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Other Stuff => Archived Manufacturer Circles => Music Reference => Topic started by: Roger A. Modjeski on 22 Aug 2014, 03:10 am

Title: Amplifier Bias
Post by: Roger A. Modjeski on 22 Aug 2014, 03:10 am
Here is a little quiz on bias.

You get to vote for as many options as you want.

The poll closing date is noted and results will be shown and discussed then.

In the meantime lets hear what people think about bias.
Title: Re: Amplifier Bias
Post by: bdp24 on 22 Aug 2014, 12:42 pm
Roger, this seems like a good place to ask about the recommended bias for KT120 tubes when used in the RM200 amp. In the RM200 manual, the recommended and maximum values for all the tubes that can be used in the amp are listed, for both Ram Labs tubes and those tested by others. The list was written, however, before the introduction of the 120 tube. Can you specify the recommended and maximum bias values for the KT120 tubes you offer when they are used in the RM200? 
Title: Re: Amplifier Bias
Post by: Roger A. Modjeski on 22 Aug 2014, 05:00 pm
Roger, this seems like a good place to ask about the recommended bias for KT120 tubes when used in the RM200 amp. In the RM200 manual, the recommended and maximum values for all the tubes that can be used in the amp are listed, for both Ram Labs tubes and those tested by others. The list was written, however, before the introduction of the 120 tube. Can you specify the recommended and maximum bias values for the KT120 tubes you offer when they are used in the RM200?

You can bias a KT-120 at a meter reading of 50-65 mV (50-65 mA idle current) as it has higher dissipation than a KT-88. Whether it sounds better there is up to you. I usually bias them at 40. Higher current does shorten life and run the amp hotter, though still much cooler than most amplifiers. I wonder if designers of high idle current amps bother to check if they are getting any advantage from high idle current or just assuming that it is better?

I am finding in my OTL amp that higher bias does not always result in lower distortion. One must be careful about what one assumes without checking it out.

Title: Re: Amplifier Bias
Post by: BobRex on 22 Aug 2014, 06:50 pm
Well, you really need a "none of the above" based on how you worded your selections. 

Having a newbie user setting a meter to "ma" is asking for trouble.  Using the "mv" range might peg the meter, depending upon the resistor measured.  The actual bias range is as much a function of the design of the output stage (since few people worry about the bias of small signal tubes), so the exact reading is never really exact. 

That should hint at my vote.
Title: Re: Amplifier Bias
Post by: Roger A. Modjeski on 23 Aug 2014, 12:06 am
Well, you really need a "none of the above" based on how you worded your selections. 

Having a newbie user setting a meter to "ma" is asking for trouble.  Using the "mv" range might peg the meter, depending upon the resistor measured.  The actual bias range is as much a function of the design of the output stage (since few people worry about the bias of small signal tubes), so the exact reading is never really exact. 

That should hint at my vote.
 

Ok,  I added none of the above however I think that invites a question. The question concerns traditional push-pull output stages.
Title: Re: Amplifier Bias
Post by: bdp24 on 23 Aug 2014, 10:24 am
You can bias a KT-120 at a meter reading of 50-65 mV (50-65 mA idle current) as it has higher dissipation than a KT-88. Whether it sounds better there is up to you. I usually bias them at 40. Higher current does shorten life and run the amp hotter, though still much cooler than most amplifiers. I wonder if designers of high idle current amps bother to check if they are getting any advantage from high idle current or just assuming that it is better?

I am finding in my OTL amp that higher bias does not always result in lower distortion. One must be careful about what one assumes without checking it out.

