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Old 3rd November 2005, 03:23 AM   #1
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Default Marantz 8 clone build

Hi.. i'm newbie to tube building ..

i bought an PCB from Kitparts.com for the Marantz m8 amp clone ..

but i'm not sure about the output transformer ..

i'm looking for two :

1st : primary 5k ohm PP , 35W 140mAh

2nd : primary 8k ohm PP , 35W 140mAh ( modified for more bass)

can i use one of these ?

thanks
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Old 3rd November 2005, 03:37 AM   #2
MOER is offline MOER  United States
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Default 8B clone

There are NO output transformers available that even come close to the performance of the Marantz 8B's.

If you study the circuit you will see that each and every transformer was "matched" to the base circuit.

I have worked on so many 8Bs and no two are alike interms of transformer performance. I agree with what they did in terms of optimizing each transformer+electronics.

This is my Marantz 8B which I did a 100% ground up restoration on. many mods were done to the power supply (4,000mfd capacitance, slow turn on for Ht and filaments, DC on small tubes' filaments, conductive plastic pots for bias and balance adjust, massive capacitance on HT for driver tubes). Please change EL34's cathode resistors to separate resistors for each tube. Helps on non matching requirements.

Steve
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Old 3rd November 2005, 10:16 PM   #3
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Default Re: 8B clone

Quote:
Originally posted by MOER
There are NO output transformers available that even come close to the performance of the Marantz 8B's.

If you study the circuit you will see that each and every transformer was "matched" to the base circuit.

I have worked on so many 8Bs and no two are alike interms of transformer performance. I agree with what they did in terms of optimizing each transformer+electronics.

Steve
Could you please esplain what transformer quantity/quality was matched to what circuit parameter? If you can, please also detail how this matching was accomlished.

Also, could you detail how the OPTx differed in terms of measurments( which ones, I'll leave to you ).

it sounds *WAY* too 'Urban Legend' to me. I have seen where a TX winder's blueprint differs from what is shown in a careful teardown more than once. I would be quite interested in your experiences.

Before I answer the original poster, one should ask, what is the spec of the original Marantz OPTx? How big is its core, and wht is it made out of? If you want to make a clone, one should thoroughly investigate what you are copying, in order to be successful in duplicating it.
cheers,
Douglas
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Old 4th November 2005, 01:37 AM   #4
MOER is offline MOER  United States
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Default Marnatz 8B

Visit this link for info on these xfrs

http://www.one-electron.com/Trans_Tests.html

Square wave tests were done to optimize the snubbers and feedback components. Some 8B's had small coils in the feedback circuits. I of course cannot be sure what other tests were done by Marantz in the 1950's as there is no information available. I have probably worked on 20-30 Marantz 8Bs and no two were 100% alike
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Old 9th August 2010, 10:17 PM   #5
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Hello,

I also want to build an 8B clone. I have a pair of Acrosound TO 300 output transformers. In the Heath W3M amp they used a simple cap/resistor combination off the 16 ohm output to drive the feedback circuit. I see that the 8B transformer has separate windings dedicated to the feedback circuit. Would it be possible to "tune" the Acrosounds to approximate the 8B?

Do you know what the output windings impedance for the original transformers was?

Kevin
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Old 15th January 2012, 06:55 AM   #6
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I ran across this while looking for another old thread. I finished my 8b clone a while ago. And I love the way it sounds. I used Dynaco ST70 OPT's. I had friend that used to own an 8b listen to it. He thought it sounded like an 8b but with better bass.
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