|
Post by hikari on Sept 19, 2022 20:51:58 GMT -7
I have a 2014 Maz JR reverb 2x10 combo. Bought used, had for about a year or so. I have nothing bad to say about this amp except for it's appetite for power tubes.
Sovtek EL84's that came with the amp (used) lasted about 3 months. Finally blew the fuse when taking off standby.
Switched to a set of used 60s Holland Amparex el84s from my Vox. Got about 3 months out of those till bad sounds started happening and I lost power.
Put in a set of NOS Team/Polam el84. Sounded great for about a month until one started redplating and the amp started misbehaving.
Have a set of 6P14p in now that seem to be doing alright. I dont like the sound as much but they seem to be hanging in there. I had a previous set of 6p14p that redplated. I also have tried a set of JJ el84s that lasted longer than a month but I didnt like the sound of those.
I've popped open the chassis. No burnt resistors or anything, nothing visually wrong. I just cant seem to get any life out of the power tubes. 3-6 months seems kinda lame and expensive especially when using some Euro NOS tubes. Ive changed to rectifier as well, same issues remain with power tubes. Ive also swapped every preamp tube just to try to isolate the problem.
Is this normal? This is a cathode bias amp. No bias adjustment. The tubes were all matched pair. I play maybe an hour or two a day. Master is often wide open.
|
|
|
Post by DRZ on Sept 19, 2022 23:56:35 GMT -7
What is your wall voltage feeding the amp ?
|
|
|
Post by John on Sept 20, 2022 5:04:21 GMT -7
In addition to Doc's question....if you have the ability, perhaps it would be worth shipping the amp chassis to the factory for a diagnostic overhaul?
|
|
|
Post by hikari on Sept 20, 2022 8:33:49 GMT -7
What is your wall voltage feeding the amp ? Wall voltage is 119V.
|
|
|
Post by hikari on Sept 20, 2022 12:27:34 GMT -7
I guess I need to take a bias measurement as the next step. I dont have a bias probe socket for el84s but I'll pick one up.
Anything else I should look out for? I am experienced working on amps...I am not a tech but I've built some amps. I gotta say, the build quality inside this amp is off the charts. Like, really nice. Light years ahead of anything from the 60s except maybe a Hiwatt.
|
|
|
Post by DRZ on Sept 20, 2022 12:49:47 GMT -7
I guess I need to take a bias measurement as the next step. I dont have a bias probe socket for el84s but I'll pick one up. Anything else I should look out for? I am experienced working on amps...I am not a tech but I've built some amps. I gotta say, the build quality inside this amp is off the charts. Like, really nice. Light years ahead of anything from the 60s except maybe a Hiwatt. Bias check would be good. Wall voltage seems correct. Measure the bias resistor should be 150 Ohm 10 watt. And bi-pass cap should be 25uF/50 V across it. Make sure the 2.2K 5 watt dropping resistor that feed the screen voltage to the EL 84's is there and the right value. Also the 10" speakers if they are the stock Z 10's are 16 ohm each wired in parallel to 8 ohm , if they are plugged into the 4 ohm speaker tap which is the typical 2 X10 load, you would be mismatching the OT and causing it to try and put out more power then it should and over heat. I'll say the standard EH El 84's don't last long in a MAZ 18. NOS EL 84's well that can be a crap shoot as to their age and prior usage. JJ EL 84's should last a good year with daily use before they start to weaken. And not sure what you don't like about the 6n14n's but they will last years in the MAZ 18 . Z
|
|
|
Post by hikari on Sept 20, 2022 14:06:34 GMT -7
Thanks Doc. Will check that stuff. I am running the 2x10 Z speakers (16 ohm each) into the 8 ohm tap. So should be good there.
I dont mind the 6p14p...it's just not my favorite. I have the "K" version in it now...maybe other versions sound better. But it's running fine with them now.
Thanks for the help though.
|
|
|
Post by "Z" Steve on Sept 20, 2022 15:10:39 GMT -7
Thanks Doc. Will check that stuff. I am running the 2x10 Z speakers (16 ohm each) into the 8 ohm tap. So should be good there. I dont mind the 6p14p...it's just not my favorite. I have the "K" version in it now...maybe other versions sound better. But it's running fine with them now. Thanks for the help though. If I may add one more thing to this, thank you for being courteous and honest about your issue on your used Maz 18. Some people get kind of pissy (and I'm being kind here) if they run into an issue with a used amp and proceed to bad mouth their purchase along with the help and advice they are given. Asking for help as you did will always get an informed and concerned answer from the owner/builder/Doctor!
|
|
|
Post by helmi on Sept 20, 2022 16:33:24 GMT -7
Thanks Doc. Will check that stuff. I am running the 2x10 Z speakers (16 ohm each) into the 8 ohm tap. So should be good there. I dont mind the 6p14p...it's just not my favorite. I have the "K" version in it now...maybe other versions sound better. But it's running fine with them now. Thanks for the help though. If I may add one more thing to this, thank you for being courteous and honest about your issue on your used Maz 18. Some people get kind of pissy (and I'm being kind here) if they run into an issue with a used amp and proceed to bad mouth their purchase along with the help and advice they are given. Asking for help as you did will always get an informed and concerned answer from the owner/builder/Doctor! Well said Mr. Steve.
|
|
|
Post by hikari on Sept 20, 2022 21:21:05 GMT -7
I agree. And having some experience inside other amps and building my own I can tell you that there are not a lot of build quality issues or design problems in this amp. It’s not a bad product…in fact it’s built really well.
