New Design, SE 6005 Directly Coupled Audio Amplifier

[grindstone]

Thank you for posting your work (and in such detail). This will take more time for me to think about. While I am here, one question if you have time:
I can not tell if the star ground itself penetrates the powder-coating to earth the chassis as well (presumably to the green included in a terminal from the safety ground IEC input). Does the chassis itself electrically float or is there a star washer or something I missed? Thanks again for posting.

 

[fcon]

Hmmm... I do not want to inflame, to turn the world around and stir up controversy.
Right: wood cannot and would not be acceptable for industrial use, because of its weakness (it burns!) but it is far superior to steel as a chassis in all respects... but this is ONLY my opinion; do not expect to be believed and I really do not want a debate/argument pro/against it.
It is just a personal approach and a way of doing things!
-----------------
Jeff, I do not want/need advertising, neither do I want to argue, or pollute your topic.
-----------------
Looking forward to hearing experience from you, after such a complex, over-engineered tube amplifier (well, 6 of them, afterall!).
Then we can then talk about acoustics, enclosures and tube amplifiers in other topics.
I am only glad to have found a builder with such a passion and who works down to the ultimate detail, just like you.
With friendship...

 

[drlowmu]

Thank you for posting your work (and in such detail). This will take more time for me to think about. While I am here, one question if you have time:
I can not tell if the star ground itself penetrates the powder-coating to earth the chassis as well (presumably to the green included in a terminal from the safety ground IEC input). Does the chassis itself electrically float or is there a star washer or something I missed? Thanks again for posting.

Good question !! The 8-32 by one inch long brass bolt is threaded into the 14 gauge steel chassis, so that this star ground bolt is grounded. The IEC ground is also attached at that center-of-chassis position.

We am almost done replacing the second Input socket, on the repair. Besides using far better lighting,we inserted a spare 9 Pin vacuum tube into the NOS AMPHENOL socket. So, any excessive solder should not flow into the tube-pin contact area.

Amp's first full fire-up, is after Dinner !!

How close to designed will - these actual VDCs be ????? Curious to measure it all.

Jeff

 

[Dr.Gary]

Looks like you have heard this amplifier for long duration to arrive at this conclusion or are you speculating and have lots of free time?

My comments pertained to the design philosophy of this amplifier, not to its sonic performance. More specifically, my comments pertaind to the consequences of using an unregulated power supply that is fundamentally no different than those that were used in TVs back in the 1950s. No speculation on my part is involved, and my comments are facts, not conclusions.. The consequences of using an unregulated power supply are as well documented and well established as the fact that a rock that is dropped toward the earth will accelerate at a rate of 9.8m/s/s. Rather than representing a design that is "over-engineered" this build reflects the total absence of the sort of technical knowledge that nearly a century of real engineering has produced.

 

[grindstone]

Thank you.

 

[Hari Iyer]

My comments pertained to the design philosophy of this amplifier, not to its sonic performance. More specifically, my comments pertaind to the consequences of using an unregulated power supply that is fundamentally no different than those that were used in TVs back in the 1950s. No speculation on my part is involved, and my comments are facts, not conclusions.. The consequences of using an unregulated power supply are as well documented and well established as the fact that a rock that is dropped toward the earth will accelerate at a rate of 9.8m/s/s. Rather than representing a design that is "over-engineered" this build reflects the total absence of the sort of technical knowledge that nearly a century of real engineering has produced.

Ok thanks for your point of view. Recently i removed 10,000 uF of power supply capacitor from my SS phono preamplifier and replaced them with just 270 uF x 2. By this change they sound much superior, less noisy and more dynamic. It's popular wisdom to add tons of filter capacitors to a power supply or use regulation. I have not seen any power amplifier using regulated power supply much. It all depends on current drawn imo. If you are considering only a few mA draw you can live with low filter capacitor without any risk of noise or hum. IME higher Capacitor used in power supply filters make music very dull and boring.

 

[drlowmu]

We are very familiar with full regulation of tube amps.

The very first amp we ever self designed from scratch and built, a P-P-P 6B4G DHT amp starting out in 1982, was not just actively regulated, but double series regulated, for each of it's three separate B+ supplies.

Yes, we agree it was superior to an unregulated tube amp.

