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.

'67 Blackface Vibro Champ -- restored

Discussion in 'Amp Central Station' started by King Fan, Jul 10, 2017.

  1. King Fan

    King Fan Poster Extraordinaire Ad Free Member

    Posts:
    6,158
    Joined:
    Jan 1, 2013
    Location:
    Salt Lake City
    My NAD thread a month back started to wander as I found the original trannies, Jensen speaker, and wires were connected not only to a bunch of scary-old original capacitors, but that the newer caps and resistors that had been swapped in were almost all non-spec values: All the tone caps, V1 plate resistors, slope resistor, etc. It turns out these had all been 'mods', not updates. And even those 'new' parts looked very old.

    IMG_0021.jpg

    Not only that, but some smart folks here pointed out the neutral went to the switch. Plus the switch was static-y when moved, B+ was 423 and bias was scary high, and etc. etc.

    So a month later I've done the following:
    1. Inventory and inspect. Screws tight and sound? Etc.
    2. Loosen chassis bolts (PT end second), remove chassis
    3. Discharge caps just in case
    4. Check fuse size and speed (replaced 2A with 1A Slo-blo)
    5. Check and repair speaker wiring
    6. Check power mains wiring, safety ground, continuity
    7. Check PT OT and speaker code for make and date
    8. Photograph everything as it is now and file the pics
    9. Clean up chrome, Tolex, etc.
    10. Replace uneven feet with 'relic'd' identical 'prong' feet
    11. Clean up grill cloth and Fender emblem
    12. Install replacement speaker (4 ohm): Fat Jimmy (a WGS variant)
    13. Bring amp up on light-bulb limiter to check for shorts
    14. Bring amp up on mains power and measure B+ 1, 2, 3
    15. At this point B+ was high, as expected, preamp voltages looked pretty good
    16. Pull / save death cap
    17. Pull pre-amp e-caps and non-spec resistors
    18. Pull metal film resistors in tone stack, trem stack, input jacks
    19. Pull 6V6 odd green cathode resistor and cap
    20. Take down the flying bundle joints on left side of board for access
    21. Pull power section caps and old resistors
    22. Unwire cap can connections and clear / insulate nearby items (I used a multi-layer aluminum-foil donut to surround the cap can before I went in with the 120W iron)
    23. Remove old cap can (hard even with 120W iron)
    24. Clean up solder in that area
    25. Install new cap can
    26. Wire cap can with inline 470R 5w wirewound resistor (drop B+)
    27. Replace 2 oddball heater wire runs with green cloth 18gaj
    28. Replace metal film resistors with NOS A-Bs
    29. Measure remaining CC resistors on board — replace if far out of spec
    30. Install the new Allen-Bradley dropping resistors
    31. Populate board with new e-caps and stock value A-B resistors
    32. Replace non-spec OD bass cap with rescued death cap (.047 spec tests .048)
    33. Replace non-spec OD mids cap with Sozo (.1 uF)
    34. Replace non-spec CD treble cap with styrene (250 pf)
    35. Reuse .02 CD coupling cap
    36. Put in new metal oxide bias resistor and Sprague cap
    37. All e-caps on board upgraded to 50V
    38. V1 plate resistors upgraded to 1W — reduce hiss
    39. Check and re-check populated board
    40. Replace the wiring bundle removed for access
    41. Rewire power wiring (was hot-fuse-PT and neutral-switch-PT). Goal is hot-fuse-switch-PT and neutral direct to the other PT primary)
    42. Put heat shrink on exposed fuse and switch lugs
    43. Replace ‘70s 6V6 and 5Y3 with ‘50s RCA and Sylvania that I know and trust
    44. Replace 18k tone resistor on bass pot with 10k (value used on DR ‘Nashville mod’) for slightly more scoop, slightly less hair
    45. Tack .01 caps alongside the two .01s currently in trem chain to slow trem (this took it from 200 bpm to 120 bpm. M-m-m-m-m.)
    This list kept growing and may contain some repetition -- I'm not *that* OCD -- and there may have been more steps than that, who knows, summer vacations keep interrupting. :D

    My B+ is now (kind of by accident) within a volt or two of scheme voltages. This still gives me 107% dissipation (but that’s a lot better than the 150+% I had originally, and sounds great).

