ampeg svt capacitor question

Discussion in 'Amps and Cabs [BG]' started by notforrobots, Jan 23, 2009.

  1. I was told by an amp tech that if i double the size of my capacitors in the svt when i recap it then ill improve the performance of the head. just wondering what everyones thoughts were on this.
  2. rbonner


    Sep 25, 2008
    If you were to double the POWER SUPPLY CAPS only, it would improve the transient response of the amplifier. BOB
  3. thanks for the info. so the other caps really wont effect the sound
  4. bongomania

    bongomania Commercial User

    Oct 17, 2005
    PDX, OR
    owner, OVNIFX and OVNILabs
    Oh they might very well affect the sound, but it might not be an effect you want.
  5. rbonner


    Sep 25, 2008
    Power supply is power supply... there's only a small collection that are PS. Others would change the tone.
  6. bassman251


    Jan 30, 2007
    Are you talking about the physical size or value? You can increase the size of some capacitors by increasing voltage rating, yet keep the same value.
  7. Bassamatic

    Bassamatic keepin' the beat since the 60's

    Surely the tech was talking about the PS filter caps. The larger they are the better the amp can provide high power impulses. It is like the super large caps you can get for car stereo power amps to provide better bottom.

    To increase the power supply filter caps - you can get larger caps or simply add additional caps if there is room, say on the bottom of the chassis. This is actually better as a lot of smaller caps can provide power faster than one large one.
  8. Jerrold Tiers

    Jerrold Tiers

    Nov 14, 2003
    St Louis
    Actually, making the PS caps bigger is NOT a good idea....... it increases the currents in the rectifiers and transformer, a reliability issue, and may not change the sound significantly enough to be worth the risk.
  9. Hoss


    Jan 9, 2006
    Vienna, Austria
    As I recapped my SVT recently, my Tech was offering me to put some extra caps inside, too.
    He said, that it is possible without problems and it would improve the low frequency response, but will also change the sound.

    You could not predict it, but it probably would sound "stiffer", "colder". less compressed and therefore may loose some of its "character".
    So I kept the original specs as I love the SVTs tone so much. The recap with the fliptops kit was a very good idea. Sounds clearer and "more direct" now with an even better midrange.
  10. billfitzmaurice

    billfitzmaurice Commercial User

    Sep 15, 2004
    New Hampshire
    Owner, Bill Fitzmaurice Loudspeaker Design
    CBS had the same idea after taking over Fender in the mid '60s. The amp circuits weren't significantly changed, but the components and wiring were upgraded. The universal concensus was that in so doing CBS ruined the amps. That's why Blackfaces and Blondes far exceed Silverfaces in value to this day.
    So the answer is yes, you can swap all sorts of components, but not always for the better.
  11. I think im just going to grab the cap kit from the flip tops web site. its a slight upgrade in size and i dont think the risk will be there
  12. Bassmec


    May 9, 2008
    Ipswich UK
    Proprietor Springvale Studios
    This is a similar conundrum to the one facing me on a very old Matamp 100 with glass rectifiers.
    It has a fecking huge radial capacitor rated 50uf 500v do I replace it with a small modern Lytic of the same value or go up in Voltage until its approx the same size component (thinks a modern small capacitor cant deliver the current? the old one is 5 inches tall by 2 3/4) or try one of these expensive german thingies.

    Who is the PSU Cap expert here?, I tried making a metalized Polyprop power supply cap set with Ducati motor run caps once but I had to bypass them all with small Lytics because the pre amp motor boated slightly on high gain and with big transients without them. It was only driving via a single GZ34 rectifier into 3 6J7 Pentodes in an old RCA OP-6 mic pre.
    I don't want to burn the rectifier tubes charging a heap more microfarads do I?. so can smaller modern lytic caps really do the same current as the gobsmackingly huge old ones?.
  13. Bassmec


    May 9, 2008
    Ipswich UK
    Proprietor Springvale Studios
    Anybody tried one of these polyprop mundorf tubey cap things in a half decent 100 watt tube amps power supply.
  14. I agree completely. An amplifier circuit is a mathematical Differential Equation (I get headaches just thinking about them!). If you change or add values in the equation you also change the result. Not sure if some of these original amp designers were math experts but their equation no matter how it was formulated produced a certain result - the sound of the amp. If you change the circuit you risk changing the character of the amp.

