420vdc, 415v, and 380v . Yes the 50v difference between red/white PT secondaries is pretty dreadful (and I thought the cause of the low rectified dc score)- it seems ok though thankfully.

          While Im here, different Q: how do I tell what primary ohms I have for choosing which colour OT secondaries for my 8 ohm speaker? no info on the Weber W125130(EU) PT bumf to say.. I have a hammond 125ESE with 3 different choice wires for 8 ohms, dependent on '2500- 10,000'. (I'd assumed it was the obligatory green to tip & black to spkr jack's gnd.. but no sound at all ).

          Thanks for the help

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          • #6
            I used the 2ohm tap in my tweed 5f8a as it sounded the best. I think the reason is because of the -feedback coming off it. Its an old bogen recycle.

            You could try them all and choose the one which sounds the best. Just dont ever have "none". I think thats the best way since we are after the best sound.




            http://www.hammondmfg.com/125SE.htm

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