    The Fat Jimmy speaker is amazing, and you can really hear the ceramic -– is ‘instananeity’ a word??

    IMG_5007.jpg IMG_5008.jpg IMG_5016.jpg
     
    Last edited: Jul 11, 2017
    ce24, dannyh, FrontPU and 16 others like this.
  2. CoyotesGator

    CoyotesGator Tele-Holic

    Posts:
    524
    Joined:
    Jul 12, 2014
    Location:
    Gulf Coast
    Well done!

    In the best of health!
     
    King Fan likes this.
  3. theprofessor

    theprofessor Poster Extraordinaire

    Posts:
    5,535
    Joined:
    Aug 8, 2016
    Location:
    Chattanooga, TN
    Wow! What a great job! It looks beautiful. So happy to hear that it sounds good, too. 107% plate dissipation is right on target. No sweat there. Also glad to hear you like the Fat Jimmy. I've been wondering what you thought of it. Old Fender amps need more people like you.

    Cheers, and rock on!
     
    King Fan likes this.
  4. String Tree

    String Tree Doctor of Teleocity Ad Free Member

    Posts:
    16,151
    Joined:
    Dec 8, 2010
    Location:
    Up North
    Sweet! I rebuilt my '73 Champ and Vibrochamp about 4 years ago.
    You are going to LOVE how they sound!
    -ST
     
    King Fan likes this.
  5. Milspec

    Milspec Poster Extraordinaire

    Posts:
    5,565
    Joined:
    Feb 15, 2016
    Location:
    Nebraska
    Wow, that was a lot of work.....looks fantastic.
     
    King Fan likes this.
  6. keithb7

    keithb7 Friend of Leo's

    Posts:
    4,990
    Joined:
    Jan 9, 2010
    Location:
    Western Canada
    I can hear it and smell the cookies from here!

    Congrats. I bet it does sound as great as it looks.
     
    King Fan likes this.
  7. TwangToInfinity

    TwangToInfinity Tele-Afflicted

    Age:
    54
    Posts:
    1,168
    Joined:
    May 2, 2013
    Location:
    Twangville
    Nice one ! it is a beauty!
     
    King Fan likes this.
  8. King Fan

    King Fan Poster Extraordinaire Ad Free Member

    Posts:
    6,158
    Joined:
    Jan 1, 2013
    Location:
    Salt Lake City
    Thanks, all, you're too kind.

    I need to thank a lot of TDPRI folks for help. Let me especially mention @keithb7 , @peteb , and @theprofessor . And of course many others who've posted VC builds, fixes, and rescues over the years.
     
    Staypuft1652 likes this.
  9. jimytheassassin

    jimytheassassin TDPRI Member

    Age:
    42
    Posts:
    91
    Joined:
    Apr 29, 2016
    Location:
    Oneida, NY
    Great story. The visual results tell it all! Your time and effort was totally worth it. Cheers
     
    King Fan likes this.
  10. peteb

    peteb Friend of Leo's

    Posts:
    4,208
    Joined:
    Apr 25, 2003
    Location:
    Cascadia
    Way to go King!

    You took that one to the house.




    Should be good for another fifty years, with maintenance.

    It would be interesting to know more about the operating point that you have found, i.e. Current, plate and cathode voltages.
     
    King Fan likes this.
  11. King Fan

    King Fan Poster Extraordinaire Ad Free Member

    Posts:
    6,158
    Joined:
    Jan 1, 2013
    Location:
    Salt Lake City
    Thanks, Pete. Good idea. I didn't remeasure V1, which was fairly on target, but here's my final voltage chart.

    Partial final chart copy.png

    Measured bias current was about 39mA, which if I'm right equates to about 12.7 watts.
     
    trouserpress likes this.
  12. hrstrat57

    hrstrat57 Tele-Afflicted

    Posts:
    1,500
    Joined:
    Nov 21, 2016
    Location:
    Rhode Island
    Nice, nice, nice.....