Follow-up question:

The instructions in the RM200 manual for setting the bias were (to quote the manual) "written for 4-ohm speaker tap use". If one has connected his speakers to the 8-ohm tap, I assume the bias is set off of those taps? If so, should the bias settings be different than those set off of the 4-ohm taps (I highly doubt it, but better to ask and be sure)?
Title: Re: Amplifier Bias
Post by: Roger A. Modjeski on 25 Aug 2014, 02:24 pm
Follow-up question:

The instructions in the RM200 manual for setting the bias were (to quote the manual) "written for 4-ohm speaker tap use". If one has connected his speakers to the 8-ohm tap, I assume the bias is set off of those taps? If so, should the bias settings be different than those set off of the 4-ohm taps (I highly doubt it, but better to ask and be sure)?

The bias difference to either the 4 or 8 ohm tap is so small as to not matter. I often put the meter negative on the center (ground tap) as it is available to clamp the probe and I can check all 4 tubes faster. Since it is ground I can leave it for both channels. Bias is not a critical value as most voters correctly stated in the poll.  Just ground the meter negative and check tubes 1-4.
Title: Re: Amplifier Bias
Post by: Roger A. Modjeski on 25 Aug 2014, 03:04 pm
Thanks for your votes. I hope the results are shown now. As you see close is good enough. There is no equation for bias. I find it by careful experimentation.

We are not talking about what is traditionally meant by the term "bias". Unfortunately what we call "bias" is actually idle current measured across some (often unknown) resistor. The term likely became skewed by transistor amplifier biasing where one can only measure idle current. This got called bias, which I would not have done as the "bias voltage" (base voltage is fixed around 0.7 volts). Confusing, yes!!

When I am done with the move I can write up something more on the topic and in the meantime read your tube manuals.

In both transistor and tube amplifiers you are really measuring the idle current of the device and I would prefer we call it that. Bias is the negative voltage on the grid and it is an important distinction.
Title: Re: Amplifier Bias
Post by: kenkirk on 25 Aug 2014, 05:02 pm
Roger,

Maybe you can expand on why bias will change as a tube amp warms up over 20 or 30 mins. Also why we see bias change as the power tubes age, and should one readjust the bias as the tubes age, or should we just leave it alone.

Thanks,

Ken
Title: Re: Amplifier Bias
Post by: kenkirk on 25 Aug 2014, 05:25 pm
Also, could you explain bias run away as it relates to tube amps. I have seen this problem with KT90's that were probably a little gassy. It will get your attention.

Ken
Title: Re: Amplifier Bias
Post by: Roger A. Modjeski on 26 Aug 2014, 02:00 pm
Roger,

Maybe you can expand on why bias will change as a tube amp warms up over 20 or 30 mins. Also why we see bias change as the power tubes age, and should one readjust the bias as the tubes age, or should we just leave it alone.

Thanks,

Ken

Now we really need to get particular about our terms. What I believe you are asking is why the idle current changes as the amp warms up. That is due to the cathode emission coming up in the first minute from zero. The remaining rise is due to elements changing shape due to heat. It takes perhaps 20 minutes for the grid side rods and other mechanical components to settle into their final shape due to simple expansion.

However in some amps the BIAS (negative voltage on the grid) may be changing due to circuit parameters and capacitors coming up to full charge. Here is why we need to correct our language. The thing you are measuring is not the bias on the tube but the idle current which is set by the bias on the grid.

Typical numbers are 20-100 mA for idle current which is typically read across a 1 ohm resistor. In the RM-10 I chose a 10 ohm resistor and in the Dynaco Stereo 70 David Hafler chose a 15.6 ohm resistor so that 100 mA=1.56 volts, the value of a fresh flashlight battery. Now why would he do that?

For BIAS typical numbers are as low as 10 volts for a EL-84 and as high at 60 volts for a KT-88. Again a big range. These are negative voltages placed on the grid through a large resistor of 47 K to 470 K ohms. They come from a regulated or un-regulated BIAS supply via a BIAS pot that you adjust. When you BIAS your amplifier you are adjusting one thing while measuring something else.

Also, could you explain bias run away as it relates to tube amps. I have seen this problem with KT90's that were probably a little gassy. It will get your attention.

