• WARNING: Tube/Valve amplifiers use potentially LETHAL HIGH VOLTAGES.
    Building, troubleshooting and testing of these amplifiers should only be
    performed by someone who is thoroughly familiar with
    the safety precautions around high voltages.

6V6 line preamp

Member
Joined 2003
Paid Member
New 6V6 Bootstrapped CF.

It has been awhile since I have had time to do more than lurk in the forum. Came across some 6V6G's a while back and decide it was high time to sling some solder.

This is the test bed for the preamp. Still missing is the volume, a selector knobs. I am also waiting on the MJE5731 for the SSHV(1) regulator.
B+will be 330V @ 25-30mA fed by the SSHV regulator running at 60-65mA. The cathode load will be various from different styles of CCS's to a good old resistor. Right now I have CCS's galore from a previous project I was doing so they went in. The filament will either be the universal reg or LM317 setup in CCS mode.

The power supply is seperate and sports a single PT 5UG4 rectifier splitting into parallel 20H inductor and res caps of 100uF. All motor run caps. The raw filtered B+ will be 365V.
 

Attachments

  • DSC03239.JPG
    DSC03239.JPG
    138.9 KB · Views: 1,659
  • DSC03238.JPG
    DSC03238.JPG
    138.6 KB · Views: 1,638
  • DSC03237.JPG
    DSC03237.JPG
    145.2 KB · Views: 1,608
Member
Joined 2003
Paid Member
6V6 Update

In a matter of minutes my 124b preamp was removed from the room. The 6V6 CF with raw DC feed (380V) and AC heaters biased at 25mA by far beats the 124b. Waiting on the 400V transistors and need time to design the SSHV2 circuit board. So I still have some work to do including building a dedicated measurement PC to document this thing. Until then will just be kicking back and listening.

The clarity, and depth of the soundstage is fantastic. Excuse the dust on the Opus's. Will have to clean them tomorrow. The have performed flawlessly for almost two years now. Every day.
 

Attachments

  • DSC03240.JPG
    DSC03240.JPG
    146.3 KB · Views: 1,518
  • DSC03241.JPG
    DSC03241.JPG
    155 KB · Views: 1,831
  • DSC03242.JPG
    DSC03242.JPG
    153.1 KB · Views: 686
Disabled Account
Joined 2004
Well, a friend says he wants a great line stage. He has given me cash to play with. I bought two reds 5692's but weeks have passed and I haven't started yet.

I want something different, I have read this thread and I think I'm going for it. It troubles me the microphonics problem though. How should I build the chassis? I was planning a wooden base with a top metal plate. I can choose the thickness of the metal plate, the base will be made by some carpenter. If anyone can offer me some good tips to avoid problems I'd appreciate it.



EDIT

Suspend or soft rubber decouple the tubes on a small sub chassis, it pays off.


I don't understand this.
 
Last edited:
Member
Joined 2003
Paid Member
Isolation Grommets

This is what I do. For the test rig I just used a piece of pcboard. In final version will be aluminum, copper, or steel. Not sure yet.


I have no noise pick-up that is discernable. I can tap the tubes and hear a ring but not as bad as my 12b4 pre was.
 

Attachments

  • DSC03244.JPG
    DSC03244.JPG
    128.5 KB · Views: 788
  • DSC03245.JPG
    DSC03245.JPG
    137.1 KB · Views: 780
diyAudio Chief Moderator
Joined 2002
Paid Member
Sgregory I like your chassis (knobs too).

Salas isn't leaking any info out on the sub chassis. Top secret?

What secret? From early in the thread I recommend some form of isolation. The less microphonic on steady chassis with the gain circuit was the new Tungsol from those I checked. In CF things are easier, and Scott's combination of CF and grommets won't create trouble with any make, even the most sensitive ST bottle ones.
 
Ex-Moderator R.I.P.
Joined 2005
rubber grommets

mount tubes in a just big enough alu or copper plate
use rubber grommets in its chassis mounting holes
and in your main chassis, use grommets as well

mount a small piece of soft neoprene between plates, on mounting screw
use selflocking nut

mount your trafos with anti vibration rubbers too

screws should be very carefully 'adjusted'
it really makes a big difference on how much buzzing is transferred to the chassis
with a simple wooden stick(or stetoscope) you can easily hear how much