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SET amps.............


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Seems like everyone misses their SET amps. What's going on there?

I kept mine

If you aren't into gobs of SPL/power, have a small room, or listen to little Fostex FR speakers in bass reflex boxes, the little Magnavox single-ended pentode connected 6BQ5 console amplifiers are excellent entry level canidates.

A little DIY/TLC, and the little console amps are rather nice sounding. A cheap way to get into a DHT triode similiar sound.

They mesh up with Klipsch nicely as well.

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If what you have is a push-pull, most SETs aren't going to be what you want. Does your MiniMax use the 6BM8 tube? This is pretty much the power you will get from a SET:

A SET made with a 45 output tube is only about 1.5 watts,

2A3 tube about 3.5 watts,

300B tube 8-10 watts.

You can get some SET amps made with higher powered exotic tubes, but they will cost you a lot more money.

YMMV

Bruce

Yes, the Mini Max has 6BM8 tubes along with the Mullard rectifier tube.
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As everyone is going on about how much they like their SET amps, I think the big problem will be the efficiency of the RB75s. After hearing the higher power on the HT system, using the lower power on the RB75s for two channel will probably come across as a bit weak.

There are very good tube amps in all kinds of flavors covering a wide price range... just take your time and try some others out if you can.

Bruce

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A SET amp can be very rewarding with the proper setup. My SET amp is a DIY using Eimac 75TL outputs and my speakers are of course Khorns. My amp is capable of 6 watts with plate voltage of 485V that I'm currently using, but I normally run the amp at a comfortable listening level of about 1/10 of a watt. With my current setup I get all the power I need to drive my Khorns to very loud levels without distortion. The key to having a sucessful SET amp is very efficient speakers, no less than 102db @ 1 watt IMO, the lower the efficiency of the speaker the harder it will be for the SET to drive them at higher levels without distortion. I have had all kinds of tube amps, Marantz 8b, Eico HF-87, Dynaco ST-70, etc. and my current SET amp blows them all away. Don't get me wrong, push-pull amps sound wonderful and pack quite a nice punch, but they are no match for a nice SET amp setup IMHO.

Yes, this Eastern Electric Mini Max push pull type amp has beautiful sound indeed...........but does not pack a punch. That's ashame because the sound is wonderful. I will be looking for a tube amp to pair up with the RB-75's and the JM Peach ll that has very good sound quality and significant power if the mood strikes me...........and it often does.[:D]
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As everyone is going on about how much they like their SET amps, I think the big problem will be the efficiency of the RB75s. After hearing the higher power on the HT system, using the lower power on the RB75s for two channel will probably come across as a bit weak.

There are very good tube amps in all kinds of flavors covering a wide price range... just take your time and try some others out if you can.

Bruce

Thanks Bruce. I think you're exactly right and that is the approach I plan on taking.

I've learned quite a bit in the last few years with all of this. "Upgradeitis" can put a serious dent in the old bank account. I plan on buying used and hopefully I can find someone/someplace locally to be able to listen to a tube amp with RB-75's.

Now for a slightly different scenario..........JM Peach and Heresy's...........Will the Heresy's jive well with a SET amp?

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Now for a slightly different scenario..........JM Peach and Heresy's...........Will the Heresy's jive well with a SET amp?

I keep telling myself to hook up my Moondogs to my Heresy IIs, so I could give my own opinion/half baked/ partially qualified answer. The Heresies aren't as efficient as the LaScalas, etc., which I have my 2A3 amps hooked up to.

Almost the same efficiency as the RB-75s (RB-75 is higher). I've not heard the RB-75s, so I don't know the sound of them. They are rated slightly lower in the bass than the Heresies.

All that being said, I don't listen to my HIIs at a very high volume level. I might find it acceptable.

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I bought my 6.5Wpc 300B SET stereo amp originally for my '79 Cornwalls, and they were a match made in heaven when I auditioned the combo in my large family room! Unfortunantly, that room was already reserved for my brother's HT setup, so a spare bedroom became my tiny listening room, which was a problem for the massive CWs since they seem to need lots of room to be tuned properly and be able to breath!