In stereo however, it also weighed almost 500 pounds and required SIX chassis. It was named " The Triode Music Amp ". One channel looked like so :




The underside of each AUDIO chassis looked like so :





The underside of each of our larger Power Supply chassis, looked like so :



....................................................

Both channels fit inside a 1988 VW Mini Buss. like so :


..................................................................


Others, in fact, some famous tube amp designers, started off like we did, building fully regulated Tube amps. Wm. Z. Johnson, prominent founder of Audio Research Corp, did a fully regulated tube amp, as his " top of the line" unit, called a Peploe Dual 100. We personally had one !!


.......

So, in our early years, fully regulated B+ amplifiers were built by certain individuals. But, with experience, we each abandoned the approach, cost, and effort.

In this world, 99.99999 percent of the total tube amps built today by Manufacturers are not fully regulated.

The amplifiers Dr. Gary uses at home, for the last 40 years ( a Harmon Kardon 430 receiver ) , and his newest - use amp ( a Jim Bonjiorno GAS "Ampzilla " ), both solid state, are likely not fully - regulated.

Every power amp Wm. Z. Johnson ( RIP ) and A.R.C. built, after the Peploe Dual 100, has not been fully - regulated. All Audio Research tube amps are not fully regulated ! Why ???

One time, the above - displayed 1980's " Triode Music Amplifier " , was sufficient for us . Not today.

In 2021, do we really NEED and want a multi-chassis 350 pound 1.5 WATT per channel tube amp, to power high efficiency ALTEC VOTT A7-8s, playing inside a modest sized living room ???

We build this 2021 two stage stereo 6005 amp, all DC coupled, with much anticipation, great joy and true satisfaction.


Jeff

 

[Dr.Gary]

Ok thanks for your point of view. Recently i removed 10,000 uF of power supply capacitor from my SS phono preamplifier and replaced them with just 270 uF x 2. By this change they sound much superior, less noisy and more dynamic. It's popular wisdom to add tons of filter capacitors to a power supply or use regulation. I have not seen any power amplifier using regulated power supply much. It all depends on current drawn imo. If you are considering only a few mA draw you can live with low filter capacitor without any risk of noise or hum. IME higher Capacitor used in power supply filters make music very dull and boring.

For a multitude of reasons, it is bad engineering to use significantly more than 1000uF in the power supply of a preamplifier. Also, while I am not up to date on popular wisdom, I can assure you that a large amount of capacitance in a power supply does not achieve the same result as active regulation.

 

[Dr.Gary]

We are very familiar with full regulation of tube amps.

The very first amp we ever self designed from scratch and built, a P-P-P 6B4G DHT amp starting out in 1982, was not just actively regulated, but double series regulated, for each of it's three separate B+ supplies.

Yes, we agree it was superior to an unregulated tube amp.

In stereo however, it also weighed almost 500 pounds and required SIX chassis. It was named " The Triode Music Amp ". One channel looked like so :


View attachment 65528

The underside of each AUDIO chassis looked like so :


View attachment 65529


The underside of each of our larger Power Supply chassis, looked like so :



....................................................View attachment 65530

Both channels fit inside a 1988 VW Mini Buss. like so :


..................................................................View attachment 65532


Others, in fact, some famous tube amp designers, started off like we did, building fully regulated Tube amps. Wm. Z. Johnson, prominent founder of Audio Research Corp, did a fully regulated tube amp, as his " top of the line" unit, called a Peploe Dual 100. We personally had one !!


.......View attachment 65534

So, in our early years, fully regulated B+ amplifiers were built by certain individuals. But, with experience, we each abandoned the approach, cost, and effort.

In this world, 99.99999 percent of the total tube amps built today by Manufacturers are not fully regulated.

The amplifiers Dr. Gary uses at home, for the last 40 years ( a Harmon Kardon 430 receiver ) , and his newest - use amp ( a Jim Bonjiorno GAS "Ampzilla " ), both solid state, are likely not fully - regulated.

Every power amp Wm. Z. Johnson ( RIP ) and A.R.C. built, after the Peploe Dual 100, has not been fully - regulated. All Audio Research tube amps are not fully regulated ! Why ???

One time, the above - displayed 1980's " Triode Music Amplifier " , was sufficient for us . Not today.

In 2021, do we really NEED and want a multi-chassis 350 pound 1.5 WATT per channel tube amp, to power high efficiency ALTEC VOTT A7-8s, playing inside a modest sized living room ???

