[Thomas0322]

I ordered the following tube amplifier.  It's 3 watts in Class A.  Initially, I was not impressed.  I tried tube rolling, and that made a significant improvement.  I have experience with the 3116 amps.  In comparison, the tube amp with the upgraded tubes has a richer and smoother sound, and it has greater detail and communicates the emotion in the music much better.  To sound right, these tubes need hours to warm up. 
 
I will mention two cuts from Stereophile Test CD No. 3.  In Sibley Sanctus Lydian, the drums are clearly delineated with the tube amp and they are more muddled together on the 3116.  My speakers are Mark Audio 6 cm Alpair with aluminum cones.  It is a fast driver.  The other cut is Blue Bird by Jimmy Rogers.  The honky-tonk sound, the emotional qualities of the music, are presented much better with the tube amp.  The volume is decent considering the 3-watt rating for the amp.  The drivers are about 82 dB w/m.

Here's a link to the amp in stock form.  The amp is available from a number of sources. 

https://www.aliexpress.com/item/32966535773.html?spm=a2g0o.productlist.0.0.782f1624amB9Ga&algo_pvid=1f2689be-c4ab-4d45-98f8-8c9023cb93e4&algo_expid=1f2689be-c4ab-4d45-98f8-8c9023cb93e4-1&btsid=0b0a555e16162487081544162e41f7&ws_ab_test=searchweb0_0,searchweb201602_,searchweb201603_

I chose the following tubes for the upgrade: 

https://smile.amazon.com/gp/product/B01BFJDTW0/ref=ppx_yo_dt_b_search_asin_title?ie=UTF8&psc=1

https://smile.amazon.com/gp/product/B003FO67WI/ref=ppx_yo_dt_b_search_asin_title?ie=UTF8&psc=1

This is a discussion from Wikipedia on tube equivalents. 

https://en.wikipedia.org/wiki/6V6#:~:text=6V6GT%20%E2%80%93%20smaller%20%22Glass%20Tube%22,a%20controlled%20warm%2Dup%20period.&text=6V6S%20%E2%80%93%20A%20modern%20production%2C%20large,plate%20and%20screen%20voltage%20rating

This is a comparison of preamp tubes from a vendor.

https://tubedepot.com/pages/tube-comparison-tool

The same vendor's power tubes.

https://tubedepot.com/t/tubes/power-tubes/6v6

[FullRangeMan]

For a 3W SE you will need a bening impedance  and a 100dB speaker, see the Paul Joppa rules.

Too bad you are using 3W with 82dB speaker, its not 92dB ?

[Thomas0322]

It's in my bedroom.  Good enough for there.  I bet that it would rock with a 92 dB speaker.  I'd like to hear it with K-horns.

[planet10]

What loudspeakers?

As Gustavo suggests due to the typically highish R_out of an SE amplifier really needs a loudspeaker with a benign impedance curve.

It is questionable how much bandwidth those output transformers have. The amp is dirt cheap and the quaity might follow from that.

dave

[FullRangeMan]

Small tube amps always benefit from 16Ω speakers, unfortunately they are rare today, in this case one should use two 8Ω FR drivers in serial 

[Thomas0322]

Between the original amp purchase and the upgraded tubes, I have about $160 in the amplifier.
My post was done with the intent to say that, for the money, it is quite good, and it smokes the chip amps. 
This amp has taps for 4, 6, and 8-ohm loads.
I will include a link that shows the impedance of the current model of my driver.  Mine is an older model.
On the new model of the driver, the impedance barely drops below 10 ohms.

I cannot find information on the phase angle for the driver. 
The phase angle is relevant when considering the driver's load on a tube amp.
I do not detect anomalies in the sound that suggest the amp has a problem with the driver.
My driver may be a little more sensitive than 82 dB.  The new driver (significant differences) is more like 86 dB.
This is all I am saying:  This little amp has detail and it communicates the emotional quality of the music very well.
It is just a good bang for the buck.  Just recognize the power limits.
https://www.madisoundspeakerstore.com/approx-5-fullrange/markaudio-alpair-7ms-grey-cone-5-full-range/

[planet10]

The phase angle is relevant when considering the driver's load

Another way of looking at the loudspeaker impedance.

