Marantz Model 33 restoration

M

MrJackson

Member
I just scored an early (S/N < 3000) champagne faceplate Model 33 I will restore! The 1060 I did last summer opened up my apetite for this.

Right now, the unit seems to have all original parts, but it was converted to 220V operation. It’s in decent shape cosmetic-wise, but it will require new screws, feet (didn’t have any, but it didn’t have the woodcase either) and new knobs (these are not original I’m afraid)

It sounds pretty good, but not as detailed as my restored 1060, unless I EQ in some +4dB on the treble side. It’s also quite noisy, having a constant hiss that the 1060 doesn’t have - sounds a bit like surface noise on vinyl I guess :))

I’m really on the fence regarding the poweramp - I’d go with a 16 for the dual mono construction, but I feel it’s way too powerful for my current setup and I’ve also seen a 32 available. What would you guys get?

Last but not least, I’d look to get a replacement for the volume slider. It’s working ok now, but it has quite a bit of side-to-side play and I know they’re very rare, so I’d be sleeping better knowing I have a replacement at hand. Do you know of a good source for such parts, outside of a donor unit?
 

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Well, it's been awhile, but I've finally started restoring this unit. I've mapped out the power supply and filter/center channel/output amplifier boards. Now I'm looking at the main pre board and honestly... I could really use a board layout to figure out which is which quicker.

Also, if anyone has any advice on equivalent transistors, I'd be very grateful. I really want to remove the hiss from this unit.
 
Slowly, I am making progress with this unit.

I have almost finished the upgraded part list and I've also created a layout of the preamp board(s) that was missing from the service manual. It's pain to change anything without a layout and/or silk screen on the board. I will upload this next to the service manual on the proper websites once I properly label the connections.

In the meantime, I think/hope I found transistor equivalents for most of the parts:
- 2N5461 to NTE326
- MPSA10 to 2N6517 or ZTX1051A (I'll probably go with the 2N6517 for the lower hFE in the power supply board and the ZTX in the amp which requires higher hFE)
- S33369 to 2N2219A (got this pair from a french forum, seems to be a successful swap)
- S33370 to 2N2905A (same as above)
- MPF109 to NTE451 (complementary to 2N5461... it seems only NTE has something similar)
- MPSA70 to 2N4403
- MPSA09 to 2N6515
- SPS2296 (could this be a 2N2296 actually?) to ?
- 2N4250 to ?
- 2N4356 to ?
- SE6021 to ?

Any help with these (either filling the blanks, confirming or not replacements) is very much helpful.

Model 33 preamp board layout.png
 
I have seen 2n4250 being replaced with 2N5087 on 240/250s. As for the diff pairs, this model asks for high hFE on the first two and between 200 and 399 for the last pair. For high hFE I was thinking on using BC550C (different pinnage) which can be easily above 500.

Do you have hiss on both channels simultaneously or only on one? Mine has a random hiss on the right channel.
 
It's hissing on both channels equally, I'd say. Thanks for your input, it's a good starting point.

I'll report back with my other findings later today. I'm usually starting from the datasheet and filtering stuff on Mouser and/or TME until I find something in stock that seems to fit the bill. Pins don't worry me that much. I've switched them around on my 1060, where I couldn't find the proper ones with a center collector, so I ordered whatever was in stock and reversed them carefully - funny thing is I noticed the pinout when I was putting it back together, not when ordering. Good thing I didn't power it up before.
 
Which board revision is yours? Mine is Revision 1 which has two extra MPF109 and a trimpot which one of the service bulletins remove them to become rev2. As for MPSA70 I came up with BC557 (high hFE) and 2N3906 (lower hFE). I also have the impression that NTEs are not well liked overall, being used as last resort. I can't say for sure because I never have used them.
 
Mine's a rev2, without the extra parts. I got the same impression regarding NTE, but as an EE engineer (friend of mine) said... most **** transistors from today are better than the good ones from 50yrs ago. Technology advances. Some people said that you'd lose the Marantz sound if you change the transistors (if they're not faulty that is). I changed *all* of them on my 1060 and I didn't hear any loss of its specific sound. It got more refined and punchy.

I'll keep on digging after work today and see what I come up. How far along are you with your 33?
 
I have no problems replacing transistors if they are close enough. I did that for my 1120 with great results. The MPF109 threw me off because they are FETs and I am not that familiar with matching specs for these.

