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Marantz 8B - hints and kinks?

kkib

kkib

Member
Well, I stole the title from dewickt in the McIntosh forum.:o

I have a stock Marantz 8B that I am planning to use regularly. I was wondering if you could share your experiences with your restoration projects.

Which caps did you replace and what did you replace them with?

What did you use to replace the selenium rectifier?

I also wanted to know what tubes you are using in your 8B?

Kudret
 
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I have a stock 8B aswell - and I do not feel, that it needs anything to be replaced - yet! Replacing stuff in an 8B can be devaluing (sp?) if it is not absolutely nessacary. When you have such an amp - it should be quite important to replace parts with similar parts/type. Most 8B owners think( at least that's my experience) - that the 8B is a superb sounding unit, that doesn't need tweaks of any kind.
But most parts - especially the electrolytic capacitors - have a life span, so they probably could need some attention in the future, no doubt. Maybe it is possible to get those from the 8B reuissue production. I know that they are selling kits for classic tubed Marantz in Japan.
I use mostly Mullard-produced el34's tubes in my 8B - and the RCA Cleartop
6CG7 - and the 6BH6's are in fact the Philips made E90F - which is a superversion of the 6BH6. But...during the years I have stocked up a lot of different brands and types of tubes to be used in the 8B - then i have the possiblility to roll the tubes and do some sound-experiments from time to time.

Regards
Freddy
 
Thanks for your reply, Freddy.

We are in 100% agreement . My only intention is to have a safe amp for daily use. If any part needs to be replaced I intend to keep its appearence and sonics as close to the original as possible. Having said that, one of the caps under the chassis is leaking paint like substance. It is wrapped in a plastic enclosure and held by two clips (mounted near the bias meter). Any idea where I can find a similar replacement?

I know that selenium rectifiers on vintage units are recommended to be replaced. Is this the case with 8B?

As for the output tubes, how are the new production EL 34s regarded? Price seems to be righ.

Kudret
 
Coupling caps are almost certainly a must. The 8B deserves the best. The one (and only) one I restored was done with inexpensive Illinois caps supplied by its owner.

The bias supply' selenium should be replaced, as well as that twin cap in the bias supply. VTV supplies a Schottky (which was DOA in my case); I used a cheap-Jack 3A 1000 PIV I got locally. Since the bias of each tube is adjustable, no mods to the supply resistor should be needed.

VTV supplies hexFREDs to replace the stock HV rectifiers. They were a little tricky to install, but probably worth replacing prophylactically.

All the electrolytics in my "patient" were OK after I brought it up (first time) on a Variac. It was easy to work on and it sounded absolutely (effing ABSOLUTELY) magnificent when I was done.

EDIT:

Before:

Marantz8Bbefore.jpg



After:

Marantz8Bafter.jpg
 
Very nice job Mr. Hardy:thmbsp: I like the top view of this unit that you posted on the Polk Forum.

Carl
 
Yeah, me too.... :-)

As Will Smith said in ID4: "I have got to get me one of these".
I'll settle for a homely one.
 
"I know that selenium rectifiers on vintage units are recommended to be replaced. Is this the case with 8B?"

My unsolicited, out of nowhere 2 cents worth? If it sounds good leave it alone and enjoy it. I have 2 8b's and use them bridged. I use Mullard el-34s and have used Svetlana as well with good results.
I think you have one of the finest amps of its time, or any time for that matter. If you need the schematic/manual PM me and Ill scan it for you.
 
No, the selenium really should be changed, for two good reasons.

1) Unlike a silicon rectifier (or even a vacuumm tube rectifier), the seleniums "age", and their efficiency drops over time. The voltage coming out of a 40-year-old selenium is NOT the one the amp designer was expecting. The 8B's variable bias might allow one to compensate that, but there is still Reason...

2) When a selenium fails catastrophically, the stench is terrible. Selenium is not human friendly (except in very small quantities) nor is it environmentally friendly.

