Fybertech Forums

Projects and Development => Hardware Dorkery => Topic started by: Rotary_Turbo on February 10, 2011, 01:28:37 pm

Title: DIY tube preamplifier kit
Post by: Rotary_Turbo on February 10, 2011, 01:28:37 pm
Well, here is the link to what I found:  http://cgi.ebay.com/12AX7-ECC83-MM-MC-Phono-Tube-Preamplifier-Kit-ref-VTL-/220724091149?pt=LH_DefaultDomain_0&hash=item33642e590d  Since it hails from China, it appears to operate on 250v.  Everything elce I can work with, but how could I deal with the fact it's looking for 250v and likley at 50hz not 60hz?  A step up transformer would be large, heavy and generate alot of heat...that and it would be un-efficient.  Maybie I need to find another kit with a different design, but one like that would work well when put into a nice case of some sort.  I'd really like to build one, just to say I have and to see how it sounds with my setup.
Title: Re: DIY tube preamplifier kit
Post by: FyberOptic on February 10, 2011, 02:38:32 pm
Yeah it looks like that kit is designed to use an external power supply.  Which they just so happen to also offer apparently, going by the description.  That would likely use a tube as well.  What kinda confuses me is the two connections for 260v, since it's a three screw terminal block.  Dunno if that means it wants two 260v supplies out of phase with one another or what.  The schematic is too low quality for me to read all of the text.  Either way I'm pretty sure it means the step-up transformer would be at least 520v, center-tapped, giving + and - 260v.  Then it'd be smoothed out and rectified.  Pretty much any tube amp is likely going to be a high voltage like that.  Dunno how low they can go for sure.

On the bright side, those are triodes, so it is in fact a true tube amp.
Title: Re: DIY tube preamplifier kit
Post by: Rotary_Turbo on February 10, 2011, 06:42:23 pm
http://cgi.ebay.com/Toroid-Transformer-T30-69W-0-120-200-220-260-280-320V-/320630230299?pt=Vintage_Electronics_R2&hash=item4aa70d0d1b  This is the kindof thing they have in their ebay stores.  It steps up from 110 to the neccicary voltage and has other outputs as well which it seems the amp needs at least one of, if you notice.  Go down through the pics to the overhead pic of the board that has the signal path layed out.  There's a "ground" then two poles for "260v", and beside that is a set for a ground and 12.6v.  The others are the input from the stereo and output to the amplifier.  I may just try this in the future, but probably not soon.