We build this 2021 two stage stereo 6005 amp, all DC coupled, with much anticipation, great joy and true satisfaction.


Jeff

That's a very interesting and informative review of some of the power amps from the early 1980s that used regulated power supplies. Nonetheless, if you really want to be honest about it, your review is nothing other than a red herring that is aimed at diverting attention from the philosophical design issue that I raised. Specifically, the fact that the multitude of space-consuming paralleled capacitors do not reflect any "over-engineering", but instead constitute a multitude of cumbersome and space-consuming band aids that are used in an attempt to mitigate the gross interstage and intrastage coupling via the power supply lines that would not be needed if independent, hard-regulated power supplies were used for each of the two amplifier stages.

 

[drlowmu]

12-24-21 ....................... Mini REPORT ............................Measuring Running AMP

Amp has been running past two days, Am taking a multitude of measurements, with various tubes substituted in different locations, to discover

..........................................." what is circuit caused and what is tube-difference caused."

After putting together such a brand new design, one must become fully familiar with all the the direct couple operating voltages. This step is mandatory.

One must be sure, both stages are biased and operating on a long-term conservative basis, and at the desired Operating Points, one had in mind when designing the amp.

So far, on a 460 VDC B+ supply, we measure within 6 VDC of what we had planned for overall. Under 2%, not too bad at all.
However, we are about 15 VDC " off " in two places, from what we wanted the two tubes to settle in at, VDC-wise. This is about 6% off, and ..... it has our attention.

Today, 12-24, only after doing "one more " tube swap and full measurement, we will be making a decision and likely try two small incremental resistor value changes, which should " center " the direct couple's operating points - of BOTH stages rather nicely.

The above process, ( minor resistor value change - decisions ), is normal and to be expected, in any brand new circuit DC design. In DC tube amps, when you change one resistor value, multiple voltage changes occur !! It is highly inter-related. All the voltage results must be recognized, documented, and accounted - for in the design.

We can see in the photo below, how the big yellow 12 AWG Mil Spec wire has now been more directly routed, to feed the Input stage's two B+ Modules, for either channel. Looks like a truncated " V ". This change reduced that wire's length, by about 55%. We like it.




Again, thank you for looking - and following along.

Jeff

Ohh, I forgot to report, thermally, this amp operates cool to the touch and as good or better as we would have hoped for ! Resistors seem to operate very unstressed. Only one resistor's heat sinking will be changed some. ( Yes !!! It is the one we previously talked about ! ). LOL.

J

 

[drlowmu]

11-24-21 AGAIN......................Tiny mini report !!!!! ........................BLOWN AWAY.........................

Well we swapped tubes and have good news. It now seems that the first set of tubes, and the voltage differences reported in the above post, were abnormal !!

We are pleasantly surprised.

With new tubes installed, and a 125 VAC line :

1) We wanted 211.5 VDC on the Direct Couple.

It now measures 213.3 VDC. ....... ( VS 190.3 VDC, measured initally !! )

2) We expected 222.3 VDC for the 6005 "across" the tube ( ie : Plate to Cathode or P-K ), and we wanted no more than 225.0 VDC.

It now measures 224.7 VDC. ........ ( VS 251.5 VDC, measured initially ).

These above two new key measurements tell us : both the input tube and the output tube are operating at " ideally sought after " voltage points,. This is as good a result - as good as we know how to make it.

The 6005 has a " by the book " maximum suggested 250 VDC Plate to Cathode voltage rating. However, since this is a small tube, with unusual -TIGHTLY spaced ( and fully symmetrical !! +++ ) elements. We wanted to have NO possible arcing - as the 6005 output tube ages. Thus, our conservatively selected 225 VDC P-K operating goal.

On a 120 VAC line input ( a lower line VAC ) the 6N23P-EV Input tube still has 205 VDC measured on it's plate. We were hoping for 200 VDC or more on the plate, so the Input tube would " swing ", and we have it !!!!

This is all really great news, after many months of work and planning.

Thanks for following along,

Jeff

 

[drlowmu]

 

[drlowmu]

12- 26 -2021 ........................... INITIAL LISTENING IMPRESSION .......................... and WHY

We have not visited my Audio Mentor, over the last 2.5 years, to hear his very latest SE DC amps, (eg : 6E6P-DRU DCed to a KT150 ) which I am willing to bet.... are fabulous sounding.

