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Building an octal princeton from an old reel to reel

Discussion in 'Shock Brother's DIY Amps' started by Nickfl, Apr 3, 2018.

  1. Nickfl

    Nickfl Tele-Holic

    873
    May 24, 2016
    Florida
    My new project, a SE 6v6, octal preamp build based on a couple of different early Princeton and champ schematics. My schematic is here in the thread where I worked out the idea a while back. It has volume, tone, and two different inputs; one with a grid leak biased 6sj7 pentode input stage and one with a cathode biased input using half of a 6sl7 triode. I have been wanting to do an octal preamp build of some kind for a while now and the dual inputs allow me to combine both the early and later styles in one build.

    I was inspired by @Snfoilhat repurposing of various old reel to reel tape decks and I am using the cabinet and chassis from an old Webcor reel to reel that I found on Facebook marketplace thanks to @sds1, along with the PT and choke pulled from an old console radio (the webcor transformers weren't quite right for this and will have to wait to be used another day).

    So far I've stripped the chassis (desoldering those old tube sockets was a nightmare) and started wiring my power supply:

    IMG_20180401_170132.jpg

    This is going to be my first foray into true point to point wiring, which should be a fun new challenge.

    I've also come up with what I think is a pretty clever way to convert the cabinet into a 1x10" combo, which should be more suited to the amp than the original small, side mounted speaker. More on that to come...
     
    Last edited: Apr 3, 2018
    dan40, Wally, magic smoke and 2 others like this.

  2. Nickfl

    Nickfl Tele-Holic

    873
    May 24, 2016
    Florida
    Got some time today to do a little work out in the garage and routed a grill into the front panel of the cabinet. I am going for a look inspired by the Supro, Vaco, etc amps from the 50s with slots routed directly into the cabinet. I've removed the tape recorder components and controls to allow me to front mount a 10" speaker and I will be making a control panel to mount on the side of the box where the original speaker was mounted.

    I made a template from 1/2" mdf:

    IMG_20180403_190942.jpg

    and routed the front of the cabinet today:

    IMG_20180403_191043.jpg

    I'm pretty happy with how it turned out. I think that once I paint the bare wood to match the original covering and install some grille cloth it will look pretty nice.

    I got some more wiring done as well:

    IMG_20180404_032931.jpg

    The point to point wiring is going smoothly, its really nice to work with the big, dual hole solder lugs on these old sockets. I can't imagine trying to mount all this on cheap miniature 9 pin sockets...
     

  3. Nickfl

    Nickfl Tele-Holic

    873
    May 24, 2016
    Florida
    I made some more progress on the wiring, all the sockets are done so really just the controls left now.

    IMG_20180406_034915.jpg

    I also masked off the grille route on the cabinet and sprayed the bare wood with some burgundy paint I had that roughly matches the original covering. Not a perfect solution, but I think it should work.

    IMG_20180405_203428.jpg
     
    magic smoke likes this.

  4. magic smoke

    magic smoke Tele-Meister Silver Supporter

    117
    May 28, 2017
    Quantum Entanglement
    This is coming out way cool! I really like what you’re doing with the grill. I’m going to have to try this .
     
    Nickfl likes this.

  5. Mongo Park

    Mongo Park Tele-Holic

    547
    Nov 28, 2010
    Winnipeg
    What a great build, I am envious of your ability to put something together like this from scratch, kudos to you.
    It will be interesting to here how the tubes shape the sound from a champ style build as well as being able to AB the different preamp tubes.
     
    Nickfl likes this.

  6. Mongo Park

    Mongo Park Tele-Holic

    547
    Nov 28, 2010
    Winnipeg
    What a great build, kudos to you with the ability to put this all together from scratch. It will be interesting to herer how the different preamp tubes sound as well as the departure form the traditional champ sound.
    Cheers Ron
     
    Nickfl likes this.

  7. Nickfl

    Nickfl Tele-Holic

    873
    May 24, 2016
    Florida
    Were just about done now. I got the wiring finished and ran through my startup procedure. The bias was running a little hot (around 110%) with an ANOS sylvania 6v6 and the 370ohm cathode resistor. I went ahead and upped the cathode resistor value to 420ohm, which put me right at 99.5%

    IMG_20180406_214517.jpg

    I played it a bit plugged into my 5e3 cab (loaded with a weber alnico sig 12) and it sounds very promising. The tone control was a little weird though and I discovered I made a mistake in the last version of my schematic, I had a 0.005 where I should have had a 0.0005... So I changed that out as well, which made for a much more reasonable range of tone!

    I also put some grille cloth in the cab, which is coming together pretty well:

    IMG_20180406_214559.jpg

    Now I just need to put it all together tomorrow and see how it sounds in its finished form!
     
    sds1 likes this.

  8. LocoTex

    LocoTex Tele-Meister

    Age:
    63
    451
    Jan 16, 2018
    Waxahachie, TX.
    I am constantly amazed by the creativity and craftsmanship of the people on this forum! This is way better than the others. Seriously.
     
