Tube Amp Archive

Leo_Gnardo wrote:

And a good review on the KT66's?

I love the KT66s but I "had" to leave on vacation in the middle of my tone searching. Had a bit of volume drop with the mod some I'm just tweeking stuff around

tubeswell wrote:

Martin manning wrote:

My brain just exploded [/quote]

The fix is reducing the effective value of R76 so you can get a lower (more negative) voltage out of the bias supply. Woops we wuz wrong: Just had a HRD on the workbench and we have to re-address this solution. There's not much voltage to be gained by reducing the upper branch resistor in this bias...

You should also use the plate voltage - cathode voltage for your "plate voltage" in the dissipation calculations so that will drop your dissipation % too. I have a tube bias calculator webpage that's pretty easy to use: https://robrobinette.com/Tube_Bias_Calculator.htm Okay got it. How do I measure...

Well, I tend to be biased (LOL) when it comes to bias. I might urge you to take it lower, and work your way up. Again, if you find a tone you like at a lower bias setting, you're ahead of the game in terms if tube longevity. How do you like the tone at 71%? Also, when I said 475V, I was ballparking...

It's a bit of a moving target. Read Note 5 on the schematic: the specified voltage (-54.6V) is for reference only - it will get you in the balloark, but it's going to be different for each set of output tubes you put in it. The more important number is the current through the tubes. Note 5 says to ...

The schematic says the bias should be adjusted to -54.6V for 6L6's. It would be nice if you could find a value for R83 that will allow you to get up to, maybe -50V at the top end, down to a little more negative than what you need for the KT's at the bottom end. Okay how do those bias reading transl...

Not to mention the amp tech that offered to do it for $100 :? He heard you have those Cadillac tubes, up goes the price, what a gouger. To. be. avoided. Hell I'd do it for free just to hear some Genny 66's in a modern Fender. Yup! Haha I asked him if I could just pay him for his time to show me how...

My first thought was to reduce the value of R76, as others have suggested. This will cause the bias circuit to draw more current which, I believe is unnecessary. Increasing R83 will get you the same net effect from the standpoint of getting the bias supply output more negative, and it will slightly...

JazzGuitarGimp wrote:You're welcome! I just duscovered you have a more actice thread on this in Garage Talk. That's what I get for starting at the For Sale subforum and working my way up!

I submitted that response prematurely on accident haha. I had some questions

Increasing the value of R83 will allow the bias pot to go more negative. Hey thank you so much for your response! I have this posted on the technical discussion forum also and some people recommended me lowering the value of R76 to get a lower voltage out of the bias supply. Can you explain the dif...

The fix is reducing the effective value of R76 so you can get a lower (more negative) voltage out of the bias supply. You could just replace it with a resistor of say half the current value, but that would probably require lifting the circuit board. An easier way to accomplish the same thing is to ...

Thanks for pitching in Martin, I had to participate in Sunday Dinner. Yes that sounds about right, anything from say 27K to 10K ought to do in case you don't have a 15K resistor in your collection. Price on those 66's sounds fair, they are premium tubes after all. The hi fi crowd seems very happy w...

Just curious, how much did you have to shell out for your Genny KT66's? I paid 79.96 for the pair. Didn't seem crazy high but I haven't had my foot in the tube market for long. If I'm that close to being in the ballpark, do you think I should return them and get new ones? Or is it a toss up if they...

Hey people question about biasing KT66 tubes in my HRD 4x10. I got a new set of Genelax Gold Lion Kt66 tubes to replace the 6L6s(was advised this would be okay by the place I bought them) the problem is with my bias adjustment pot all the way down, I'm getting a reading of 104mv at my bias test poin...

Hey people question about biasing KT66 tubes in my HRD 4x10. I got a new set of Genelax Gold Lion Kt66 tubes to replace the 6L6s(was advised this would be okay by the place I bought them) the problem is with my bias adjustment pot all the way down, I'm getting a reading of 104mv at my bias test poin...