Flat phase leads to flat impedance, but you need the loudspeaker impednce not the driver.

Don’t pay much attention to power ratings on any drivers ysed in the home. It is more or less irrelevant.

What box do you have the A7ms in?

dave

[FullRangeMan]

I cannot find information on the phase angle for the driver.
The phase angle is relevant when considering the driver's load on a tube amp.
How it works ?
The phase angle of a driver are continuously variable,
its a full graphic from 20 - 20kHz as the freq chart.

[Thomas0322]

Again, my Alpair 7s are an older iteration.  I posted the specs that I could find on the new version as that was the best that I found.  I have the drivers in a T-line with about 1.5 cu ft internal volume.  I used PVC pipe to make the T-line.  It's all internal, and I don't remember just what I did.  It has been years since I built those speakers.

Flat impedance is all well and good.  However, except for some ribbon drivers, it does not exist.  If the phase angle is negative (capacitive), then it is good if the impedance is high at the same frequency.  Low impedance and high capacitance require more power.  I can post the impedance curve of the newer model of this driver (above).  I do not see a graph of the phase angle.  So, all I can say is that the combination of amp and speaker
seem to work well, again within the power limits of the amplifier. 

We are getting away from what I wanted to do with this post, and that is to say, this is a neat little amplifier for the money after the tubes have been upgraded. 

[Thomas0322]

FRM, agreed.  The phase angle is continuously variable, and it varies with frequency from one speaker to another.  Unless we can compare the impedance and phase angle to the driver that I am using, we are not getting much useful information.  I am using an older model of the driver, and I just did not find that information online. 

[planet10]

https://frugal-phile.com/downloads/Alpair_7_data.pdf

In a TL (modeled or using classic design?) will have an impedance that looks similar to the data above, but will have a double peak from the box. How big and where it is exactly depends on the TL geomery and how damped it is. If it is lightly damped they will be fairly high, if dmped sufficiently they can be completely eliminated (but with little or no bass reinforcement).

In such a loudspeaker you can actually tune the bass in room with more of less damping. Bass too fat. Add damping.

dave

[planet10]

The phase curve is reflected in the impedance magnitude. Both capacitive reactiance and inductive reatance add to the DCR of the driver.

The resonant peak at the bottom is where capacitance resonantes with the inductance. The rise at the top is due to the VC inductance. In this case small because of very lower inductance due to the copper cap on the dustcap. Capacitve reactance usually comes from cross-overs. The little glitch you see below 1kHz is the transition frequency between [pistonic and chaotic radiation.

With a highish R_out amplifier it is the often significant impeance peaks in the regions of an XO point that most affect the interaction with the amplifier. This is often why FR speakers often work better with amplifiers such as we are discussing.

We know going in that we could have issues with the bass resonance. As mentioned eariler, this can be, in some loudspeakers, be tuned to best match the amplifier (The Frugel-Horns use this trick to (help) allow for accomodation of a very wide set of drivers.

Or, knowing the  R_out you can specifically design a loudspeaker to use with it. Here an example done by Dr Scott (Woden Design).

http://wodendesign.com/downloads/King-of-Swingers.pdf

dave

[FullRangeMan]

Thanks Dave appreciated

[Thomas0322]

It was my intent with this post to mention an inexpensive tube amplifier that, considering the cost, performed well.
It was not my intention to begin a theoretical discussion on loudspeaker design.
I do not plan to continue with that discussion.  I will review this topic from time to time.
If I see a post relevant to the amplifier, I will consider responding to that.

[Tyson]

Thomas,
I agree with you, if you're listening at moderate volumes in a small-to-medium sized room, low powered tube amps can be magical even if the speakers aren't a perfect match. 

[genjamon]

I used to use a little Miniwatt/APPJ cheap chinese tube amp (around 2.5 watts or less, as I recall) with upgraded tubes on my stock Pioneer SP-BS22-LR, which are 85dB monitors.  This was in a TV system in a small/medium sized den environment.  Sounded great.