However, over the last two days, our SE DC amp has been playing music, breaking in, and we thought it apropos, to share a subjective listening initial impression.

This amp is showing signs of being the best tube amp we have ever built or ever heard.

Compared to our 2019 SE build ( 1/2 12BZ7 DCed into a KT88 ) ( and ALL other amps we have personally heard ), this initially seems to play music with about 12 to 18 percent more definition, or audio resolution. In dynamic terms, it seems to excel by 10 to 15 % over all else - we have ever heard. Speakers used for this evaluation are very-well-set-up ALTEC Voice of the Theatre A7-8s, with top-of-the-line ALTEC 515B woofers and ALTEC 802D compression drivers.


This highly positive sonic 2021 result was planned for........................... and is not totally surprising to us .


AS we often repeated in this thread ..........." In the end, we all listen to a modulated power supply. How good is it ?? "

In the first three pages of this thread, ( if one takes the time, and has the actual interest to read this ), we described our preference of a unique passive power supply over any active regulated supply. We are much in favor of the actual listening results with OUR passive build approach. Also we described in this thread the ( largely unrealized ) need and reasons for using multiple film cap bypassing, in all key circuit locations.

- - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - -

Here is why we feel this 2021 effort ( 6005 amp ) is playing better, right off the bat, than the 2019 ( KT88 amp ) effort :

Realize, both amps are similarly built with 1/2 a triode, directly connected to a TETRODE, and operating with ZERO negative feedback :

.
KT88's G2 power supply : One B+ SHUNT and one Final Filter ( L1/C1 ) .

6005's G2 power supply : Two B+ SHUNTS, in series, and two Final Filters in series ( L1/C1/L2/C2 ).

KT88s Ra power supply ( Input tube's plate resistor = "Ra" ) : ......................................

.......................................................Two B+ SHUNTS, in series, and one Final Filter ( L1/C1 ).

6005's Ra power supply : Two B+ SHUNTS , in series, and two Final Filters in series ( L1/C1/L2/C2 ).


So, the new 2021 design, for Ra AND G2, has become Double SHUNTED and Double Final Filtered !

From what has been heard, from reference - familiar source material the last two days, we feel it was well worth the effort !!

Kindly realize this, ( and except for amps by our Mentor, Dennis Fraker of Serious Stereo ) no amps to our knowledge, ( in ALL of the tube audio amps ever made in this world ), use B+ SHUNTING, and / or B+ FINAL Filters !!! ZERO, let alone one, or better yet, two in series !!

Whoops, we do know of one notable exception. In a lovely place in this world called Thane, India. Hari Iyer's self-built 2020 KT88 amp, is an offshoot of our 2019 design.

- - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - -

Other initial comments :

1) Measured circuit voltages match, very much as planned, conservative.
2) Thermal operation is decent, no hot spots on chassis
3) So far, NO ( multiple ) power transformer PHASE orientation-work has been done. We will do it by ear, is important.
4) It takes about 75 hours, for the 6 Ohm chokes to break - in, and lose their midrange recessiveness.
5) It takes time, for the film caps, solder joints, rectifier tubes etc. to break in.
6) This amp, with a new-found level of resolution and dynamics, is actually EXCITING to hear.

Thanks everyone, for following along. Need next, to show some " top side " photos. OHH...............

7) The Softone RW-20 transformers sound much better, with their metal covers removed, as do all outputs. No contest on any really good hi fi system.


Jeff

 

[Hari Iyer]

12- 26 -2021 ........................... INITIAL LISTENING IMPRESSION .......................... and WHY

We have not visited my Audio Mentor, over the last 2.5 years, to hear his very latest SE DC amps, (eg : 6E6P-DRU DCed to a KT150 ) which I am willing to bet.... are fabulous sounding.

However, over the last two days, our SE DC amp has been playing music, breaking in, and we thought it apropos, to share a subjective listening initial impression.

This amp is showing signs of being the best tube amp we have ever built or ever heard.

Compared to our 2019 SE build ( 1/2 12BZ7 DCed into a KT88 ) ( and ALL other amps we have personally heard ), this initially seems to play music with about 12 to 18 percent more definition, or audio resolution. In dynamic terms, it seems to excel by 10 to 15 % over all else - we have ever heard. Speakers used for this evaluation are very-well-set-up ALTEC Voice of the Theatre A7-8s, with top-of-the-line ALTEC 515B woofers and ALTEC 802D compression drivers.