Ken

Again terms: It's the idle current that is running away. However that is due to the bias on the tube actually being reduced by grid leakage or gas. In a good tube the grid current is zero. We actually measure this at RAM TUBES and anything over 1 micro amp is rejected. It is interesting you mention KT-90s as they are problematic in that way but the amplifier has something to do with it also. David Manley, the man behind that tube, did a strange thing in his amplifiers. If you read the VTL book you see that he tended to run large value grid (bias) resistors and in the bigger amps they were even larger. The reason for this is another topic of great length. In any event, the larger the grid resistor the more chance for a tube to run away. I used a 47 K ohm resistor in the RM-9 and similar in the RM-10. He used as high as 470 K ohm (the maximum allowed in the tube manual) to bias his grid. The short answer was to make the driver simple in his amps. He is not the only one who uses high value resistors.  A 470 K resistor has 1/10 the ability to hold the negative voltage on the grid. In an ideal world the grid bias resistor would be stated as a spec and a wise person would stay away from amps with high valued resistors. As you may see I take issue with designers who take things to the limit. Does anyone want a list?

As a tube ages grid leakage may go up and thus the negative bias on the tube is reduced, the idle current rises heating the tube and increasing the leakage. This is a regenerative process and the tube runs away. If a fuse or the user stops the process in time the tube may work fine for many months if kept in check. This also explains why a tube can run way (get a red plate) when played hard but be fine when played at low level. Harder play heats the tube to the point where the process may start.

If a tube is really gassy there is no hope for it as the gas in the tube prevents the grid from doing it job at all. However this is a rare case as the problem is usually simple grid leakage. ARC specified "Low gas 6550s" in their amps but what they really were saying is low grid leakage which is not usually caused by gas.

To make a really stable amplifier one either needs low value grid resistors (which are harder to drive) or do what I did in the RM-200 which is do drive them via a directly connected driver tube. The RM-200 can hold idle current 100 times better than most amplifiers. You can actually take tubes with high grid leakage that run away in other amplifiers and use them successfully in an RM-200.
Title: Re: Amplifier Bias
Post by: bdp24 on 26 Aug 2014, 07:39 pm
Roger, this is SUCH great information!
Title: Re: Amplifier Bias
Post by: RDavidson on 26 Aug 2014, 08:00 pm
As you may see I take issue with designers who take things to the limit. Does anyone want a list?


YES! The last thing I (or likely most other reasonable people) want, is to get into a tube amp that requires constant tube replacement or constant monitoring and repairs. Who gives a crap how great it sounds if you can't just turn it on and relax, over, and over, and over with consistency and reliability day in and day out for MANY months if not years.
Title: Re: Amplifier Bias
Post by: bdp24 on 26 Aug 2014, 08:35 pm

YES! The last thing I (or likely most other reasonable people) want, is to get into a tube amp that requires constant tube replacement or constant monitoring and repairs. Who gives a crap how great it sounds if you can't just turn it on and relax, over, and over, and over with consistency and reliability day in and day out for MANY months if not years.

That's one reason I finally got a Music Reference, after having owned ARC, Atma-Sphere, Dynaco, and Quad tube amps. Shoulda done it a long time ago!
Title: Re: Amplifier Bias
Post by: kenkirk on 27 Aug 2014, 04:52 pm
Thank you Roger!  Yes that did clear up things for me.  I have witnessed idle current run away with new KT 90's in my CAT JL-1 amps. I also witnessed a bank of EL34's glowing so bright they were lighting up a large closet. They were not new, but I set the bias ( idle current ) correctly for the tubes in the JL-1's, then went about listening to music pretty loud. When I went to flip the record I was shocked at the bank of el34's lit up like light bulbs. No damage to the amp, but I am sure the tubes were toast. I pulled them. It was just an experiement with EL 34's anyway. I have seen KT 90's when new start to runaway in the JL-1's. If I kept the idle voltage around 5mv for a day, then gradually raised it to 25mv over several days, the tubes settled down and were good for 10,000 hours. I loved those KT 90 type II's. Anyway, my next set of CAT JL-1 tubes will come from you. But my RM 9 MKII and my RM 10 MKII seem to be stealing the show lately.

