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 Post subject: Best choice for building a tube amp, 6L6GC/6V6/EL84?
PostPosted: Apr Thu 04, 2019 4:49 am 
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Hi,

I've a twin EL84 based tube regulated power supply with me. I plan to convert it to an amp since I have another power supply with me. Going through my collection, I've a pair of Sylvania 6L6GCs, some 6V6s too.

Though I have a couple of power and output transformers, due to space issues I plan to build only one amp. If I'm going to build the 6L6GC/6V6 then I need to drill out a bigger hole for the tubes. So cannot go back to the EL84 design back. Which one a better choice in terms of sound? I'm a little more bass guy :D

Thanks,
Raul

UPDATE: Guys, by bass I didn't mean the thumping type of bass we get in powerful Solid-State amps. I mean the type of warm slightly bass themed music/tone that we get in tube amps. Sorry if it wasn't clear.

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Last edited by Vintage Collector on Apr Thu 04, 2019 8:33 pm, edited 1 time in total.

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 Post subject: Re: Best choice for building a tube amp, 6L6GC/6V6/EL84?
PostPosted: Apr Thu 04, 2019 11:37 am 
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An amp is supposed to be linear, so looking for a 'tube that has more bass' ain't gonna happen. What WILL happen is that since bass of course requires more power, you'll eventually run out of output from the tubes, or power supply.

6V6 and 6L6 can both build excellent amplifiers. There is a long running thread on this forum regarding 6V6 design. Possibly the same with 6L6 but not sure about that one. I'd read all you can before deciding. It's really a preference issue, not necessarily a performance issue, except for the limitations of any given tube you selected as your outputs. The output transformer can make a huge difference as well. And don't skimp on the power supply. :)

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 Post subject: Re: Best choice for building a tube amp, 6L6GC/6V6/EL84?
PostPosted: Apr Thu 04, 2019 1:36 pm 
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Output transformer is the most critical component - and it costs a lot more than the tubes. Build around the iron you have. The power transformer may be rather high voltage for a regulated supply - so you may want to use a choke input power supply to get a more reasonable output voltage

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 Post subject: Re: Best choice for building a tube amp, 6L6GC/6V6/EL84?
PostPosted: Apr Thu 04, 2019 5:01 pm 
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Tom Bavis wrote:
Output transformer is the most critical component - and it costs a lot more than the tubes. Build around the iron you have.


And that is ultimately the limitation on the bass response. You can't do any better than the output transformer(s) can handle. There are two approaches to dealing with this limitation - the best option being is a high-pass filter on the input to prevent the entire amplifier from seeing bass that the transformer can't play, the overwhelming most common option is to let everything in, then try to keep the circuit out of trouble by adjusting the feedback or coupling capacitors somehow to improve the situation. The latter is why you usually have massive distortion at low frequencies on tube amps, either from the transformer saturating, or the gyrations you have to go through to prevent it. It's also why you have problems trying to get more than about 35 watts out of one - the larger transformer to handle bass at higher power levels, and you get frequency limitations on the high end, smaller transformer saturates sooner. A 6V6, etc, is relatively easy to get working well, and the only downside is the power.

Brett


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 Post subject: Re: Best choice for building a tube amp, 6L6GC/6V6/EL84?
PostPosted: Apr Thu 04, 2019 5:11 pm 
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Asking what is the "better choice" in terms of sound doesn't make any sense. One can build excellent sounding amplifiers from either of the three output tubes, or horrible amplifiers from either of the three output tubes.

Three of my favorite commercially manufactured amplifiers are the McIntosh A-116, the RCA SP-20, and the Heathkit UA-2. The McIntosh uses a 6L6 variant (the 6BG6G), the RCA uses 6V6s, and the Heathkit EL84s. If I had to pick a "winner" I don't think I could.

When people mention bass, there are two issues at play: amplifier power required, and damping factor. An output topology that can adequately drive your woofer with regard to power output is absolutely necessary. Damping factor is a bit more complicated. I prefer to keep it as low as possible in order to exert as much control over the voice coil as is reasonably possible. Others enjoy the "one note bass" that results from a poor damping factor and perceive it as "better" or fuller bass. That's more of a personal preference.

