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Marantz 8B Restoration Saga

Here's the 8B buttoned up with speakers and portable CD player hooked up for initial testing.

At first, I connected a 100 watt lamp in series with the AC line to reform the electrolytics. The light was dim meaning there are no shorts in the power supply.

There is no such thing as a free lunch though. I hooked it up directly to the wall outlet. Sound came in faintly, channel A was distorted with motorboating distortion.

Well, the prognosis is actually not bad. I will double check the wiring against the schematic for errors. The power supply is fine, by the dim glow of the lamp on the initial test and because there was no hum on the speakers when unit was connected directly.

The old "Good-all" capacitors are suspect. Perhaps they are very leaky. However, I didn't observe red plates or signs of overheating.

I assume the output trannies are good because I hear sound on both speakers.

The fun is just beginning...
 
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Damn, it's a good thing you know what you're doing...I would've had the 8B smokin' in no time flat! Or the whole house go up in flames. You are very thorough in your work...nice and neat. Great job so far!:bigok:
 
hehe, well let me tell you the "smoke test" is always pretty scary, anything can happen!

Fortunately, I believe I have the wiring pretty much sorted out. A couple of errors on the ultralinear connection taps. Previous owner had wired the amp for triode using resistors without standard color coding. I threw those out and installed 100 ohm 5 watt jobies for the standard ultralinear connection.

Can't wait to fire her up again!

Regards,

crooner
 
I plan to use my humble Paradigm Atoms MKII with stands and custom modified Rat Shat SW100 passive sub.

I love the sound of the Atoms, not at all shabby for such an inexpensive speaker. I hope it matches well with the 8B.

Regards,

crooner
 
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Did another test. I have motorboating (low frequency pulses) on channel "A". The other channel appears to be normal.

"Motorboating" can be caused by a filter cap or decoupling cap gone bad or a feedback loop out of phase.

I'll resume my postings next week, hopefully by then it should be running smoothly. Thanks to all for your comments and support!


Regards,

crooner
 
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The nice thing, is that now that you have one channel working properly, it makes a nice "template model" to check out functions on the one that is NOT woriking. Comparison of the good one to the bad one, should lead to SOMETHING that ain't the same!

Regards,
Gordon.
 
absolutely correct!
That's what I've been doing, taking resistance measurements and such, and making comparisons between channels.

Even though, the "good" channel gives sound with no hum and no red plates, the bias reading on the meter is still low. I suspect I will have to replace all the remaining original caps as originally planned.

The good thing is that I know the output transformer on the offending channel is not shot (my biggest concern). The fact that "motorboating" or low frequency pulses could be heard loud and clear, confirms it. I could also hear faint music in the background on that channel.

Best regards,

crooner
 
Complete Recap

Hi Guys,

Given the amp's motorboating problem, and since I want a reliable unit for day to day use, I went and did a wholesale capacitor replacement on the unit.

For signal and coupling caps, I used mostly Orange Drops. I also used a couple of Illinois Cap film types. I left the stock subsonic filter caps in the circuit, since I will be using the "test" inputs, meaning the signal will not go through these.

The filter cans were a bear to replace with under the chassis caps. The new caps are huge! (see pics). I tried to be as neat and professional as possible. The original cans remain on top of the chassis for looks, of course.

Haven't done the smoke test with the new caps yet. This is going to be the moment of truth. Wish me luck!

Best regards,

crooner
 
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crooner said:
Hi Guys,

Given the amp's motorboating problem, and since I want a reliable unit for day to day use, I went and did a wholesale capacitor replacement on the unit.

For signal and coupling caps, I used mostly Orange Drops. I also used a couple of Illinois Cap film types. I left the stock subsonic filter caps in the circuit, since I will be using the "test" inputs, meaning the signal will not go through these.

The filter cans were a bear to replace with under the chassis caps. The new caps are huge! (see pics). I tried to be as neat and professional as possible. The original cans remain on top of the chassis for looks, of course.

Haven't done the smoke test with the new caps yet. This is going to be the moment of truth. Wish me luck!

Best regards,

crooner
Click to expand...

Hi Crooner,

I have been following a more recent Marantz 8B mod thread and came upon yours in a search. Since all your photos disappeared and you never quite finished this thread about the motorboating distortion, do you think you could do a nice update here and possibly restore some pix? I've got a couple of 8B's that I'd love to get running again.

Always love to look at those Vintage Marantz tube gear! Thanks

Regards,

Bart
 
crooner said:
For signal and coupling caps, I used mostly Orange Drops.
Click to expand...

Just my opinion, but that amp will never live up to its potential with Orange Drop caps. I've used Sprague 715P in many amps (got hundreds NOS in a deal). In every case there was a better-sounding choice to be found.
 
tubino said:
Just my opinion, but that amp will never live up to its potential with Orange Drop caps. I've used Sprague 715P in many amps (got hundreds NOS in a deal). In every case there was a better-sounding choice to be found.
Click to expand...

