What Tubes Can I Use?

[gtrplayr1976]

What part of VA are you in Justin?

[Leo_Gnardo]

Hey Leo,

I meant, the "generic" tubes don't. I've seen Valve Art & such, Audio Glass, Groove Tubes, T.A.D., etc, all on Chinese tubes. What I meant was, when I order "Shuguang" or "Chinese" tubes from say, Tube Depot, they just say "Made In China," usually with just a white sticker attached. I even get em in plain white boxes. JJ & Sovtek at least have their own boxes, too. When I order at the basest level, there's no logo. But when I order JJ & Sovtek, even though they're both relabeled & rebranded by others, they still say Sovtek & JJ. Anything more is a relabel.

Though as Stan had poibted out, the Chinese factories will print anything you want on them if you order a thousand of one type.

Justin

Okee dokee. One more not so recent development, New Sensor has been selling some Shuggies for a couple years now besides their Saratov Russia made tubes. What confusement for tube buyers.

[Justin Thomas]

So Sovtek has become a multinational corporation now? Alright! Subcontracting? I guess it's been going on for years, what with all those Telefunkens that got bought & relabeled by Mullard & such... Luckily I can EASILY spot a Chinese preamp tube...

Thing is, and I wasn't around at the time to know, but seems there wasn't quite the intent to deceive. And even if you really DID get a Telefunken instead of a Mullard or a Sylvania instead of a Tung-Sol, at least they were guaranteed to meet SOME sort of soec, & you weren't just getting a piece of junk with a blot of ink on it that was masquerading as something else...

Justin

[gtrplayr1976]

I'll stick with what I've had good luck with. JJs from Eurotubes. Preamp tubes are a little different. I like Tungsol sometimes ,and I have a few vintage , but some seem a little noisy.

[Leo_Gnardo]

I'll stick with what I've had good luck with. JJs from Eurotubes. Preamp tubes are a little different. I like Tungsol sometimes ,and I have a few vintage , but some seem a little noisy.

At least a dodgy pre tube won't pop fuses or damage a transformer. Plug n play until you find one you especially like. Only problem, you might wear out the tube socket after a while.

[pdf64]

The 5881 IS a 6L6, just a 6L6G beefed up a little; the successive upgraded versions were always backwards compatible, so as (by definition) all 6L6 type tubes have the same characteristics, there's no technical reason why a 6L6GC subbed into a circuit designed for 5881 need idle at a higher plate current than would be appropriate for a 5881.

My take on the respective charts is that the JJ 5881 may have a higher gm than the type bogey?
https://tubedata.altanatubes.com.br/...127/5/5881.pdf
https://www.jj-electronic.com/en/5881

I always thought Marshalls liked a higher bias in the 70% range? Fenders more in the 50-60% range?

Bear in mind the differing rating systems in use to derive the limiting values for the tubes typically used in these amps; 70% of an EL34's 25W design centre plate results in the same idle plate current as 57% of a 6L6GC's 30W design max plate limit.

It's plate current that sets the operating point (and therefore all the important stuff that actually affects performance) on a tubes characteristic curves; plate dissipation is purely a limit.
As Leo notes, for the class AB1 operation of a typical tube guitar amp, 30mA idle current is plenty to keep these big octals way out of the obnoxious sounding 'zero crossing' crossover distortion.

And the 23W plate rating of the 5881 is under the design centre system; it would presumably be somewhat higher under the design max system (ie by which the 6L6GC gets its 30W rating).

Unfortunately the info for currently manufactured tubes doesn't indicate the rating system used to derive the limiting values provided. But that's assuming the manufacturers or ourselves give any credence whatsoever to such info.

[Justin Thomas]

Correct on all points, but what I usually run into is people trying to put vintage or new-fangled REAL 5881s into circuits where 5881WXTs are fitted or designed for. And while I'd happily put a 5881WXT running at about 600 plate volts I certainly wouldn't put any vintage or "reissue" 5881s in the same circuit.

