1. Win a Broadcaster or one of 3 Teles! The annual Supporting Member Giveaway is on. To enter Click Here. To see all the prizes and full details Click Here. To view the thread about the giveaway Click Here.

5F2a completed, and working....

Discussion in 'Shock Brother's DIY Amps' started by DougalC, Mar 2, 2021.

  1. DougalC

    DougalC TDPRI Member

    Age:
    64
    Posts:
    26
    Joined:
    Sep 16, 2020
    Location:
    Edinburgh, UK
    After faffing about with a Chinese tube amp for a while, and increasing my understanding about how amps work, I decided to build a 5F2a Princeton, from a kit supplied by Modulus Amps.

    The build went well, and was completed over a period of three days, with the amp working first time. (No smoke, sparks or explosions!)

    The build was done to the Modulus layout, with the exception of the 68K Grid stopper resistors, which were changed to metal film, mounted on the input jacks and connected to the preamp tube by shielded cable. (Shield grounded at the jack end) I read somewhere that this was a good idea!

    The amp is temporarily housed in a cab with a 12” speaker. I’ll get a cab built for it soon, but it may get a 10” speaker. Not decided yet. I’m currently trying to figure out if a slab of hardwood I have will be big enough for the box. Cardboard templates being produced.

    Only minor issue is a slight amount of hum, so I may do some wiring adjustments to see if it makes any difference.

    IMG_1971.JPG IMG_1973.JPG IMG_1974(2).jpg IMG_8050.JPG
     
  2. Paul-T

    Paul-T Tele-Holic

    Posts:
    615
    Joined:
    Nov 23, 2018
    Location:
    London
    If that's your first real build then.... it's fantastic!

    If you're getting some noise, have a look at Rob Robinette's site and how he separates the Power amp and preamp grounds.
     
  3. Preacher

    Preacher Friend of Leo's

    Posts:
    4,520
    Joined:
    Apr 17, 2007
    Location:
    Big D
    That looks really clean.

    I second checking out RobRob's site for the seperation of the pre-amp and power amp grounds.

    I also had a slight hum and found a bad input jack after I literally tore everything else apart.
     
  4. gigante

    gigante Tele-Meister

    Posts:
    163
    Joined:
    Mar 7, 2016
    Location:
    Kansas City
    Good work, @DougalC. Other than the hum, what do you think about the sound?
     
  5. tubeToaster

    tubeToaster Tele-Meister

    Posts:
    123
    Joined:
    Nov 9, 2007
    Location:
    Brentwood,Tn.
    Nice job. First build ? Looks like you have building amps for years.
     
  6. screefer

    screefer Tele-Holic Silver Supporter

    Posts:
    673
    Joined:
    Feb 28, 2016
    Location:
    kildonan
    Looks great!
    What purpose for the shrink on the heater wires etc.?
     
  7. tele_savales

    tele_savales Tele-Holic Platinum Supporter

    Age:
    55
    Posts:
    970
    Joined:
    Apr 30, 2018
    Location:
    Brooklyn, Joey!
    Nicely done. I've been using metal film 1 or even 2 watt for the plate load resistors ala Rob and it really does make a difference in overall noise. They don't look as cool, tho.
     
  8. DougalC

    DougalC TDPRI Member

    Age:
    64
    Posts:
    26
    Joined:
    Sep 16, 2020
    Location:
    Edinburgh, UK
    Thanks for the compliments. I'm quite pleased with the result!
    Yes, first build, although I've done soldering on a few occasions for other purposes. I then rewired the heater wires on my Chinese amp, so that gave me some practice working inside a box!
    I had originally planned to build a Harvard, and have collected a lot of the components for that. I then decided it might be better to practice on a kit first.
    It was just an idea to hold them tight together until I got around to terminating them. Just seemed to tidy things up.

    I'm a novice guitarist, with old ears, but it sounds fine to me. I've been playing around with the settings, and different pickup settings just to see what they do!

    Modulus recommend sticking with their layout, so I'll leave it as-is for the moment. I may try some of the other ideas in the future. (Elevated centre tap, split preamp/power ground etc etc.)

