Bi amp and bias issue

With two different amps you need an electronic crossover. That separates the bands and allows adjustment of the volume for each amp. Not sure about your bias meter oscillation issue. Maybe try the other speaker taps on the amp. The crossover might also help by stripping and separating the frequency bands, not sure but worth a try, otherwise you'll need a different amp.  

+1 for electronic crossover. This is an absolute necessity when you bi-amp. Also tube amps don't like low impedances, I would run in triode mode. I bet the mid and tweeter impedance is dropping below 4 ohms.

Thank you for suggestion of active crossover I’ve  been researching trying to find one that has single ended inputs because my preamp only has single ended out but cant find anything under 1k besides the marchand .

There are a TON of active single ended crossovers. Do you want rca or phone plugs? Balanced or unbalanced? Analog or digital? 2-way, 3-way, 4-way?

Rca analog please thank you I was trying to find one reasonably priced under 1k with goos sound quality.

     I helped a friend of mine bi-amp his (recently purchased, used of course) EP CS2's, with one of these.  
     If one is somewhat computer literate, it's a cakewalk:  https://www.minidsp.com/products/minidsp-in-a-box/minidsp-2x4-hd   
     Wouldn't call it, "high-end", but it isn't bad, at all.    Perhaps with a better power supply...  
     There are a few apps, that can be added, allowing for such things as Automatic room correction, parametic EQ, etc.  
     I've been using a majorly upgraded, TacT RCS 2.2Xaaa, for a number of years, but: Tact is out of business, so support has to be through online blog, etc.  
     To me: it's an absolute necessity, to bi-amp actively, if using dissimilar (output power, sensitivity, etc) amps.    I used and really enjoyed my modded Dahlquist DQ-LP1, for a few decades, before finding the Tact.  
                                    Good luck, have fun, and enjoy the journey!

I tried using stock crossover using krell for bass and rogue for mid and tweeter and it works but only when i use triode mode on rogue if i switch to ultra linear when I try to bias the meter on rogue oscillates.

If this diagram is correct, there is on the mid/hf panel a .387H choke across the amps speaker terminals, it will seem like a nasty load at certain frequencies, more so in UL than Triode mode https://ibb.co/h7Rw0N2

I would try for a couple of dollars, a big 20-50w 1ohm resistor in series between the Rouge amps + terminal and the + input to the mid tweeter panel terminal, (at the speaker end) this should cure the problem. (may lower the mid/hi level just a touch)
https://www.newark.com/vishay/rh0501r000fe02/wirewound-resistor-1-ohm-50w-1/dp/41K9144



Cheers George

Bi-amping through the factory passive crossovers typically yields minimal improvements. Identical amps must be used with this configuration.

To correctly use active crossovers the factory passive crossovers must be bypassed. Furthermore, whatever other filters existing in the factory passive crossovers (baffle step, zobel, etc.) must be duplicated in the active crossover. The type of crossover filters (first order, second order, Butterworth, Linkwitz-Riley, etc.) should be duplicated or the response and phase can be altered in a very negative way.

While many believe using active crossovers have many benefits (and they do) just swapping out the factory passive crossovers for active crossovers does not guaranty better results. You might get lucky. Building active crossovers that are correct for the speakers and drivers will.

Duplicating the passive Magnepan crossovers in your active crossovers is the right way otherwise you are designing your own speakers. Digital crossovers (DSP) work great as long as you know what you are doing. Maybe a Magnepan person can share the 3.5r crossover specs so you know what needs to be duplicated.

Designing and manufacturing speaker system, we have tried passive, analog active and digital (DSP) active on the same speakers. They all have their pros and cons. Digital crossovers usually win, as long as you use a good quality DSP.

Read as much as you can about active crossovers before you make your decision. There is much written on the subject.

https://www.marchandelec.com/xm9-electronic-crossover.html

https://www.xkitz.com/

For bass ok use active xovers, but mids and highs to me are always more natural sounding using good quality passive xovers no matter what active xover were used.

So as I said in my last post just use the 20w 1ohm resistor and your triode mode tube should then be stable

Cheers George

I don't agree George, keep all resistances to a minimum. I use analog active crossovers all the way, you should try them. Only wire between the voice coils and the amplifier outputs! I'm using TDM 24CX-4 for my tri-amp system and Phase Linear X20 for my bi-amp system. I prefer to stay with analog as I like the sound. I don't like mixing digital and analog unless I must. Digital crossovers are much more versatile and usually less expensive, but to be honest I have not tried them... I vote for a good analog electronic crossover. I know Ashley made some with RCA's, but they are super rare now, just like the Phase Linear X20's. I use gold plated TS phone to RCA adapters because I can't find silver TS phone adapters... Any suggestions?

I don’t agree George, keep all resistances to a minimum.

That’s your prerogative,

Yes (min resistance) that is normally the way for full range, and when the bass is involved, for better damping factor.
But because it’s just the mids and treble, it won’t make any difference, and will be beneficial to the stability of the amp.
As the amp will be a little less stable in UL mode compared to Triode, and goes into semi oscillation when it sees that inductor across it’s output and certain frequencies. And the 50w 1ohm series resistor should cure that without any side effects.
beep23 Planers and ESL’s are known for their naturalness through the mids and highs, don’t "sterilize" them up with using active electronic xovers, keep the passive to feed them.

Cheers George

Yes I know it is. Your opinion George, everyone is entitled to theirs. If your amps can't handle the current, change amps. Add a resistor if needed, but adding resistance will be detrimental to the high frequency response. I like accuracy, that's why I use solid silver wire or silver plated copper wire for most applications when I can afford it.

You can use a passive line level crossover with attenuators with some speakers, not sure about the magnepans.

Add a resistor if needed, but adding resistance will be detrimental to the high frequency response. I like accuracy

Sorry, no it won't.Cheers George

Here is why, for the 1ohm resistor to create even the slightest HF filter in the highs on these Maggies. The Maggie’s panel themselves would have to have a parallel capacitance from pos to ground as seen by the 1ohm resistor of 10uF or higher which no amp could handle.

Like I said beep23, just use the $6.00 50watt 1ohm resistor to make the Rogue stable when in UL mode.
https://www.newark.com/vishay/rh0501r000fe02/wirewound-resistor-1-ohm-50w-1/dp/41K9144

https://ibb.co/HT8w2jz

Cheers George

Thank you all for your suggestions I went ahead and purchase the 50w1ohm resistor because they are cheap and wont hurt to try it out. Georgehifi you mentioned to install these “Rouge amps + terminal and the + input to the mid tweeter panel terminal” is that on the external crossover or bypass external crossover and directly on the magnepan mid tweeter input and if it goes directly on the mid and tweeter does that mean the mid and tweeter will not have a high pass filter