Unfortunately most musicians aren't going to concern themselves with the minutae of tube finery, ie, the distinctions between 6L6, 6L6G, 6L6GB, 6L6GC, 5881, 7581, 7027, and whatever else there is out there. I still run into confusion over ECC83/12AX7/7025 & EL34/EL84. I think we get a little spoiled & used to most knowing stuff here... Try a hugebrand-centric worldwide public FB group on for a week & see if you don't pull your hair out! :P

I jist keep trying to do my best to educate...

Justin

[g1]

The 5881 IS a 6L6, just a 6L6G beefed up a little; the successive upgraded versions were always backwards compatible, so as (by definition) all 6L6 type tubes have the same characteristics, there's no technical reason why a 6L6GC subbed into a circuit designed for 5881 need idle at a higher plate current than would be appropriate for a 5881.

Agree but the problem is going the other way, as Justin outlined above. For example the era when Marshall dropped EL34's due to reliability issues and had stickers on their amps that said 'equipped with 5881's'. Those were the WXT's like Justin said, and had no problem meeting the 6L6GC requirements. A vintage or re-ish proper 5881 is probably not going to do well in such a circuit. Same as all the Fender amps that came stock with the Sovtek 5881/6L6, the 5881 moniker was being used in a non-traditional manner.

[gtrplayr1976]

Agree but the problem is going the other way, as Justin outlined above. For example the era when Marshall dropped EL34's due to reliability issues and had stickers on their amps that said 'equipped with 5881's'. Those were the WXT's like Justin said, and had no problem meeting the 6L6GC requirements. A vintage or re-ish proper 5881 is probably not going to do well in such a circuit. Same as all the Fender amps that came stock with the Sovtek 5881/6L6, the 5881 moniker was being used in a non-traditional manner.

So the 5881 JJs I just put in my JTM45 build are the wrong ones?

[gtrplayr1976]

I just played the JTM45 with the 5881s, biased at 32mA ,set on 8 ohm tap. It doesn't sound bad except when I use the MV. With the MV all the way up ,and just using my channel volume(s) it's on the clean side. If I crank the volume ,and bring the MV up some I get the distortion ,but it just doesn't sound good. It was mentioned I could put a cap on the MV to lessen the bass (which it sounds like may be causing the bad tone with the MV) ,but I never got details for how to do that with the MV I have.

[Justin Thomas]

The JJs are probably built at or close to original 5881 specs. JJ already has a 6L6GC. If the JJ 5881s work in your amp & sound good & don't explode, then they are good. It's a matter of knowing the specs of what you're using & adjusting things accordingly. Check the JJ spec sheet on the tubes you're using - they have the decency to make their own, rather than just reprint the old ones from the 60s like some other manufacturers (cough NewSensorReissues cough).

Justin

[Justin Thomas]

I just played the JTM45 with the 5881s, biased at 32mA ,set on 8 ohm tap....

As long as you're not exceeding the plate dissipation you're okay, as far as using those tubes go. No suggestions on tone.

[gtrplayr1976]

As long as you're not exceeding the plate dissipation you're okay, as far as using those tubes go. No suggestions on tone.

Seems it should handle it. I have 450 plate voltage.

[Helmholtz]

Caps on the MV don't lessen the bass but increase high treble at lower MV setting. No effect with MV fully up.

As said before, if you post your schematic I could give some advice.

As a first step to lessen bass you may reduce the capacitance of the power tube coupling caps from 0.1µF to 0.022µF

[gtrplayr1976]

Caps on the MV don't lessen the bass but increase high treble at lower MV setting. No effect with MV fully up.

As said before, if you post your schematic I could give some advice.

As a first step to lessen bass you may reduce the capacitance of the power tube coupling caps from 0.1µF to 0.022µF

My mistake. I didn't really use a particular schematic ,but I used the MV on this layout ,and pretty much the rest of it I believe.