    I need to go back and concentrate on practicing, rather than building. Although the temperature in my workshop has now risen enough tto start thinking about woodwork......
     
    screefer likes this.
  9. King Fan

    King Fan Poster Extraordinaire Ad Free Member

    Posts:
    6,384
    Joined:
    Jan 1, 2013
    Location:
    Salt Lake City
    No, no, practicing is a waste of time. All you get is better, and for free. Amps, on the other hand, are delightfully addictive and cost lots of valuable money. Hey, if you practice, you'll just impress other people; build an amp, the main one impressed is you -- well, and all of us!!! :):):) That's a beauty.

    Re the hum, an elevated heater CT would be an easy enough test fix on a cathode-bias amp. Is this the layout you used?

    [​IMG]
     
  10. DougalC

    DougalC TDPRI Member

    Age:
    64
    Posts:
    26
    Joined:
    Sep 16, 2020
    Location:
    Edinburgh, UK
    Yes, that's the one.
    The hum is just low background, so not an issue at the moment. It starts the instant the power is switched on, before anything heats up, so I'm thinking its just PT noise. I'll try sometime with all the valves out and see what effect that has.
     
  11. jimgchord

    jimgchord Tele-Afflicted

    Age:
    47
    Posts:
    1,566
    Joined:
    Apr 3, 2018
    Location:
    victor,ny
    Try splitting that ground buss and adding a virtual ct.
     
    Paul-T likes this.
  12. King Fan

    King Fan Poster Extraordinaire Ad Free Member

    Posts:
    6,384
    Joined:
    Jan 1, 2013
    Location:
    Salt Lake City
    I may be missing something — often do — but do you mean an artificial CT with two 100Rs? If so, doesn’t he already have a real CT per the pics? Doing both is a bad idea. That’s why I thought elevated, not artificial.

    Would heater hum come on right away, or take a minute? Not sure. Do they have 6V batteries in the UK? Taking the tube heater wiring off the PT for a test on battery DC is an easy check to see if you have heater hum.

    Another good hum question: is it 50Hz or 100? Somewhere on the web you may be able to find audio samples to compare.
     
    Last edited: Mar 4, 2021
  13. DougalC

    DougalC TDPRI Member

    Age:
    64
    Posts:
    26
    Joined:
    Sep 16, 2020
    Location:
    Edinburgh, UK
    Some further progress with this project.
    Cab now nearing completion.
    This was built from an old wardrobe side panel which was, I believe, mahogany.
    Cab size was based on the online 5E3 dimensions, but scaled down slightly to suit the size of panel that I had.
    A couple of minor joinery issues, but nothing that needs covered in fabric!
    Next crucial decision is what colour/type of grill cloth? I was thinking oxblood, without the gold stripes, but open to suggestions.

    IMG_1987.JPG
     
    Fixcinater, GlenroseMedia and 2L man like this.
  14. robrob

    robrob Poster Extraordinaire Ad Free Member

    Posts:
    8,346
    Joined:
    Dec 29, 2012
    Location:
    United States
    Very nice looking build. It looks like your V1A plate and cathode wires are sitting on top of one another. Separate them as much as possible and it might kill the hum.
     
  15. Uncle Daddy

    Uncle Daddy Tele-Afflicted

    Posts:
    1,715
    Joined:
    Sep 26, 2015
    Location:
    Maldon, England
    Nice build!

    My first foray into burnt finger territory was a Modulus Champ; it too had a little background hum, which I now understand to be pretty normal. We did the "elevated heater" mod which is simple enough but it didn't make any difference. Knowing what I know now, I'd have separated the filters and used metal film resistors all round.

    The main thing I learned was I'm not a real fan of the tweed sound, especially played quietly; I find them too mumbly. Once you go blackface, there's no going back!
     
    RollingBender likes this.
  16. NTC

    NTC Tele-Holic

    Posts:
    593
    Joined:
    Mar 17, 2003
    "The main thing I learned was I'm not a real fan of the tweed sound, especially played quietly; I find them too mumbly. Once you go blackface, there's no going back!"

    A 5F1 is only one flavor. Personally I prefer the various tweed sounds to straight up BF/SF - they need more midrange.
     
  17. DougalC

    DougalC TDPRI Member

    Age:
    64
    Posts:
    26
    Joined:
    Sep 16, 2020
    Location:
    Edinburgh, UK
    Cab now completed.
    Fitted with a Jensen 10" C10R Ceramic Speaker.

    IMG_8085.JPG IMG_8087.JPG IMG_8089.JPG
     
IMPORTANT: Treat everyone here with respect, no matter how difficult!
No sex, drug, political, religion or hate discussion permitted here.