Tube Recommendation for a '92 Dual Rec

[FourT6and2]

How do you deal with the ‘non mesa tubes’ and fixed bias thing with rectos?

What I did with mine was use bias probes to see what current the stock tubes draw. Then I calculated the plate dissipation percentage from that. Then I tested the tubes in my Maxi-Matcher. The tubes bias up to like 38% in the amp. So I know if I want to reach my target (50-55%), I need to go up at least 1, if not 2, color codes on Mesa's rating system.

Or, if I want to use tubes from some other vendor, I just tell them the specific current draw I want. But you need to know what the tubes pull in the amp first. So without a way of measuring them and testing them, you can't really do that.

Beware of vendors promising to put together sets that will bias up fine for you, without them knowing the specific numbers of your amp. It's impossible. Mesa biases their amps so cold that pretty much any middle of the road tube set will bias up somewhere between 30% - 70%. So any "Mesa specific" tubes a retailer sells you will technically "bias" fine. But if you want to hit a specific setting, you can't.

The best way is the "bias mod" and install an adjustable trim pot.

 

[The~Kid]

You can get some 9th Gen Shuguang or GT Chinese Preamps..... Id go for those for the preamps.


Ruby Tubes and others have some still.

 

[Dale B]

What I did with mine was use bias probes to see what current the stock tubes draw. Then I calculated the plate dissipation percentage from that. Then I tested the tubes in my Maxi-Matcher. The tubes bias up to like 38% in the amp. So I know if I want to reach my target (50-55%), I need to go up at least 1, if not 2, color codes on Mesa's rating system.

Or, if I want to use tubes from some other vendor, I just tell them the specific current draw I want. But you need to know what the tubes pull in the amp first. So without a way of measuring them and testing them, you can't really do that.

Beware of vendors promising to put together sets that will bias up fine for you, without them knowing the specific numbers of your amp. It's impossible. Mesa biases their amps so cold that pretty much any middle of the road tube set will bias up somewhere between 30% - 70%. So any "Mesa specific" tubes a retailer sells you will technically "bias" fine. But if you want to hit a specific setting, you can't.

The best way is the "bias mod" and install an adjustable trim pot.

I had a sextet of =C= that were hot as hell that the previous owner had bought from The Tube Store. They sounded awful. Most of the manufacturers want the middle of the road tubes because it's the best of both worlds for headroom and breakup.

I still have 12 matched Ruby EL34B-STRs I pulled from a Diezel Herbert back in the day. Those particular tubes would start doing their thing around 50% at idle. It was like having an EL34 that did what the JJ 6L6 tends to do. They added depth. The JJs would do the same thing when I would run them hotter under the EL34 bias setting. I would just keep them around 30 to 35 mA in whatever mode gave it to me.

I LOVED KT66s in those amps! I remember nuking one after I forgot to put the bias back to the 6L6 side. It was a pretty light show with a screen grid resistor change afterward! LOL

 

[BesaMoogie]

The amp was build around Mesa Str 420 which are old Shuguang 6L6. Sometimes you can find them as NOS tubes. In the preamp, 8th gen Shuguang 12ax7 tubes were used.
You can find the preamp tubes easily, they have the triple mica and square getter foil.

This is just in case, you are shooting for the original sound.

 

[Kordoba]

I think that was just dust CharvelDan

Ceiling dandruff

 

[Holy-diver]

JJ kt-77 is a nice option, feels like a beefy el-34 in rectos. Their 6l6 is a great value as well
Tung-sol 6l6 rules too

 

[Hiwatts-n-Gibsons]

How do you deal with the ‘non mesa tubes’ and fixed bias thing with rectos?

A competent tech can adjust the bias and set it fixed for the tubes. They could also add bias pots for each pair of tubes instead of hardwiring it to a set bias.

 

[napalmdeath]

JJ 6L6GC
Sweet spot for bias in that amp is 55%.

Yeah. Have Eurotubes hand-pick the right grade. They're my go-to.

I actually had a multi-watt that they talked me into 6CA7's for. Sounded phenomenal.

 

[Alpha Stryke]

A competent tech can adjust the bias and set it fixed for the tubes. They could also add bias pots for each pair of tubes instead of hardwiring it to a set bias.

Some Rectifiers have pads on the PCB for bias trimmers.

 

[napalmdeath]

What I did with mine was use bias probes to see what current the stock tubes draw. Then I calculated the plate dissipation percentage from that. Then I tested the tubes in my Maxi-Matcher. The tubes bias up to like 38% in the amp. So I know if I want to reach my target (50-55%), I need to go up at least 1, if not 2, color codes on Mesa's rating system.

Or, if I want to use tubes from some other vendor, I just tell them the specific current draw I want. But you need to know what the tubes pull in the amp first. So without a way of measuring them and testing them, you can't really do that.

Beware of vendors promising to put together sets that will bias up fine for you, without them knowing the specific numbers of your amp. It's impossible. Mesa biases their amps so cold that pretty much any middle of the road tube set will bias up somewhere between 30% - 70%. So any "Mesa specific" tubes a retailer sells you will technically "bias" fine. But if you want to hit a specific setting, you can't.

The best way is the "bias mod" and install an adjustable trim pot.

My Multiwatt was running at 19mA from the factory. That's stupid cold.

 

[Hiwatts-n-Gibsons]

Some Rectifiers have pads on the PCB for bias trimmers.

I didn't know that.

 

[FourT6and2]

My Multiwatt was running at 19mA from the factory. That's stupid cold.

What plate voltage?

But yeah, for 6L6GC, 19mA at something like 475v = 30%

Ultimately, it doesn't really matter as long as you're hot enough to be out of crossover distortion territory and don't exceed 70%. Anywhere in that range that sounds good is fine.