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kkcinc 20th March 2012 02:12 AM

Simple SE 6l6 tube types
I am now using Transcendar 3k opt's with new production 6l6wxt+. Using 680 ohm cathode resistor and B+ of 440v on the nose. Sounds fantastic in triode or ul, but might like to try old tubes. 6l6 has so many designations and I don't know what is safe to use. Can anyone help? I would like to not change the resistor all the time either.

While I'm at it does anyone know how to wire the Transcendar opt's for negative feedback?

boywonder 20th March 2012 03:49 PM

Check out duncan amps TDSL data for 6L6 types.

TDSL Tube search [6L6]

The 6L6GC types can handle lots more power than the older, non -GC types, so you would need to adjust your bias current and/or B+ to run the older designations at less output power. The B+ voltage and bias adjustments may need to be reduced significantly......

To calculate power dissipation, multiply your B+ voltage by your bias current....then look at the max dissipation values for the various 6L6 types. For UL and pentode mode, the above gets you close, but neglects screen grid current.

kkcinc 20th March 2012 06:16 PM

6l6 types
Maybe I'll stick with the GC's. Any word on the Transcendar windings for NFB?

rknize 20th March 2012 09:26 PM

Your main concern with older 6L6 types will be plate and screen voltage limitations. What does your B+ voltage look like?

Edit: sorry...missed that you said 440. That is pretty high for an older 6L6 type.

w5jag 21st March 2012 09:43 PM

440 minus the cathode voltage, to get the voltage across the tube - will probably be more like 425 -420 volts.

That kind of voltage should not be a problem for any true 6L6GC, 7581A, or KT66. The 6L6GC/7581A plate voltage rating is 500.

The lesser variants are rated at 360 and can take more. A 5Y3 or 5W4 might shed enough voltage to let him use those.


kkcinc 23rd March 2012 07:41 PM

6l6 questions
That 440 B+ was measured with a 5ar4. A 5y3 will drop 80 volts?

w5jag 23rd March 2012 08:15 PM

For what they are worth, these are my rules of thumb:

A 5W4 will drop about 55 more volts than a 5AR4;

A 5Y3 will drop about 50 more volts than a 5AR4;

A 5R4 will drop about 35-40 more volts than a 5AR4;

A GZ-37 will drop about 25-27 more volts than a 5AR4;

A 5T4 or 5U4 will drop about 23-25 more volts than a 5AR4;

A 5V4 will drop about 15-16 more volts than a 5AR4.

Each of these tubes has reduced current ratings compared to a 5AR4, and the amount of current the rectifier has to provide will affect the current drop, so YMMV.

Also, if you have not done so, the cathode voltage is subtracted from the voltage at the tube plate (anode) to determine the actual voltage across the tube.


edit: also, the Sovtek 5Y3GT is not a 5Y3GT. It's more like a reduced current 5V4. I haven't tried JJ's new 5Y3, but it looks like a real 5Y3.

kkcinc 24th March 2012 10:45 PM

So by changing the rectifier tube I can use regular 6l6's and g's. And not be stuck with gc's only?
Can anyone tell me roughly where I stand for voltage across the tube with 5ar4 , B+ at 440v, using a 680
Cathode resistor in the standard sse layout? If not, I'll pull it out of the cabinet and take measurements.

kkcinc 24th March 2012 11:09 PM

I wish George would chime in. I would love to hear his advice on setting up the amp for 6l6's other than gc's.

boywonder 25th March 2012 12:31 AM

Pull it out, take a few measurements, then model what you have in PSUDII, it's very straightforward. There are plenty of folks here to help you. Once you get the model close to reality, then change the rectifier type and current draw in the PSUD model to your heart's desire and see what B+ you end up with.........

If you need help with the PSUD model just ask.......

If you know your power transformer specs (or at least close) and the current draw of your power tubes (measure across the cathode R and use ohm's law), you're half done with your model.

Georges tables on the Tubelab "tubes and transformers" page can give you lots of that and keep in mind that the power out values there are for triode mode.

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