Marantz 7 preamp upgade??

Hoppes · Mar 15, 2012

I have been lucky to inherit 3 of the classic Marantz products:

Marantz 8b stereo amp with original RCA Fat Boy 6CA7 tubes
Marantz 7 pre-amp with Amperex 12ax7a tubes Serial number 7-21568
Marantz 10b tuner
I have the 8b up and running with all the correct voltages and bias. It appears to be original. The 7 is also up and running well but appears to be modified. The case has a service sticker from 1979. Some of the caps are Electrocubes, PRns and Tektronix. There is also a Sprague Atom 1000uf in the power supply side. I assume these were not the originals ?? The preamp hs not been touched since 1979.Anyone tell what caps Marantz used for the 7 of that vintage ?? Thanks, Hoppes

jstang · Mar 16, 2012

Picture would help, but yes they sound not to be stock....

That is a very late serial number. My is even later by a 100. The later units used different brand caps and resistors in some locations.

The 10b is likely to need some caps too... I love mine, I just replaced the dial glass which made the visual aspect out of this world...sound is the best.

JohnK

Hoppes · Mar 16, 2012

Posting some pics

Sorry I couldn't get pics yesterday. Here's 2. Hoppes

Brian · Mar 16, 2012

if not original, looks like the tech did a decent job. I'd suggest not obsessing about it unless you find something objectionalbe. Finding NOS in spec will not be easy if, at all possible.

jstang · Mar 16, 2012

Correct that is not original. But that is not all bad as Brian mentions.

You will find the 7c a pleasure.....

jk

ruffian · Mar 16, 2012

Essentially you can't -upgrade- this amp, you can only service it. With that said yours has been serviced. It looks like much of it has been replaced. Mine came to me in exactly the same way as yours and the place that serviced my Grandmothers were complete butchers compared to the job you have.

No speakers or turntable in that impressive inheritance? You are missing the Thorens TD-124 and the Jensen speakers. :thmbsp:

Hoppes · Mar 16, 2012

One addition

I did get an Empire 498 table and 980 tonearm with a Shure m95ej cartridge. Unfortunately someone cut the tonearm cable in half !? So the turntable has to go very close to the preamp!! I'm running a pair of Spica TC-50 speakers with a Velodyne sub. Things sound pretty nice !! I have a Pair of Silverline Panetella speakers that will be next to try when everything is working properly. The younger generation don't know what they are missing!! Hoppes

ruffian · Mar 17, 2012

What compliment of tubes are in the Model 7? 1-2-3 are the phono section, 4-5-6 are the line stage. They they do not need to be the same between sections and tubes 3 and 6 can be different. I have found that changing tube 6 has the most effect on sound, at least to my ears.

My favorite is a Sovtek LP in 6. (not the LPS). Teles and Mullard tubes will impart their house sound exactly as people describe if you roll them in 4 and 5.

Hoppes · Mar 17, 2012

Tubes in 7C preamp

All tubes are from the late 60's---Amperex 12AX7A' s. Haven't had the unit long enough to try other tubes at this time. Hoppes

kirk57 · Mar 19, 2012

Sid Smith himself (the designer of the 7) had a business doing mods to that preamp, in the late 70s. The modded preamp was reviewed in The Absolute Sound and found to be far superior to the original. I do recall something about Sprague caps and other cap upgrades being part of the mod.

Best case scenario would be he did the mods

PB_Audio · Mar 20, 2012

kirk57 said:
Sid Smith himself (the designer of the 7) had a business doing mods to that preamp, in the late 70s. The modded preamp was reviewed in The Absolute Sound and found to be far superior to the original. I do recall something about Sprague caps and other cap upgrades being part of the mod.

Best case scenario would be he did the mods

Any additional info regarding the Sid Smith mods would be much appreciated.
Thanks in advance.

kirk57 · Mar 20, 2012

Well, The Absolute Sound is/was famously non-technical in their reviews, so a detailed overview of what exactly Sid did would not be found there.

I suppose your best hope is Google.

chinacave · Mar 21, 2012

Tagged as I will soon be tackling service / possible 'upgrades' on 2 7c's and an 8b.

Audio Amateur published an oft-cited detailed article in 1981 I think, about improvements in the 7 through updating components, of the same value, and voltage regulation. I have it, wonder what y'all's take on it is?

Not sure if its public domain.....

jstang · Mar 22, 2012

Hmmmm.... My 7c is staying stock. If a cap or other part goes bad I would replace after complete testing.