This highly positive sonic 2021 result was planned for........................... and is not totally surprising to us .


AS we often repeated in this thread ..........." In the end, we all listen to a modulated power supply. How good is it ?? "

In the first three pages of this thread, ( if one takes the time, and has the actual interest to read this ), we described our preference of a unique passive power supply over any active regulated supply. We are much in favor of the actual listening results with OUR passive build approach. Also we described in this thread the ( largely unrealized ) need and reasons for using multiple film cap bypassing, in all key circuit locations.

- - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - -

Here is why we feel this 2021 effort ( 6005 amp ) is playing better, right off the bat, than the 2019 ( KT88 amp ) effort :

Realize, both amps are similarly built with 1/2 a triode, directly connected to a TETRODE, and operating with ZERO negative feedback :

.
KT88's G2 power supply : One B+ SHUNT and one Final Filter ( L1/C1 ) .

6005's G2 power supply : Two B+ SHUNTS, in series, and two Final Filters in series ( L1/C1/L2/C2 ).

KT88s Ra power supply ( Input tube's plate resistor = "Ra" ) : ......................................

.......................................................Two B+ SHUNTS, in series, and one Final Filter ( L1/C1 ).

6005's Ra power supply : Two B+ SHUNTS , in series, and two Final Filters in series ( L1/C1/L2/C2 ).


So, the new 2021 design, for Ra AND G2, has become Double SHUNTED and Double Final Filtered !

From what has been heard, from reference - familiar source material the last two days, we feel it was well worth the effort !!

Kindly realize this, ( and except for amps by our Mentor, Dennis Fraker of Serious Stereo ) no amps to our knowledge, ( in ALL of the tube audio amps ever made in this world ), use B+ SHUNTING, and / or B+ FINAL Filters !!! ZERO, let alone one, or better yet, two in series !!

Whoops, we do know of one notable exception. In a lovely place in this world called Thane, India. Hari Iyer's self-built 2020 KT88 amp, is an offshoot of our 2019 design.

- - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - -

Other initial comments :

1) Measured circuit voltages match, very much as planned, conservative.
2) Thermal operation is decent, no hot spots on chassis
3) So far, NO ( multiple ) power transformer PHASE orientation-work has been done. We will do it by ear, is important.
4) It takes about 75 hours, for the 6 Ohm chokes to break - in, and lose their midrange recessiveness.
5) It takes time, for the film caps, solder joints, rectifier tubes etc. to break in.
6) This amp, with a new-found level of resolution and dynamics, is actually EXCITING to hear.

Thanks everyone, for following along. Need next, to show some " top side " photos. OHH...............

7) The Softone RW-20 transformers sound much better, with their metal covers removed, as do all outputs. No contest on any really good hi fi system.


Jeff

Thanks for the exclusive subjective listening report. My 2020 KT88 also use a double shunt, double series filter and also a double DFFF. It's astonishing to know how silent this amplifier can be with just 330mH x 2 of series inductor and just 2 film capacitors of 30 uF and 50uF. Only listening is believing .

 

[drlowmu]

Thanks for the exclusive subjective listening report. My 2020 KT88 also use a double shunt, double series filter and also a double DFFF. It's astonishing to know how silent this amplifier can be with just 330mH x 2 of series inductor and just 2 film capacitors of 30 uF and 50uF. Only listening is believing .

Hello dear Hari,

Your response is not as accurate as I would like to see here, and it confuses my post and my above descriptions, and people who may try to understand them.

The double series SHUNTING to your 2020 KT88 amp is exactly like my 2019 KT88 amp I described.

G2 is single shunted ( ONLY ) . The SHUNT for G2, splits the B+ and the B+ split after G2 ( or a " Y " ) feeds a separate SHUNT for the Ra (and also feeds G2) .

Effectively, a separate Ra SHUNT is fed from the G2 SHUNT, so the Ra is "double shunted ".

Each of your 2020 mono amps has only TWO SHUNT assemblies total. ONLY the Ra is being effectively double shunted.

For your mono amps to be double shunted for EACH Ra and EACH G2 , ( as per the description of the new 2021 6005 amp ), would require the mono amp to employ FOUR separate SHUNTS. It would need to split the B+ off of C2 at an amp's main L1/C1/L2/C2 filter.