Pitch 'em.

On the other hand: I (personally) don't believe in changing an electrolytic just because it is old... if the (power supply) electrolytics are re-formed, they run cool (cold), and there is no hum, let 'em stand.
 
mrh, Nice and clean job.

I will look into replacing the selenium rectifier. Any experience with hexfreds? any instructions for instaling them in 8b?

I was also hoping to hear more about the new production EL34s. Which ones you tried? Which ones you liked/didn't like, etc. There's go to be more 8B owners out there.:dunno:

Kudret
 
fredmarantz said:
...and the 6BH6's are in fact the Philips made E90F - which is a superversion of the 6BH6.
Click to expand...

Freddy, I am interested in getting a couple of Philips E90Fs. Is it easy to identify other brand 6BH6s that are in fact Philips E90F?

Kudret
 
Those are the hexFRED's in the 8B photo above (from the VTV rebuild kit). The only tip is that they don't fit very well. I was pretty happy with my final results, but a pro would have been aghast I am sure!

EDIT: We had "cannon fodder" Sovtek EL34's in the 8B when I re-hab'bed it. They are cheap and cheerful, but damn the amp sounded good on my Cornwalls! I think they have some QC problems with the Sovteks; one of the 4 on the 8B went south (no emission) shortly after I got the amp going again. A friend spotted me a pair of "Groove Tube" EL34's just to finish testing and "burn-in". The amp's owner had good old EL-34's for it.

Otherwise I don't know much about the new production tubes.
 
mrh, Apparently I need to study your pictures closer.

Mine came with JJ Tesla EL34 tubes and they sounded good to me for the brief period I listened to them. Unfortunately I broke one of them while trying to move the amp. 55lbs monster tilted towards me and bent the pins on one of the tubes. Luckily the tube socket is ok (a bit loose but ok). I need to get a new set of EL 34s and keep these as spares.

Kudret
 
I suspect the JJ's would be pretty good but I haven't heard 'em myself. I use JJ EL84's in my EICO HF-81 and think they're fine.

I'll post a better photo of the HV rectifiers... gimme a minute :-)
 
I bent the two little legs of the hexFRED's out and spliced them into the residual leads from the old silicon diodes. Note that there is no heatsinking of the FRED's. Good ol' VTV provides absolutely NO specific instructions on how to install these things they sell people, BTW.

I improvised as best I could. The rectifiers run cool, so I believe they're OK hanging out in the breeze. I DID give the amp PLENTY of "bench testing" before returning it to its rightful owner! :-)

See if this "before and after" photo is helpful.
8Bbiasbeforeandafter.jpg
 

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  • 8B bias for AK.jpg
    8B bias for AK.jpg
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Mind you, I'm not a tube guy per se but I've recently listened to a Model 8 that was sold by a local audio store here in 1958. The adult children of the man who bought it new, contacted the current owner of the store to see if he'd be interested in purchasing it, as their father has now passed away. Obviously he jumped on it, and he swears by Telefunken tubes. That's the only tube he said he'd ever put in it. Interested in everyones comment with regards to them. I'm considering taking the tube plunge and I can't imagine an 8 or 8B sounding any better than this one that I heard. :music:
 
Old Telefunken tubes were great. I imagine that the 8 or 8B's would've come with Mullard EL34's, though. I suspect that the small-signal tubes Marantz used might've even been US-made, but I don't know.
 
As far as the tubes go, I have the Seimens DimpleTop EL 34's and they are the best I have heard. Seems to be a nice match.
 
kkib said:
Freddy, I am interested in getting a couple of Philips E90Fs. Is it easy to identify other brand 6BH6s that are in fact Philips E90F?

Kudret
Click to expand...

Well - I think that most "Philips-brands" - Valvo - Etc - carried the E90F - and they can be searched thorough dealers and Ebay. They are usually easy to identifi, since they have a Mesh-plate.

Regards
Freddy
 
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