Ken
Title: Re: Amplifier Bias
Post by: kenkirk on 27 Aug 2014, 05:00 pm

YES! The last thing I (or likely most other reasonable people) want, is to get into a tube amp that requires constant tube replacement or constant monitoring and repairs. Who gives a crap how great it sounds if you can't just turn it on and relax, over, and over, and over with consistency and reliability day in and day out for MANY months if not years.

oh so true. I think poor reliability has driven many a music lover back to solid state amps.

Ken
Title: Re: Amplifier Bias
Post by: Roger A. Modjeski on 28 Aug 2014, 03:16 pm
Thank you Roger!  Yes that did clear up things for me.  I have witnessed idle current run away with new KT 90's in my CAT JL-1 amps. I also witnessed a bank of EL34's glowing so bright they were lighting up a large closet. They were not new, but I set the bias ( idle current ) correctly for the tubes in the JL-1's, then went about listening to music pretty loud. When I went to flip the record I was shocked at the bank of el34's lit up like light bulbs. No damage to the amp, but I am sure the tubes were toast. I pulled them. It was just an experiement with EL 34's anyway. I have seen KT 90's when new start to runaway in the JL-1's. If I kept the idle voltage around 5mv for a day, then gradually raised it to 25mv over several days, the tubes settled down and were good for 10,000 hours. I loved those KT 90 type II's. Anyway, my next set of CAT JL-1 tubes will come from you. But my RM 9 MKII and my RM 10 MKII seem to be stealing the show lately.

Ken

I have a good relationship with Ken Stevens (CAT designer) and have done some special testing for him. He wants very low grid leakage. The tubes I supplied him, and people he sends to me, have leakage below 0.1 micro amp which is 10 times lower than my usual limit. You have to be careful what you put in a CAT amplifier to prevent runaway idle current. As the tubes are connected in parallel in a bank, one tube with high grid leakage will take the others along on the trip to hell.
Title: Re: Amplifier Bias
Post by: airhead on 1 Sep 2014, 06:28 pm
This is indeed very interesting, although I do not have the technical knowledge to really understand it.   I've been told that tube runaway can be a frequent problem when trying to set up NYAL (Futterman design) amps, and one of mine caught fire once!.  Most the time though, these amps  are indeed "turn them on and forget them."
Title: Re: Amplifier Bias
Post by: enochrome on 12 Sep 2014, 04:26 pm
I am a new owner of RM-10 mkii amps that I have bought second hand. I am also new to tube amps and would like to set "bias" correctly for them but I have never done this before. Any help would be appreciated. I am concerned because I have set both amps up to be used as mono's. They are set at the 4 ohm tap for "light loading". When I play music I have to crank my Pass Aleph P preamp to almost 3 o'clock to get music to play at 75db. My speakers are 87db @ 6 ohms Revel M20's. I thought 70 tube watts bridged would be enough for my small room, but it isn't, and I think something is up that is not normal  :scratch:

Any advice would be greatly appreciated.
Title: Re: Amplifier Bias
Post by: Roger A. Modjeski on 19 Sep 2014, 04:27 am
I am a new owner of RM-10 mkii amps that I have bought second hand. I am also new to tube amps and would like to set "bias" correctly for them but I have never done this before. Any help would be appreciated. I am concerned because I have set both amps up to be used as mono's. They are set at the 4 ohm tap for "light loading". When I play music I have to crank my Pass Aleph P preamp to almost 3 o'clock to get music to play at 75db. My speakers are 87db @ 6 ohms Revel M20's. I thought 70 tube watts bridged would be enough for my small room, but it isn't, and I think something is up that is not normal  :scratch:

Any advice would be greatly appreciated.