As far as other characteristics go, low harmonic distortion, low hum and noise, low intermodulation distortion, and keeping the slew rate in check are sort of absolute minimum considerations for any amplifier.

I personally would stick with the EL84s or move to the 6V6s. Both have similar load requirements, and thus you could use your existing output transformers to the best of their ability. Most reasonable 6L6 output stages require something on the order of 3.8k to 6.6k plate to plate impedance, whereas your existing output transformers would be about 8k to 10k plate to plate.

The 6V6 requires greater drive voltage than the EL84. The EL84 behaves better, as a general rule, in a UL circuit. Other than that the two tubes are pretty comparable in terms of performance.


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 Post subject: Re: Best choice for building a tube amp, 6L6GC/6V6/EL84?
PostPosted: Apr Fri 05, 2019 4:44 am 
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Vintage Collector wrote:
UPDATE: Guys, by bass I didn't mean the thumping type of bass we get in powerful Solid-State amps. I mean the type of warm slightly bass themed music/tone that we get in tube amps. Sorry if it wasn't clear.


If it is properly designed you won't be able to tell the difference until you start running out of power. "Thumping bass" and "warm tone" are defects to be designed out.

This sounds like a first or early attempt at building an amplifier. I would strongly suggest one of the many ultralinear designs from the mid-late 50's using any of the tubes you mention, and if you are starting from scratch, get the Triode electronics Z565 copy of the Dynaco ST-35 output transformer. I have used this one (and the originals) on many of these small amplifier projects using 6V6/12V6 and EL-84/7189, with very good success. I was generally happier with the performance (measured and audible) of the xV6 types. although if you can find an appropriate power amplifier, you can usually get more power out of a 7189. If everything is right, there is very little difference in any way.

It's a good idea if 12-15 watts are sufficient.

Brett


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 Post subject: Re: Best choice for building a tube amp, 6L6GC/6V6/EL84?
PostPosted: Apr Fri 05, 2019 5:18 am 
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Vintage Collector wrote:
Hi,

I've a twin EL84 based tube regulated power supply with me. I plan to convert it to an amp since I have another power supply with me. Going through my collection, I've a pair of Sylvania 6L6GCs, some 6V6s too.

Though I have a couple of power and output transformers, due to space issues I plan to build only one amp. If I'm going to build the 6L6GC/6V6 then I need to drill out a bigger hole for the tubes. So cannot go back to the EL84 design back. Which one a better choice in terms of sound? I'm a little more bass guy :D

Thanks,
Raul

UPDATE: Guys, by bass I didn't mean the thumping type of bass we get in powerful Solid-State amps. I mean the type of warm slightly bass themed music/tone that we get in tube amps. Sorry if it wasn't clear.
A couple of designs for you to consider, all built by John over in Homebrew Radios and Equipment.

The first is a 6HB6 (6BQ5 on steroids) amp. viewtopic.php?f=12&t=307525&hilit=Prince+John
(He's good at keeping the links of his first message up to date with the final design) The amp uses "dollar days" tubes.

The next is an 807 Williamson (a little more ambitious) viewtopic.php?f=12&t=338702&hilit=807+Williamson
The '807' amp can use any of the '807' type pentodes, aka 6L6(GC), 6BG6, etc.

He's rather pleased with both of them.


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 Post subject: Re: Best choice for building a tube amp, 6L6GC/6V6/EL84?
PostPosted: Apr Fri 05, 2019 8:37 am 
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STOP!
What speakers do you intend to use?
The efficiency and impedance curves are very important factors to keep in mind.
I tend to consider the speakers and power amps as a system. The more compatible the speakers and pwr amps, the more realism can be achieved in sound reproduction.


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 Post subject: Re: Best choice for building a tube amp, 6L6GC/6V6/EL84?
PostPosted: Apr Fri 05, 2019 9:25 am 
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DrRick wrote:
STOP!
What speakers do you intend to use?
The efficiency and impedance curves are very important factors to keep in mind.
I tend to consider the speakers and power amps as a system. The more compatible the speakers and pwr amps, the more realism can be achieved in sound reproduction.


