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I bought a close out set of Russian EL34s and my Picovalve likes 6L6s better. I remember EL34 might be able to be used in the Triwatt.

Zaphod Wrote on another forum:


I think you would want the KT66 switch setting, besides running a 4 Ohm Speaker Load at 8 ohms, but does anyone know the ideal bias setting for EL34s. (I am trying to dig thru the Triwatt Build Doc's in my basement, and cannot find the exact plate voltages for the Triwatt.)

Thanks:

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ROB

Rob, are you familiar with the whole process of fixed bias (grid bias) adjustment?
The El34 has a max plate dissapation of 25 watts. This means that the current flowing in the plate multiplied by the plate voltage cannot exceed 25. Most people bias to 60 or 70% of that. Capice?
Stew

That is not a problem. I was wondering what the plate voltage was when the Triwatt was switched to the KT66 setting in order to calculate the mA. Also if people have tried the EL34s in the Triwatt - was there an ideal setting. (Most people like the KT66 when they run hot)

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ROB

I found a "Soft Copy" of the Build Manual. Looks like the plate voltage is 441.

Also KT66s are 25 Watt Tubes - figures are pre-calculated.

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ROB

I need to point out that EL34s and KT66s bias differently. When the amp is set for 6V6 operation, the bias happens to turn out about right for EL34s. There's a Floyd cover band that's been touring with a Triwatt set this way to run EL34s.

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Great tones come in small glass jars!

One thing I am a little concerned about would be the heater current draw (EL34 - 1.5 Amps vs. 6V6 - .45 Amps). If I need the extra clean headroom I should just get a pair of KT66s. (Unless the Power Transformer is close to the DR504 Spec's)

Loudness wise the Triwatt was able to be heard without a problem, last night playing with a 100 Watt Sundown Amp.

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ROB

No problems there. The PT and OT were designed and built for Trinity by Heyboer, based on Partridge's 50W Hiwatt transformer set.

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Great tones come in small glass jars!

Zaphod Wrote:
[quote][When the amp is set for 6V6 operation, the bias happens to turn out about right for EL34s. /quote]

So I will set the bias switch for the 6V6 not the KT66 setting & set the Impedance Switch to 8 Ohms for a 4 Ohm Load, for the EL34s.

Thanks!

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ROB

.. and be sure to adjust the bias accordingly so the EL34 runs correctly.

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Stephen
Web: www.trinityamps.com. Facebook: facebook.com/trinityamps. Twitter: @trinityamps

Of course I will set the Bias!

Hopefully this week I will get a chance to tinker with the Triwatt. At least I have finished the soldering end of my Franken-Tele Project, so unless the my new bridge comes in sooner than I think, I will try the tube swap on Thursday.

Thanks:

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ROB

Productive Day! Installed Compensated Saddles on the Franken-Tele (At work during my lunch hour), and just switched the tubes to the EL34s, on the Triwatt. I biased them on the cooler side, at about 62%. They sound great, at low volumes (My wife was sleeping). They play spongier that the JJ 6V6s, and are a little less midrangier. Tomorrow I will open it up a little bit more. Ran the amp about 15 minutes to check for burning smells, and glowing plates. All seems fine.

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ROB

You may also like to experiment with simply shorting out the zener, when running EL34s. That will give you a little more voltage, power and headroom.

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Great tones come in small glass jars!

Zaphod said:


I opened the Triwatt up this morning. It sounds great, super chimely. I am at work now and was talking to a friend who worked for Line 6 in the 1990s, and did a lot of testing on the Vetta, comparing the models to the original amps. He was wondering why the Triwatt would be than much spoungier with the EL34s vs. the 6V6. The zener is probably why. I like it as it is, tonewise. So if it's not hurting anything I will keep it as is. It has enough power to be hear with a drummer with 6V6s so with the EL34s there should no problem.

The Chime with the EL34s is great.

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ROB

Sooo let me get this right (because I want to try EL34s as well).

I set the switch to 6V6 and then bias the EL34 as normal? The way this bias set up appears is much like a bias right, where you set the current on the meter's voltage setting. I usually set my EL34s to around 35mA. I'm not sure how to calculate the 70% or whatever... I guess first take a plate voltage reading?

Finally, do I have to run the EL34 at an 8 ohm bias setting for a 16 ohm cab? What if I have a 16 ohm cab, will it hurt the transformer to run bias at 16 into a 16 ohm load?

Thanks.

You can set to 6V6 and bias. Run the impedance one setting higher than the speaker cab impedance. i..e 8 ohm cab at 16 ohm impedance setting. 16 at 16 is not idela but wont hurt anything.

Note that in 6V6 mode, the zener in the supply reduces the plate voltage. As Phil suggested, you can short out the zener for a 30V higher plate voltage. That would be my recommendation.

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Stephen
Web: www.trinityamps.com. Facebook: facebook.com/trinityamps. Twitter: @trinityamps

Been running the EL34s since August. No Problems! I actually like the spongyness, so I didn't short the zener.

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ROB