Something does sound wrong. The amps should play well above 75 db. They should hit over 100 at 1 meter. Which input jack are you using? try the other one. Also note that in mono the 8 ohm tap is actually 4 ohms and the 4 is 2. That is the way with all stereo amps when put into mono. It is a good idea to check each amp as a stereo amp to make sure both channels are working and have equal volume. When in mono, one channel can be out and it is not obvious.

Are you able to measure the bias between the two jacks of each channel as something close to 300 mV?

Do you have a manual?
Title: Re: Amplifier Bias
Post by: tubegroove on 19 Sep 2014, 09:31 am
Hi enochrome
Not sure if you have since solved your issue but setting the bias on the RM10MkII is super easy.  300mV is the suggested value but that's not cast in stone.  On what aspect exactly do you need help?

Also, when running the RM10MkIIs in parallel (mono) mode, you have to pay attention to how you load the taps.  It can be a little confusing at first but if I have understood it correctly, to extract the full 70W/monoblock you should connect a speaker of half the impedance value of the tap selected (for eg a 4ohm speaker on the 8ohm tap in parallel mode).  In your case, casually looking at the Stereophile measurements of the M20s, it seems that the speaker is probably behaving more like a 4ohm nominal rather than a 8ohm load.  I would try connecting them to the 8ohm tap in parallel mode and see if that makes an improvement.  On the 4ohm tap, I believe the power will be only 1.4x the 35W stereo power and Revels are power hungry in general from what little I know about them.

Note: I use my RM10MkII in stereo mode so you may want to phone Roger/Ben and confirm the above.
Title: Re: Amplifier Bias
Post by: enochrome on 20 Sep 2014, 03:29 pm
Thanks for replying.

I have never biased an amp before and I don't have the manual. Do I take the negative(black) connection and connect to the ground post of the speaker terminal? Then, I insert the positive(red) contact into the holes in front of the tubes; one for each tube? I then adjust bias by turning the flat head screw attentuator to read 300mv?

Sorry you guys are going to dumb down for me, but I do appreciate it.

Thanks
Title: Re: Amplifier Bias
Post by: Freo-1 on 20 Sep 2014, 04:08 pm
Here is a little quiz on bias.

You get to vote for as many options as you want.

The poll closing date is noted and results will be shown and discussed then.

In the meantime lets hear what people think about bias.

I think fixed bias is the best way to go.   Can't see any advantage to using cathode bias from a performance aspect.  In addition, I also think each output tube should have it's own bias pot.  The DIY amps I've had all employ this, and measure in Milliamps.
Title: Re: Amplifier Bias
Post by: pehare on 20 Sep 2014, 04:48 pm
To adjust & check your bias voltage on the RM10 you use the 2 test jacks or bias pots in front of each pair of tubes.  Begin by letting the amp & tubes warm up for 20 minutes.  Each channel is biased as a pair so there is only one adjustment screw for each channel or pair of output tubes.  Left bias pot or test jack is for your negative voltmeter probe & right is positive.  Set each pair at 300mV as per manual or less for more tube life.  enjoy!
Title: Re: Amplifier Bias
Post by: Freo-1 on 20 Sep 2014, 04:59 pm
To adjust & check your bias voltage on the RM10 you use the 2 test jacks or bias pots in front of each pair of tubes.  Begin by letting the amp & tubes warm up for 20 minutes.  Each channel is biased as a pair so there is only one adjustment screw for each channel or pair of output tubes.  Left bias pot or test jack is for your negative voltmeter probe & right is positive.  Set each pair at 300mV as per manual or less for more tube life.  enjoy!

Is that 300ma or 30ma?   300ma seems way too high.

Update:  It IS 30 ma.  At 300ma, you would cherry the tubes quickly!  Read the link provided:

http://www.ramlabs-musicreference.com/rm10design.html (http://www.ramlabs-musicreference.com/rm10design.html)
Title: Re: Amplifier Bias
Post by: pehare on 20 Sep 2014, 05:52 pm
bias on the RM10 is set in millivolts so the multimeter is set for V not A
Title: Re: Amplifier Bias
Post by: enochrome on 20 Sep 2014, 06:56 pm
Thanks pehare and everyone, that is exactly what I needed to know. I will let you know how it turns out.

