Anybody use solid state rectifiers with tube amp circuits?

Discussion in 'Shock Brother's DIY Amps' started by OhioJohn, Feb 21, 2009.

  1. OhioJohn

    OhioJohn TDPRI Member

    Posts:
    32
    Joined:
    Feb 13, 2009
    Location:
    Germantown, OH
    Many of the home brew circuits I've seen on this forum still use rectifier tubes for the B+ voltages. It would seem to me that this task would be better served by solid state rectifiers.

    The advantages: Much less heat, and one less tube to replace. The preamp and output stages wouldn't know, or care, how the rectification took place. Those little diodes would even be handy to make a dedicated -V fixed cathode bias circuit for the output tubes.
     
  2. GUITARmole

    GUITARmole Tele-Afflicted

    Posts:
    1,166
    Joined:
    Mar 13, 2005
    Location:
    Portland, OR
    Many people use SS rectifiers in place of tubes. Usually you include a 'sag' resistor though to simulate the sag of the tube rectifier and and drop the B+ by a few volts so it's in the range you want.
     
  3. Wayne Alexander

    Wayne Alexander Friend of Leo's Silver Supporter

    Posts:
    2,820
    Joined:
    Mar 16, 2003
    Location:
    Los Angeles, CA, USA
    SS and tube rectification sound completely different. Compare two "plexi" type Marshalls - the JTM45 and the 1987. The former is a singing, bluesy amp, the latter is a tighter, rock-ier amp, the primary difference is the GZ34 in the JTM45 and the diode rectifiers in the 1987.
     
  4. GUITARmole

    GUITARmole Tele-Afflicted

    Posts:
    1,166
    Joined:
    Mar 13, 2005
    Location:
    Portland, OR
    ?? Are you serious?

    The GZ34 vs the diode rectifiers is a minor difference compared to split vs shared cathode inputs, signal cap values, lowered filtering, different output coupling cap values, different tone slope resistor value, and lastly COMPLETELY DIFFERENT OUTPUT TUBES (5881/KT66 vs EL34).

    You could switch a JTM45 to SS rectification but it won't make it into a 1987.
     
  5. celeste

    celeste Friend of Leo's

    Age:
    58
    Posts:
    2,905
    Joined:
    Jun 24, 2006
    Location:
    Maryland
    Many people do use SS diodes on tube circuits. They bring as many problems as they cure, so it is kind of pick your poison.

    Vacuum diodes do not have a reverse recovery phase and so isolate the inductance of the PT from the filter caps, breaking up a tank circuit. Vacuum diodes switch quietly, so there is little high frequency noise being added that is hard to filter out.

    SS diode rectifiers are pretty much one of two types, silicon junction and schottky. Schottky's have no reverse recovery phase, but they switch so fast that there is very considerable high frequency dV/dT noise.

    Standard silicon junction diodes ( 1n400X ect.) have very long reverse recovery phase where the cap can discharge through the diode back into the PT. This can cause the PT to ring, putting noise into the B+. They switch slow enough that dV/dT noise is not a big problem to filter.

    Ultra fast diodes ( UF400X, HEXFRED's, ultra fast sort recovery and all manor of names) reduce, not eliminate, reverse recovery, so reduce the chance of the PT ringing. dV/dT noise is a big problem and needs to be dealt with or it gets everywhere in the amp.

    There are ways to deal with SS diode issues, but they are not just a drop in replacement. If good sound is the point, then reducing heat and tube count is hardly an improvement it it makes the amp sound less good.
     
  6. 11 Gauge

    11 Gauge Doctor of Teleocity

    Posts:
    10,923
    Joined:
    Mar 21, 2003
    Location:
    Near BWI Int'l
    My solution has been the Weber Copper Caps, which also come in hardwired varieties.

    Technical issues aside, any audible differences between them and glass bottles are negligible in my experience. I've now installed them in a bunch of old amps that have been popping tube rectos left and right, both current production and NOS. I've used most of the entire range from the GZ34 down to the 5Y3, with good results.

    The Copper Caps do raise the B+ ~15V versus a tube recto, IME. Just something to consider when biasing, but it just alters the numbers a little.

    The other benefit to the CC's is that you can get one custom made to your specs if you want a different voltage drop or similar design elements.

    I'm sure that one could be built DIY, but Weber's prices are reasonable, so I haven't bothered.
     
  7. Tim Swartz

    Tim Swartz Friend of Leo's

    Posts:
    2,009
    Joined:
    Mar 18, 2003
    Location:
    Michigan - Tweenst the Great Lakes
    I've used and use both and find no real advantage or disadvantage with either except that a lot of the current production rectifier tubes are crap.
     
  8. 6x47

    6x47 Tele-Holic

    Posts:
    804
    Joined:
    Mar 28, 2007
    Location:
    Northern ON
    Sovtek also sells a plug-in solid state rectifier replacement but you'll have to reset the bias before plugging in the power tubes as it's a one size fits all deal.
     
  9. GUITARmole

    GUITARmole Tele-Afflicted

    Posts:
    1,166
    Joined:
    Mar 13, 2005
    Location:
    Portland, OR
    I think your "Problem" examples are a bit exaggerated though! In the real world there are plenty of amps with SS rectifiers that sound good or arguably better than those with tube rectos. My home stereo has SS rectifiers for both the preamp and poweramp...am I constantly bothered by high frequency noise? Ummm....NO.

