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Old 1st December 2006, 07:06 PM   #1
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Default Project madness

I've got a number of projects I'm working on and I'm curious if anyone out there has any experience with similar projects:

***Current config***

I'm currently using a Calbest (Musicall) stereo tube amp that is EL84/12AX7 based. I believe it is a model 8211? It needs a lot of cleanup, but it's my only working amp.

My preamp is a Yamaha C-6. Very nice specs but the switches are dirty. Any suggestions on cleaning?

Audio Nirvana Super 6.5 speakers in SteinAudio cabinets with 2inch flared ports. The cabinets are way too small for these speakers so I hope to have Scott build a larger pair. I've also tied in a cheapish Pioneer horn tweeter. 100db efficient and they sound rather nice to me. Narrow dispersion though.

AudioSource PSW100 subwoofer. The Nirvana's make much tighter bass, but the sub adds kick way down low.

***Future config***

I've recently been given a slightly modified Marantz 8B. The real thing! It's dirty, and I intend to fire it up once I get the tubes. I know there are a lot of mods for this thing. Any suggestions?

I'm working on a 41hz amp-4. SMT soldering is going to take me an eternity. Hopes are high! Any suggestions for a power source? I'd like to use something toroidal, but I'm not sure what specs I need yet. No volume adjustment either. I'll fit a resistor to an appropriate fixed input value.

I've also bought a Lite LS-7B (Marantz 7 modified clone) from DIYgene on ebay. Nice looking board. I'll have to buy his power supply too, but that's no big deal. My hope is that this will compliment the Marantz 8b. Anyone else try this? Suggestions?
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Old 5th December 2006, 07:44 PM   #2
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Default Marantz 8B Rebuild

My father in law who passed me his old Marantz 8B had spoken to one of the guys who assembled the amp. He suggested that you should not replace any of the caps because they should last forever.

The amp has not been powered on for more than a decade, and I suspect trouble is brewing.

I guess I'll power it up for a smoke test. Smoke = Rebuild.

More later...
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Old 5th December 2006, 11:05 PM   #3
SY is offline SY  United States
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Refurbish the Marantz to its original circuit, replacing only the necessary parts, and try to use originals where possible. Then put it on Ebay. With the proceeds, you can build a new amp that's much better and have enough left over for a two week vacation in Fiji, 1000 CDs, and a motorcycle.
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Old 6th December 2006, 01:00 AM   #4
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Quote:
Originally posted by SY
Refurbish the Marantz to its original circuit, replacing only the necessary parts, and try to use originals where possible. Then put it on Ebay. With the proceeds, you can build a new amp that's much better and have enough left over for a two week vacation in Fiji, 1000 CDs, and a motorcycle.

I Agree on the Marantz!

I recently aquired a Marantz 7 pre-amp so cheap I was drooling. It was a $75.00 estate sale find.

Cleaned it up, fixed the selinium rectifer, Put it on ebay in a 7 day auction and it sold for $4485.00.
For a tenth of that you could build a better sounding unit and still take a heck of a vacation.

My Guess is that board off ebay from DIYgene would most likely blow it away properly assembled with quality parts.

Quote:
My father in law who passed me his old Marantz 8B had spoken to one of the guys who assembled the amp. He suggested that you should not replace any of the caps because they should last forever.
So, that means all those bumble bee sprague caps leaked when they were new? haha Im guessing they did.

I left them all original when I sold the unit, But, I can honestly say, That every bumble bee caps I have ever tested were not anything special and even un-used NOS ones in my collection are either off spec, leak, or both.


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Old 6th December 2006, 02:49 PM   #5
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Here's my project website. Ugly.

Photos of the bits and pieces of the Marantz 8B to be seen.

http://mysite.verizon.net/oldamps/
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Old 6th December 2006, 02:52 PM   #6
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Trout - I've seen your site and I'm particularly intrigued with the idea of replacing the Selenium rectifiers with a silicon diode, but I suspect a 1:1 replacement would put things out of spec: http://yarchive.net/electr/selenium_rectifiers.html. I'll have to research some more.

Sy - This 8B still has all it's stock parts and could easily go back to it's original circuit. Part of me would rather bypass restoration and sell the 8B to put my kids through private school, after buying a new amp. But I swore to the previous owner that I would actually use this amp for myself. It has a lot of sentimental value to our family. No complaining here!

I'm considering the VTV Marantz 8B rebuild kit:
http://www.vacuumtube.com/Products.htm

I've also gotten a look at the tubes. NICE! A set of Dynaco (Mullard) EL34's and a pair of unused Pope EL34's. These boys have been sitting around for a LONG time. More on the way. I know these are highly desired toobs and their value is likely lost to me. I'll likely sell them in exchange for a couple sets of less expensive tubes. I'd feel awful if I blew an of these by accident.
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Old 6th December 2006, 03:11 PM   #7
Trout is offline Trout  United States
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Quote:
Trout - I've seen your site and I'm particularly intrigued with the idea of replacing the Selenium rectifiers with a silicon diode,
I only did the one that was bad, The DC filament selenium rect was bad. I did however add a series resistor. If I remember correctly it was around 470 ohm.

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Old 19th February 2007, 01:50 PM   #8
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Default Preamp problems

I got my Lite Audio LS7b preamp assembled last night and ran some testing on it. I've installed a stepped attenuator that seems to work well:

http://glass-ware.stores.yahoo.net/aikampstepat.html

There is some buzzing though, and I suspect that something is wrong that relates to the input. If I disconnect the inputs there is a terrible buzzing, at 60Hz. A short? Grounding problem? Input's not wired correctly? I've gone over the schematics a million times and I believe everything is correct, but something isn't right.

I tested things out using a Bela Fleck DVD-A and something just didn't seem right. Almost like the channels were out of phase or something.
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