The Dynaco Tube Audio Forum

Dedicated to the restoration and preservation of all original Dynaco tube audio equipment - Customer support for Dynaco VTA tube amp kits, all Tubes4hifi.com products and all Dynakitparts.com products


    Is anyone using fast recovery diodes in a VTA 70 or PAS?

    Share

    viridian

    Posts : 14
    Join date : 2010-02-19

    Is anyone using fast recovery diodes in a VTA 70 or PAS?

    Post by viridian on Fri May 07, 2010 6:11 pm

    Can anyone give me guidance on any benefits of using soft recovery diodes in a 70 or PAS and, if you have done this, the parts used and any physical problems or issues that you had to overcome? Practically, I am interested in using them in the bias supply and keeping the tube rectifier, but would also like to hear if anyone if using them in place of the 5AR4 or 12X4.

    Bob Latino
    Admin

    Posts : 2374
    Join date : 2008-11-26
    Location : Massachusetts

    Re: Is anyone using fast recovery diodes in a VTA 70 or PAS?

    Post by Bob Latino on Sat May 08, 2010 10:06 am

    viridian wrote:Can anyone give me guidance on any benefits of using soft recovery diodes in a 70 or PAS and, if you have done this, the parts used and any physical problems or issues that you had to overcome? Practically, I am interested in using them in the bias supply and keeping the tube rectifier, but would also like to hear if anyone if using them in place of the 5AR4 or 12X4.

    Hi viridian,

    At least in the VTA ST-70, the use of a fast recovery diode to replace the standard 1N4007 diode for the bias system, (IMHO) won't make ANY difference in the sound of the amp. I actually did this once when I ran out of 1N4007 diodes and my local Radio Shack didn't have any either. I had a couple of FRED (fast recovery epitaxial diode) diodes around. I remember having to install it on the bottom of the driver board because it stuck up too high under the lip of the chassis. The amp, when built, sounded just the same as other VTA board installations that I had done.

    I have never installed a diode to replace a 5AR4 or a 12X4 other than the use of a solid state rectifier replacement module in an ST-70 or ST-120. Understand that if you do this the voltages will become higher than with the use of a 5AR4 or 12X4 tube rectifier. This higher voltage may or may not become an issue depending on use. In an older original ST-70 I would not install a replacement diode or SS rectifier if you have an original quad cap. Those older quad caps are probably marginal now and the use of any SS rectifier (which will raise the B+ voltage) could send a 40 - 50 year old quad cap over the edge into tube amp heaven.

    Bob

    viridian

    Posts : 14
    Join date : 2010-02-19

    Re: Is anyone using fast recovery diodes in a VTA 70 or PAS?

    Post by viridian on Sat May 08, 2010 11:34 am

    Bob, thanks so much for educating me on this! As I said, my practical interest was in using a FRED in the bias supply. The part about replacing the 5AR4 was mostly academic. I really appreciate the guidance; hopefully I can build this thing once and be good for a while. It's just better, for me, to sort out all of these details now.

    Sponsored content

    Re: Is anyone using fast recovery diodes in a VTA 70 or PAS?

    Post by Sponsored content Today at 1:17 am


      Current date/time is Tue Sep 27, 2016 1:17 am