7868 vs 6bq5 tube which one is sonically better?

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philips fx82

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Hi , I am considering 2 different amplifiers for a room. Both are single ended. My music is mainly classical
and opera. Could anyone give me an opinion which tube would be better for this application?
The current speakers would be the ADS L520's.

my thanks in advance
 
To be honest, I would recommend neither in a single ended amp configuration, with ADS speakers. Classical and opera both require some oomph to get their delivery out there, and these tubes won't be up to the task.

I have 300B SET amps, and 811 SET amps that can do both adequately to superbly with Altec 19s. However, both the amps and the speakers are markedly above the target amps/tubes and speakers you have.

You are throwing a pair of the most demanding types of musical performances at a pair of speakers that are compromised for these formats, and then asking for a miracle out of limited tube amps that don't have it in them to do this job well, even with superb speakers.

A conventional push-pull 7591 based output tube would provide much more enjoyment, while minimizing the twin compromises of dynamic headroom and power/tone.
 
Exactly as they are rated at 92 dB & 15 to 100 Watts. EL84/6BQ5 will give at the most 4W in SE and 20W in PP. 7591/7868 should give you almost double the power in both SE & PP. It's nice to have headroom for the dynamics in your music and no doubt longer tube life so I too agree with Dave above. I have only heard EL84/6BQ5 in PP and really liked SE 6V6 RCA radio with CD player plugged in to it's input jack as it had a great mid range.
 
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The 6BQ5 makes a wonderful A-M modulator for a 10 watt transmitter. Previously, the 6AQ5 was
commonly deployed, but it could not develop the required oomph to upward modulate
a 2E26, so many designers upgraded to the 6BQ5, which required some elevated anode voltage
to develop the required wattage in the final stage output transformer.

However, all-in-all, the choice of a 6BQ5 for a hifi (essentially a speech amp) power amplifier
is okay if 5 watts per channel is plenty enough for your tastes.

But life is too short for flea power.

Find yourself a power amp that uses push-pull 6550's, or really go to the exotic and find
a homebrewed 3CX300A7 ceramic tube power amp. They're all over Japan.
 
The 7868 would make roughly double the power. I think that would fit the bill better given the options presented. Personally I suspect a bit more power would be an advantage, especially given the dynamics of classical.

I don't have any SE amps but I own push-pull 6bq5 and 7868 amps. Honestly I feel they sound fairly similar.
 
The 7868, in almost every quantifiable way, is a lot like an up-sized 6BQ5. Similar transconductance and grid gain, and similar distortion characteristics.Both of them were designed in the latter part of the "tube golden era"- so the prime design goals were very similar.

Given that, in this case where power is a prime goal (due to the speakers not being extremely efficient), the 7868 would seem to be the obvious choice.

Regards,
Gordon.
 
I thank every one for their advice. Could some one tell me what type of high efficient speakers you would use with either of these single ended amps/
my thanks in advance
 
What are the dimensions of your listening room and what will be your listening position (i.e how far away from the speaker will you be seated)?

Steve
 
If I was going to the effort of high efficiency speakers, I wouldn't use either of those amps.

If you have the L520's put some moderate push pull power (7591A's or EL34's) behind them and enjoy. While researching a high efficiency system, of course (the madness just gets worse :D)
 
The LDS520 specification shows 92DB at 1 watt at 1 meter. Your room is small and your listening position is close. Look at this sound pressure level calculator designed to help you determine what you need for power and speaker sensitivity to achieve an spl goal at your listening position ( http://myhometheater.homestead.com/splcalculator.html ). Enter 92DB for you speaker sensitivity, 4 watts for amp power ((6BQ5/El84/6V6), 8 feet for distance, 2 speakers, select near wall and calculate. That will achieve 96 DB at your listening position. 8 watts will make 99 DB at your listening position.

These SPL's can be ear damaging loud. But, that is not the whole picture. In my home office (listening position 10 feet) I use Klipsch MTM bookshelf speakers rated at 95DB/1 meter/1watt. I drive them with a 6V6 Pentode SE amp that produces 4 watts RMS per channel. On some High Def symphonic recordings I get SPL peaks in the mid 90's when the amp is at full power. I am happy with this most of the time and especially like the sound of the 6V6 SE amp. However, the speakers need 10 DB of boost on the low end if I want to get flat response at or below 30 hz (organ music). I can do that with the 4 watt amp but it will distort on peaks if there is substantial higher frequency content. So when I want to listen to that type of music at a high volume I connect my 30 watt per channel parallel SE amp. How important is that to me? The 30 watt PPSE has been collecting dust for a couple of years.

The high def recordings that I refer to have peaks typically 10-15 DB higher than the average level and the dynamic range is a real 40+DB. With the 4 watt amp I can apply a small amount of bass boost and listen at an average level of 80DB with peaks in the mid 90's. Anything more will distort. With the 30watt amp I can apply 10DB of boost and blow myself out of the room with undistorted sound. In my experience the people that listen to my system are shocked when I show them the amps are producing only 1 watt on peaks. You may be as well.

