Dennis Had Inspire Amps

[FloridaBoy]

Originally Posted by pstrisik

Glenn..... I'm currently using a Voskhod 6N23P driver and Visseaux 6V6 power tubes with the 5V4G. The Omega Super Alnico Monitors have more hi freq extension than the previous Omegas that I had and my tube preferences have shifted around.

The Brimar 6V6's weren't anything special when I tried them. I can't recall if I've tried them with these speakers though, so I will again and post back.

I saw a NOS quad of Visseaux 6V6's go on ebay the other day. I was curious if anyone here had snagged them. They don't come up much any more. The Popes sound a bit soft to me these days.

Changing speakers will most always change tube preferences. Especially input /driver tubes.

[robert_kc]

Originally Posted by FloridaBoy

Where do you live?

Kansas City.

You highlighted my reference to our symphony hall. We’re very fortunate that benefactors donated money for the Kauffman Center for the Performing Arts, which includes Helzberg Hall (home to the Kansas City Symphony), and Kauffman Theatre (home to the Lyric Opera of Kansas City, and the Kansas City Ballet).





(The fisheye lens distorts the photos somewhat.)

[pstrisik]

Originally Posted by FloridaBoy

The unknown variable is Dennis' auto bias implementation in the circuit. You may be over thinking this. The beauty of this gear is the simplicity. Just experiment with tubes until you hit the combo that does it for YOU in your room with your source(s).

I've been doing that for a year and a half with very good results. I like to understand and to learn!

[FloridaBoy]

Originally Posted by robert_kc

Kansas City.

You highlighted my reference to our symphony hall. We’re very fortunate that benefactors donated money for the Kauffman Center for the Performing Arts, which includes Helzberg Hall (home to the Kansas City Symphony), and Kauffman Theatre (home to the Lyric Opera of Kansas City, and the Kansas City Ballet).





(The fisheye lens distorts the photos somewhat.)

Great Plains Audio...check them out. Wow..a hall like that and Arthur Bryant's BBQ!

GPA is serious American audio and with what you are considering spending you need to take a road trip. Bring your Inspire gear. You may be done 4 ever.

[robert_kc]

Originally Posted by FloridaBoy

Great Plains Audio...check them out.

Thanks for making me aware of Great Plains Audio. Do you own any of their products?

I see the following statement on their website, however there has been no update in more than 3 years: “Great Plains Audio is in the process of designing a whole new generation of complete loudspeaker systems for home and professional use. Watch for announcements about these exciting new systems in our GPA NEWS page.” Do they manufacture complete home hi-fi speaker systems, or just Altec drivers?

I’ve spent a little time “googling” GPA – are they still a “one man operation”?

[pstrisik]

Pair of Visseaux 6V6 - NIB just came up on ebay for $150. Go get 'um!

edit: Gone within hours! Anyone here get them?

[pstrisik]

Fellow Inspirerers:

Dennis generously described some about his design thoughts, particularly with relevance to the current rectifier thread of conversation here.

I'm digging back a ways and giving an old RCA 5U4G a try after reading what he says.

Unlike most single-ended and also push-pull tube amplifier designs my Inspire amplifiers have a regulated B+ voltage circuit in one section of the power supply. The nominal value of this regulated voltage is 250 volts DC. I apply this voltage to the plate (anode) of the driver tube and in the newer designs the cathode bias of the driver tube as well. In the single-ended pentode (beam-power) design I also apply this regulated B+ to the output tube screen grids as well. Utilizing this regulated controlled voltage on the driver tube and the screen grids has many attributes that I'll save for another discussion but one that is most relevant is the fact that no matter the type of rectifier tube one places in the Inspire Amp design the input tube and screens remain the same voltage. NO CHANGE IN CHARACTERISTICS OF THE DRIVER TUBE STAGE. The change occurs in the output stage where the output tube plate voltage varies with the type of rectifier tube. Fortunately, with the screen voltage stable in the output stage one is able to listen and hear dramatic sonic changes of the output tube itself without having to take into account the input driver selection. The auto bias system becomes very broad banded because of the constant regulated screen voltage. In other words a huge variety of beam power output tubes maybe used with sometime dramatic sonic changes and others more subtle. I design these amplifier circuits with the second harmonic as the key ingredient in choice of bias circuit values. The changes one hears as the various tubes are selected is revealing harmonic output changes. Here is an example of what may occur given a static speaker selection. In other words one loudspeaker type in the system and then varying output tubes. The 6V6 will yield a high level of 2nd harmonic content even when driven way past linear amplification output. Yet the second harmonic masks the nasty third and fifth harmonics yielding a smooth clean sound musical signal even in over drive condition. Now the same static condition with a KT88 output in the same amplifier. The output power will be greater but may contain additional uneven (odd order) harmonics when driven near clipping. Given this same situation and inserting the 5AR4 rectifier tube with the KT88 then the similar output pattern with even order harmonics with the second predominate will occur. So one would prefer a 5AR4 higher plate voltage rectifier for the higher dissipation KT88. In other words the output spectrum is very similar with a 5U4 and 6V6 output tube combination as is the 5AR4 and KT88 combo.

Now I have completely scrambled your thinking ... LOL ... Anyway in simplistic terms ... using any rectifier will not change the input tube characteristics of the Inspire Amplifiers. The sonic changes are dependent on the output tube selection and rectifier tube for a particular loudspeaker load. The rectifier tube will only effectively change the usable output tube plate voltage in the amplifier. Since the Inspire amps are all class A the operating voltage remains very constant because the output stage is running at full conduction level at all times. This is class A bias.

PS: I am not aware of any other SEP or SET tube amps using regulated voltage power supplies.

PSS: I have four different output transformer designs and impedances I use for the various amplifier designs and power levels. SET and SEP

Just one more thought ... personally I prefer the sonic presentations of the directly heated (5y3,5U4) rectifier tubes vs the indirectly (5AR4 type) in my amplifiers. If one wants to push the amps to the limit then the indirect cathode type (5AR4) would be the choice. Just a personal listening choice. Some times the sonic presentation preferred choice defies engineering parameters.

[nhparrot]

Originally Posted by pstrisik

Pair of Visseaux 6V6 - NIB just came up on ebay for $150. Go get 'um!

edit: Gone within hours! Anyone here get them?

Peter,
Christmas present to myself, to go along with the KT88's and KT77's the missus gave me.

Glenn

[pstrisik]

Originally Posted by nhparrot

Peter,
Christmas present to myself, to go along with the KT88's and KT77's the missus gave me.

Glenn

Oh good! Glad to hear it. Kind of like "keeping it in the family!" I look forward to your impressions.

KT-77's are current production I assume? The old GECs are something, but quite expensive.

[nhparrot]

Originally Posted by pstrisik

Oh good! Glad to hear it. Kind of like "keeping it in the family!" I look forward to your impressions.

KT-77's are current production I assume? The old GECs are something, but quite expensive.

Yes the KT77's and KT88's are both current production Genalex Gold Lions.

Thanks for the heads up on the Visseaux's. Happy New Year.

Glenn