5F2A Build 2020

Discussion in 'Shock Brother's DIY Amps' started by Expaticus, Jul 18, 2020.

  1. Expaticus

    Expaticus TDPRI Member

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    Hey folks, first build, just received a 'kit' for a 5F2A Princeton Tweed, specced in a 5E3 sized cab with a 12" Jenson. Will be 240AC.

    I'm a total newby, some basic soldering skills. Reading up on some of the threads, but it is looking far more daunting than I was expecting, so will probably not just be a few evenings.

    I guess this is well trodden territory, but its all new for me so any advice welcome. I will try to post updates and pictures as I go.
     
  2. Expaticus

    Expaticus TDPRI Member

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    Ok so it's more a bag a bits than a kit. No idea what I'm doing, but I started by trying to figure out where all the major parts go by looking at some photos. The turret board in the chassis and all the jacks, sockets etc. I think the next step is to bend the tabs on the pots so they can be fitted, and to drill out a hole through the chassis top for the output transformer because it doesn't line up with the stock chassis holes.
     

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  3. Jorgen83

    Jorgen83 Tele-Meister

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  4. Tele Slacker

    Tele Slacker Tele-Meister Silver Supporter

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    The 5f2a and the 5f1 are essentially identical, with the addition of a tone pot. It might be helpful to generally follow the build guidance offered by MojoTone or StewMac in their 5f1 build manuals. Where you see discrepancies between what you have and what those build manuals discuss... ask Qs here.

    Those manuals - coupled with frequent questions & great advice found in these pages - & you’ll have a wonderful amp. Don’t rush it though... enjoy every solder joint!
     
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  5. Paul-T

    Paul-T Tele-Meister

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    IIRC, positionging the output transformer was the only hassle of my build. I used the cardboard template method. It's slightly easier if you position the transformer so its bolts don't lie under the board.

    I'm remaking my 5F2a cabinet right now, sized down slightly, can't wait to fire it up.
     
  6. Expaticus

    Expaticus TDPRI Member

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    Cheers. My kit came from a local amp builder Farfield. He sent a schema. I’m not what the etiquette is about sharing - is that ok?

    Transformers are in, i just used one of the holes for the output transformer and marked the other hole. I put washers under the tabs because they arent flush with the bottom of the transformer. All in tight. I guess i need to start looking at the turret board next? Will have a look at other plans. I’m kinda trying to figure out what is the best order to put it together
     
  7. Expaticus

    Expaticus TDPRI Member

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    [​IMG]
    Haha looks nice! Nothing inside yet


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  8. Nickfl

    Nickfl Tele-Afflicted

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    Since he's copying a 60 year old fender design that was itself mostly lifted from RCA tube manuals, I'd say yes it's okay to share it...
     
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  9. Lowerleftcoast

    Lowerleftcoast Tele-Afflicted

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    Welcome to TDPRI.

    Before you get too far, let's make sure you have a hole or two in the chassis.

    Best practice for installing the power cord in the amp is to have a dedicated bolt (hole) for the ground wire. This is usually placed on the side panel of the chassis next to the power transformer. It can be placed anywhere on the side panel but generally it is closer to the power cord inlet. The location should allow easy access for tools to secure the bolt.

    Best practice is not to use the power transformer bolts to secure ground wires. Another hole near the transformer is needed if grounding the circuit near the PT is desired. On your picture, I see a couple of holes, one of which is near the light and power switch. If it is not going to be used for anything else it will work as a circuit ground bolt (hole).

    Drilling a chassis is much easier when it is bare.
     
  10. Jesco

    Jesco TDPRI Member

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    Since it sounds like you’re just starting out in the wonderful world of amp building, I would highly suggest you read the “how amps work” page of Rob Robinette’s amazing website before you start building.

    It all makes so much more sense when you have a general idea of what the parts do, and it won’t take that long to read.

    https://robrobinette.com/How_Amps_Work.htm

    And ignore this advice if you have already read up on the topic.
     
  11. Expaticus

    Expaticus TDPRI Member

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    [​IMG]
    So here is the schema. Looks like two grounds in the chassis? Will reread rob’s documentation. I think i read it once but understood half at best :)


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  12. Expaticus

    Expaticus TDPRI Member

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    [​IMG]

    Compared to the plan, there is no hole near the power cable inlet, but i can add one in behind the transformer.


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  13. Jorgen83

    Jorgen83 Tele-Meister

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    Ah Farfield, nice. He made my 5e3 cabinet (in aged nitro lacquered tweed, very nice) and his kits are with high quality components.
     
