Disclaimer! I'm not am expert and don't do this for a living. Double check with someone more knowledgeable before you go messing with anything on my behalf!
That said, I've a pair of JJ6L6's in my JAZ for the last few weeks. The way I see it, or best understand is that a 6L6 is sort of like two 6v6's in one. It draws twice the heater current and wants twice the current. So in theory (at least my limited theory :-)) if a single 6L6 is similar to a pair of 6v6's then a pair of 6L6's would be a similar impedance match to two pairs (one quad) of 6v's. If you looked inside the amp you would see that the the power tube sockets are arranged in pairs. The voltage supplied to the plates (pin 3) is ran to the first power tube socket, then jumpered to pin 3 on the second creating one pair. Another wire is run to pin 3 on the thrid power tube socket and jumlered to pin 3 on socket four. Another pair. So you can sort of visualize how sockets 1+2 are a pair and 3+4.
I did take some measurements to calm my nerves about it. With a quad of 6v6's installed I read a plate voltage of 374v. I measured the cathode idle current draw per 6v6 tube, then pulled them and installed 6L6's in socket 2+3 only. Rechecked plate voltage and measured the current of each 6L6. The readings is very close to the same for a pair of 6v's or a single 6L. Within a few Ma.
I have have been running it with a pair of JJ6L6GC's in the center sockets for a few weeks. No smoke yet. Sounds really nice this way. I've actually been doing a speaker shootout with it this way for the last few weeks. I have a Alnico Cream in it now and it sounds pretty great. Tomorrow a totally different speaker shows up, a Warehouse G12 C/S. I'm excited about that!
But like I said about the tubes, i feel comfortable with it, but ask someone that knows more than me before you go messing around with your amp.
Last Edit: Dec 29, 2016 22:07:39 GMT -7 by nicholas
You are going to have an impedance mismatch with the output transformer by using only 2 tubes.
You would if you simply pulled out two of the 6v6's. You would be halfing your load, just like a basic half power switch that shuts off two tubes, you should then half your impedance to the speaker and plug a single 16 ohm speaker into the 8 ohm tap.
But because the 6L6 draws the same current as two 6v6's the impedance shouldn't be off by much. Both halves of the PT should be balanced and seeing the same draw as when the quad of 6v's were in there. I forget the exact numbers, but I believe (and to keep the math simple) each 6v6 was pulling 25 ma. So 100 ma for the whole amp, or 50 per pair of tubes. With the 6L6's it pulls 50 ma per tube, 100 for the whole amp.
If my theory or math is off feel free to correct me.
Last Edit: Dec 30, 2016 12:02:21 GMT -7 by nicholas
I'm referring to the primary impedance. I don't have the numbers in front of me but I'm pretty sure the plate resistance of two 6V6's in parallel is different from one 6L6. I think I remember that it would be about a 30% mismatch.
I guess it boils down to: a) Do you like the sound? b) Do the tubes redplate? c) Are you willing to live with tubes wearing out earlier due to the mismatch?
I know what my answer would be. I've always tried to keep things on the primary side of the tranny pretty close to how the amp was designed.
The secondary is different. I've pulled two tubes on several four-tube amps I've used to make them "half-power". Mostly Twin Reverbs. I used this little phrase to help me remember how to correctly match up things: Half the tubes/Twice the impedance. So, (in a TR, which likes to see a 4 ohm load) 2 tubes = 8 ohm speaker load.
I've pulled two tubes on several four-tube amps I've used to make them "half-power". Mostly Twin Reverbs. I used this little phrase to help me remember how to correctly match up things: Half the tubes/Twice the impedance. So, (in a TR, which likes to see a 4 ohm load) 2 tubes = 8 ohm speaker load.
Your right. I miss spoke on that.
My point was that I am removing a pair of 6v's in parallel and replacing with a single 6L. IMO it is close enough to not worry in a cathode biased design.
