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bharat

Diving into tube amp world with Marantz 8

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Back in the day, when I had my shop, I owned many including offerings from Eico, Knight, Lafayette, and Heathkit.  They were all quite decent and provided some useful information but certainly were not the last word.  Now, I don't have any!  Modern caps are so reliable, and cost effective, that I don't find it worth spending the time to test old caps especially when they have to be desoldered to do so (sometimes, in spite of using a heat sink on the lead, the heat from the iron is enough to cause a cap to fail).  If I'm going to guarantee a piece of equipment which I've restored or constructed I don't want to deal with a call-back due to failure of an old part.  This works for me.  Others have their own philosophy.

 

Some day, if I have time, I'll start a thread entitled "Tales from the service bench" and will relate stories about hours spent tracking down resistor and capacitor failures in audio equipment, radios, and TVs.  Some are quite humorous!  

 

 

Maynard

 

 

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I own an 8B and got some some static from a wonderful member of this Forum whom I greatly admire, when I re-did all the caps , resistors etc.  because I would be changing that special 8b sound. True the sound did change, but not as much as you would imagine, and it's still the amp I use the most.

 

One thing that will be difficult to source is the can-type cans on top.  The values are not reproduced in can-style caps these days and it's a tough fit to get the five different values installed under the chassis.  There was a company, whose name escapes me, that made a reproduction of the 8b for several years, and they had spare cans that they were selling.  They may be out of stock by now, but I would do a little online research, track them down and see if they have any left. 

 

I'm with Maynard on a rebuild. However, I do believe you can  safely play it for awhile, just do not leave the room or, indeed, the house for very long if it's plugged in, because something could fail.  

 

If your only interest is resale, leave it alone, but otherwise do not be concerned about a rebuild. Indeed make sure that you do.  If can guarantee you that neither myself nor that amp is same sixty years later.

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1 hour ago, thebes said:

There was a company, whose name escapes me, that made a reproduction of the 8b for several years, and they had spare cans that they were selling.  They may be out of stock by now, but I would do a little online research, track them down and see if they have any left. 

 

It was VAC but I’d be surprised if they still sell them.

 

http://www.vac-amps.com/

 

miketn

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On 10/22/2019 at 1:53 PM, mikebse2a3 said:

 

It was VAC but I’d be surprised if they still sell them.

 

http://www.vac-amps.com/

 

miketn

Good memory Mike!

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Here's the 9

 

https://www.audioclassics.com/detail?detail=9B&nav=cat

 

 

Home > Amplifiers > 9B
ACL 9B   Product Brochure [pdf]
80 WPC 160 Watt Mono Tube Original List Price: 9999.00

Grade: NEW NEW: 4999.00
New in a box
Comments:Champagne Chrome
 

Grade: B1 B1: 4399.00
Physical: Some light scratches - Excellent Condition
Electrical: Meets or exceeds original specs, all functions operate
Comments:Champagne Chrome.
 

ACL 9B
File Photo for Representation of item. May not be the actual item offered for sale.
 
 
 
Shipping weight: 70 lbs.

Related Categories:   Interconnect

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21 hours ago, dirtmudd said:

Here's the 9

 

https://www.audioclassics.com/detail?detail=9B&nav=cat

 

 

Home > Amplifiers > 9B
ACL 9B   Product Brochure [pdf]
80 WPC 160 Watt Mono Tube Original List Price: 9999.00

Grade: NEW NEW: 4999.00
New in a box
Comments:Champagne Chrome
 

Grade: B1 B1: 4399.00
Physical: Some light scratches - Excellent Condition
Electrical: Meets or exceeds original specs, all functions operate
Comments:Champagne Chrome.
 

ACL 9B
File Photo for Representation of item. May not be the actual item offered for sale.
 
 
 
Shipping weight: 70 lbs.

Related Categories:   Interconnect

 

 

The highly revered Malantz Model Nine monoblock !! 

 

Here is an interesting and true tidbit on its design.  In the 1980s, I had befriended an avid audiophile, who was also the DEAN of E.E. at the University of Alabama  His name was Charles A. Halijak, PhD.  During his career, he published 20 papers at the University, and received 27 different Citations ( not for speeding, gents !! ).  His published paper record can be seen on-line here :

 

https://www.researchgate.net/scientific-contributions/2017834553_Charles_A_Halijak

 

Here is what I want to tell you all.  Dr.  Halijak's worst-liked amplifier, from a E.E. design point of view, was the Marantz Number Nine.   He felt it had so many design errors, that yearly he would have the students in his class, critique the design, and offer improvements to submit to Dr. Halijak.  This was his own requirement, before they would be able to pass his E.E. course !!!!!!