I recapped the whole thing but kept the original values (the revision sheet asks to change one of them from 32uf to 16uf I might do that at some point). I used Silmic IIs where I could, and Vishays for the power supply because they are the only reasonably good ones that are axials. Every time I think about investigating the hiss it goes away so I back off. I think the issue on mine is the second diff pair right because it seems to be affected by freeze spray.

Also I got the original service manual if you need better scans of anything.
 
Yeah, the MPF109 and the 2N5461 (its counterpart on the positive rail) threw me off as well. I just couldn't find anything in those specs. What I'll do when I actually start replacing them next week is to carefully pack and label the old transistors so I can put them back if need be.

ocdecio said:
I recapped the whole thing but kept the original values (the revision sheet asks to change one of them from 32uf to 16uf I might do that at some point). I used Silmic IIs where I could, and Vishays for the power supply because they are the only reasonably good ones that are axials.
Click to expand...

When in comes to recapping, I have a habit of replacing any electrolytic in the signal chain with films (usually WIMA, but I'm adding Mundorfs where it makes sense and they fit - C212, I'm looking at you). I did have to make some compromises due to space limitations on this one... I would've wanted film in C131 at least, but I just couldn't find something small enough to fit in that place. I got Vishays as well for the power supply - did find Mundorf ECap axials, but there were too big for the space. However, I did increase one 470uF to 680uF in the initial reservoir section.

ocdecio said:
Also I got the original service manual if you need better scans of anything.
Click to expand...

Please tell me it doesn't have the layout for the preamp board :)) I'd hate to know I worked so much to recreate that layout for nothing.
 
Interesting you mention C212 and C131 - I am not really worried about these because C212 is for the center channel that I don't really care for and C131 is for the headphone amplifier which although it is nice to have doesn't get any benefit from the tone controls. And that is where the odd SE6021 transistor is located I wonder if it together with 2N4356 are the complementary "power" pair.
 
ocdecio said:
Interesting you mention C212 and C131 - I am not really worried about these because C212 is for the center channel that I don't really care for and C131 is for the headphone amplifier which although it is nice to have doesn't get any benefit from the tone controls. And that is where the odd SE6021 transistor is located I wonder if it together with 2N4356 are the complementary "power" pair.
Click to expand...

Yeah, I'm thinking about using the center channel output with an active sub in my system (I'm running bookshelves). Also, I plan on using the headphone amp, even without tone controls.

You're probably right about the transistors. I'm far from an expert, but it looks like a push-pull topology between Q119 (2N4356) and Q120 (SE6021).

ocdecio said:
As for MPSA70 I came up with BC557 (high hFE) and 2N3906 (lower hFE).
Click to expand...

Great shout on the BC557 - do note the hFE classes though. Right now I'm scratching my head if I could actually use a BC559 as it's lower noise (but its Vce is 30V - I can't see it exceed 15V on the schematic though)
 
Can't find BC560 on Mouser, just on TME and it's made by CDIL (don't know about them)... Still, they're pretty cheap, so I can try both 557 and 559 and see how that works.

Now I've moved on to SPS2296, which was MPSA09 before ECN 1337. I'm figuring I can use something equivalent to MPSA09 still. Current contender is BC550 in versions C for high hFE (Q101/2 and Q107/8) and B for mid hFE (Q113/4).
 
MrJackson said:
Can't find BC560 on Mouser, just on TME and it's made by CDIL (don't know about them)... Still, they're pretty cheap, so I can try both 557 and 559 and see how that works.

Now I've moved on to SPS2296, which was MPSA09 before ECN 1337. I'm figuring I can use something equivalent to MPSA09 still. Current contender is BC550 in versions C for high hFE (Q101/2 and Q107/8) and B for mid hFE (Q113/4).
Click to expand...
That would be my take as well - I used BC550C on the 1120 X10 board and it worked well.
 
I ordered 10 MPSA09 just to have a feeling as to what their hFE would be. I wonder if SPS2296 is just a different name for it.
 
I'd be very interested in that as well. Please post your findings when you get them.

In the meantime, I think I'm gonna call it a day and see more on this tomorrow. At first glance, BC5xx can be used throughout the whole preamp board (seems it can replace 2N4356 and SE6021, with the single mention that their fT is higher than BC5xx)
 
So, for the JFETs I've decided on a complement of J111 and J175. I've ordered a couple hundred assorted BC5xx and also some 2N4403 (as a low hFE alternative to the BC557/559). Also ordered replacement Zeners

As a side note, it's funny how you can sometimes find JAN spec parts for the price of their normal versions. The wonders of Mouser.
 
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