Please check my 5F2-A Schematic drawing

Discussion in 'Shock Brother's DIY Amps' started by LightWeight, Jun 27, 2020 at 12:50 PM.

  1. LightWeight

    LightWeight TDPRI Member

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    Hi all,
    I've been trying to learn to use the DIY-Layout Creator drawing program and did this schematic of the 5F2-A that I am building. I'm looking for folks to check my work for errors and to give any other insight.
    Thank You.
    -Tim
    5F2-A Princeton Sch.png
     
  2. King Fan

    King Fan Poster Extraordinaire

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    Wow, I'm just impressed -- I can do layouts in DIYLC, but schematics (tho I know it does 'em) I've been unable to get my head around. Any tips to get started? :)

    Likewise I'm not the guy to review a schematic for accuracy. I'm guessing you're modding it up a bit -- my 5F2a doesn't have a choke, for example. It might help those checking it to call out any mods.

    And I'm not sure -- do you show both a 6.3V CT and an artificial heater CT? IIRC the 40-18019 has a heater CT, so for sure you don't want to do both. (If I had a heater CT I'd probably use it, but I would 'elevate' it by connection at your point 'X'.)

    But again, hats off for such a complete, detailed diagram...
     
  3. hamerfan

    hamerfan Tele-Meister

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    Two Questions: Did you ever play a 5F2? What will be your cab/speaker?

    My two points are: i did not like the tone control and skipped it in favor of a master volume. I made the NFB resistor switchable, 11k for smoother sound at full distortion and 470k for max raw tweed tone with a little less farting out - using a 8 inch speaker.
     
  4. LightWeight

    LightWeight TDPRI Member

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    King Fan, Thank you for your input and kind words. Good catch I coped and pasted that PT while I was getting together the basics of this drawing. Most likely I stole it from Rob Robinette. The PT that I'm using does not have a CT. I updated the drawing and I marked some of the "Mods" in red, I also added some layout notes for the octal tubes.
    Thanks Again, -Tim

    5F2-A Princeton Sch.png
     

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    Last edited: Jun 27, 2020 at 8:19 PM
  5. LightWeight

    LightWeight TDPRI Member

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    HamerFan
    No, I have not. I own a Vibro Champ, Deluxe Reverb, Bassman (50), and now a Micro Deluxe. I have built junk-parts amps that are similar to the 5F2-A design and liked the sound. This pandemic has allowed me time to build nicer stuff, so it's the Princeton clone now.

    I have already built the cabinet. And I am pretty lucky in that I have five classic 10" speakers to choose from. I tried them out using the Micro-Amp, the Champ, and a small SS guitar amp. My fav for this cab is the 1965 Jensen C10N.
    49717512428_154e302e37_c.jpg
    my-big-ten-inch.jpg
     
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  6. LightWeight

    LightWeight TDPRI Member

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    HamerFan, Thank you for your insight.
    When I built Rob Robinette's Deluxe Micro, Check it out here (Macro-Fun With Micro-Amp!) which is really a Micro Princeton with a change to the Coupling Cap, I had no use for the Tone control. But I have changed my mind. I love it. At 9, 12, and 3:00 I get three very different tones that work for me! The other thing the Micro has is a Master Volume. Why don't all guitar amps have MV? I am thinking about drilling another hole and adding Master Volume to the Princeton.

    I have my NFB In-or-Out, with a somewhat standard 22K. I'll play with other values (10K & 470K) once she's up and running.
    Thank You, -Tim
     
    Last edited: Jun 27, 2020 at 6:40 PM
  7. jeff_e

    jeff_e TDPRI Member

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    That's a nice looking cabinet.:cool:

    I think you probably meant 470 ohm, but the screen resistor on the schematic is 470k
     
  8. LightWeight

    LightWeight TDPRI Member

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    Thank You Jeff, And you're right 470ohm, not 470K. I need all the help that I can get.

    Thank you. I am proud of the way it turned out. Luckily I finished all the cutting of the wood early, before the safer at home order and the pandemic, the woodworking club that I belong to shut down but I was able to finish the tweed at home.
    Thank you again
    -Tim
     
    Last edited: Jun 27, 2020 at 10:27 PM
  9. Lowerleftcoast

    Lowerleftcoast Tele-Afflicted

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    Hey LW,

    A couple things I noticed:
    The HT CT could be shown to attach to the neg side of first filter cap.
    The 50mA choke is wimpy for that location. I would think at a minimum it should be 90mA.
    I would spec the bias cap at 63V. OMMV.
     
    Last edited: Jun 28, 2020 at 12:52 PM
  10. King Fan

    King Fan Poster Extraordinaire

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    This is great planning. I like it.

    FWIW, many folks find a full NFB cut 'too much' on this circuit; smart money says use a pot (maybe 100K???) to try out different amounts of cut. If you find you really like a certain setting, measure the pot at that setting and sub in a resistor that size on a switch...
     