This is a very old thread.

I no longer use Orange Drops (or Illinois caps for that matter) in my restorations.

Actually, the original Good-All caps were mylar and of superb quality. They rarely go bad. I have a Marantz 2 in my bench right now. The Good-Alls test perfectly. Needless to say, they will stay.

Saul Marantz used the best possible quality parts. Why mess with such classics?
 
Hi Bart,
Man, how time flies.

That 8B is long gone. The motorboating issue was fixed, IIRC.

The pics I still have but they are very low resolution. I had a crappy camera back then! :-)

My advice to anyone restoring this classic is to only replace what's broken.
Marantz used top quality parts to begin with.

If the unit does not hum and tubes bias properly, I would replace the selenium rectifier for the bias supply, the small electrolytics related to the aforementioned bias circuit and perhaps the diode rectifier bridge for the main supply. That's it.

The original caps used in the Marantz 8B were of superb quality. Telephone Grade Sprague twist lock electrolytics, for instance. I've never seen them in other consumer grade gear.

The coupling caps used were Good-All Mylars. The finest available then. They rarely go bad. Mylar (polyester) is a very stable dielectric. These caps are also responsible for the smooth, satisfying sound quality. Replacing them would be a shame.

Regards,
crooner
mech986 said:
Hi Crooner,

I have been following a more recent Marantz 8B mod thread and came upon yours in a search. Since all your photos disappeared and you never quite finished this thread about the motorboating distortion, do you think you could do a nice update here and possibly restore some pix? I've got a couple of 8B's that I'd love to get running again.

Always love to look at those Vintage Marantz tube gear! Thanks

Regards,

Bart
Click to expand...
 
The coupling caps used were Good-All Mylars. The finest available then. They rarely go bad. Mylar is a very stable dielectric. These caps are also responsible for the smooth, satisfying sound quality. Replacing them would be a shame.
Click to expand...

in my case with my fairchild amps i unfortunately had to replace every last one of them as they were leaking.sure would like to find some NOS ones someday and return the amps back to the good -all to see what im missing .it;s been awhile but i think i replaced them with orange drops.:tears: do you have any recommendations of what brand caps might come close to the sound of the good-alls?
 
radioactive said:
in my case with my fairchild amps i unfortunately had to replace every last one of them as they were leaking.sure would like to find some NOS ones someday and return the amps back to the good -all to see what im missing .it;s been awhile but i think i replaced them with orange drops.:tears: do you have any recommendations of what brand caps might come close to the sound of the good-alls?
Click to expand...

That's too bad you had to replace them.

The Good-Alls were available as early as 1955, as my Marantz 2 clearly attests.
Certainly groundbreaking back then. Nearly all coupling caps were molded paper or oil.

I would suggest contacting Kevin Hayes of VAC. He did the Marantz reissues a decade ago. Back then he used the same company that made the Good-Alls. They looked different on the outside but apparently the same as the originals.
 
I wish the pics of your process were still available. I found an 8B at a hifi shop once but the owner wouldn't part with it. Looked at me like I was crazy for even asking about it. This was probably 1996. I kept going back and asking for it but they wouldn't sell. Shop closed up and who knows what happened.

Someday...
 
radioactive said:
in my case with my fairchild amps i unfortunately had to replace every last one of them as they were leaking.sure would like to find some NOS ones someday and return the amps back to the good -all to see what im missing .it;s been awhile but i think i replaced them with orange drops.:tears: do you have any recommendations of what brand caps might come close to the sound of the good-alls?
Click to expand...

I have a friend who used Mundorfs in his Marantz 7C and he's quite happy with the sound. Depending on the amount of NFB the type of coupling cap used in such an amp will make less difference than in a preamp say.

Vitamin Q's or Russian K40Ys might be the ticket. What values are you needing? I do have some NOS goodalls around.

Lar
 
crooner said:
That's too bad you had to replace them.

The Good-Alls were available as early as 1955, as my Marantz 2 clearly attests.
Certainly groundbreaking back then. Nearly all coupling caps were molded paper or oil.
Click to expand...

I plan to throw away a large number of Good-All wax-encased capacitors that I just ripped out of my Bogen DB230A. They look like the typical time bombs you'd find in an old radio, just waiting to destroy an output tube. Whatever Good-All part was used in the Marantz must be a very different cap :scratch2:

To preserve the original sound in amps like the Marantz, a quality film-and-foil mylar cap would probably be the best replacement option, if-needed. These might be a custom order, and won't be cheap unless you can find a distributor with some in stock. RTI Electronics lists them on their website, Wesco 32M would be good too, same with Sprague/SBE mylars. Even if my hypothetical Marantz 8b were working with Good-Alls, I would be very tempted replace the caps anyways with tasteful modern substitutes, to protect the expensive and unobtainious output transformers.
 
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