I regretably went from the Cornwalls to a pair of fabulous sounding Triangle Zephyr 2-way towers (91dB @ 1W/1M into 4 ohms). As much as these floorstanders would sing, at higher volume they'd clip horribly due to their lower sensitivity rating. What I needed was a highly efficient small loudspeaker for my small listening space...hence, my cherry RB-75s!

Granted, at 97dB sensitivity, they're not in uber-efficient Klipschorn territory, and with my SET amp being only 6.5 watts per channel, the RB-75s can't be blasted to near-live levels (even with two subwoofers handling bass frequencies from 40Hz on down). Nonetheless, I can listen to my favorite music at higher volume if I want before any major clipping ocurrs, and these RB-75s really do open up with all the niceties SET amps are known for (clear highs and sweet, lush mids).

Since I'm running dual subs, I can't remark on how well the RB-75s alone handle SET-powered bass frenquencies, which may very well be a concern for you if you don't use a subwoofer. But IMHO if your music room is small and you don't listen at live stadium rock levels, then a SET power amp of at least 7 watts (more is better if you can afford it) can certainly bring out the best in both your amp and your RB-75s...just my own personal observation, natch.

FWIW, YMMV, and all that jazz...[;)]

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I bought my 6.5Wpc 300B SET stereo amp originally for my '79 Cornwalls, and they were a match made in heaven when I auditioned the combo in my large family room! Unfortunantly, that room was already reserved for my brother's HT setup, so a spare bedroom became my tiny listening room, which was a problem for the massive CWs since they seem to need lots of room to be tuned properly and be able to breath!

I regretably went from the Cornwalls to a pair of fabulous sounding Triangle Zephyr 2-way towers (91dB @ 1W/1M into 4 ohms). As much as these floorstanders would sing, at higher volume they'd clip horribly due to their lower sensitivity rating. What I needed was a highly efficient small loudspeaker for my small listening space...hence, my cherry RB-75s!

Granted, at 97dB sensitivity, they're not in uber-efficient Klipschorn territory, and with my SET amp being only 6.5 watts per channel, the RB-75s can't be blasted to near-live levels (even with two subwoofers handling bass frequencies from 40Hz on down). Nonetheless, I can listen to my favorite music at higher volume if I want before any major clipping ocurrs, and these RB-75s really do open up with all the niceties SET amps are known for (clear highs and sweet, lush mids).

Since I'm running dual subs, I can't remark on how well the RB-75s alone handle SET-powered bass frenquencies, which may very well be a concern for you if you don't use a subwoofer. But IMHO if your music room is small and you don't listen at live stadium rock levels, then a SET power amp of at least 7 watts (more is better if you can afford it) can certainly bring out the best in both your amp and your RB-75s...just my own personal observation, natch.

FWIW, YMMV, and all that jazz...Wink

That's really cool jt. What subs are you using with the 75's? I know a lot of guys here frown on subs with their two channel systems but I use a Klipsch LF-10 on the high impedance and it fills the bottom very nicely for a bedroom system.[:D]
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Mark,

Thanks for the info. All I know is I love my setup with the pCats. I have no intentions on making any changes as far as amps go. Was just curious on how the 2 compared.

Not to go on and on about it, but my entire design criteria for the pCAT from day one, was to capture the midrange lucidity of SET amps, while "curing" the most common problems with many SET amps: low headroom, weak'ish bass, a bit noisy. I am a midrange guy - I listen to S.D. speakers most of the time. So, if the midrange had failed, I would not have even bothered making them. They are more similar to SET than to PP. They are Class A, they are all Triode, they have zero feedback. They are just double ended instead of single ended. I've been in a room with pCATS and SET amps and I have no doubt whatsoever that the "mission was accomplished." Glad to hear you are enjoying them!

I'd love to hear the pCAT amps. They are beautiful. Triode, Class A, and zero feedback......HELL YEAH! Does anyone in Arkansas have a pair?

Not all SET amps are created equal. The Canary Audio CA300 monoblocks with the George Wright preamp were absolutely silent at idle. It oozed quality craftsmanship. I must have another pair.

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I think I do have someone in Arkansas.

If they are up for auditions or plan to attend any audio events I would really love to hear them sometime. They come in at a whopping 55lbs zowee man. The easy bias is also very cool.

What are your favorite KT88 tubes?

