[tdinut]

I've been thinking (dangerous, I know) about some of the other Music-Reference amps. My RM-200T has exceeded my expectations by a long shot and constantly puts a smile on my face. I plan on getting the additional bias modification done to it so I can feel more comfortable about tube biasing. Now this has me thinking about what else Roger has designed and makes. There's not much info on the website about the other amps available, like the RM-6 OTL. Is there a more complete list of the current amps Roger makes and a short description of their characteristics. Thanks!

[Ericus Rex]

The website definitely needs to be updated to include his new OTLs.  Other than what you'll find in this circle I haven't seen much info on Roger's other designs except the RM10 (and of course the long discontinued RM9).

[nnck]

tdinut-

What was the 'additional bias modification' you were considering having done on the RM-200T? I havent been able to find any info online about a mod for this.

[rbwalt]

the bias range for the RM200T should be more than adequate. the best tube and i think the only tubes for that amp are KT88's and maybe the 120's. running normal bias is all one needs. the gains at running higher bias are offset by lower tube life. if you do decide to make changes then consulate  with roger on it and let him make the changes and only him.

good luck.

[tdinut]

tdinut-

What was the 'additional bias modification' you were considering having done on the RM-200T? I havent been able to find any info online about a mod for this.

They can add a bias balance for each channel which allows you to easily balance out the idle current and adjust the bias up and down with the standard bias control. It's really not necessary and just adds complication. I was advised not to even worry about it. Obviously the amp is spectacular without the mod.

[nnck]

Thanks guys. I'm sure the amp works and sounds excellent as is. However, I was compelled to ask since Im curious to know about any and all options that might be available for the amp. In my communications with the folks at Music Reference, I was told there is no auto-bias option available for this amp, which is what I thought you were referring to.

Also, they first told me the amp could us KT-88, KT-120, 6550, EL34 and others. When I asked further questions about trying EL34, they then told me they didn't really recommend it. Apparently they might work but its not the best choice   Maybe someone here could explain why?

They said KT88 and KT120 are both excellent choices. I didn't question further on 6550 yet since I am not as familiar with those tubes.

[rbwalt]

the RM200 was built to drive difficult loads. the EL34's are limited in their power output. thus the reason for KT88's and such. stay with what roger recommends for tubes. i just bought some NOS Siemens EL34's from him for my RM9SE. the amp came with them but they were getting long in the tooth. tried JJ E34L's but they were not reliable. also tried EL34 Valve Arts but went back to what roger recommended and he was spot on.

might want to experiment with different power cords.did that on my amp.

good luck.

let us know how you are making out.

[nnck]

Right. I do understand the RM200 was mainly built to drive difficult loads. But in my case, I am using Daedalus DA1.1 speakers. So in theory, these should NOT be too difficult of a load (sensitivity is 94 or 95db, however, they do have many drivers).

Regardless of Daedalus not being too difficult of a load, I wanted to try out a RM200II rather than something like an RM10, since it looked like I would have several different tube types available for me to try. I was expecting that EL34 tubes might still work fine for these speakers, although I havent heard of anyone trying them first-hand with Daedalus.

So I guess I am still curious if Music Reference are not recommending the EL34 in the RM200 only because of the more limited power (which in my case, might still be fine) or for some other reason.

I think 6550 tubes might still be okay in the RM200 as well. So I am also wondering if users have any comments on those and how they all might compare to one another:   KT88 vs KT120 vs 6550 vs EL34 (if the latter are even an option).

[corndog71]

6550's are ok for KT88 amps. 

[nnck]

6550's are ok for KT88 amps. 

I've heard the same. Can anyone comment on the difference in sound between KT88 vs 6550 or KT88 vs KT120? Especially in this amp, but maybe some generalizations may help as well.

Also still want to clear up whether Music Reference does not recommend EL34 in this amp simply because the power output will be diminished or for some other reason.

[rbwalt]

first off the amp only uses 2 output tubes per channel. you can not get the power out of just two EL34's per side. that is the reason why the 88's  are used. the 88's have a tendency for a bigger bottom end. also they tend to push the mids. i would think the 120's are going to be the same. i would stay away from 6550's. they tend to a sizzle sound to them. the best is going to be the 88's for it. you did not mention what kind of power cord you are using. that is going to play into it also. though some will say no.

it all comes down to what is important to you and how you like your sound. remember it is part of a chain. a change here or there might make a big difference, small one or none at all that you are able to hear.

luck!!!

[Roger A. Modjeski]

The amp will run with EL-34's just fine up to about 80 watts. See if you like it. You should however lower the bias to 25 MV as the tube has a lower dissipation rating than the others. Let us know how you like it. Also if you don't need much power try the lower taps. Everyone should try the lower taps, that's what they are for. Won't  hurt anything and you will get better damping.

[nnck]

Thanks Roger. I do hope to give the EL34s a try sometime in this amp, and will let you know what I think. I am expecting that replacing the KT88s with EL34s might change the sound from this amp more so than replacing with KT120s. This is an assumption, however. The descriptions I often read of KT88 and KT120 are somewhat more similar, and the EL34 seem to be regarded in a different way (more of  traditional 'tube' sound?). But if anyone has tried any of these other tubes in this amp I'd love to hear your experiences.

I am actually hoping that the different tube types offer some variation in sound. Not that there is anything wrong with the sound from this amp using KT88s. Just more differences in sound = more choices to play around and experiment with.

FWIW- I hooked the Daedalus DA1.1 speakers up to the 4 ohm tap first thing (already had seen your comments about this). It's actually a 6 ohm speaker I believe. Maybe I should try an even lower tap? 4 ohm is the only tap I've tried thus far.

[Roger A. Modjeski]

Try all the taps. Moving taps generally makes more difference than rolling tubes and its much easier. Keep in mind when you roll tubes you have to re-adjust the bias and you take chances with breaking things, blowing fuses and other frustrations. It's my opinion that people over-state the differences in tubes.

[nnck]

Try all the taps. Moving taps generally makes more difference than rolling tubes and its much easier. Keep in mind when you roll tubes you have to re-adjust the bias and you take chances with breaking things, blowing fuses and other frustrations. It's my opinion that people over-state the differences in tubes.

Thanks for all the info you've provided in the various threads these past few days Roger. I feel like I am learning more about this amp through your explanations.

Based on your suggestion, I switched from the 4ohm to the 1ohm taps this morning. I wasn't doing what I would all 'critical listening' yet, but what I heard was sounding excellent. I had it playing rather loudly as well, and did not notice anything distorted about the sound. The bass impact was sounding very impressive. I had the impression I had to turn the volume knob up a bit higher to achieve the same level, but I could be wrong.

Someday I'm sure I'll try a set of KT120s or EL34s out of curiosity, but for now I will probably enjoy the amp as is, or experimenting with the taps a bit more.