This is the output transformer that I plan to use. 8.5K at 25W it says.

https://www.banzaimusic.com/25-Watt-Out ... ormer.html

I'm planning to use a zenith 7" 49-1310 speaker for testing purpose.

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 Post subject: Re: Best choice for building a tube amp, 6L6GC/6V6/EL84?
PostPosted: Apr Fri 05, 2019 9:56 am 
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Barry H Bennett wrote:
An amp is supposed to be linear, so looking for a 'tube that has more bass' ain't gonna happen. What WILL happen is that since bass of course requires more power, you'll eventually run out of output from the tubes, or power supply.

6V6 and 6L6 can both build excellent amplifiers. There is a long running thread on this forum regarding 6V6 design. Possibly the same with 6L6 but not sure about that one. I'd read all you can before deciding. It's really a preference issue, not necessarily a performance issue, except for the limitations of any given tube you selected as your outputs. The output transformer can make a huge difference as well. And don't skimp on the power supply. :)


I've added a small update the original post. By bass I meant the type of slight bass you get in tube amps, not heavy stuff. I'm looking more into the output transformer selection part now. Currently I've only 8 ohm speakers with me. The 4 ohm ones I've are sub woofers. Also I saw that 30W and above are usually the 4 ohm.

Power Transformer is a 800V CT, (280mA to 300mA the seller had told me) , with one 5V and three 6.3V taps. It's quite a chunky transformer with 4.15"x3.5"x3.5'' dimensions.

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 Post subject: Re: Best choice for building a tube amp, 6L6GC/6V6/EL84?
PostPosted: Apr Fri 05, 2019 12:52 pm 
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"impedance curves " ????? Are manufacturers posting this data now? Even if you knew the curves, how are you compensating for this? With a tube amp, get the speaker to output tube impedance ratio close enough with the output transformer and you will have no problems.


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 Post subject: Re: Best choice for building a tube amp, 6L6GC/6V6/EL84?
PostPosted: Apr Fri 05, 2019 4:49 pm 
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One now has to wonder .... does the impedance curve change if you use cryogenically treated oxygen free wire when you wind a transformer ?? ;-)

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 Post subject: Re: Best choice for building a tube amp, 6L6GC/6V6/EL84?
PostPosted: Apr Fri 05, 2019 8:29 pm 
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n3uvt wrote:
"impedance curves " ????? Are manufacturers posting this data now? Even if you knew the curves, how are you compensating for this? With a tube amp, get the speaker to output tube impedance ratio close enough with the output transformer and you will have no problems.


Flattening out the impedance curve of a loudspeaker is trivial, but shouldn't matter for the OPs amplifier design in any case.

Use a Zobel to flatten out the upper octaves and use proper acoustic loading to flatten out the resonant peak in the bass frequencies.

For a two or three way speaker, the same principles apply, only you use Zobels for the squaker and tweeter, and play with the acoustic loading of the woofer. Then use typical crossovers.


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 Post subject: Re: Best choice for building a tube amp, 6L6GC/6V6/EL84?
PostPosted: Apr Sat 06, 2019 3:35 am 
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Barry H Bennett wrote:
One now has to wonder .... does the impedance curve change if you use cryogenically treated oxygen free wire when you wind a transformer ?? ;-)


Still using wire? That's so 1995. I use mercury-filled tubes, myself. The mid-fi guys are using Gallium/Indium:

http://www.teoaudio.com/products/liquid-audio-cables/

but that is a bit too pedestrian for someone like me.

Brett


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 Post subject: Re: Best choice for building a tube amp, 6L6GC/6V6/EL84?
PostPosted: Apr Sat 06, 2019 4:29 am 
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DrRick wrote:
STOP!
What speakers do you intend to use?
The efficiency and impedance curves are very important factors to keep in mind.
I tend to consider the speakers and power amps as a system. The more compatible the speakers and pwr amps, the more realism can be achieved in sound reproduction.
Er, yes and no. If you're trying to imply that a power amp should cater to the failings of the particular speakers one is using then that's a terrible idea. Ideally a power amp should be flat across the band with 0 distortion (not 100% achievable), period.