Your C2 would need to have THREE B+ feeds off of it, one B+ feed for the finals ( output XFR ) , one B+ feed for G2 ( with two SHUNTS - to be true double SHUNTED ) , and one B+ feed for the front end's plate resistor, or Ra ( with TWO B+ SHUNTS - to be true double SHUNTED. )

"Double Final Filters", intellectual property of Dennis Fraker ( hence the initials DF FF ), is a whole other complex topic. No need to cover it herein.

Got it ?? Thanks.

Jeff

 

[drlowmu]

12-27-2021................................Commentary...............................On OUTPUT TUBES ....................................

I mentioned, two posts above, that this new amp was exciting to hear.

This is true. I proposed it was due to the amp's extra power supply engineering, that no other amps employ. This is only PARTIALLY the cause of the excitement when listening.

The other reason for the awesome performance is the 6005 ( or a 6AQ5 ) tube ITSELF !!!!! This tube " ROCKS and BELTS OUT THE MUSIC, bottom to top. This is largely UNKNOWN among audiophiles and tube amp enthusiasts !! .

As inferred several times in my thread, we build a single amplifier that will play the entire musical experience, from the very bottom octaves to the top-most highs. We do not usually " biamp" speakers, with differing amps splitting the spectrum. NO, that is not good enough for us. IF we were to biamp, both amps would be exactly the same, and neither would employ NFB ( negative feed back ). This is the ONLY way to ideally biamp, if you are a serious listener !!!

There are two particular output tubes, popular for decades in the tube audio output world, that DO NOT and CAN NOT perform a full range playback. They only play the midrange well, and flunk at playing real highs ( a cymbal in a drum kit ) and are incapable of playing the lows, ( such as the bottom portion of a grand piano. )

Typically, inexperienced and unknowing audiophiles HOARD these two tubes,as though they are the Holy Grail, but they are not - at all. It is really hilarious to me. Tube audio people become deflated and highly disappointed ( or get defensive and argue ) when I tell them about this !!

The first small popular output tube, that can not play full range, is the 6BQ5, used decades ago, in the popular ( in the USA ) Dynaco Stereo 35. Many " smaller " tube amps have since used this small sleepy sounding midrange only tube. Realize this : a $2.00 6AQ5, or any $10.00 6005, will absolutely KILL, in full-range music performance, any 6BQ5 tube in existence. The problem being..... with the 6BQ5 tube itself.

The 6AQ5, and its military brother, the 6005, have distinct advantages that are highly audible and almost UNKNOWN today in audio. Guess what, they will likely remain that way also !!

The elements in the 6AQ5/6005 are symmetrically shaped and spaced apart from each other. So this tube has NO CORNERS OR BENDS in it's construction. A round cathode, round grid, and a round plate structure !!! Much like the desirable USA-made EIMAC Transmitting tubes !! See :

..........

Love those ribbed plates for extra strength and rigidity !!

Additionally, and unusually, there is very TIGHT spacing between the elements in the 6AQ5/ 6005 tube, VS: other vacuum tubes. This means, with the previously mentioned NO CORNERS.........AND ..... the addedTIGHT spacing,............ the path of the electron flow is very DIRECT.

So this tube has an unusually high electron-TRANSFER factor, it is highly efficient VS other tubes.

The tube operates at 250 degrees Centigrade !!

It DOES SOMETHING to move the speaker, when a music signal is imposed upon it's grid , and it does this,, due to its efficient design, WIDE BAND...... bottom to top.

Put this tube in a really good audio circuit, with a good power supply, and this tube EXCELS. It becomes special and EXCITING to hear, VS most all other common vacuum tubes people use.

I have been building and listening to this tube for several years now, and more so, the last two days in this newest optimized amp design. IT trounces the best I was able to get with a JJ 2A3-40 or a decent KT88. Hearing this music playback is so evident when using large radiating surface efficient speakers such as my ALTEC VOTT A7-8s.

Now there is a second " turkey tube ", that I like to call a " first cousin " to the 6BQ5, in its midrange -only performance. I want to tell you ALL about it !!! This is the funniest one of all to me, because it is HIGHLY sought after and highly hyped world-wide !! That is the vintage ST ( or globe ) shaped TYPE 45 tube !!!

