Dual rectifier tube mixing

[zosojjc]

I am considering purchasing an old dual rectifier (serial # in the 700s) but the current owner tells me he's running two 6L6s and two EL34s. I'm waiting to hear back from him on more details but in the meantime thought I'd run it by you guys. Can this be safe or should I pass on this one (the price is very good)?

 

[redmax61]

I would find out if he meant 6L6's and EL-84's. This is definitely a valid combination using THD YellowJackets. I've running 34's and 84's in my DR for several years now.

As far as mixing EL34's and 6L6's, I don't think that's possible without modding two of the sockets. I seem to remember hearing that the way the amp is biased, you'd fry the thing if you attempted to run 6L6's with the tube selector switch in the EL-34 position and vice versa. Hopefully someone with a little more knowledge of tinkering will pipe in here.

 

[MakoBlink]

how do you like your sound with the el84's and 34's? I have stock 6l6's in my dual right now and i want to mess around with some different sounds. What characteristics do the el84's have? do you have any sound clips? Also, if i want to switch up tubes to the el 34's and yellow jackets, or is it just a matter of switching the bias over?

 

[musicbox]

I can't believe all of you guys shop at Eurotubes.com, yet have never noticed all the hype about his Integrated quads. The man got ALOT of smack about them from peavey and various forums, and is the number one reason that alot of people will not do buisness with him/ why he has a bad name. Most of it is just unfounded talk and people really don't know what they are talking about. Heres a link to his website with a letter to someone at peavey explaining why these are safe to use. I believe they are most populare in 5150's, but it says on his site that he can bias them for Rectos as well.

http://www.eurotubes.com/euro-kb.htm

Basically the deal is, he will set up the tubes so that the 6L6's are really hot, and the el34's are really cold, or perhaps the reverse. That way they draw the same voltage from the trany, and the amp runs ok.

Here is a description from his online store:

"DESC: These are a great option for players looking for the combined tones of the E34L's and 6L6GC and work great in any 100 watt amp that can run either EL34's or 6L6's and Dual Rectifiers, Carvin Legacy and MTS amps. These tubes are matched quads. Integrated quads consist of hand picked 6L6GC's and E34L's that all draw the same exact amount of natural plate current which is how tubes are matched. The integrated quads do provide a very cool mixture of tones combining the deep thump and clean smooth highs of the JJ 6L6GC's and the aggressive punch and classic British sound of the JJ E34L's."

Also, according to Bob you can run 6L6's which are biased specifically for the EL34 mode selected. This has the effect of warming up the bias and getting some more heat out of the tubes. Browse around the website and you'll find some interesting facts about retubing recto's.

Here is a link to the Mesa section of the Eurotubes website pertaining to the above paragraph. https://ssl.eurotubes.com/euro-n.htm

Hope this answers any question. Perhaps this was a waste of time if he really was talking about the yellowjackets.

Andrew

 

[redmax61]

OK, I guess I'm a bit in the dark about this. I've heard of integrated quads, but I didn't realize that they were combinations of tubes like that. I will look into them a little more. I haven't checked out Eurotubes, but I will have to now. Thanks for the info, Andrew!

As far as my current setup, I really like the combination of 34's and YJ's in my amp. IMHO, I've only heard one amp that sounds thicker and tighter. And I'm a long way from being able to afford an Uberschall. If you get a chance to experiment with different tube combinations, I very highly recommend it.

 

[Dale B.]

Basically the deal is, he will set up the tubes so that the 6L6's are really hot, and the el34's are really cold, or perhaps the reverse. That way they draw the same voltage from the trany, and the amp runs ok.

It's the other way around. The 6L6GC's that he supplies in the integrated quads are very cool 6L6GC's that draw very small amounts of plate current. The E34L's that he supplies draw are hotter and draw more plate current.

The actual bias voltage (negative screen grid voltage) is going to be the same. It's just a matching issue and that's what he has done.

If I remember what was said correctly, Roger was griping about both sets of those tubes being really far out of spec. If you blended that vibe in a power section, you could argue with Roger's point of view by saying that yes, there is less headroom with the 6L6GC's, but there is more headroom with the E34L's, which in a way would equal things out to a certain degree and give the power section a unique tone.

Roger was mainly ticked off that Bob was recommending JJ E34L's for amplifiers like the Peavey XXX at the time. The screen grid resistors in the Peavey XXX could handle the JJ EL34's, but they couldn't handle the JJ E34L. Once a screen grid resistor goes, the power tube will not bias up due to there being no negative grid voltage applied to the screen grid of that particular power tube and this can happen in every power tube socket. In some instances, when power tubes cause components on the amp to fail, this can cause fuses to blow.

With all that said, it kind of makes you wonder about some Mesa amplifiers. If you buy used, always ask the person you are buying from if they have had any power tubes fail on them while the amplifier was in operation. It's always good to have some sort of bias probe on hand as well. You can detect this very easily with a probe of some sort because, like I said earlier, a power tube will not bias up if the screen grid resistor has blown. You will still be able to see the plate voltage, but there will be no cathode current reading (bias current - mA reading).

I mention all of this due to this happening to me once before with a Bogner XTC 101B, which I still own. The guy had a power tube go bad and Bogner sent him a new set out to him. He put the new set in there and played the amp for about two more hours and then never really played it a whole lot again. When I got the amp from him, it appeared to be fine when I first fired it up. Then I pulled the chassis on the amp to see where it was biased up to because the previous owner mentioned to me that he didn't have a bias probe and that Bogner had supplied him the tubes. So, Ine tube checked the bias. One pair of tubes were drawing 50+ mA. As for the other pair, one was drawing 25 to 30 mA and the other wasn't drawing anything.

I had to replace the screen grid resistor and buy new power tubes. It's not a hard fix if you can solder and have a steady hand, but it can be a pain it's still a pain the backside. After all of that, the amp biased up very smoothly and it's drawing 32 mA across the board with a healthy plate voltage between 525 and 535.

Dale

 

[musicbox]

Thanks for the educated side of things! I just posted as far as I knew, that's why its riddled with 'or possibly the reverse'. It's good to have a few people on here who actually know their stuff.

One question. What causes a screen resistor to go? Shitty workmanship? Or overly hot tubes? In a sense, it seems like Roger was mostly ticked off because he built his amps with sub par parts what couldnt handle anything more than the coldest tubes, thus why he set it up without a bias adjustment. That way no one would discover that his parts couldnt handle anything else. It's nice to know that Mesa on the other hand built their amps to handle tubes, even beyond the set bias that Mr. Smith determined was appropriated.

Also, what's your opinion on the integrated quads in Dual Recto's for those that might be interested..