    Bet she sounds magical
     
    King Fan likes this.
  13. bryan83

    bryan83 Tele-Meister

    Posts:
    227
    Joined:
    Nov 25, 2006
    Location:
    HI
    Excellent work and beautiful Vibro Champ!
     
    King Fan likes this.
  14. chemobrain

    chemobrain Friend of Leo's

    Posts:
    3,293
    Joined:
    Nov 5, 2016
    Location:
    oakland ca.
     
  15. chemobrain

    chemobrain Friend of Leo's

    Posts:
    3,293
    Joined:
    Nov 5, 2016
    Location:
    oakland ca.
    Yes ! good for you!
     
    King Fan likes this.
  16. Darkness

    Darkness Tele-Afflicted

    Age:
    52
    Posts:
    1,131
    Joined:
    Apr 7, 2016
    Location:
    Stygian Gulf
    Most excellent work! Champs rool!!!
     
    King Fan likes this.
  17. peteb

    peteb Friend of Leo's

    Posts:
    4,208
    Joined:
    Apr 25, 2003
    Location:
    Cascadia
    Thanks for the numbers kingfan.


    The thing that stands out to me as to the affect of lowering the B+ with the resistor, is that the current thru the tube stays relatively high even though the voltage across the tube is significantly lower.
     
    King Fan likes this.
  18. King Fan

    King Fan Poster Extraordinaire Ad Free Member

    Posts:
    6,158
    Joined:
    Jan 1, 2013
    Location:
    Salt Lake City
    You're right. I expected a bigger drop. And even to get the current that low I had to try 3 or 4 different tubes -- others were a few mA higher.

    I have a friend who runs 940R --twice what I do -- inline off the 5Y3. He gets well under 12W dissipation. But I'm kinda happy at schematic B+ and 107%. It sure sounds good.
     
  19. theprofessor

    theprofessor Poster Extraordinaire

    Posts:
    5,535
    Joined:
    Aug 8, 2016
    Location:
    Chattanooga, TN
    Yep. Leave it alone. It sounds good. Don't go messin'.
     
    King Fan likes this.
  20. King Fan

    King Fan Poster Extraordinaire Ad Free Member

    Posts:
    6,158
    Joined:
    Jan 1, 2013
    Location:
    Salt Lake City
    Thanks again, kind people. Kind and helpful!

    For those who have a Vibro Champ (and I think the AA764 Champ is the same) I was really impressed by the subtle change swapping the stock 18k 'tone resistor' (on the bass pot) for a 10k.

    This was suggested by my amp-sensei brother. He knows 1000x what I do, so I may not explain it very well. He pointed out that this value is usually 6.8k on typical BF/SF amps like a PR. Running 18k is like having an Allen 'Mids' knob turned up slightly. If you have one, you'll know it brings in mids, ups volume, stiffens the tone a bit, and adds some hair. Not a big change, going from 6.8k to 18k -- but that is nearly triple, and this is a sensitive function determining how much signal goes through the tone stack.

    He kinda figures it was Fender's way of preventing the little 8" amps from sounding tinny. But with an upgraded modern speaker, this is maybe less a goal. The 10k value is arbitrary, but happens to be the value that folks swap into DRs (as an *increase* from 6.8k) in the so-called Nashville mod.

    As noted, the effect is subtle. I found the original setup had a kind of stiff quality in the bass (esp. with the MHS buckers in my 335) and a slight brittle quality in the highs (esp. with, say, a Tele bridge). With the resistor swap, all is cured; the bass sounds more open, and the highs are more fluid. And it moves the onset of early breakup a bit further up the dial -- like 3 instead of 2. :D

    If you're tempted, you might try just clipping the existing resistor off the back of the pot and on the replacement attach that end to some nearby ground wire that goes to the brass plate. Unsoldering and desoldering from the pot while the pot is in place is a pain.
     
IMPORTANT: Treat everyone here with respect, no matter how difficult!
No sex, drug, political, religion or hate discussion permitted here.