5f2a Princeton / 2 Stroke build

Discussion in 'Shock Brother's DIY Amps' started by BigDaddy23, Nov 3, 2019.

  1. BigDaddy23

    BigDaddy23 Tele-Meister

    Age:
    45
    Posts:
    274
    Joined:
    Jan 4, 2019
    Location:
    Australia
    So I have been planning on building a SE amp and have gathered a few bits and pieces to give a 5f2a / 2 Stroke a go.

    Two_Stroke_TAN_Schematic.jpg.jpeg

    The power transformer I have is a Hammond 291AEX and have a couple of questions. (See attached pdf of the windings)

    1. 650VDC and 550VDC secondary options. Is one more preferable in this type of circuit?
    2. To achieve the 240v primary, do I need to series jumper the 2 primary sides? Ie Blue to active power cord (thru fuse), jumper black and brown, white to neutral power cord.
    I reckon I'll give the single 6L6 a go as I have a suitable multi tap OT (Hammond 125ESE)
     

    Attached Files:

    Last edited: Nov 3, 2019
    Magnuseklof likes this.
  2. jimgchord

    jimgchord Tele-Afflicted

    Age:
    46
    Posts:
    1,026
    Joined:
    Apr 3, 2018
    Location:
    victor,ny
    Neither voltage is really ideal. Id probably go for the lower one and use a different rectifier tube to get the voltage up just slightly. A 5v4 rectifier and the 550 volt sec should get you around 340v on the plate which is perfect.
     
    BigDaddy23 likes this.
  3. jsnwhite619

    jsnwhite619 Friend of Leo's

    Age:
    35
    Posts:
    2,521
    Joined:
    Sep 10, 2013
    Location:
    Georgia
    BigDaddy23 likes this.
  4. BigDaddy23

    BigDaddy23 Tele-Meister

    Age:
    45
    Posts:
    274
    Joined:
    Jan 4, 2019
    Location:
    Australia
    Thanks @jimgchord and @jsnwhite619 - Without plate voltages on the schematic I wasn't sure what I should be aiming for.....I know it shows the 275VDC secondaries in use but then I've read that some folks like higher B+........remember that this amp can use either 6v6, 6L6 or EL34 power tube.


    Any thoughts on the Tranny hookup for 240v?
     
  5. jsnwhite619

    jsnwhite619 Friend of Leo's

    Age:
    35
    Posts:
    2,521
    Joined:
    Sep 10, 2013
    Location:
    Georgia
    I'll let someone else jump in on the 240v wiring. But, if you are looking at using the bigger tubes as well, I would go with the higher voltage secondary to make the most out of the differences. A gz34 on the 275v tap was around 370-380v on mine. You can stand a lot more than that with the bigger tubes.

    Looking at the schematic, I think that a 48uf first capacitor - if I am reading that right - and a 5y3 is not a suggested combination. I think 30uf - 33uf is as high as a 5y3 needs to see.


    EDIT: Now that I'm on a real screen and not my phone it looks like it's 40uf, not 48uf, but I think that's still higher than what most consider safe with a 5y3. If you know you are wanting to use the 6L6 and make the most of it, I would probably keep the the 40uf in there and use a 5U4B or a GZ34 for the rectifier instead of the 5y3 listed on there.

    Sent from my moto g(6) using Tapatalk
     
    Last edited: Nov 3, 2019
  6. BigDaddy23

    BigDaddy23 Tele-Meister

    Age:
    45
    Posts:
    274
    Joined:
    Jan 4, 2019
    Location:
    Australia
    Thanks mate - I have both those rectifiers handy as well as the 5Y3. The first filter cap in Dave Hunter's book (which shows the most up to date layout only for this amp design) is listed as 22uf which sits nicely with the 5y3....I've used 30uf with one without any issues but I reckon thats as far as I'd push that. According to the book, 22uf will work nicely with those tubes with output impedance adjustment according to what tube is sitting in V2.