Thanks again!! :D
Title: Re: Amplifier Bias
Post by: Freo-1 on 20 Sep 2014, 09:21 pm
bias on the RM10 is set in millivolts so the multimeter is set for V not A

So, the ratio is 10mv to 1ma.  Makes sense.  The old Dynaco amps had a scaling factor to set bias at 1.56V, which equaled the correct bias in ma.
Title: Re: Amplifier Bias
Post by: pehare on 20 Sep 2014, 09:42 pm
Yes, it's measured across a 10 ohm resistor thus the current is 30mA for a 300mV reading (as per owner manual).  enjoy!
Title: Re: Amplifier Bias
Post by: enochrome on 20 Sep 2014, 10:26 pm
So I biased the amps to 300mv with no problem. I hooked up each amp in stereo to check both channels, which indeed they both worked for each amp. I am still having the same problem, in which I need to turn my preamp to 3 o'clock or more to get reasonable volume. What's weirder is that I don't get hardly any improvement running them in mono as I do when they are each hooked up in stereo to my speakers.  :scratch:

Obvious question, if I hook it up in mono I need to use the left channel speaker connections correct? I assume so, because the mono input is the left channel one.

Are the tubes or my pre the problem? I thought these amps could run with a passive pre? I got a lot more power with my Exposure 2010s, that used a passive pre and was 70 watts solid state. I thought tube watts were more powerful than solid state?

Title: Re: Amplifier Bias
Post by: bdp24 on 20 Sep 2014, 10:49 pm
Giving up already, Eno? (I just saw the amp on U.S. Audiomart). Give Roger a chance to sort out your situation---it's probable something simple. It doesn't sound like a lack of power issue to me, and the amp's sensitivity can be increased by changing the input impedance-determining resistor.
Title: Re: Amplifier Bias
Post by: Freo-1 on 20 Sep 2014, 10:53 pm
So I biased the amps to 300mv with no problem. I hooked up each amp in stereo to check both channels, which indeed they both worked for each amp. I am still having the same problem, in which I need to turn my preamp to 3 o'clock or more to get reasonable volume. What's weirder is that I don't get hardly any improvement running them in mono as I do when they are each hooked up in stereo to my speakers.  :scratch:

Obvious question, if I hook it up in mono I need to use the left channel speaker connections correct? I assume so, because the mono input is the left channel one.

Are the tubes or my pre the problem? I thought these amps could run with a passive pre? I got a lot more power with my Exposure 2010s, that used a passive pre and was 70 watts solid state. I thought tube watts were more powerful than solid state?








I think that the red goes on the left 8 Ohm tap, while the black goes on the right common.   That is how my old McIntosh amps were. The left input has to go to both sets of output tubes, and across both output transformers.
Title: Re: Amplifier Bias
Post by: tubegroove on 21 Sep 2014, 06:46 am
So I biased the amps to 300mv with no problem. I hooked up each amp in stereo to check both channels, which indeed they both worked for each amp. I am still having the same problem, in which I need to turn my preamp to 3 o'clock or more to get reasonable volume. What's weirder is that I don't get hardly any improvement running them in mono as I do when they are each hooked up in stereo to my speakers.  :scratch:

.....
Did you try different output taps as I mentioned in my earlier post?
Title: Re: Amplifier Bias
Post by: enochrome on 21 Sep 2014, 06:59 am
Did you try different output taps as I mentioned in my earlier post?

Yes, I ran it this time with the 8ohm taps.

I think my speakers are just too power hungry.  :|

Title: Re: Amplifier Bias
Post by: enochrome on 21 Sep 2014, 07:01 am
Giving up already, Eno? (I just saw the amp on U.S. Audiomart). Give Roger a chance to sort out your situation---it's probable something simple. It doesn't sound like a lack of power issue to me, and the amp's sensitivity can be increased by changing the input impedance-determining resistor.