    As mentioned, a far bigger problem (IMO) is the quality of some of the new rectifier tubes.
     
  10. morroben

    morroben Friend of Leo's

    Posts:
    4,350
    Joined:
    Jun 25, 2006
    Location:
    Morro Bay, Ca
    I use a Weber Copper Cap on my 5E3. Sounds slightly different...maybe a bit punchier. I like it better.
     
  11. ThermionicScott

    ThermionicScott Poster Extraordinaire

    Age:
    39
    Posts:
    5,913
    Joined:
    Dec 3, 2005
    Location:
    SW CR IA US NA PE
    I use tube rectifiers in my projects. Just seems like the old-school way to do things, and it gives me another challenge in my design. The argument of replacing tubes with more reliable solid-state devices is a slippery slope... :p

    - Scott
     
  12. celeste

    celeste Friend of Leo's

    Age:
    58
    Posts:
    2,905
    Joined:
    Jun 24, 2006
    Location:
    Maryland
    Like all things it is a matter of what is good enough. In my home stereo I can hear the difference between 1N UF, Schottky and tube diodes, if I do not add filters to the PS to handle their unique issues. My favorite are damper diodes from TV sets.

    I would never be so bold as to suggest what you can or can not perceive. If you are happy with what you have, great. If others are bothered by short comings of some parts and seeks ways to their own nirvana, good for them.

    I did not intend to suggest one way was better then any other, just inform about some of the real reasons each has it's draw backs.

    As far as quality of new tubes, that comes down to knowing what you have and it's limitations. The market is periodically full of counterfeit caps, same deal, know what you have and how to use it within it's limitations. I do not do clones, I build original, unique designs and that frees me to use parts more conservatively, or radically as I see fit.
     
  13. Jelle

    Jelle Tele-Meister

    Posts:
    373
    Joined:
    Jul 18, 2008
    Location:
    Netherlands
    I sometimes use SS rectification in my SE tube amps. Like mentioned above I also use a dropping resistor to trim back the B+ to spec.
     
  14. JohnnyCrash

    JohnnyCrash Doctor of Teleocity

    Posts:
    10,979
    Joined:
    Mar 12, 2005
    Location:
    Fullerton, CA
    This aint hi-fi, these are noisey classic tube amps.

    To simplify and generalize:
    Solid state rectifiers allow for larger filtering (tighter Bass) and do not have sag.

    Tube rectifiers have limits to their filtering cap sizes, and CAN sag (depending on circuit and rectifier).

    And finally, solid state rectifiers produce more DC ripple (rectified) B+ voltages than tube rectifiers.

    On all single ended amps I build, I've come to simply use Solid State rectifiers (sag can't happen on Single Ended/Class A amps and I like to keep my tubes to a minimum on those type builds). On my Marshall style builds, I'm aiming for huge/tight Bass and hard rock sounds, so again SS rects. On older Fender or other style amps I like the bluesy sag.

    On my 5E3 tweed Deluxe build, I added a switch underneath the chassis to go from stock 5Y3 rectifier to a SS rect with an additional 40uF filter cap added parallel to the 1st filter cap... best of both worlds.

    Speaking of diodes - on my tiny 1x10" practice amp (sorta a Kalamazoo Model One clone) I added diode clippers to a 3-way switch. Symetrical clipping on one setting, no clipping on the other setting, and assymetrical clipping on the last setting. It makes for decent crunch at very low levels on a little 5 watt tube amp, where on something like a Twin it would sound awful and harsh.
     
  15. celeste

    celeste Friend of Leo's

    Age:
    58
    Posts:
    2,905
    Joined:
    Jun 24, 2006
    Location:
    Maryland
    Ture, but they do not have to be with some careful attention to detail.
    But inductors can be used to stiffen it up, and the tube does not care what size the cap is after the first series resistance. As an example, Look at the Talon PS over at AX84. http://www.moonguitaramps.com/images/talon_schematic.png
    Yes, SS has a lower internal resistance so B+ is higher, but that is just a matter of spec'ing the right PT. Of course the difference also gives yoiu the ability to change the amp quickly if you choose.
    Try small signal vacuum diodes, like those in a 6AV6. I think you will be pleasantly surprised.

    Edit: added links
     
  16. ThermionicScott

    ThermionicScott Poster Extraordinaire

    Age:
    39
    Posts:
    5,913
    Joined:
    Dec 3, 2005
    Location:
    SW CR IA US NA PE
    You know, I've got a bunch of damper diodes (6AU4, 6AX4, 12D4, etc) in my stash. I should really use them for something. :twisted: Are there any special considerations, besides the high heater current? celeste, do you run yours like separate halves of the usual fullwave rectifier tubes, or are your setups more esoteric?

    Thanks,
    - Scott
     
  17. celeste

    celeste Friend of Leo's

    Age:
    58
    Posts:
    2,905
    Joined:
    Jun 24, 2006
    Location:
    Maryland
    I just set them up as a full wave. I know others have used them in a hybrid bridge with the tubes on the positive side and the SS on the ground side, but I have no personal experience there.
     
IMPORTANT: Treat everyone here with respect, no matter how difficult!
No sex, drug, political, religion or hate discussion permitted here.


  1. This site uses cookies to help personalise content, tailor your experience and to keep you logged in if you register.
    By continuing to use this site, you are consenting to our use of cookies.