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Hammond 1750B OT for a Single Ended 10 Watt Build?

Discussion in 'Shock Brother's DIY Amps' started by James Knox, Dec 4, 2020.

  1. James Knox

    James Knox Tele-Holic Silver Supporter

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    This OT is listed as a Reverb Driver for a Fender Vibro King. It has a Primary of 5482 ohms and a Secondary of 8 ohms. Paper Bobbin and 10 watts.

    Could one build a 5F1 or 5F2A with this?

    DE1E03EF-99BC-4119-ACB7-0589DEE8C123.jpeg
     
  2. ThermionicScott

    ThermionicScott Poster Extraordinaire

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    Can't see why not! :cool:
     
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  3. Nickfl

    Nickfl Friend of Leo's

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    That will work fine. 8k is a better primary impedance for 6v6 IMO but 5.5k will definitely work too. If this is for the 6L6 powered champ you mentioned in another thread, then it should work nicely.
     
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  4. NTC

    NTC Tele-Meister

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    I bought a couple similar ot's years ago that were billed as being for a 5F2. When I looked up tge number recently online, I got this Hammond as the cross reference. I used to have them on a 2 x 6 with some of those octal relay sockets with screw terminals to try things. They sounded good. Got a great sound with a power MOSFET as a 6V6 replacement, though the bias point moves around with heat....
     
    Last edited: Dec 5, 2020
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  5. Kevin Wolfe

    Kevin Wolfe Tele-Meister

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    I’ve been wondering that myself. Maybe a 5881 behind a lower voltage OT.
     
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  6. 2L man

    2L man Tele-Meister

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    I bought 1750B few weeks ago to be used on about 10W SE 5F2 circuit using new Tungsol 5881 or NOS Sylvania 6L6A power tube and toroid power transformer. I just made chassis and next I drill turrett board and I can put it together. I also have planned to use it for hot biased 6P6S tube.
     
    Last edited: Dec 12, 2020
  7. James Knox

    James Knox Tele-Holic Silver Supporter

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    Keep us posted! Love to hear how it turns out. Will you be doing a “build thread”?
     
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  8. 2L man

    2L man Tele-Meister

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    Actually I could when it is not going to be too ordinary other than actual circuit...
     
  9. jsnwhite619

    jsnwhite619 Friend of Leo's

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    On that one I built, I was surprised how low the B+ ended up with the 5881. 100mA PT & 325v secondary with a 5u4 was still in the 350v+ range in the end I think. Loaded it down a lot more than I expected. 6v6 would have been 370v-380v with a 5y3.
     
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  10. James Knox

    James Knox Tele-Holic Silver Supporter

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    I got one to try out!

    Question... to run a GZ34 with a 6L6GC, I would tap the Hammond 290AX Power Transformer 650VCT Rather than the 550VCT normally used for 5Y3/6V6. Correct?

    How do I know what B+ I am shooting for?

    0279993B-5AB0-4918-A2F2-8F4E4CE29929.jpeg 4DAA1C4E-3F28-4F65-BBD2-D9AD334ABEF6.jpeg
     
  11. Wally

    Wally Telefied Ad Free Member

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    More voltage equals more power.
     
  12. Wally

    Wally Telefied Ad Free Member

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    650vac.... 325 x 1.3 = 423vdc.
    225 x 1.3 = 293vdc
    Guesstimates.
     
  13. jsnwhite619

    jsnwhite619 Friend of Leo's

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  14. 2L man

    2L man Tele-Meister

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    If you don't use choke you should install two 100 ohm current limiter resistors between plates pins 4 and 6 and ransformer outputs. I know they are not always used but they should. Look tube datasheet to veryfy it!

    Datasheet often has craphs where you can look what voltage comes out with certain input voltage and output current. Other craph is for choke circuit and other for current limiter resistor circuit. When choke is used the output voltage comes lower but it stays more stable against changing current but when current limiting resistors are used the voltage changes more when current changes. When you see that for example 1,3 is used to multiply AC to have DC it can not be very accurate!

    Perhaps you should also add two silicon diodes which protects circuit in case tube rectifier shorts. Also without choke max regulation capacitor GZ34 is 60uF but only when choke or resistors are used to limit current.

    Current limiter resistor makes rectifier circuit to take current longer time when it "flattens" sine wave peak and then rectifier tube life increases. Choke stores energy taking current delayed and obviously releases it even more delayed.
     
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