 

If any E.E. schooled by Dr. Halijak at the University of Alabama in the 1980s is reading this, I would enjoy your confirmation, of what I am reporting herein, and believe to be true.

 

Dr. Halijak was also a big believer of low as possible / practical DCR  ( Direct Current Resistance ) power supplies.   I wrote about that on page 8 of a KT88 build thread, earlier this year.

 

His favorite value power supply choke, for his own personal tube amp builds, had to be custom made back then.  He had Stancor build for him to his spec :  1 HY at 8 Ohm DCR power supply chokes.   Isn't that interesting, because it does not necessarily meet critical inductance, as is always taught the last maybe 100 years in all the conventional EE courses.  Dr. Halijak was brilliant, look at his papers.   

 

Today, Hammond has a off-the-shelf 159ZA choke, six ohms, and it requires 75 hours of music - playing to break in.  One would always use at least two of these, in each tube amp's supply, as a L1/C1/L2/C2 B+ filter to feed the Finals.  Two 159ZAs, connected in series, is only 12 Ohms total DCR feeding the Finals tube,  from inductors .

 

Jeffrey Medwin

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11 hours ago, Jeffrey D. Medwin said:

 

 

The highly revered Malantz Model Nine monoblock !! 

 

Here is an interesting and true tidbit on its design.  In the 1980s, I had befriended an avid audiophile, who was also the DEAN of E.E. at the University of Alabama  His name was Charles A. Halijak, PhD.  During his career, he published 20 papers at the University, and received 27 different Citations ( not for speeding, gents !! ).  His published paper record can be seen on-line here :

 

https://www.researchgate.net/scientific-contributions/2017834553_Charles_A_Halijak

 

Here is what I want to tell you all.  Dr.  Halijak's worst-liked amplifier, from a E.E. design point of view, was the Marantz Number Nine.   He felt it had so many design errors, that yearly he would have the students in his class, critique the design, and offer improvements to submit to Dr. Halijak.  This was his own requirement, before they would be able to pass his E.E. course !!!!!!

 

If any E.E. schooled by Dr. Halijak at the University of Alabama in the 1980s is reading this, I would enjoy your confirmation, of what I am reporting herein, and believe to be true.

 

Dr. Halijak was also a big believer of low as possible / practical DCR  ( Direct Current Resistance ) power supplies.   I wrote about that on page 8 of a KT88 build thread, earlier this year.

 

His favorite value power supply choke, for his own personal tube amp builds, had to be custom made back then.  He had Stancor build for him to his spec :  1 HY at 8 Ohm DCR power supply chokes.   Isn't that interesting, because it does not meet critical inductance, as is always taught the last maybe 100 years in all the conventional EE courses.  Dr. Halijak was brilliant, look at his papers.   

 

Today, Hammond has a off-the-shelf 159ZA choke, six ohms, and it requires 75 hours of music - playing to break in.  One would always use at least two of these, in each tube amp's supply, as a L1/C1/L2/C2 B+ filter to feed the Finals.  Two 159ZAs, connected in series, is only 12 Ohms total DCR feeding the Finals tube,  from inductors .

 

Jeffrey Medwin

 

I agree with the belief of better sound through Direct Current power supplies. Especially with tube amps.

 

Unusual in today's world though. See: http://www.emissionlabs.com/Articles/TECH-BULLETIN/TB-09-Why-DC-Heated-Tubes-can-still-hum/TB-09-WHY-DC-heated-tubes-can-still-hum.html

 

Wb

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Wolfbane, 

 

Your referenced article deals with DC heating of tube filaments, typically done with DHTs ( directly heated triodes ).

 

I TRY to totally avoid DHT Finals ( output ) tubes that require DC heating, because AC heating sounds better to me.

 

This means, in DHT tube amps,  use of a lower voltage rated AC filament -  2.5 V-rated filament Finals tubes, rather than use of 5 V-rated  (or higher ) filament Finals tubes. 

 

This means starting a DHT design with a 2A3 as the Finals tube choice, or maybe a 45 if you like them,  not a 300B, or a 6B4G, etc etc. 

