Model 16 Rebulid

acetate

Active Member
I have decided to rebuild my Model 16. In addition to a standard recap I also want to get as close to a 16B as possible. I compared the schematics and have found 9 differences. Most of them are just part swaps, three involve some rewiring. The transformers are different between the models I do not plan to make any changes there. So I likely won't get the power boost but am hoping for the sonic improvements. Below are my plans. Any input is appreciated.

I want to thank Chris for his awesome post on Faultline for his Model 32 rebuild. I would not be attempting this without that post.

Part swaps
  • Q1 - MPSA70 (considering NOS)
  • C8 - .022uf 100V cap
  • Q2 - MPSA20 (considering NOS)
  • Q5 - MPSA20 (considering NOS)
  • R35 - 2.2K 2W Resistor
  • R39 - 750k .5W Resistor
New parts
  • C22 - 10uf 64V cap (across R39 and R40)
  • CR6 thru CR9 - Are replaced with an actual bridge rectifier. I plan to just replace the diode network with four UF4004. Originals were SR154 and SR154R. I can't find any info on the SR154R. The UF4004 seems to be good to replace the SR154 though. Any input here is appreciated.
  • CR7 and CR8 are now 1N5393 and wired across the bridge rectifier
Chris's relay board rebuild (Originally on a 32)
  • Replace all resistors
  • Replace bridge rectifier with KBPC602PBF (but my 16 is different than the 32 here so I won't be doing this)
  • Replace Q13 & Q14 - BC546B (pinout is reversed)
  • Replace Q12 - MJE182G (pinout is different)
  • Replace all caps - I will use Elna Silmics here
In addition all caps will be replaced
  • I will follow Chris and use Nichicon TVX. For the oddball 125uf, I will piggyback a 100uf and a 33uf.
  • Considering Nichicon LKG for the filter caps. They are larger capacitance than I want (8200uf) but with it starting at 5000uf then the first service bulletin to 6800uf, then another to 6900uf, I don't want to go with the 6800uf.
Service Bulletins
  • I can't find R44 referenced in 69-12/16-1. I'm guessing I am either blind or this was added after the schematics that I have.

I will also remount the outputs with some fresh insulators and compound.

I need to sit on this for a couple days to think through this some more. I hope to get my order in this weekend.
 
You should be fine with the bigger filter caps I used 10,000uf caps with no problems. If its the non B model the rectifiers are very beefy. I was told to leave them alone. I found many of the old carbon comp. Resistors way out of spec on mine. I replaced all the carbon comps with carbon films. Also replaced all the carbon comp looking wire wounds with mills precision wire wounds. Chris and his site helped a lot. The blue metal film resistors will probably be OK, I replaced mine just because I was already in there. Good luck! Its a sweet sounding amp. Chris showed how an Omron MY2- 02 relay can be used if you reverse the internal wiring. I did this as well. Be very careful with the PNP and NPN boards. The traces are held on with little more than spit. :D
 
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Good to know about the filter caps.

It is a non-B version. Serial # is around 1500.

Thanks for the pointers on resistors and the reminder on the relay. I left that off the list on accident.

I am in the middle of PM with Chris where I think he is also giving me guidance to not replace the diodes. Looks like I will scratch that off the list.
 
I made some good progress on the power supply, PNP, and NPN boards. I have not done the relay or transistors on the power supply at this point. I wanted to get the resistors and caps done first and then go back through and do the rest.

I missed some parts on my first order so had to order some parts for the amp board. I also discovered the TO-66 packages which I missed until I took the back cover off. So I added some new mica insulators for those.

I did eventually find R44 on the amp board.

I will likely replace the opamps based on a thread here. However, the person chose LM301 which has an 18V supply voltage as opposed to the LM201 which has a 22V supply voltage. Since Mouser carries new LM201's I will likely just order a pair of those.

I was going mad trying to track down what components were which so I made a component layout and have attached it here. It is still a project in motion as I need to take pics of the PNP, NPN, and bias boards as they are not in the SM.

I am pleased with the improvements thus far. The low end still seems muted though. So far I have only been testing with my phone. After the amp board is done I will get a proper preamp hooked up so I can get a better input signal.

Probably not much progress is likely over next couple of weeks as family life is hectic.
 

Attachments

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Some pics attached of the rebuild. I have one monoblock fully completed (except the opamp, which is still enroute). I got it hooked up with a 2250 as a premap and it sounds great. The low end problem was fully due to using the phone as a source.

I am still learning to use my HP 333A to measure distortion. I found a video last night and hope to walk through it later. I also need to walk through the eight tests in the SM.

Anyone know any good sign companies that can make new faceplates? I have the vector art near ready. This is just for the black/blue faceplate. I have the diffuser plate. My buddy is working to 3D print the black bezel. Then I will have a completely rebuilt unit.
 

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What did you find to replace the screw top filter caps? You should be able to download a manual for the analyzer. The 333 that was given to me came with it, I got lucky.
 
I got the manual but it didn't make sense for me. I watched a youtube video and it makes sense now. I just need another go with it.

If only I could find something similar for my sound technology 1000a. I'm totally lost with that thing but I think the unit has an issue. I need some hours to troubleshoot with it.

Screw caps

Full project
 
I am still learning to use my HP 333A to measure distortion.

Remember that when your measuring distortion the measurement will/can only be as low as the distortion of your signal source.

Also, to get the most accurate measurements your should use coaxial cable for the test leads between the 333A and the amplifier
 
I have learned today, via troubleshooting a Pioneer unit, that my signal source is garbage. I will be buying a new one. Thanks for the tips on the cables. I will need to buy some other cables to remake the balun for my sound tech 1000a too.

BTW Chris you were right on the diameter of the filter caps. They are 35mm. My calipers were crazy off. I now have learned to just rezero each time I turn them on. I love that your memory is better than me with the right tools and holding the part. Chalk another one up to experience.

Chris - Thanks for your help.

Lavane - Thanks for the compliment and the pointer on the resistors. When I pulled the C/C ones I spot checked them and they were just horrible. Every one of them.
 
The other monoblock has a bad Q4 transistor. Datasheet has it as SS9305 and the component in the unit is FS40447. Searches online have not helped in finding a substitute. Any of you with the old books or other means have any suggestions?

When I swapped in my other Q4 the unit still has power up issues so I am still swapping parts looking for more problem components.
 
I did successfully replace SS9305 with 2N3440 from some help in the DIY forum. I got a lot of great guidance on how to sub out transistors. Also the two zeners on the amp board were bad. But everything is working now.

At this point I have two completely rebuilt monoblocks. Offset and bias and set. I was able to measure clipping at 35V. Which looks like a promising improvement compared to the spec of 21V. However, my distortion measurement capabilities are not where they need to be yet. I have an HP 8903A on the way so hopefully that will enable measuring distortion on the unit post-mods.

Fingers crossed.
 
Hi Acetate
I have been reading threads on this amp, including yours. It is a nice writeup and will help me on my Model 16B. One thing I noticed in your rebuild, is you used a 48 volt Omron Relay. Isn't this relay supposed to be 24 volt.

Thanks
George
 
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