I figured that my Revels just need too much power and that I should cut my losses and keep one for a single driver project
and sell off the other.
Title: Re: Amplifier Bias
Post by: Freo-1 on 21 Sep 2014, 03:28 pm
Yes, I ran it this time with the 8ohm taps.

I think my speakers are just too power hungry.  :|

Did you connect the positive connection to the 8 ohm tap left channel, and the common to the right common?  In order to get the extra power, need to use all the tubes and iron.
Title: Re: Amplifier Bias
Post by: enochrome on 21 Sep 2014, 03:39 pm
Did you connect the positive connection to the 8 ohm tap left channel, and the common to the right common?  In order to get the extra power, need to use all the tubes and iron.

No, I used the left common. Do I need to use the right when in mono? Is that what tubegroove meant by "in parallel"?
Title: Re: Amplifier Bias
Post by: Freo-1 on 21 Sep 2014, 06:49 pm
No, I used the left common. Do I need to use the right when in mono? Is that what tubegroove meant by "in parallel"?

Yes, for the reasons stated above. 
Title: Re: Amplifier Bias
Post by: Roger A. Modjeski on 25 Sep 2014, 11:49 am
I am a new owner of RM-10 mkii amps that I have bought second hand. I am also new to tube amps and would like to set "bias" correctly for them but I have never done this before. Any help would be appreciated. I am concerned because I have set both amps up to be used as mono's. They are set at the 4 ohm tap for "light loading". When I play music I have to crank my Pass Aleph P preamp to almost 3 o'clock to get music to play at 75db. My speakers are 87db @ 6 ohms Revel M20's. I thought 70 tube watts bridged would be enough for my small room, but it isn't, and I think something is up that is not normal  :scratch:

Any advice would be greatly appreciated.

Thanks to all for your efforts. I dont know if eonochrome has written Ben (tubeaudiostore@gmail.com) but these numbers are all out of whack and it seems no one has mentioned that he should be using the 8 ohm tap for a 4 ohm speaker. When you parallel (mono) a tube amp the voltage stays the same and the current doubles. The taps all go to 1/2 their impedance. This is true for all tube amps! It is just the opposite for transistor amps when bridged the voltage doubles and the power quadruples. This is basic electronics that I teach in my classes or you can find in books.

The setting of the volume control is absolutely immaterial as long as its not full up and not enough volume. VOLUME CONTROL SETTING HAS NOTING TO DO WITH POWER OUTPUT. Its all relative to gain of the amp and voltage of the source. The RM-10 will produce full power with 1 volt input and most CD players have 2 volts output.

It would be nice to know your listening level at 1 meter. 


Title: Re: Amplifier Bias
Post by: Freo-1 on 26 Sep 2014, 06:36 pm
So, did you ever get around to trying this out?
Title: Re: Amplifier Bias
Post by: Gearmonster on 26 Sep 2014, 06:50 pm
eno, did you get this worked out yet, You can write tubeaudiostore@gmail.com and Roger or Ben will help you.
Title: Re: Amplifier Bias
Post by: enochrome on 29 Sep 2014, 04:29 am
Sorry, I was away for a bit.

It turned out well. Listening to music now. I have realized that they are not a good fit for my speakers and I think the preamp was not a good match. Using the preamp from my integrated was more agreeable . I am going to keep one of the RM-10's and use it with a fullrange project that I am about to begin. I do like the sound of the amp; it is sooo composed, has body, and avoids the syrupy characteristics of poorly constructed tube amps. I thought RM 10's low end is outstanding, better than that of a primare a30.1 that I had, and that was dual mono. :roll:

Thanks everyone for helping me with this. I will post upcoming results with my speaker project. I also will combine the amp with a First Watt B1 in the future and let you know how that sounds.

Cheers