Princeton Kit on the way

Discussion in 'Shock Brother's DIY Amps' started by Mark the Moose, Dec 2, 2019.

  1. Mark the Moose

    Mark the Moose Tele-Holic

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    Weber had a sale on amp kits so I ordered up the 6A14HP kit with a 12" speaker. It's a Princeton Reverb kit with DR transformers and 6l6 power tubes. Here's my question: if I decide to use 6v6 tubes and rebias the amp, do I also need a different impedance match? Or can I still run 8ohm output to an 8ohm speaker?
     
  2. Snfoilhat

    Snfoilhat Tele-Afflicted

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    Weber has a data sheet for each of its transformers. If you grab the relevant ones from their site and post them, people will be able to give you more accurate advice based on the specs
     
  3. Mark the Moose

    Mark the Moose Tele-Holic

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    I see that the layout uses the yellow, 8ohm tap for 6L6 power tubes, but the impedance of the speaker isn't listed.

    For specs, this was all I could find...

    W404248 TRANSFORMER: 40 watt Output Transformer; 4K Primary, 2-4-8 secondary
    Screen Shot 2019-12-02 at 12.46.12 PM.png

    W025130 TRANSFORMER: 20 to 25 watt Power Transformer
    Screen Shot 2019-12-02 at 12.45.15 PM.png

    6a14hp_layout.jpg
     
  4. kingofdogs1950

    kingofdogs1950 Tele-Holic

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    I had an Allen Accomplice that had similar multi-tap transformers. It had a switch on the back to change from 6l6 to 6v6. I don't recall the numbers but it was easy to wire and very handy.

    Mark
     
  5. Les Gear

    Les Gear TDPRI Member

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    I've built two Weber 6A14HP amps. You have chosen wisely -- it's a great package. There are a million ways to skin this particular cat but here are a few points worth noting:

    1. TJ at Weber might know the answer to the question you asked about the Weber transformer. There's also a Weber forum which is extremely low-key but helpful.

    2. Drilling holes on the PR back panel can be a PITA and you seem to want at least two -- one for a master volume pot and one for a speaker impedance switch. The 6A14 has one open slot where the polarity switch would have been in 1964. You can gain another slot by ditching the fuse nipple and using an integrated AC socket / fuse block instead. You'll need to enlarge the socket hole with a file.

    After that things get tight; I wound up omitting the reverb/trem footswitch to put the reverb knob on the back. (I put a mid pot in the reverb slot on the front.)

    [​IMG]

    3. Consider the Hoffman turret PR board instead of Weber's cardboard eyelet circuit-board. Eyelets are a PITA.

    4. Ground-isolated reverb jacks are a must. I also use Cliff-style jacks for the 1/4" plugs FWIW. The step after that is ditching the can to use regular caps for power filtering so you can separate preamp and power grounding. You can wind up with a pretty quiet amp!

    5. The PR is a crowded chassis. My builds never look like a Hiwatt. Don't beat yourself up.


    Have fun. If I can do it you can do it a lot better!
     
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  6. Mark the Moose

    Mark the Moose Tele-Holic

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    Thanks
    Thanks for the tips. I think I'll forgo the MV for an L-pad attenuator mounted to the inside of the cabinet. I also hoped to put a NFB switch where the death cap went.
     
    Les Gear likes this.
  7. dan40

    dan40 Tele-Afflicted

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    The OT is rated for a primary impedance of 4000ohms (4k) which is correct for a pair of 6l6's. You can run 6v6's but ideally you would want to an OT in the 6.6k-8k range. Some builders have run 6v6's at 4k (Jim Kelley) with no ill effects though. In your case you could simply change the speaker load to better match the rated load.
     
  8. schmee

    schmee Poster Extraordinaire

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    -You want an ot that will run 16 ohms out when you change to 6V6's... and a 16 ohm speaker for that. Or use a 4 ohm speaker tap and speaker for 6L6's and then go to the 8 ohm speaker and tap when you go with 6V6's.
    -I strongly prefer the eyelet board myself. Different strokes I guess. Turrets if overheated will come right out of the board.
    -BTW, Weber's kit has front panel hole spacing that doesn't match the Fender or Mojo spacing. SO dont think you will put an after market faceplate on!
    -I hope Weber has adjusted the rectangular hole for their IEC AC cord receptacle. Two chassis I had the hole was too big and the receptacle would come right out of the chassis.
     
    Last edited: Dec 2, 2019
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  9. muchxs

    muchxs Doctor of Teleocity

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    The green wire on your OT is correct for 6V6s into 8 ohms.

    I was disrespecting a Podunk town up north recently. A resident asked me,

    "What's wrong with it?"

    I replied,

    "Nothing you'd notice if you've never been anywhere else."

