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Mozz's Filmosound 179 Conversion Plus Tweaks

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  • #46
    I have started to sketch the layout and begun a more detailed review. These comments about the schematic are for posterity's sake, in case anyone in the future decides to use the schematic.

    1) 390K dropping resistor in the rectifier heater/B+ circuit - it's in the original (Mozz's) but it only make sense to me if its 390R (maybe dropping about 60v for the missing 6v6 and the CE-1C tube ?). Probably best to omit and measure voltage first before deciding to drop voltage since there is an added a 6SL7.

    edit: its correct, see next reply for explanation.
    Last edited by willard; 05-19-2022, 11:49 AM.

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    • #47
      The 390k is just a bleeder resistor. I don't know if i mentioned it, there is not a lot of room in those chassis. You would be best off to build it first before you do any mods.

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      • #48
        Originally posted by mozz View Post
        The 390k is just a bleeder resistor. I don't know if i mentioned it, there is not a lot of room in those chassis. You would be best off to build it first before you do any mods.
        I am building but I like to know what things are for. So a dropping resistor would be in series and a bleeder is in parallel, right?

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        • #49
          Chassis question:

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          I've made a new socket on the top left side so all preamp tubes are together and away from rectifier and PT. There will only be 2 6V6s in the center. The stock chassis has a metal wall between the rectifier+PT and the signal+power tube side of the chassis. I have cut apart one of the old metal multisection caps to act as another wall between power tubes and preamps. Is there any benefit to adding this second wall this in terms of noise reduction?

          Also, I have removed the coating on the chassis underside to ensure that if chassis grounding is required, there will be no uneveness in contact/resistance.


          For posterity/lurkers: this is what I'm going with ...

          The resonance control proposed previously is an attempt to have control over bass. Instead, now there is a straightforward bass tone control but not a Fender tone stack because I wanted bass and (treble) tones to be at different locations to optimize their influence on distortion shaping (an assumption based on internet posts). To hedge against the "location error", I will wire them to be relocatable with toggles (bass 4p2t, treble 2p2t) . These aren't intended to flipped during playing.

          To increase the versatility of the amp and for testing configurations without resoldering, I'm adding 2 effects loop. Hopefully not only is there basic effects send and receive with variation based on location, there is simultaneous FX loop operation, preamp out only use (1 preamp tube with choice or both), first preamp bypass, second preamp bypass, a "0" preamp/super clean, lower output power tube configuration, etc . Relocatable C1 exist just to utilize the gain pot or not.

          The choice of effects loop location has been adapted from some R. Robinette posts (C2) and his 5E3 FX loop mod (C1) on his website.

          All these tweaks, so little time
          Click image for larger version

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