 

This above, is not a concern with INdirectly heated 6.3 VAC Finals tubes ( 6BQ5, 6AQ5, KT88, etc. )

 

The 2A3 DHT's lower rated voltage, applied to the filament,  allows one to get away with AC heating, on 100+ dB speakers, with very acceptable hum levels.  AC heating ( VS: DC ) of a 2A3 amp will sound better to most experienced builders, who experiment with good equipment, sources, speakers, wire, etc. For a tube power amplifier's front end tubes, typically indirectly heated, most will use AC heating.  

 

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

 

In 2019,  I have changed my designs to use totally separate Filament Transformers, for the front end - and ALSO for the rectifier tube's filament supply.  

 

When you use a single power transformer in a power amp, that is doing duty for the High Voltage B+ / Plate supply to the Finals.  This INTERMODULATES all the amp's other powered filament supplies.  The intermodulation, or "buckling" on transients,  of PULSED musical information is very audible to me.  This occurs, even when the front end tubes are (usually)  INDIRECTLY heated ( have a cathode).  Amazingly to me, we hear the filament's intermodulation "through" the cathode. 

 

Tube preamps have different filament heating requirements !  Of course.  Lower signal levels prevail.

 

People have found,  the use of a separate Filament transformer for amplifier's rectifier tube ( only ) always plays music better, more dynamic , more FUN to hear  - than if it was powered by the same Transformer that powers the B+/Plates of the Finals.  The rectifier is the first tube that demands a separate Filament Transformer, IMHO.  Hammond makes em,  3 A. rated ( 167M5 ) and 6 A. rated ( 167Q5 ).  Small, reasonably priced. 

 

Next in line for a " separate" treatment is the Input/ Front end, the very FIRST tube in the circuit.  Hammond again - for those Filament Transformers.

 

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

 

Another important design pointer: 

 

It is VERY important, when ever one adds separate transformers to an amp, that ALL leads, on the transformers' Primaries, and the Secondaries be PHASE ALIGNED, to each other,........ and uniformly connected to the tube socket positions, and...... also, channel to channel. Very important !! 

 

A dual trace scope and two probes is the simplest way to commence, and determine relative phases.

 

All these things discussed are audible, to me, and to others.   In my opinion,  separating the two Filament Transformers from each other, and both from the main B+/ Plate Transformer, produces the difference between any good tube amp...... and a great tube amp !!

 

Jeffrey Medwin

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Hi Jeffrey,

 

Thanks for the reply.

 

It is an Amp that can use either a pair of 45's or a pair 2A3 tubes that I use in rotation: Yamamoto A08. It sounds great with my Belles. All 2 WPC. etc... notwithstanding what an old curmugen that makes Crossovers had to say about low out put wattage. ;)

 

I also have amps that can output 300 WPC and more too but they are solid state, multi-channel (5 and 7) and are used for Home Theatre. Some times to my neighbor's expressed discomfort. She particularly didn't like the pictures shaking on her walls from the opening scene of the movie Predator (Helicopter). Wife was away and my buddies and I got too far into the wine, Beer, Scotch and Rye Whiskey.:emotion-22::emotion-46:🍺

 

Not a mixture I recommend.

 

Regards,

 

Wb 

(Greg)

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On 10/20/2019 at 1:14 PM, Jeffrey D. Medwin said:

Out of all the replies to this thread, what Tom1066 said rings truest to "me",  about Crooner's ( seemingly experienced ) 8B updating approach.  

 

I feel, one should not try to change " all the caps" or " all the resistors",  as SOP - standard operating procedure,  because it changes the SOUND of the stock amplifier.

 

However :  

 

One can MEASURE, individually, methodically, all the caps, as to their uF value, and measure each cap as to their ESR , and determine if ANY are way out of spec, and needing attention. 

 

Likewise, one can easily MEASURE, individually, methodically, all the resistors, to see if they drifted, and vary greatly from their intended ( schematic ) values.

 

- - - - - - - - - - -

 

There MAY possibly be no parts that are GROSSLY out-of-spec.  This might take up to 3 hours of time / labor to do and carefully document these measurements in 2019, VS this piece being around and unchanged, virgin,  since about 1959 ... six decades !!

 

- - - - - - - - - - -

 

I am sure I personally could  easily improve upon the sound of this amp, by using well-thought-out new film caps, and highest-quality resistors. 

 

But then, it is no longer a Marantz 8B one is listening to.  That's the RUB !!!!

 

Have fun, but think twice, before acting.  Its up to the Original Poster.   This is just little-ole-me's " two cents " worth of thoughts. 

 

Jeffrey  Medwin

 

 

Well, you are not wrong with any of it!

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