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That's really cool jt. What subs are you using with the 75's? I know a lot of guys here frown on subs with their two channel systems but I use a Klipsch LF-10 on the high impedance and it fills the bottom very nicely for a bedroom system.Big Smile

I use a discontinued pair of affordable 10" Dayton Audio subs from PartsExpress.com (click on my link below to see the specs and pics). I mostly listen to pipe organ music with their deep, bottom octave bass, and I can't expect the RB-75s to satisfy my listening enjoyment if they're not capable of producing bass frequencies from 30Hz thru the low 20s (and below) that the pipe organ itself can create.

Granted, I could only afford subwoofers that were capable of producing only 25Hz at their lowest, so I am missing out somewhat in the extreme lowest octave from the organ's large 32' pedal stops (that can reach down to 16Hz at low C and be felt more than can be heard). In the end, it's about faithfully reproducing all my music as realistically as possible within my budget, and if it means using dual subs to reach the lowest fundamentals (as best they can) from my organ recordings, even if the audio snobs poo-poo sub use in 2-channel listening, then so be it.

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That looks really sweet Mike! Is that the one you started working on a few years back? Really has come a long way!

Actually, I picked this Magnavox SEP amplifier up last April from a guy over in Idaho. I still have the other one as well.

The base is Wenge.

The Magnavox 9300 series 6BQ5 push-pull console amplifiers are a nice sounding circuit that sounds a lot better than it should, along with the 6V6 PP versions. 6V6 in a SEP circuit sounds rather nice too....

Still got the ol' homebrew 2A3 stereo SET pig. The amp has good strong tight bass to me, I guess that's all that matters.....

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I keep telling myself to hook up my Moondogs to my Heresy IIs, so I could give my own opinion/half baked/ partially qualified answer. The Heresies aren't as efficient as the LaScalas, etc., which I have my 2A3 amps hooked up to.

Almost the same efficiency as the RB-75s (RB-75 is higher). I've not heard the RB-75s, so I don't know the sound of them. They are rated slightly lower in the bass than the Heresies.

All that being said, I don't listen to my HIIs at a very high volume level. I might find it acceptable.

Thinking strictly of efficiency rating of a speaker is only half the picture when dealing with low powered singled ended triode amplifiers or tube amps in general. Set amplifiers are adversely effected by wild impedance swings just as much as low efficiency.. Many speakers exist that are considered tube friendly that are not real high effeceincy... speakers in th 92 to 95db range can be driven with low powered SET if they have a relatively flat impedance curve. My point here is driving a pair of Heresy's is not going to be anything even remotely like driving a pair of RB-75's even though they have a reasonably close efficiency rating. More to the picture then just raw effeciency...

Craig

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I now drive my 2005 Belles with a 18 watts per channel single ended amplifier. A big change from my former 300 watts per channel monster. Sometimes I miss the unlimitless power from my former amplifier, but the little tube integrated amplifier provides quite satisfying spl's in my room - this gives some creedance to Craig's assertion that there is more to determining a speaker's ease of drive than mere specifications would suggest. Regarding listening at higher spl's I find that I can comfortably listen to my Belles at very high levels without any harshness or blaring. While this has something to do with the purity of PWK's oringinal design, it may also have something to do with the way my tube amplifer matches with the speakers...

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Thinking strictly of efficiency rating of a speaker is only half the picture when dealing with low powered singled ended triode amplifiers or tube amps in general. Set amplifiers are adversely effected by wild impedance swings just as much as low efficiency.. Many speakers exist that are considered tube friendly that are not real high effeceincy... speakers in th 92 to 95db range can be driven with low powered SET if they have a relatively flat impedance curve. My point here is driving a pair of Heresy's is not going to be anything even remotely like driving a pair of RB-75's even though they have a reasonably close efficiency rating. More to the picture then just raw effeciency...

Craig

I couldn't agree with you more, Craig. I think that is one of the reasons my LaScalas are working so well with my Moondogs. The crossovers are a constant impedance, which the low powered tubes like. It works for me. That's why I am not sure how the Heresies would work, or the RB-75s. They have different crossovers, even if the efficiency is almost the same. I am sure they won't work the same on any given amp.

My old JBL 4311s are only rated at 89db, yet JBL indicated they could be used with a 10 watt amp for monitoring purposes. It will depend a lot on the amp matching up with the design of the crossover.

Bruce

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