Will Mullard EL-34 bias correct in Quickrod 100

[historic]

I have a quartet of 4 matched , Mullard reissue El-34 power tubes that were included with my 2019 Splawn Quickrod 100.

There are currently JJ KT-77’s in there now.I have been reading that these amps barely have any adjustability in the Bias adjustment pot? And some people cant get the Bias Hot enough?

These Mullard Reissue’s came from Vivatubes.com

Does anyone know if these will be ok? As i mentioned i read that some people with Mullard EL-34’s could only get them too 25-29 MA

[tjdjr1]

All you can do is try it. If the mA range you want is either not high or low enough, you will have to change a resistor. Scott is a great source and can advise you what value to change it too and what R number. I believe it is R26.. I found it once here searching for limited bias adjustment.. good luck

[gtrjunior]

Yes, I depends what year your amp is. At some point Scott replaced the above mentioned resistor with one that allows greater adjustment.
My QR is a 2016 model and has the newer resistor factory installed.

[Edward]

I have never heard of a range issue with biasing between 34's and 77's. I have a 2007 QR and have swapped between Mullard EL34's and JJ KT77's more than once. I go back and fourth between what I like better. I have never done the biasing myself, I have an amp tech I use, but never has an issue been raised with it being a problem. I know there is a resistor change needed to got the KT88's but not KT77's. Hope this helps.

[gtrjunior]

Feb 2, 2022 11:06:20 GMT -5 Edward said:

I have never heard of a range issue with biasing between 34's and 77's. I have a 2007 QR and have swapped between Mullard EL34's and JJ KT77's more than once. I go back and fourth between what I like better. I have never done the biasing myself, I have an amp tech I use, but never has an issue been raised with it being a problem. I know there is a resistor change needed to got the KT88's but not KT77's. Hope this helps.

He’s asking about the bias trim pot having enough travel distance to make bias adjustments, not necessarily about switching between 34’s and 77’s.
There is a resistor that controls the amount of usable travel distance the trim pot has.
Since the op’s amp is a 2019 model I’d guess that he has the particular resistor that Scott switched to in order to increase the trim pot’s usable travel/ adjustment.

[splawndude]

Not sure it that was my comment about the Mullard tubes but mine drifted WAY down and I could not get them up in the 34ma range, at least not very easily or that I remember. If changing the variable resistor is an option for you and you have very good soldering skills that may be a thing but it would be easier just to buy new tubes. I've never heard of that dealer but if you ask for a matched quad from someone like Dougs tubes, or Eurotubes or Tube Depot they should come matches within .05 - .1 mA.

[historic]

Hi guys and thank you for all the answers…yes i must have the newer resistor, because i have miles of travel either way..first i installed my euro tubes ET Pro one bias probe , between the KT-77’s and the socket, and was reading 36MA…then i installed my Mullard EL-34’s and got a reading of 33MA, so i put the KT-77’s back in and took the bias down to 32MA per Scotts recommendation..soo the KT-77’s were running hotter than the EL-34’s…weird thing is that, i ran the amp for about a week or so with the KT-77’s, and yesturday i decided to drop in my El-34’s again with the Bias probe, and funny thing is that, this time they were reading at around 34MA.. i did test a different socket this time though but? Yeah maby its because im running the amp with 2 tubes, and looking at the back of the amp, going towards the right…i origionally adjusted the bias measuring the 3rd socket in, and this time i tested the 2nd socket in towards the right.also using a balanced set of 4 tubes they all have 1MV or so difference

[gtrjunior]

You may already be aware but I’m case you’re not, the outside 2 tubes work together and the inside 2 tubes work together. So when measuring bias be sure you check them in that fashion. Measure maybe the first tube to test that set and then test tube 2 to test that set.
Also, the bias is never 100% perfect, we just try to get it as close As possible. So if you’re off a couple of mA, I wouldn’t sweat it. You’re still in spec.

[historic]

Feb 9, 2022 10:15:14 GMT -5 gtrjunior said:

You may already be aware but I’m case you’re not, the outside 2 tubes work together and the inside 2 tubes work together. So when measuring bias be sure you check them in that fashion. Measure maybe the first tube to test that set and then test tube 2 to test that set.
Also, the bias is never 100% perfect, we just try to get it as close As possible. So if you’re off a couple of mA, I wouldn’t sweat it. You’re still in spec.