My preference is for jazz and vocal music. For that type of music the little 4 watt amp performs quite well because there is a lot less dynamic range than the symphonic music.

What would I do if I could only afford one amp? Well...I bought parts to make an 8 watt parallel SE version of the 4 watt amp....LOL

Steve
 
I have used an 86dB speaker powered by an 18 wpc amp in my bedroom for years. It has been more than adequate. I might have missed some, but I've never heard it clip. I don't know what the real world measurement of the L520's sensitivity is. Frequently they run about 3dB less than manufacturer's specs.
 
A lot is going to depend on what you want out of this system. No point going to huge cost to meet live performance levels if that is not the realistic expected use. As it's a bedroom and they are usually for resting and sleeping, you perhaps do not plan to have concert level sound in there, unless it's a dual use room. If you do, maybe a tube pre-amp and SS power amp will do it for you; otherwise the 7868 amp should be enough for a restful environment with 92dB efficient speakers. I have run both SE 6BQ5 and SE 7591 (similar to 7868) on ~92dB speakers for background music in small office rooms and they are OK.

FWIW, I tend to not use tubes in my bedroom systems partly because the thought of falling asleep to music with the risk of an output tube red-plating is not conducive to sweet dreams. YMMV.
 
I think as long as expectations meet reality (ie not 100dB listening...) it could work fine, and sound excellent. Ideally for those sort of amps efficiency of 96-100dB would be better but not necessary for low-level listening.
 
GordonW said:
The 7868, in almost every quantifiable way, is a lot like an up-sized 6BQ5. Similar transconductance and grid gain, and similar distortion characteristics.Both of them were designed in the latter part of the "tube golden era"- so the prime design goals were very similar.

Given that, in this case where power is a prime goal (due to the speakers not being extremely efficient), the 7868 would seem to be the obvious choice.

Regards,
Gordon.
Click to expand...

My favorite tube - 7868/7591. I have a single-ended with 7591s and it drives my 93dB sensitivity speakers to PLENTY loud and clean.
 
For your specific bedroom situation, I would pick up a vintage Heathkit integrated EL84 single ended. It is tiny, reasonable, and sounds very good when rebuilt.

You can also find a Decware SE84 that will also punch the clock.

I would also be wary of night time listening. Make sure you turn the sucker off. Before lights out.
 
Do you have a preamp to go with the amp or do you need an integrated amp. What will be your music source, cd player, ipod ? I think for a small bedroom or den stereo, a SE amp is an excellent choice. I like the "RH universal" amp which can be used with 6L6 type tubes up to the KT88, and EL34 which gives one a lot of choices for the power tube and from 7 to 12 watts of output. Or if you want to save on parts cost the RH84 can be made with a console amp as the donor for around 200.00 including the cost of the donor.
The SE integrated amp is a great idea but they are rather hard to find. The prices also reflect their rarity. SE amps are very simple circuits and easy to build if you are so inclined.
 
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philips fx82 said:
I thank every one for their advice. Could some one tell me what type of high efficient speakers you would use with either of these single ended amps/
my thanks in advance
Click to expand...


Yes ! First of all, go for high efficiency speakers : Two Way - go ALTEC .

Either new GPA 604s or an old VOTT A7-8 which will work in any sized room, even a garage.

They are around 100dB, and then, you can use any small Power tube, based on its sonics, and not any Watt rating !!

Rather than any 7868 or 6BQ5, with High Efficiency 100dB speakers, I suggest to use a 6AQ5 SE amp with NO feedback. I can help you with the 6AQ5 amp design. With an ALTEC 15 inch woofer, and an 802 in a VOTT, 800 Hz crossover, you are done looking for speakers. And, you get to use the best-sounding tubes.

Its HARD to beat a well implemented 6AQ5 tube IMHO.

Dowto1000
 
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dowto1000 said:
Yes ! First of all, go for high efficiency speakers : Two Way - go ALTEC .

Either new GPA 604s or an old VOTT A7-8 which will work in any sized room, even a garage.

They are around 100dB, and then, you can use any small Power tube, based on its sonics, and not any Watt rating !!

Rather than any 7868 or 6BQ5, with High Efficiency 100dB speakers, I suggest to use a 6AQ5 SE amp with NO feedback. I can help you with the 6AQ5 amp design. With an ALTEC 15 inch woofer, and an 802 in a VOTT, 800 Hz crossover, you are done looking for speakers. And, you get to use the best-sounding tubes.

Its HARD to beat a well implemented 6AQ5 tube IMHO.

Dowto1000
Click to expand...
VOTT A7 or A8 are definitely efficient but might not be something he would want to squeeze into his bedroom. :idea: Then again, some of us do like our systems to have performance first :smoke:
 
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