5U4 in place of a 5AR4?

Discussion in 'Amps/Cabs Tech Corner: Amplifier, Cab & Speakers' started by Sean, Aug 18, 2006.

  1. Sean

    Sean Supporting Member

    Messages:
    623
    Joined:
    Aug 22, 2004
    Location:
    Swamps Of NJ
    I have one of the new Vibroverbs with a rectifier switch (ss/tube). The tube chart calls for a 5AR4. I notice NO difference in sag between the 2. The only thing the 5AR4 does is mush it up at high volume a little bit. The 5AR4 is a NOS RCA.

    I put a 5U4 in- it sounds good and gives me a bit of sag at low volumes. I have done some reading that a 5U4 is a 3A filament while a 5AR4 is a 2A filament. I want to be sure that my transformer is going to be OK. The 5U4 that I have on hand is from Groove Tubes if that makes a difference.

    I took a look at what the bias was doing when switching the rectifier switch- with the amp at 35mv the bias jumps up about 5mv when I engage the switch and use the 5AR4. When I put the 5U4 in and switch it on I get a drop of 2-3mv.

    Is the 5U4 safe in this amp? I obviously don't want to wreck anything, but it seems that from everything that I have been able to read that it is a fairly safe swap if your transformers are healthy.
     
  2. brad347

    brad347 Member

    Messages:
    4,811
    Joined:
    Feb 8, 2006
    Location:
    Brooklyn, NY
    probably OK. Those transformers are generally over spec'ed a lil bit. Don't take my word for it though, wait for the real experts to weigh in.
     
  3. ES350

    ES350 Member

    Messages:
    571
    Joined:
    Feb 13, 2006
    Run it awhile and see it the PT is running hot---you are drawing 1 amp more than the PT is designed for (a non-trivial amount). While it's true that older Fenders were somewhat tolerant of larger current draws, who knows about the new stuff...? If you want more voltage drop than a 5AR4 with no increase in current draw, try a 5V4 (1 amp) instead of the 5U4 (2 amps).
     
  4. brad347

    brad347 Member

    Messages:
    4,811
    Joined:
    Feb 8, 2006
    Location:
    Brooklyn, NY
    good point! Listen to him!
     
  5. Blue Strat

    Blue Strat Member

    Messages:
    30,029
    Joined:
    Aug 2, 2002
    Location:
    Sterling, VA (not far from Washington DC)
    Best case, don't let incorrect specs (1 and 2 amps per above) or your "hand thermometer" influence your judgement.

    Get a 5R4GB for under $20 and get 5U4 performance with only 2 amps (like a 5AR4) heater current.
     
  6. Sean

    Sean Supporting Member

    Messages:
    623
    Joined:
    Aug 22, 2004
    Location:
    Swamps Of NJ
    Thanks guys. I think I have a 5R4 in my stash- have to look.
     
  7. ES350

    ES350 Member

    Messages:
    571
    Joined:
    Feb 13, 2006
    Sorry for the misinfo---I stand corrected. But if you do need one, see Mike...
     
  8. billyguitar

    billyguitar Member

    Messages:
    4,456
    Joined:
    Aug 30, 2005
    Location:
    Kansas City
    A 5V4 can give a bit more sag in some amps. I swapped rectifiers around in my Maz 38 one time. The stock tube is a 5AR4. The 5u4G felt slower but didn't seem to sag. The 5V4 reduced the output but really didn't seem to sag but I only had it 1/2 up. I am using the 5V4 in my Stang Ray for the reduced volume. 5Y3s are not recommended in the larger amps.
     

Share This Page