    Rick B. (BTW I barely made it through my Differential Equations course).
  15. johnk_10

    johnk_10 vintage bass nut Supporting Member Commercial User

    Feb 16, 2008
    Washington, Utah
    John K Custom Basses
    i finally dug my old '69 SVT out of storage and just finished servicing it over the past week. it was converted to 6550A's along time ago, and since i had some NOS GE 6550's, i left it that way. I put all new filter caps in it and retubed it with all NOS USA tubes (philips/sylvania in the pre and GE's for the power tubes). it now sounds as good as it ever did.

    the only cap that is difficult to get is the 30uf @ 600V, so I made a 40uf/900V cap out of two 80uf/450V's sprague atoms (hooked in series and shrink tubed them together). The other main filter caps are a Mallory 80-40-30-10/525V (wired the 80 and 30 in parallel) to replace the 70-40-40, which had the 70 and 40 in parallel), a Mallory 100/100/350V (wired in prallel to replace the 200/250V), a sprague atom 80uf @450, and another sprague atom 100uf/450V.

    tomorrow i'm going to A/B it with my 2007 SVT-VR to see how close they sound. i just realized that i these two amps depict oldest version of an SVT and the newest version.
  16. Jerrold Tiers

    Jerrold Tiers

    Nov 14, 2003
    St Louis
    Use the same microfarad value and voltage as original...... And use an ordinary type, not some super-duper power supply cap. The original was a plain old-technology part, and that is what will work best, sound most like what it always has sounded like.

    The German polypropylene parts are fine..... we use parts like them on some power output circuits for wind turbines and the like, but they won't do much for you except maybe last longer and definitely drain your wallet.
  17. Bassmec


    May 9, 2008
    Ipswich UK
    Proprietor Springvale Studios
    I have some perfectly normal F&T and Rifa on the way, I put big Mundorf Lytics in my Hiwatt Clone PSU they are Nice and Black and Gold and fecking expensive, the amp has killer punch but like you say the matamp is not really in need of such huge caps and I am scared I might loose some of that lovely tube rectifier power supply sag that makes it chime like a huge vox ac 30.
  18. rbonner


    Sep 25, 2008
    Well lets talk about this a little bit here. As I started saying you could increase the values and Jerrold and Bill came right back with no you shouldn't / can't.

    So I feel I need to defend my post here and take it to the next level.

    Power Supply: The amplifier was built with componants that were available and reasonably priced. I can guaranty you will not hear the difference between a 30uf cap and a 40uf cap. HOWEVER I can Guaranty a 40uf cap will perform better all the way around.

    For those of you that have seen the KID'S car stereos with the 2 FARAD caps in the amp line... Those damn things you temporarily use a small lightbulb in series to charge the cap up to keep from blowing your charging circuit. Is this stuff worth it? Well the Car Audio guys swear by them. You want a portable arc welder? Thats a charged cap like that.

    But we aren't talking that kind of capacitance.

    Jerrold is correct on start up a higher uf cap will increase the initial charge up current in the rectifiers. A tube rectifier can absorb this surge and silicon diodes have their limits.

    I do not feel increasing a cap from 30uf to 60uf will exceed the surge current limits of the silicon diodes in the power supply. If they did? Put bigger ones in. That never hurt anybody either and you will not hear a diode difference in the power supply.

    ON capacitor input filters supplies I have built and used in other types of equipment we need to use STEP START circuit as an uncharged capacitor is like a dead short and throwing instantanious 5000V to it will destroy diode strings. SO we use a resistor in primary of the transformer to absorb this shock for a second and then use a relay to short out the resistor. If we were stepping up to 200uf you would definately be blowing diodes up. I wouldn't worry about frying the transformer as they have built in resistance that absorbs some of the shock from start up.

    Both Bill and Jerrold have commented that changes to this circuitry WILL effect the sound of the amplifier. I wholeheartedly agree.

    It will become a BETTER amplifier in distortion products, hum, buzz and about everything else. Will it lose its character as an SVT?... I doubt it. Is it worth it? ahhhhh it depends on what you think.

    You just don't get crazy with anything and with these tube amps you can do all sorts of things, IMO. You get excessive and you will probably regret your mods.

    You want a crazy super change everything type mod was when the factory changed from 6146B's to 6550's... Now there was a mod.

    You will want to rebias if you make any big changes. BOB
  19. JimmyM

    JimmyM Supporting Member

    Apr 11, 2005
    Apopka, FL
    Endorsing: Yamaha, Ampeg, Line 6, EMG
    Nice, John! One of these days I look forward to playing my 69 again, too. Only been a year since I tried to get it going again :( Works for a spell, then it doesn't.
  20. thanks everyone there's a lot of solid info to take in in this thread. im taking it all into consideration in this project and ill have some time to think about it because im in no rush.

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