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Marantz 18 & 19 Receiver Restorations

I've mostly finished and then reinstalled one of the Marantz 19 drive boards. The receiver is now on another level. Without too much hyperbole, the difference in sound is like going from AM to FM.

That being said, there's a strange issue I've never encountered. If I bring my variac up above around 110V, I start getting a distortion in the channel I repaired. The distortion sounds exactly like if you were to keep your source on after turning off your receiver (any receiver or amp that doesn't automatically mute itself on power off) and the music simply faded out after several seconds (except it doesn't fade out completely in this case). So, it seems like something is causing the amp to cut out. Power consumption is around 50 watts at the point it cuts off but the receiver works fine at 45 watts of consumption (by dialing the variac back a bit). The 19 was tested prior to this work and there wasn't an issue with this channel so I know it has something to do with the work done.
 
BlackScholes said:
I've mostly finished and then reinstalled one of the Marantz 19 drive boards. The receiver is now on another level. Without too much hyperbole, the difference in sound is like going from AM to FM.

That being said, there's a strange issue I've never encountered. If I bring my variac up above around 110V, I start getting a distortion in the channel I repaired. The distortion sounds exactly like if you were to keep your source on after turning off your receiver (any receiver or amp that doesn't automatically mute itself on power off) and the music simply faded out after several seconds (except it doesn't fade out completely in this case). So, it seems like something is causing the amp to cut out. Power consumption is around 50 watts at the point it cuts off but the receiver works fine at 45 watts of consumption (by dialing the variac back a bit). The 19 was tested prior to this work and there wasn't an issue with this channel so I know it has something to do with the work done.
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Check your adjustments are per the service manual on the driver board and use the procedure. May be the constant current pot (bottom left of driver board)
 
pjrengineer said:
Any update
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I haven't worked on the 19 since I posted, but have made progress on several of the 18s.

An output heatsink before and after below:
i-87MbGfX.jpg

i-LP6wrVW.jpg
 
I just started on my 18 today. Starting with the power supply thinkin is gonna be fun. Removing all the old electrolytic and resistors. Was gonna keep the diodes but they may go too if I can figure out substitutes.
 
BlackScholes said:
Interested in how much fun you had.
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It’s more fun than working on circuit boards that’s for sure. But for me I still have a challenge removing parts that were wrapped around the terminal strip eyelets 4 times each 4 components per eyelet! Even with a desoldering gun it’s tough. I resisted leaving the leads and tying to them which would have worked fine but looked bad.
 
pjrengineer said:
It’s more fun than working on circuit boards that’s for sure. But for me I still have a challenge removing parts that were wrapped around the terminal strip eyelets 4 times each 4 components per eyelet! Even with a desoldering gun it’s tough. I resisted leaving the leads and tying to them which would have worked fine but looked bad.
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Yes, the terminal strips are difficult. If only they weren't riveted in and could just be removed and replaced easily. Compared to the terrible power supply board in the 19, I much prefer the terminal strips of the 18, but when you get out of audio and into test equipment, working on boards can actually be fun. For the era, the later boards in the 18 are not bad (aside from the scope board). They're actually nicer to work on than HP boards of the same era. It took HP until about 1967-1968 to start using boards with real heat resilience. In the end, the component mounting in the Marantz is frustrating generally and more an issue than the fragility of the boards.
 
BlackScholes said:
Yes, the terminal strips are difficult. If only they weren't riveted in and could just be removed and replaced easily. Compared to the terrible power supply board in the 19, I much prefer the terminal strips of the 18, but when you get out of audio and into test equipment, working on boards can actually be fun. For the era, the later boards in the 18 are not bad (aside from the scope board). They're actually nicer to work on than HP boards of the same era. It took HP until about 1967-1968 to start using boards with real heat resilience. In the end, the component mounting in the Marantz is frustrating generally and more an issue than the fragility of the boards.
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So I didn’t have any difficulty with the 19 boards except for the fact that they are not labeled and use multi can caps which are a pain to figure out where the leads of the individual caps all go. I had to buy a copy of the service manual that had legible pics. I wish you luck on that 19 I’m sure it will be fixed soon. If you need any service manual scans of my 18 or 19 lemme know. The 18 manual leaves a lot to be desired.
 
After three years and three days (since I made this thread), I have a working Marantz 18. This is a late unit with a serial in the 7XXX range. I'll get into the details later but since we have a good amount of misinformation here, know the following:

-2N5116 jfet is not a suitable substitute for the scope board. My own choice and second attempt which was a 2N2609 also did not allow me to center "the dot".
-My completely rebuilt driver board with all transistors substituted for low noise modern substitutes worked fine. The DC balance adjustment is no longer necessary as offset is <5 mV. If you decide to keep the original part, simply clean it.
-my controls all operate quietly with no static or pops. I didn't use a drop of deoxit. If yours make noise, it is probably the capacitors tasked with keeping them quiet.
-The tuner is plenty powerful. With a simple 300Ω antenna I was picking up stations I've never heard before. The nonsense that exists about the receiver because people don't like the faceplate is astounding.
-This is easily a higher quality unit than the 19. The boards are better (aside from the scope board), the construction quality is notably higher as well. Confirming what I already mentioned on page 1.

Below are some thermal images that may be helpful:

i-Xm7jxjB.jpg

i-GJ7nCJ4.jpg
 
Moving on to another receiver... Using the TIP47G transistor on the scope board is not an appropriate substitute for Q1202, Q1203, Q1205, or Q1206 it appears. This is probably the most common suggestion for replacement of these transistors. None of you tried this and determined the same thing?
 
Check this out i posted on my thread from another thread. I am leaving mine be and replacing the thermal grease. Even if the scope image drifts a tiny bit I account that somewhat to heat.
 

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Since I'm not sure entirely sure what is causing the issue that eventually takes out the HV winding in the 18, I am completely rebuilding the least burnt scope boards that I have using parts far more precise than the originals. The variance in values for the original resistors certainly did not help any other issues that may already exist with this board/receiver as a whole. I've socketed the jfets so that I may conduct further testing on what an appropriate replacement is for them. Today, I purchased two more candidates that may work. One of them even matches the original pinout. Also ordered the KSC3503. On this board, the original jfets are close matches as are the four transistors mounted to the heatsink/bracket. Just need to remount the x and y adjustments and the socket, the connections were poor on both.


i-FCCxZ8m-L.jpg
 
While I haven't yet tested the jfets I ordered, the KSC3503s were a great success. The scope image is noticeably clearer and more stable than in the previous rebuilt board. Versus that well matched set of original transistors in the other 18, the temperatures were similar, not the over 270 degrees as with the TIP47s. Additionally, since these are an all plastic case, it is no longer necessary to go through the additional step of adding an insulator to the heatsink/bracket. For the record, since there is a visual difference, the delta between the four 10k resistors is about 20 degrees f. I believe this is attributable to the tube as this one was a bit tired.

i-kMK5B8j.jpg
 
How are the voltages per the schematic after the subs? Are the transistor sub design ratings exceeded? That’s important stuff.
 
pjrengineer said:
How are the voltages per the schematic after the subs? Are the transistor sub design ratings exceeded? That’s important stuff.
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Good or the dot wouldn't be dead center with the controls centered. No instability, no hum, no buzz, the dot is like a rock unless you've got a signal. The transistors are barely visible heat-wise and are clearly far cooler than the 10k resistors. We're good here. I'll be flipping the unit over for some phono board and tone board work. At that time, I'll measure the voltages again.
 
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