A) it sounds incredible
B) no red plate
C) I don't think there is a mismatch of value to be concerned
Give it a whirl bro. It really sounds incredible. Quite a different amp for sure set up this way. Been at it all day at full clean volume. The only thing smoking are my ears... He he.
From Dr. Z himself to me, "you can drop 5881's in directly with no bias needed" Same as the Z-lux. Doc says it makes it sound like a mini twin to a degree. No mention of 6L6 tubes as they are not the same thing.
I saw a post where Z said you could drop em in a Z-lux no bias needed. He liked em'. I inquired as to would that work in a JAZ. I didn;t get any responses from the Z-lux post so I asked Z himself. As always he was there with the answer. So now since the Z-lux and the JAZ are the same I believe the JAZ can use 6V6, and now 5881's.
here is the answer.
Jul 25, 2016 14:17:55 GMT -4 drz said:
Yes the power voltage , bias resistors, and half power circuit is identical in the JAZ 20/40 and the Z -Lux.
So a Medium range , matched Quad of TungSol RI 5881's will drop in and work fine in a JAZ 20/40.
GuitarZ: I'm okay with the AARP letters. You're still living and breathing? What the heck am I to think when a funeral home sends me a free consultation offer? Ouch!
Jun 21, 2019 15:41:26 GMT -7
The Bad Poodle: I bought airline tickets online... now every few days i get emails that read "Your trip is almost here but aren't you forgetting something?? You don't have trip insurance!" and i'm thinking..."is there something i should know about your plane maintenance?"
Jun 21, 2019 16:02:32 GMT -7
GuitarZ: Reminds me of buying my Honda. When they tried to sell me the maintenance package, I said "Is your car not reliable?" Long story short my wife teamed up with the sales lady to buy the maint package. Never again!
Jun 21, 2019 16:16:53 GMT -7
roscoenyc: I have never in my life experienced tube rattle. That said, I've only been playing electric guitar for 49 years.
Aug 2, 2019 6:39:37 GMT -7
The Bad Poodle: What cures tube SHAKE and tube RATTLE? A tube ROLL?
Aug 11, 2019 17:22:10 GMT -7
capofirstfret: I've experienced tube rattle in two different amps that I've had. In both cases I bought the rubber rings from Eurotubes and it fixed it for me.
Aug 14, 2019 12:57:35 GMT -7
roscoenyc: Guitar amps on carpet make me sad.
Aug 16, 2019 5:23:37 GMT -7
The Bad Poodle: Sunshine on my shoulders makes me happy, Sunshine in my eyes can make me cry
Aug 16, 2019 14:12:09 GMT -7
GuitarZ: Thank you for neighbors with gardens. Fresh veggies and no hassle!
Aug 17, 2019 18:12:08 GMT -7
"Z" Steve: Sunshine Superman? Call any vegetable - call it by name!
Aug 19, 2019 11:53:09 GMT -7
GuitarZ: Idiot! I wanted to put a little air on my Zoom H1's circuit board to clear out any residual Deoxit from spraying the input connector. Guess which can I picked up to spray. Yup! Not the air can.
Aug 23, 2019 10:07:40 GMT -7
premiumplus (Dave): I was wondering why a Frisbee gets larger the closer it gets. Then it hit me.
Aug 24, 2019 6:14:55 GMT -7
easyed: Call any vegetable - call it by name! And the chances are good, that the vegetable will respond to you. F-Zappa.
Oct 1, 2019 19:49:10 GMT -7
The Bad Poodle: rutabay-ayga... rutabay-ayga
Oct 2, 2019 12:33:25 GMT -7
"Z" Steve: I'm losing status at the high school - I used to think that is was MY school
Oct 8, 2019 15:01:34 GMT -7
The Bad Poodle: A bunch of pom-pom girls, Looked down their nose at me. They had painted tons of posters, I had painted three. I hear the secret whispers Everywhere I go, My school spirit is at an All time low...
Oct 8, 2019 17:11:32 GMT -7
"Z" Steve: Oh Look! My hair is getting good in the back!
Oct 10, 2019 20:48:05 GMT -7