    Nickfl likes this.

  9. Nickfl

    Nickfl Tele-Holic

    873
    May 24, 2016
    Florida
    I boxed it up today.

    IMG_20180408_210325.jpg

    Then I had some intermittent static and loud buzzing when playing and had to pull it back out... I re-tensioned the socket pins and re-soldered one potentially questionable grounding point and between the two it seems to be good now.

    IMG_20180408_210409.jpg

    I am pretty happy with the sound so far. There is a big difference between the grid biased 6sj7 and the cathode biased 6sl7. The grid biased pentode is slightly louder and much hotter sounding.

    IMG_20180408_210340.jpg


    As you can see I left most of the "patina" of age intact, with the exception of the tube compartment cover, which was so corroded I decided to go ahead and repaint it.

    IMG_20180408_210500.jpg
     

  10. D'tar

    D'tar Tele-Afflicted

    Jan 11, 2013
    WNY
    Nick!

    That turned out really sweet. I just wanna sit under the shade tree a play slide guitar with that all day long!
     
    Nickfl likes this.

  11. D'tar

    D'tar Tele-Afflicted

    Jan 11, 2013
    WNY
    After the F N snow melts of course!!!!!!
     

  12. Nickfl

    Nickfl Tele-Holic

    873
    May 24, 2016
    Florida
    Here's a short demo clip of the 6SJ7 channel. This is the clean tone, which is up to maybe 10-11 O'clock on the knob... depending on where the tone knob is adjusted. The volume and tone controls are very interactive, especially on the grid biased 6SJ7 input. This was recorded with a SM57 and a telecaster, you can hear me switch between the pickup positions a bit but no changes to the amp controls.



    I will post some more sound clips of the overdrive sound and the 6SL7 channel at some point. I only had a few minutes to mess with recording today and I'm still getting some intermittent static/cutting out that ruined the other takes. I'm pretty sure I just need to clean the tube sockets, but of course my only can of deoxit is at work and I keep forgetting to bring it home with me...
     
    ecoast and Artslap like this.

  13. JohnnyCrash

    JohnnyCrash Doctor of Teleocity Silver Supporter

    Mar 12, 2005
    Fullerton, CA

  14. archiemax

    archiemax Tele-Meister

    Age:
    66
    175
    Oct 11, 2016
    Phoenix AZ

  15. Nickfl

    Nickfl Tele-Holic

    873
    May 24, 2016
    Florida
    Man this cutting out problem is one persistent PITA! I cleaned the tube sockets and that was definitely not the issue. I opened the chassis back up and discovered that I had a loose connection where the two mixing resistors coming off the input stages meet and connect to the volume pot. After fixing that it is much better, but still there at higher volume, mostly on the 6sj7 channel now, but also a hint of it on the 6sl7 input. Apparently I still have some sort of loose connection... I'm wondering if it might have been a mistake to use solid core wire for the runs to the control panel, those are long wires that get moved around a bit when taking the amp in and out of the cabinet so I wonder if I have a break inside of one of those wires? This thing sounds real good though, so I will be worth it when I get this sorted out.
     

  16. nasdak

    nasdak Tele-Meister

    161
    Mar 22, 2013
    france
    Nice build !!!
    I'm sure you can salcage great old cloth wire grom the old recorder ?
     

  17. Snfoilhat

    Snfoilhat Tele-Meister

    Age:
    37
    487
    Apr 8, 2016
    Oakland, CA
    I especially like how you repurposed the original oval speaker cutout for the new control panel. That looks great.
     

  18. Nickfl

    Nickfl Tele-Holic

    873
    May 24, 2016
    Florida
    Thanks! I spent a lot of time thinking about the best way to re use the old cabinet and I'm pretty happy with how it came out. I figured I had come up with something good after I encouraged you to use the cabinet in your tape deck thread!
     

  19. Nickfl

    Nickfl Tele-Holic

    873
    May 24, 2016
    Florida
    Finally!!!

    I got the amp sorted out this afternoon, it turned out that I had two more loose connections... one on each of the input jacks :eek: Apparently I did some embarrassingly sloppy work on my last session working on this build!

    In any case, it sounds good now. Dead quiet at idle, with not even a hint of hum. The two channels are distinctly different, with the 6sl7 staying clean most of the way up the dial and the 6sj7 getting dirty early and reaching full "amp on fire" fuzz a couple of notches below max. All of this at volumes that aren't exactly apartment friendly but stay well away from hearing damage level. I think I might like this thing a lot!

    Stay tuned, more sound clips to come...
     
    sds1 likes this.

  20. Nickfl

    Nickfl Tele-Holic

    873
    May 24, 2016
    Florida
    Some more clean tone clips, this time with humbuckers, recorded with a ribbon mic. Unfortunately they are a little on the quiet side, I didn't have the mic preamp turned up quite high enough.

    The 6SL7 channel:



    and the 6SJ7 channel:

     

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