The problem is likely the tubes.
|
|
|
Post by hikari on Sept 21, 2022 19:43:14 GMT -7
So CURIOUS RESULTS with the bias probe.
With 6p14p tubes (supposedly matched) I am getting 29ma on one tube and 49ma on the other. 29ma seems reasonable. 49ma does not. And that's the tube position that is always redplating.
Any ideas where to look? Doc, help me out.
|
|
|
Post by DRZ on Sept 22, 2022 3:59:25 GMT -7
Check for DC leakage on the .01 uF driver cap on the board that feeds that tube. Also verify if all voltages on the two sockets are the same , Plate, Screen, and Cathode bias. Check the Grid load resistor 220K for that tube, and the grid stopper resistor on the socket. Swap tube positions, high reading stay with the position or does it follow the tube swap.
|
|
|
Post by adam on Sept 22, 2022 4:52:38 GMT -7
I'm always blown away by the company when I see this stuff.
|
|
|
Post by purpletele on Sept 22, 2022 9:21:29 GMT -7
I'm always blown away by the company when I see this stuff. We're all a bunch of geeks that loves this stuff, especially solving unique issues. Pretty cool community!
|
|
|
Post by hikari on Sept 22, 2022 12:09:32 GMT -7
TUBE FIASCO UPDATE:
Well, I swapped the tubes and the tube with the high bias (49ma) followed the position of the tube, not the socket.
So it appears the problem WAS THE TUBES. I have a "supposedly" matched quad of 6p14p...the values are written on the tubes as 40ma. But they are as far off as 20ma from each other. I did find a pair though which are sitting at 29 and 33ma in the amp. So that should be good.
So, non of this is the good doctor's fault. Seems I have a bunch of NOS that are not a good match.
|
|
|
Post by heynewguy (Ol’ Bill) on Sept 22, 2022 13:30:01 GMT -7
The 6n14n tubes sound wonderful in my Maz 18, Maz 8, Z Wreck and Z Wreck JR. As always YMMV. I hope you get it straightened out.
|
|
|
Post by adam on Sept 22, 2022 14:36:16 GMT -7
I'm always blown away by the company when I see this stuff. We're all a bunch of geeks that loves this stuff, especially solving unique issues. Pretty cool community! Yeah, lots of amp enthusiasts here that like to tinker with amps. Fun for me to read, but I'm just glad I can have a 20 year old Z that who knows what has been done to it, send it in, and have it be as good as new. A lot to be said for that too.
|
|
|
Post by hikari on Sept 22, 2022 17:35:45 GMT -7
For the curious:
I tested the set of "matched" Team/Polam that were redplating in this amp and both tested around 45ma in this circuit. So, they are matched but thats pretty hot...I can see why they didnt last long.
For those of you looking for education the Maz, like almost all cathode biased el-84 amps (Vox and the like) runs the tubes hot. Its not a flaw, it's just the way these amps work. If you choose a "hotter" tube you may not get much tube life out of it. Likely will sound glorious though. But if you have the option of buying "graded" tubes I'd choose something on the cool side.
I had been using tubes that "graded" on the hot side unknowingly. And some were not matched well which leads one tube to bias hotter than the other or can lead to a "bias hogging" situation. So you get runaway thermal energy which kills the tube.
The hard part is unless you are buying new tubes which come "graded" you dont really know what a tube is gonna bias up at until you get it.
The 6p14p can handle a little more heat...so it's a good choice for this amp. Unfortunately the ones I had were not matched well which lead to problems.
Now I have a pair of 6p14p in the amp that are matched well and bias up at 30 or so ma. It has not had problems so far.
Again, this is not an amp issue. If I had put these tubes in a Vox or other amp I would've likely had the same outcome.
|
|
|
Post by hikari on Sept 26, 2022 11:04:51 GMT -7
UPDATE:
I still seem to be having problems. Seems that the amp does not act up and replete unless its been on for a hour or so. Bias measures fine...just seems to occasionally run away and replete after playing for an hour or two. And it doesnt seem to be doing it with the bias probe attached.
I will open it up again but for now I am suspecting the tube sockets. Will retention and try again.
|
|
|
Post by purpletele on Sept 26, 2022 11:21:33 GMT -7
Bummer!
|
|
|
Post by hikari on Sept 27, 2022 20:32:08 GMT -7
Ok, another update:
So with the 6p14p in I measured pin voltages.
All was well except I was getting about 300-400mv and climbing on pin 2 of one el84. I shut it down after it reached a volt or so. This condition remained after I replaced the .01uf coupling cap and retensioned the tube socket. This is unusual, should be close to zero or a few mv as the cap should block the dc.
So I decided to swap tubes to a different set…and the dc condition on pin 2 went down to 20mv or so.
So I guess this would indicate the 6p14p I have are leaky.
Iam running a set of JJs now biased at 37 and 44ma and things seem to be going well so far. Cross your fingers.
|
|
|
Post by DRZ on Sept 28, 2022 0:52:53 GMT -7
What I call " Tube Roller Syndrome "....... And swapping tubes with uncertain known performance, can make you chase your tail .
|
|