Never in one million years, can it play the bottom end of a grand piano properly. It was a mass produced tube in its day, and is made as cheaply as possible. It has THIN wires leading to the four tube pins, that lose energy transfer. It was designed to be made as cheaply as possible, to power table radios in it's day. THAT today, in 2021, is the BEST use of this sorry " nice midrange " only tube.

Yes, the 6BQ5 and the ST TYPE 45, are to be avoided at all costs, if you want superior full range playback , with a single amp on a single speaker.

These two popular tube choices DON'T and CAN NOT do it !!

I grew up, having had heard all my life that a TYPE 45 tube was the best sounding Finals tube in audio. It made sense to me, being beneficially, a non paralleled 2A3 biplate.

I WASTED two years of my audio life ( 2015-2017 ) building two different " all-out " directly coupled Type 45 amplifiers. While the amp played nicely in many areas, ( especially being Direct Coupled ), in NO WAY could it play the bottom end of a grand piano on a highly efficient ALTEC VOTT. !!! No way,........... it flunked !! Two years wasted.

It was, not the amp's fault, nor the circuit's fault, but SOLELY the ST 45s' fault !! A modern JJ 2A3-40, a MONO plate, in the same circuit, played the grand piano properly. In all my reading on line, I have found only THREE mentions of the Type 45 being somewhat weak on the bottom end. This tube most certainly is lacking / weak down there, and it belongs with a 6BQ5, in someone else's home audio amplifier !!

The 6005 EATS them both, and many other tubes due to its inherent element SYMMETRY and TIGHT spacing. ( BTW, that 6005's tight element spacing is why we operate the 6005 at 225 VDC P-K , rather than the 250 VDC rated maximum !! ) It helps avoids arcing as the tube ages over many years of use.

With this 2021's latest power supply design, R-Core transformers, and general execution, we are looking forward to using and hearing our new amps !! So far, after two days only, 6005 playback seems very decent !!

Now, you all know my mind. YMMV, and that is fine with me !!!!!!!!

Jeff

 

[prem]

Drlowmu, what pre amp do you use with your power amp? And do you listen primarily to vinyl or digital? And if vinyl, what phono do you use?

 

[drlowmu]

Drlowmu, what pre amp do you use with your power amp? And do you listen primarily to vinyl or digital? And if vinyl, what phono do you use?

Thanks, good question !

I currently have a Trevor Lees cascode 12AX7 phono preamp, no line stage, sometimes a DIY passive ATTENUATOR. I own about 12 to 13,000 LPs collected since 1960 . Have plans for my own 12AX7 preamp build, with SHUNTS, DCed, and Final Filters, maybe in mid 2022.

Also own a Pioneer ELITE BDP-09FD 31 pound bluray player, for CD playback. My only digital.

For amplifier evaluations the last five years, and designing by ear, I run the BDP-09FD directly into an amp, one set of interconnect cables and RCA jack interfaces, full signal. This eliminates any ATTENUATOR and a second set of interconnects and RCA jack interfaces needing to be in the circuit.

Yes, it is loud, but ' have no neighbors to worry about. Just my own hearing damage to consider.

Jeff

 

[prem]

Like you, I too found the 45, 300, EL 84 lacking when it comes to full bandwidth. 2a3 was the only DHT tube that I found to be acceptable. I think the Siemens F2A in SE mode has merit. What is your opinion of the GM 70 and the 6c33 tubes?

 

[drlowmu]

Like you, I too found the 45, 300, EL 84 lacking when it comes to full bandwidth. 2a3 was the only DHT tube that I found to be acceptable. I think the Siemens F2A in SE mode has merit. What is your opinion of the GM 70 and the 6c33 tubes?

This which you report is encouraging for me to hear.

Yes, I avoid 300Bs also, prefer the 2.5 VAC filament on a 2A3. Never worked with F2As.

In 2019, I was able to easily outperform a VAIC MESH 2A3, with a $39.00 Electro Harmonix KT88 !!! Due to my own amp's power supply design.

I prefer tubes that are smaller than things like the GM70, and would never consider them.

I now will only use speakers that are about 101 db with a large radiating surface. I will NOT need more than a couple of decent Watts.

I will ONLY use two stage DC amps, never a three stage. I keep the system SIMPLE. A two way speaker. Don't even use any crossover on my 515Bs, they run full range !!

Jeff

I VERY much - enjoy A-7 ALTEC enclosures, and ALTEC drivers, as I have executed them.

Jeff