1. Please take 30 seconds to register your free account to remove most ads, post topics, make friends, earn reward points at our store, and more!  
    TalkBass.com has been uniting the low end since 1998.  Join us! :)

Help me! 70's SVT Rear Fan Direction?

Discussion in 'Amps and Cabs [BG]' started by Warpeg, Aug 13, 2005.

  1. Warpeg

    Warpeg Supporting Member

    Jun 20, 2005
    Howdy. I have an early 70's SVT. Everything is peachy on it thus far--except the fan on the back. The fan works fine; I'm just not sure if it is mounted properly. There are 4 possible ways to mount the fan: 1. Inside cage and blowing inward 2. Inside cage and blowing outward 3. Outside cage and blowing inward 4. Outside cage and blowing outward. Right now it is mounted outside of cage and blowing inward. Is this right? There is no fan guard (I'm not sure if it came with one), but there is a large, black plastic ring that fits into the fan cavity. Please help!
  2. drd07


    Jan 19, 2003
    I have a 70's SVT and the fan on mine is inside, blowing towards the tubes. You want to keep those tubes cool! Have the fan blowing on them.
  3. i dont think it matters too much either way, because its either blowing in cold air or removing hot air

    it would seem its alot more important to keep the circuitry near the tubes cool than it is to keep the tubes themselves cool (which is silly because they are meant to heat up, hence them having heaters :rolleyes: )
  4. Know a good amp shop nearby that you trust? Just give them a call. Ususally they're a wealth of info and the ones I've talked to around here are willing to share it.
  5. Just checked my '76. The fan's mounted on the inside of the metal grille, sucking in, though I suspect blowing out would be equally effective. I'm not a thermal management expert so that's just a guess, of course....:D
  6. I have a '76 SVT and the fan is mounted on the inside blowing the air outward, it draws the air from across the front panel and exits out the rear.

  7. So, one of ours must have been modified...... Same year, different fan direction....:D

    I'm almost certain that either way is just as effective. I'm pretty sure the CLs suck in because you always see the round ring of dust in the front grille...
  8. That is true about the CL's. I also think most power amps expel the hot air instead of drawing in cool air. I could be wrong. My CA9 expels the air out the front and sometimes it feels like a heater on my back!

    It also makes more sense to me that the old SVT's expel the air out the back because the whole grate is perforated in back. If it were drawing in the air I think it would have a more focused air tunnel such as the CL. Just a thought, I really don't know and haven't seen many to compare mine with.

  9. :smug:
  10. The direction of the fan is easliy changed. It's an AC fan, so if you want it to 'push' instead of 'pull,' all you have to do is reverse its power plug.
  11. Yee Haw!

  12. :D

    Totally unintentional..........Really! :p
    Though, in terms of modern SVTs I like the 2-Pro much better than the CL. ;)
  13. BurningSkies

    BurningSkies CRAZY BALDHEAD

    Feb 20, 2005
    Seweracuse, NY

    Nope. Unfortuntately, not true.

    You do want to keep your tubes from overheating if you don't want your sound to become spongy and swampy. Yes tubes have 'heaters' to bring them up to operating temp, but that doesn't mean that you want to cook them.
  14. true i spose, maybe mine would have done with a fan on the tubes . . . heh


    I never got much of a chance with the CL and 2-Pro, but i thought you basically got the same sound, just you could alter it a bit more with the 2 pro, that was a fair while ago tho
  15. godraphonic


    Jun 6, 2005
    When I got my amp the fan was running in reverse (blowing air in) and you will get more junk into the amp.

    The front grill is a filter and a diffuser for incoming air, the fan is the exit.

    Your amp may also have a non stock fan. sounds like your amp has a generic industrial replacement fan and the rear perferated grid of the amp was cut to recieve the mounting ring. Mine was like this too. when it died the numbers matched up at the local electric place to a fan motor from an old photocopier. So you can get another one with a grill to keep you from choping you fingers off when you take it out of stand-by for about $15.
  16. On the 1979 SVT I owned the fan was mounted inside and sucking air from the back and blowing onto the tubes. I bought it new and that's the way it came.
  17. Jerrold Tiers

    Jerrold Tiers

    Nov 14, 2003
    St Louis
    That gives more positive ventilation. Blowing out, you don't know where on the perf grille the air comes in, so there may be "dead spots" in the circulation.

    Blowing on the tubes keeps the air moving inside, and it will find its own way out.

    Ampeg may have changed around at some point, I seem to recall fixing SVTs that had a "fan spot" on the front grille. That was quite a while back.....(1975?) so I don't recall details, sorry. Might have been ones that I did a 6550 conversion (from 6146) on.
  18. el_Kabong


    Jul 11, 2005
    I got a bit paranoid about how hot my svt-cl runs so I put in a couple of antec 120mm 12v pc fans. Everything is fixed in place with cable ties, no mods required. I used a power supply with selectable voltages, it's silent at 5 volts and blows a gale at 12v. The other nice thing is leaving the fans running at the end of the gig with the amp switched off. By the time I've packed up the tubes have cooled off and are less susceptible to movement damage.
  19. remo


    Jan 15, 2005
    these fans running during the gig would be good.. but I read somewhere its best to let tubes cool slowly... quick cooling could be a problem as it might make them brittle or the like... just a thought. ever put a hot glass in the fridge? C R A C K
  20. blowing what is pretty warm air onto the tubes to cool them wont cool them that quickly

    it usually takes a pretty rapid change to do it, ie cleaning a test tube you've just been heating with a bunsen burner straight after you used it, yeah, ive done that before :p

    those fans are pretty cool tho!