    Having the multi tap high voltage secondaries on this PT gives me options! As does the selection of rectifier and filter capacitance. I'll have to look at B+ voltages and adjust from there.
     
    jsnwhite619 likes this.
  7. BigDaddy23

    BigDaddy23 Tele-Meister

    Age:
    45
    Posts:
    274
    Joined:
    Jan 4, 2019
    Location:
    Australia
    So I have made some progress on this build - the amp is wired and tested. There is some very slight power hum but I believe this is common in SE as compared to PP amps? Anyways, it sounds amazing and that hum is barely perceptible. I have it running with an EH 6L6 but it can run EL34 or 6V6. I've got an EL34 on the way to try but I really like the 6L6 sound at the moment. EH 12AX7 in V1 and a Sovtek 5Y3 rectifier. On test, I ran it through an extension cab with a WGS GC10. I also have a WGS ET10 handy but not sure if I should look at a 12" speaker to get a bit more out of it. Perhaps another Jensen p12Q......decisions!
    4D2845DD-6D82-459C-937D-C9FAD47B6F9C.jpeg

    F832491A-A9E4-4FA9-9BDD-07E31496D896.jpeg

    6B93C257-ACEA-4B6C-94E3-5E7B6586BB0C.jpeg

    I ended up going with the 275V secondaries on the PT (Hammond 291BEX). The 330V taps provided too much B+ with this 5Y3 and the stock 470R K resistor - biased at about 120%PD for the 6L6 whereas the lower V tap came in at 90% and sounded great so I am going to keep this tap in place. The OT is a Hammond 125ESE with multiple taps. I have gone with 8R and 4R secondaries to use with the tube options listed earlier. Jumpering pins 8 and 1 on the output tube socket allows for the EL34 option. Fortunately the PT has enough heater current for this.

    The variable V1 bias switch is a fantastic option - essentially provides 3 different amps. Crunch comes in pretty early with either of the caps across the cathode resistor but when it is just the 1.5K resistor, there are plenty of cleans to be had with good power tube distortion in the upper 1/3 of the volume/gain. The 2 cap options really o sound quite different sso I think this will be a nice versatile amp that could be used The only thing I reckon I need to address is that the tone control is only usable in the last 1/3 of the sweep. I had x2 1M pots left in the stash and they were not linear. I think perhaps changing the tone pot to linear may be more useful/less sensitive.

    Now onto cab building! Going to go a combo in vox faun tolex again but with different grill cloth.....
     
  8. jsnwhite619

    jsnwhite619 Friend of Leo's

    Age:
    35
    Posts:
    2,521
    Joined:
    Sep 10, 2013
    Location:
    Georgia
    Sounds like a winner! I prefer the 275v tap for 5f2/5f1 builds as well. I use Hammond for everything they offer a transformer for -- no complaints yet!

    Sent from my moto g(6) using Tapatalk
     
  9. BigDaddy23

    BigDaddy23 Tele-Meister

    Age:
    45
    Posts:
    274
    Joined:
    Jan 4, 2019
    Location:
    Australia
    Give this amp a try next time you thinking about building a 5F1/5F2A.

    Please note that the schematic above does not show the jumper between power tube pins 1 and 8 (for EL34) and also the 1K 2W screen resistor. You can't see the 1.5K grid stopper going to pin 5 in the photo as it is tucked down behind the socket. I also used a 0.68uf bypass cap (in lieu of 0.47) on V1 as it sounded better to my ears. Also put diodes on the rectifier pins as per Rob Rob's amp mod for 5E3's.

    I will post an updated layout for those interested.
     
    Magnuseklof and jsnwhite619 like this.
  10. Mongo Park

    Mongo Park Tele-Holic

    Posts:
    678
    Joined:
    Nov 28, 2010
    Location:
    Winnipeg
    Yes please I would be interested in a schematic or directions
     
IMPORTANT: Treat everyone here with respect, no matter how difficult!
No sex, drug, political, religion or hate discussion permitted here.


  1. This site uses cookies to help personalise content, tailor your experience and to keep you logged in if you register.
    By continuing to use this site, you are consenting to our use of cookies.