Ok, soo , i am running 2 power tubes, as i have the amp set to half power at 50watts , and removed the 2 outside tubes per scotts request, as to save them from unnecessary use.Yes i am aware the tubes work in pairs.Thank you for the info, as well.

So i biased the KT-77’s at 32MA as thats what Scott told me to do, and simply swapping to the Mullard EL-34’s with the bias set for the KT-77’s gave me a reading of 34MA again Scott said that this was too high and to keep the bias at 32MA, however he did say that im ok at 34-36MA but its hard on the tubes.

Now, getting too the KT-77 VS EL-34 thing, i read that power tubes have no effect on the sound, so then what would have been the purpose of the original owner installing the KT-77 in my amp? Will the EL-34 give me more Dirt?

[splawndude]

They will have different bias readings because they draw different current. Like GTR said, don't sweat a few mA here or there. The amp/tubes will experience bias drift anyway. I do trust whatever Scott says in general and he knows his amps better than anyone. For all I know, he know your specific amp very well.
mo
That said, all electronic components, even if exactly the same, vary in spec to some degree. Plus you have the sum of all the parts. I try to bias my amp to tone and not to numbers. But swapping EL34s to KT77s and back and forth will not have the same bias reading. As a matter of fact, I'd be shocked if they did.

Lastly, some claim they can hear no difference and some say it makes a world of difference. I'm in the camp that is in the middle and I can hear subtle differences in power tubes. I find my EL34 II's to be the best so far. PDC turned me onto those. I also bought some EL34Ls for the fun of it but have not tried those. I'd like to try some KT77. KT77s are supposed to be in the middle of EL34s and 6L6s. So on paper, a KT77 would give you more low end. I wouldn't say EL34 provide more dirt per say, but they will have more mids so your ears may hear more dirt.

This is a decent thread on the topic and also has a lot of people that are smarter than me discussing the topic and some references to more material on this if you want it.

www.rig-talk.com/forum/threads/6l6gc-vs-el34-vs-kt77-tubes-educate-me-please.223475/

Also, make sure you drop your ohms in half when running at half power like that.

[historic]

Awsome thank you for that info, yes Scott did recognize my Amp by serial Number,..he knew who he originally built it for, and everything.

Its a Blacked out 2019 QuickRod 100, Standard

No B+ or Mid Scoop, or new Old switch.As i was going to pay more for a vintage JCM-800, this thing has more than enough bells and whistles for me anyway, but the B+ thing would have been cool

[splawndude]

Running at half power will get you closer to the B+ options as it relates to sag. I think. Not the same though.

[historic]

Really? So these amps come stock with a half power switch as it is.If you get the fully loaded Quickrod, then it includes the “New/Old” switch, a Mid scoop switch, and an added switch in the back that says B+ ,and its supposed to make the transformer run at lower voltage i think, and gives more “SAG” or an different feel, Scott said..

So the half power switch is the same thing?

[splawndude]

Feb 10, 2022 22:42:48 GMT -5 historic said:

Really? So these amps come stock with a half power switch as it is.If you get the fully loaded Quickrod, then it includes the “New/Old” switch, a Mid scoop switch, and an added switch in the back that says B+ ,and its supposed to make the transformer run at lower voltage i think, and gives more “SAG” or an different feel, Scott said..

So the half power switch is the same thing?

I think I mispoke. Not sure why I was thinking that. I edited my post.

I may have been thinking of the Competition and this thread.

splawnfans.proboards.com/thread/9647

[gtrjunior]

Feb 10, 2022 22:42:48 GMT -5 historic said:

Really? So these amps come stock with a half power switch as it is.If you get the fully loaded Quickrod, then it includes the “New/Old” switch, a Mid scoop switch, and an added switch in the back that says B+ ,and its supposed to make the transformer run at lower voltage i think, and gives more “SAG” or an different feel, Scott said..

So the half power switch is the same thing?

Not quite the same thing per se. Sag happens when the amp is starved for power. This is what Eddie did with the variac. So you aren’t necessarily starving the amp at half power but there will be a slight change is now the amp responds etc.

Scott has said that the 50w QR runs the same voltage as the B+ switched engaged by default.

I have a 2016 fully loaded QR. when I bias the amp I can toggle the B+ switch and see the voltage drop and the bias rise when I have the probe attached as a result.