Then there's speakers selection and zobles to 'flatten' the response.

Or do it vice versa but the process is the same. Each should perform properly, independently of each other.

The issue of 'efficiency', SPL. is well taken. Speaker SPL has as much effect on the overall perceived 'volume' as amp power and, in many cases, is easier to change. By that I mean, a 12 Watt amp with 92 dB SPL speakers will sound as 'loud' as a 50 Watt amp with 88 dB SPL speakers but the extra cost of the 4X power amp is likely more than the 92 dB speakers vs. 88 dB speakers. Of course, if it isn't then go ahead and quadruple your amp power but, in either case, the amp and speakers should be treated separately.


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 Post subject: Re: Best choice for building a tube amp, 6L6GC/6V6/EL84?
PostPosted: Apr Sat 06, 2019 11:49 am 
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While discussing amp linearity and flatness, speaker efficiency and flatness... don't forget about room acoustics ;-) Probably the most overlooked factor of all in overall sound reproduction. You definitely want an amp with no distortion, and speakers that are efficient. But as for overall "flatness" ... the room itself makes a major contribution

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 Post subject: Re: Best choice for building a tube amp, 6L6GC/6V6/EL84?
PostPosted: Apr Sat 06, 2019 4:26 pm 
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benman94 wrote:

Use a Zobel to flatten out the upper octaves and use proper acoustic loading to flatten out the resonant peak in the bass frequencies.

For a two or three way speaker, the same principles apply, only you use Zobels for the squaker and tweeter, and play with the acoustic loading of the woofer. Then use typical crossovers.


Huh? "Use a Zobel"?! Solve a problem with extraneous oscillatory elements by adding *more* oscillatory elements? You can "correct" the magnitude response with a filter network, sort of, or you can "correct" the phase response with a filter network, sort of, but you aren't going to fix them both at the same time, in fact, the more you "fix" one aspect, the more you mess up the other.

Oy vey...

Brett


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 Post subject: Re: Best choice for building a tube amp, 6L6GC/6V6/EL84?
PostPosted: Apr Sat 06, 2019 4:56 pm 
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Brett_Buck wrote:
benman94 wrote:
in fact, the more you "fix" one aspect, the more you mess up the other. Oy vey... Brett


I think this more or less applies to most of the topics around here by the time we all get done with them ;-)

..........beware of bored engineers, techinicians, and hobbiests with too much time on their hands...... 8)

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 Post subject: Re: Best choice for building a tube amp, 6L6GC/6V6/EL84?
PostPosted: Apr Sun 07, 2019 1:04 am 
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Brett_Buck wrote:
benman94 wrote:

Use a Zobel to flatten out the upper octaves and use proper acoustic loading to flatten out the resonant peak in the bass frequencies.

For a two or three way speaker, the same principles apply, only you use Zobels for the squaker and tweeter, and play with the acoustic loading of the woofer. Then use typical crossovers.
Huh? "Use a Zobel"?! Solve a problem with extraneous oscillatory elements by adding *more* oscillatory elements? You can "correct" the magnitude response with a filter network, sort of, or you can "correct" the phase response with a filter network, sort of, but you aren't going to fix them both at the same time, in fact, the more you "fix" one aspect, the more you mess up the other.

Oy vey...

Brett
"Solve a problem with extraneous oscillatory elements by adding *more* oscillatory elements? " Yes, it's standard practice in analog systems from audio to video to RF. What do you suggest? Just leave the problem there?


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 Post subject: Re: Best choice for building a tube amp, 6L6GC/6V6/EL84?
PostPosted: Apr Sun 07, 2019 2:28 am 
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Flipperhome wrote:

"Solve a problem with extraneous oscillatory elements by adding *more* oscillatory elements? " Yes, it's standard practice in analog systems from audio to video to RF. What do you suggest? Just leave the problem there?


You aren't "fixing" anything in this case. But far be it for me to impede you, do whatever you want.

Brett


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