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Old 19th February 2012, 06:05 AM   #1
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Default Marantz model 7t preamp

My 7t has lost one channel, I opened it up checked the fuses-all ok.

So before I fire up my 4 channel scope, I looked at the threads on this

Bad boy. In Dec 2007 , a query on transistors left the impression,

That, at least in that discussion, the devices were silicon not germanium.

So in the intervening years, has anyone learned what those devices were/are?

In worst case, I may have lost one of those as the cause of channel failure.

With only Marantz part numbers, it seems rather hopeless.

Any source for this needed information?

Thanks.
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Old 19th February 2012, 07:57 AM   #2
Mooly is offline Mooly  United Kingdom
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Substituting transistors should not be a problem and basic voltage checks will show in 99.5% of cases if a transistor has failed.

Do you have a circuit for this preamp ? One voltage measurement on any transistor will tell you if it's Si or Ge.

Are you asking for help in troubleshooting this or just about the actual devices
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Old 21st February 2012, 02:41 AM   #3
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Hello,

Thanks for the feedback.

I like to have an overall picture of what measure of success,

This project will attain.

So before I begin, I was curious as to the availability of any database,

Of appropriate active device substitutions for the original Marantz,

Devices. Does such a database exist?

And, yes I may need some trouble-shooting assistance,

However fortunately, with one working channel, I should not have,

Too many problems.

I.E. a basis of comparison of scope traces of injected signals.

I have a schematic for the 7t,

Thank you,Mooly.

It's all about music.
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Old 21st February 2012, 06:25 AM   #4
Mooly is offline Mooly  United Kingdom
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If you have a circuit all things are possible

Any change in DC conditions that appears to be a transistor fault could equally be caused by faulty passive components on vintage equipment.
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Old 21st February 2012, 07:03 AM   #5
MOER is offline MOER  United States
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Default Marantz 7T

There are no germanium transistors in this preamplifier.

Is your lost channel through the phono or one of the high level inputs?

If you need a schematic email me at zedaudio@aol.com I will send it to you.

The circuit is not difficult to follow and I have found that sometimes the connection of the transistors in their sockets is not always the best.


Steve Mantz
Zed Audio
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Old 23rd February 2012, 02:30 AM   #6
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Thanks molly and MOER,

I'd appreciate a schematic,

The high level input. It's a bit of a hassle for phono, I'll try that later.

My present schematic copy isn't too good,

Thanks again.
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Old 23rd February 2012, 12:58 PM   #7
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Schematics and service manuals for that Marantz are available here:

Marantz 7 File Sharing

Pay attention to your serial number, as apparently there are slightly different versions.
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Old 23rd February 2012, 01:08 PM   #8
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BTW, if you start upgrading parts, film capacitors (except polystyrene) should be changed too.

Small electrolytics, up to 10uF or so, if on the signal path, should be changed to film types, preferably polypropylene. It might be a refreshing move for this amp.
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