    I've got an old Weber PR board somewhere. The layout is compressed. You bet it's tight!

    I'd like to go down to Kokomo, Indiana and help them revamp and revitalize their kit offerings if they'd have me. I'm fairly certain I'm qualified.

    Last industrial job I had they told me,

    "You're going backwards if you're not continuously improving."

    The 6A14 could be such a slick little package.

    Turrets are such a PITA. Seriously. They're not what you want for builders who are still working on their soldering skills.

    Fender used eyelets. The only hassle is the two eyelets that end up with half a dozen leads in them. Five leads seems to be a good maximum.

    A turret with half a dozen leads is gettin' crowded, too.


    I have a few PR builds pending. Maybe I'll try the Hoffman board. Maybe I'll use all mustard caps so it looks like an old Marshall inside.

    If there were more Kelly amps around word might get out. They're notorious torture chambers for 6V6s.

    Early '80s, I walked into Rudy's on 48th Street. Some dude was playing an early, early black guard through an FACS. It sounded like God. Man, that tone stuck with me.

    Testify!
    :cool: :cool: :cool:
     
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  10. Les Gear

    Les Gear TDPRI Member

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    Perhaps you were talking about the municipality of T2R4, Maine?

    6A14HP is everything I need. Solid tool at an attractive price. Challenging first build but sure does reward the effort!

    There was discussion on the Weber Forum a couple of years ago that Weber was trying to sell their kit operation and getting nowhere.

    Weber has painted themselves into a corner. You know that most of the kit trade is about, 'We offer exquisitely detailed instructions and televid support.' A lot of kit folks also sell, 'We have upgraded parts containing magic smoke.' Weber purposely stays away from both of those, so they succeed in keeping their price down . . . but the competition at the very bottom of the market is Direct From China. They just can't win either way.

    Could be that's the secret to The Brown Sound.


    Maestro, you've forgotten more than I know. Thanks and greetings from the big sittay.
     
  11. Mark the Moose

    Mark the Moose Tele-Holic

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    Hoffman is taking December off, so maybe I’ll pick up a mojotone eyelet board. I built their 5f11 last year and had no problems with the eyelet board. Also thinking I’ll replace the external speaker jack (which I’ll never use) with a 4/8 ohm switch so I can swap out tubes. Robrob steps up the filter cap to 100uf in his ideal layout, any thoughts on how necessary that is?
     
  12. Uncle Daddy

    Uncle Daddy Tele-Holic

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    Modulus in the UK makes an affordable PR turret board.
     
  13. muchxs

    muchxs Doctor of Teleocity

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    The original Weber VST chrome plated chassis products were the best.

    Ted Senior had some heavy talent participate in his amp design process, guys like Bruce Collins from Mission Amps and David Allen from Allen Amps. I don't know but I been told they ended up less than happy.

    What I'd do is offer a separate and parallel line of premium kits. Maybe offer a premium Champ kit and a premium Princeton kit. See how it goes.


    There was a time they had good bones. Start with a chrome chassis that would pass for an original. They had that!

    Add transformers designed by Bruce Collins. They had that!

    Hassle was their Chinese jobber couldn't get their heads around Collin's PT. They had a rather high failure rate. No warning. They wouldn't run hot, they'd just plain quit.


    I'll comment further but I been at this long enough I lose track of time. "Years ago" could be any time in the last half century.

    "Years ago" one of the first amps I worked on was an original JTM45. Marshall had the design dialed in well enough at that point, it was really impressive inside. Most musicians will never see or hear an original.

    Van Halen's first album came out a few years later. That set me out on a quest to build amps that were as solid as that original JTM45 that had that tone.

    That makes two of us. I've forgotten more than I know.

    First filter shouldn't be more than 50uf with a tube rectifier.

    For example the old data sheets for 5Y3 rectifier tubes say use no more than 10uf for a 5Y3. Manufacturers fudged that until Fender used 40uf in some Champs.

    I never see more than 50uf in vintage hi fi with tube rectifiers.
     
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  14. D'tar

    D'tar Friend of Leo's

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    You may be looking at the bias supply cap. That is 100uf/100v. If you are building/servicing/repairing tube amps grab a dozen of them. This is pretty common value used in that application.
     
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  15. Mark the Moose

    Mark the Moose Tele-Holic

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    Ah, you’re correct!
     
  16. King Fan

    King Fan Friend of Leo's

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    FWIW the Mojo eyelet board should be fine. I’m happy Doug’s getting a month off; it’s clearly another step in his plan to retire — which he also richly deserves. But he’s gonna leave a big hole in my supply chain.

    Also, tho I haven’t reviewed Rob's PR page *this* week, it seems extremely useful both as to best layout and 'what to leave in, what to leave out.'
     
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