All of its caps were ESR tested. Need to test the tubes.

My 7t is different story, that has been modified..

Jk

PB_Audio · Mar 22, 2012

chinacave said:
Tagged as I will soon be tackling service / possible 'upgrades' on 2 7c's and an 8b.

Audio Amateur published an oft-cited detailed article in 1981 I think, about improvements in the 7 through updating components, of the same value, and voltage regulation. I have it, wonder what y'all's take on it is?

Not sure if its public domain.....

If it's been published, it's fair game.
I'm sure I'd love to see what mods were being done back then,
if you please. :yes:

crooner · May 13, 2012

Hi Folks!
Found an interesting blog describing a Sid Smith modified Marantz 7.
This is the first time I've seen such a unit up close with the covers removed.

I am not a fan of this kind of mods, even if Sid performed them himself.
I would have preferred for Mr. Smith to just introduce a new preamp with his circuit improvements.
Further, this particular unit appears to have belonged to late Wilma Cozart Fine of Mercury Living Presence fame.
Although the serial number on the manilla envelope is different from the one stamped on the chassis.

If it were mine, I'd probably reverse the mods because of the unit's historical significance. I am guessing it was used to monitor those fantastic recordings made by her husband C. Robert Fine.

http://hifiheroin.blogspot.com/2011/07/one-fine-7c.html

Sam Cogley · May 13, 2012

I don't know exactly what's been done to it or who did the work, but Sheltie Dave's hot-rodded 8B is one of the best-sounding amplifiers I've ever heard.

chinacave said:
Tagged as I will soon be tackling service / possible 'upgrades' on 2 7c's and an 8b.

Audio Amateur published an oft-cited detailed article in 1981 I think, about improvements in the 7 through updating components, of the same value, and voltage regulation. I have it, wonder what y'all's take on it is?

Not sure if its public domain.....

It's copyrighted, though I doubt anyone would get their knickers bunched up about some non-commercial sharing of the information among a small group of enthusiasts. Depends on the attitude of the copyright holder.

PB_Audio · May 13, 2012

Hoppes said:
I have been lucky to inherit 3 of the classic Marantz products:

Marantz 8b stereo amp with original RCA Fat Boy 6CA7 tubes
Marantz 7 pre-amp with Amperex 12ax7a tubes Serial number 7-21568
Marantz 10b tuner
I have the 8b up and running with all the correct voltages and bias. It appears to be original. The 7 is also up and running well but appears to be modified. The case has a service sticker from 1979. Some of the caps are Electrocubes, PRns and Tektronix. There is also a Sprague Atom 1000uf in the power supply side. I assume these were not the originals ?? The preamp hs not been touched since 1979.Anyone tell what caps Marantz used for the 7 of that vintage ?? Thanks, Hoppes

... did he say LUCKY !!!!!!!!!??????? :banana:

... sorry, I just can't get over the luck...

USMC Spike · May 19, 2012

Thanks for the pics and post of the Marantz 7 c. : )

Interesting thought from the guy blogging it to revert it back to original, thereby
killing the value AND the historical significance of the pre amp.

Ms. Fine chose to have the designer tweak her pre.

He also wonders why Sid Smith didn't make a new line of pre's?

Well if anyone has experience in it, then you know you have a
hell of a lot of headaches just getting your suppliers etc to make
things the way you want them. Forget the fact that you have
to have a big bankroll just to inventory the stuff.

I'm guessing Sid Smith didn't want to PLAY with the business end
of it all, otherwise they would have been Smith's instead of Marantz's.

Knowing of all the improvements in componant parts I'm sure Sid was quite
happy upgrading them to his spec and price point rather than the channels
price/market point....

I mean if you are the man, know one knows it better than you and you know
what you wanted to accomplish to begine with, so you just take it from whence it came and get to do all the fun things the factory wouldn't let you.

Don't mean to ramble on here, just free associating the info.

Cheers,

Spike

jstang · May 19, 2012

I agree with the "don't modify a C" approach.... But a T is a good place to have some fun....

crooner said:
Hi Folks!

I am not a fan of this kind of mods, even if Sid performed them himself.
I would have preferred for Mr. Smith to just introduce a new preamp with his circuit improvements.

If it were mine, I'd probably reverse the mods because of the unit's historical significance. I am guessing it was used to monitor those fantastic recordings made by her husband C. Robert Fine.

Marantz 7 preamp upgade??

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