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Vintage threads from the first ten years

Re: Speakers .. what do YOU like ?

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3/21/2002 4:08 PM
Bruce /Mission Amps	Re: Speakers .. what do YOU like ? What output tranny are you using Rich? You might be just fine with 6L6s and the 4 ohm load anyhow. Bruce

3/21/2002 6:40 PM
Rich	I am using the one that came with your kit, Bruce. I have heard that a 100% mismatch is OK, but will burn out the power tubes faster and will result in a power decrease. Is that true?

3/22/2002 3:35 PM

Bruce /Mission Amps

OK, I thoought maybe you had switched the OT.
Here's the deal.
The 5Y3 keeps the voltage low when using 6L6s but the 6L6s try to draw more current (then the 6V6s) through the PT and OT anyhow.
The PT will get pretty warm and that's why I suggest using a SS rectifier when using 6L6s.
When using the SS rectifiers, the extra 5v filament current is not being drawn and the PT will run a wee bit cooler because of that, however the 6L6s draw more filament current then the 6V6s so the PT runs a little warmer. The plate voltage is much higher with a SS rectifier so the tubes try and bias hotter with more idle current!!
But,the large 5K1 screen dropping resistor and cathode biasing keeps the 6L6 from delivering max typical 6L6 power and slightly lowers the idle current. Lot's of things to consider.
Tit for tat!

Your 4 ohm speaker load connected to the 8 ohm tap of the 20 watt Deluxe OT, reflects back to the power tubes with a different impedance ratio now then what is normal with an 8 ohm load so the 6L6s are looking at a 4K ohm primary instead.
Remember, if you halve the secondary load the reflected primary zed is halved also.
So in this case, the power tubes, primary zed and new secondary zed are actually OK because you didn't use an 8 ohm load.
So, a pair of cathode biased 6L6s at this plate voltage and with the lower screen voltage can run fine at 4K ohm or 8K ohm.
At least with an 8 ohm load the primary zed is closer to 8K and the 6L6s can't make as much power.
I think it's OK the way you have it but I'd keep an eye on it anyhow.

Bruce

3/25/2002 2:23 PM
Rich	OK, I think I kept up with about half of what you wrote. Bottom line, it sounds like I don't have to worry about the power tubes. Thanks, Bruce. By the way, all the fiddling around I have done with the amp has opened up a lot of alternative sounds, but in my opinion the best sound is still the original stock version with the 6V6s and the Webber Blue dog.

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