EL34 vs. 6L6GC vs. KT77 vs. 6CA7

[Simon Says]

I want to tuberoll. :iamconfused:

I am familiar with tube-rolling from high-fi tube amps, but my understanding with PRS guitar amps is that in order to swap something else in, one has to bias it to 30 (mV?), correct? So if one tube is working at 75% of its capacity (when biased at 30) and another is working at 90%, is it correct that the first one will give me more headroom (I.E. I can turn up the gain higher before I get distortion)? Or is that all in the preamp tubes?

I'm more of an EL84 guy, I should probably just get a Vox (or a Vox clone), neh? None of these will "sound" like an EL84, will they?

I believe I said that here somewhere recently but just FYI proper biasing involves more than just recommended mA adjustment. You need to take the plate voltage and calculate it with aimed plate dissipation range. Recommended 70% plate dissipation is only a guideline, high gain amps likes cold bias while vintage voiced talks with hotter bias better. Same time my Boogie Fillmore (vintage voiced) is set to 55% dissipation at the factory and it sounds awesome... i believe that PRS advised mA settings are rather on the cold side too, just a guess but I would expect that for the sake of safety / valve lifespan.

Get yourself a Eurotubes Bias meter which measures both mA range and the plate voltage and use online calculator with your choice of vaccum valve type and bias it the proper way. Then use your ear from there keeping the range in safe brackets. I would disrecommand going hotter than 70-75% plate dissipation personally

 

[boardn10]

Yeah, I mean there’s only a single set screw to adjust hotter or colder. So a good matched set, each should read about the same(25-30).

I set Tham at 32 each. I like a bit hotter.
I got confused because some of my amps measure in mV and some mA

Man, the 6CA7 tubes are amazing in this amp. Wow.

 

[boardn10]

I am surprised PRS didn't provide an external bias pot to adjust the bias. It must be on thr inside of the amp. Pain in the butt. Since they have the bias points outside the amp, not sucks you have to open up the amp and get to the board, to bias.

 

[boardn10]

Yeah, I mean there’s only a single set screw to adjust hotter or colder. So a good matched set, each should read about the same(25-30).

My tech adjusted this for me but I've done my own amps for 30 years. It happened to be at his house since he wanted to try it while he worked on a guitar. He said bias adjustment is easy. That said, is it that hole by the far left two power tubes? It's has the bias points for each tube and I just see that one opening going down to the board, so I assume that an Allen wrench set screw.
Its hard to see down in there without removing the head shell.

 

[Simon Says]

My tech adjusted this for me but I've done my own amps for 30 years. It happened to be at his house since he wanted to try it while he worked on a guitar. He said bias adjustment is easy. That said, is it that hole by the far left two power tubes? It's has the bias points for each tube and I just see that one opening going down to the board, so I assume that an Allen wrench set screw.
Its hard to see down in there without removing the head shell.

Turning a pot or trimmer is easy, setting bias is not. Read my post above

 

[Dusty Chalk]

Hi, all, just wanted to update this thread since it has been raised from the dead:

Do NOT roll tubes with Groove Tubes, I had some really bad experiences with them.

Do NOT roll tubes with unknown quantities, unless you know what you're doing with a tube tester and can faithfully determine what the tubes are capable of, in terms of specs. See Simon Says' post, above.

DO stick with known, new tubes, of the same type as is stock/factory. (I don't even remember what those are.) There's absolutely nothing wrong with non-NOS tubes.

Also, hello all! I'm not dead (yet). But I am no longer a tube-sniffer. I still prefer tube amps, but don't roll tubes no mo'.

 

[boardn10]

I tried JJ 6L6 and they sound as good as stock Ruby tubes.
JJ 6CA7 tubes sound awesome.

 

[Deleted member 5962]

Also, hello all! I'm not dead (yet). But I am no longer a tube-sniffer.

Yo, DC!

 

[Boogie]

Hey Dusty! Sounds like you über-glowed some glass! Personally, I’ve never been an experimenter with the power tubes, but the preamp has been my laboratory. The esoteric differences in V1, V2, and V3 (sometimes PI V4) tube changes sparked a decade-long experiment to make a Boogie Mark into something it’s not, relatively successfully. Rolling preamp tubes in my Twin II was about finding warmth and classic Twin in a revised circuit. The Super Dallas was about maximizing the Marshall vibe in a preamp very much not Marshall. Having specific goals was important.

Power tube-wise, the Boogie has both EL34s and 6L6s, the Fender is all 6L6s, and the SuperD is all EL34s (the back label says I can swap, but never been compelled to risk it). Once I found a good reliable brand that took the rigors of transport and gigging, I stuck with them. Never felt the need to switch things around, until the =C= stuff disappeared, which sucked. MB does a good job sorting and selecting their tubes, so I used their stuff for the power stage in all of my amps for a bunch of years.

Holy random thoughts, Batman!

The good result for me is having a handful of great old RCA, Mullard, and RFT 12ax7s that will last me a lifetime of rolling. If I get the itch, it’s a simple pop and plug.

 

[Dusty Chalk]

Hey Dusty! Sounds like you über-glowed some glass!

More like underglowed -- there were one particular Groove Tubes set that weren't even what they said they were, and required a hotter power supply, so the electrons weren't spanning the gap.

 

[Deleted member 5962]

so the electrons weren't spanning the gap.

Yeah, that can happen as we get older. So I'm told...