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  11. LightWeight

    LightWeight TDPRI Member

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    Lowerecoast, Thank you for looking at the drawing and for giving your insight.
    I chose the 50mA choke based on a few things. -A post that I read here by TubesWell. And that post actuality had me thinking that I may be pushing toward the upper end because my Deluxe reverb has this choke-
    "Replacement for Fender Deluxe and Vibrolux. Equivalent to #125C3A & #022707, 50mA." (mine is original to the DR)
    I bought the ClassicTone choke and their catalog or data sheet listed this chock for the Princeton Tweed.
    Years ago I had inserted this choke in my VibroChamp. It sounded better than without, that being said, a 90mA choke may have sounded better.
    After this pandemic, I'll visit my friends and try to get another choke to try, maybe a 90 or 120mA.
    I wish that I had posted this schematic drawing before I had started the build. I'm nearly finished.
     
  12. LightWeight

    LightWeight TDPRI Member

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    LowerLeftCoast,
    I'm not sure that I'm following you on this. I have the High Tension Center Tap grounded right at the Power Transformer mounting bolt, along with a soldering tab where the filter section ground buss and the cathode bias Resister/bypass Capacitor are grounded. Are you suggesting that I would benefit from moving that CT lead over to a different position on the ground buss?
     
  13. Lowerleftcoast

    Lowerleftcoast Tele-Afflicted

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    The point I was trying to make is there are two places in the circuit where a choke is usually placed. The smaller mA chokes are placed after the OT primary. That position does not carry as much current. When the choke is placed before the OT primary it has to carry all of the current of the amp. It needs to be large. Fender used small chokes after the OT probably to save money. The Fender Deluxe and Vibrolux used small chokes after the OT primary.

    So... change the circuit to look like the Fender Deluxe and Vibrolux.:D
    Yes. The idea is to have a short run from the CT to the negative side of the first filter cap. (As short as practical.) There is not much difference when everything is grounded close to the bolt, or *cap can* but it is best practice to keep the CT and filter cap close together. It keeps the ripple current noise down.
     
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  14. LightWeight

    LightWeight TDPRI Member

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    LowerLeftCoast, Again Thank you for your insight.
    If I'm reading you right on this one, we are looking at the Cathode bias Resistor/Capacitor that I have listed at 25uf-50V and I should list the Cap at 25uf-63V (100V). I can go along with that because I have no idea as to how I would calculate that value. Help me out, how do I come up with the right voltage for this?
     
  15. Lowerleftcoast

    Lowerleftcoast Tele-Afflicted

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    Generally the bias is around 20 volts. A rough rule is to triple that amount to make sure the cap will handle situations that take the voltage higher than 20 volts. 50v is OK but 63v to 100v is more certain. Over 100v can be too much.
     
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  16. LightWeight

    LightWeight TDPRI Member

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    LowerLeftCoast,
    I'll look deeper into this choke scheme that you are suggesting...I'm not usually a stubborn man, well you know, but I think that I have it right this time or maybe I just don't get it, yet. I'll look at other sources and I promise to get back here with whatever I find.

    Yes, ok, I see. Now that you bring it to my attention, I have seen others who draw their layouts that way, I think Rob Robinette has a 5F1 and a 5E3 and if I remember correctly, he ground that CT as you do. Now I never thought that it made an audible difference, but never tested this theory. It is just so much more covenant to attach it all to a single spot and tab.
     
  17. LightWeight

    LightWeight TDPRI Member

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    KingFan! That's just hurtful. Have you seen my portfolio lately?
     
  18. LightWeight

    LightWeight TDPRI Member

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    Kingfan Thank you for sticking in there with me. And for your continued support.
    My brother suggested the same thing, "put a Pot in there". So ok, on my bench I'll wire in a pot and try to find that sweet spot, but I never seem to find that big of a difference and end up just taking the lazy route and choose an established value or none at all. 22K is that "established value". All the best.
     
  19. Lowerleftcoast

    Lowerleftcoast Tele-Afflicted

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    The choke you will be using is rated at a scant 50mA.

    The Classictone 40-18019 is rated at 70mA. Most builders are concerned a 70mA PT will not meet the demand of this circuit and there will be PT sag. So 70mA or more will be used.

    Almost all of the current of this circuit will pass through the choke. It is only rated for 50mA. Hopefully the choke won't act as a fuse.:eek:

    If the choke is placed after the OT primary it will *see* less current draw and be within the 50mA rating.:cool:
     
  20. Lowerleftcoast

    Lowerleftcoast Tele-Afflicted

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    It is noticeable when a one star ground system is used.

    When the first filter is grounded on the same bolt as the CT in a two or more star ground scheme, I can't tell the difference.
     
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