[sdiy] best resistor types for HV tube supplies and screen supply voltages for 6V6

[Thomas Hudson]

On Nov 12, 2007, at 3:30 PM, anthony wrote:

> I'm leaning towards the big fat carbon comps because they look neat  
> & I think they're actually more like 3 watt units and I remember  
> something about them being good for tube amp supplies.

Only in certain places:

http://www.geofex.com/Article_Folders/carbon_comp/carboncomp.htm

Personally I prefer using flameproofs in the power supply, and RN65D  
mil-spec precision metal films everywhere else. I hate hiss.

You can get 2nd harmonic distortion in a tube amp without having to  
resort to crappy parts.

>
> I've noticed among different designs of amps there is a bit of  
> variation of the screen voltage: sometimes there's a 1kOhm resistor  
> between the plate supply and the screen supply and other times  
> there's as much as 10kOhm there. What gives? I'm guessing the 6V6  
> isn't picky about it's screen voltage. Does running it closer to  
> the plate voltage make it more triode-y?
>
You have to be careful about older designs which tended to minimize  
cost of the amp, rather than the cost to the owner wishing to extend  
the life of his tubes. Marshall was especially bad about changing  
tubes or raising plate voltages without changing the value of screen  
resistors. Look at the tube data sheets for the 6V6 you plan on using:

http://tdsl.duncanamps.com/tubesearch2.php?TSD=6V6&btnSubmit=Query

And choose a resistor based on rated screen voltage. Different values  
can affect the sound, and guitar amps are notorious for running tubes  
over their ratings. But this is a good starting point.

> This post may seem not to be so much to do with SDIY, but I think I  
> may actually end up using this amp for one of my monosynths after I  
> get an Epiphone valve junior or 2 to have a stereo rig for my  
> guitar. (The idea of getting 2 Valve Junior heads and making a 2X12  
> cab for them to sit atop is very appealing to me.

There's a very active and helpful community of amp builders (both in  
the US and Europe) at:

http://ampgarage.com/forum/

Besides the sections devoted to Dumble or Trainwreck amps (the two  
holy grails of guitar amps), there is a "Technical Discussion"  
section which at almost any given time of day seems to have someone  
hanging out with the knowledge to respond quickly to questions.

Tomy