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  14. Liam77

    Liam77 TDPRI Member

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    may I ask for Farfield website or online shop details? I googled it but couldnt find anything.
    I m also in Europe and looking to build a small amp (5f2a like)
     
  15. BigDaddy23

    BigDaddy23 Tele-Holic

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    The 5f2a is a great little amp. You'll enjoy this build.

    Re the power cord ground. Put it the side wall of the chassis next to the transformer (ie the left side of your pic above). The other ground point on the layout you have is the power amp ground. This is where the main filter caps ground. The preamp grounds to the chassis at the input jack No2 (see where the 22uf cap and 1.5k resistor connect to the jack ground lug). Make sure you have a star washer between the chassis and the jack (inside of chassis ) here to ensure a good ground connection.

    As @Jesco has said, have a good read of Rob's site. The information there is bloody excellent and it will help you to understand how the amp works, building and troubleshooting. Keep posting here too as the wealth of knowledge here is vast and folks are always wiling to help out. Pics are important!
     
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  16. Lowerleftcoast

    Lowerleftcoast Tele-Afflicted

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    I would suggest the following changes to the layout:
    The 1M resistor can be placed on just one input jack. If the resistor were connected to both jacks it could be damaged if/when the jack becomes loose. Connect the 1M resistor between the switch lug and the ground lug of input jack *two*.

    I noticed you were provided two switched 1/4 jacks and one jack without a switch. Input *one* does not need a switch. It can be traded with the speaker jack which would benefit by being switched. Connect the switch lug to the ground lug of the speaker jack. (If the amp was turned *on* without a speaker connected the output transformer could be damaged if there were no switch.) (The original Farfield diagram had the input jacks wired wrong, by the way.)

    *Star* ground system. The 5F2A layout is from back when Leo grounded to brass plates. There are better ways to keep the amp quiet. The 5F2A circuit is known to work well with a single *star* terminating at the input jack. Notice the purple wire has replaced the other ground wires on the layout. The red/yellow HT center tap from the power transformer will be soldered to the negative side of the first filter cap. The input jack would be the only ground for the circuit. (The Farfield layout shows a two star ground scheme. IMO, the Farfield 5F2A layout would need to be modified to keep the circuit quiet and I do not think there is anything to gain by doing so.) Some builders prefer to place a *ground bus* at the top of the board rather than ground wire from terminal to terminal. The choice is up to you. It would roughly follow the purple line at the top of the board.

    The arrows in red point to the 6V6 bias resistor and capacitor. In operation the bias resistor will be very hot. Capacitors should not get hot. I propose you switch the position of these two components so the hot bias resistor is not sitting between two capacitors. It would be a good idea to keep the bias resistor at least 6mm from the bias capacitor. (Also remember, heat rises.)
    Inked5f2a fix_LI 1.jpg
     
  17. dan40

    dan40 Tele-Afflicted

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    You will notice dotted lines on the turret board in the layout you posted. Some of these are simply wires that pass through the holes in the board and lead to the sockets or potentiometers. Others are wire jumpers that need to go between the various turrets to supply DC voltage and signal voltage to the proper places in the circuit. The original Fender method would be to install these wires on the backside of the board before adding components and mounting the board in the chassis. I prefer to run my jumpers in top of the board before adding the components because it makes troubleshooting much easier should there be a problem. Either method will work fine.

    Also be sure to observe the correct polarity on all of the 22uf and 40uf electrolytic capacitors shown on your layout. The positive end of the cap has a groove that runs around it's circumference and must be placed with this end facing the tube sockets.
     
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  18. Expaticus

    Expaticus TDPRI Member

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    I dont think Anton has a website, but you will find his listings on ebay. Search in ebay on farfield 5f2a or user: revosolutions.


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  19. Expaticus

    Expaticus TDPRI Member

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    [​IMG]

    Test fitting of the board... my bends are not beautiful but i will clean them up best i can before soldering. i swapped the position of the bias resistor. Its a big honking thing is that normal?

    I think i figured out the Dale codes for the resistors. Everything is going to go into the turret tops to make soldering/desoldering easier

    Not sure how I should do the ground bus under, over or wrap around the turrets

    Good spot on the switched jack. I have put it on the speaker out.


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  20. BigDaddy23

    BigDaddy23 Tele-Holic

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    Looking good. A good habit is to verify your resistor values with a multimeter, put it in place, then mark it off on the schematic. It is very easy to make mistakes!
     
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