C33 Update Project 2013

Thanks for sharing guys. I am not an electrically savvy kind of guy, but I have appreciated the thread and really like learning about the pieces (I have the C33). I won't be digging into mine anytime soon! (Well, I've taken the top off to do some dust cleaning and deoxit of the switches and tone controls, as well as the rca jacks on back, but that's the extent, and that made a huge difference in SQ!)

Thanks guys. Works like a charm. Misbalanced left and right channels pushed me to start to recap. After recap sound is more clear, got more hi, mid, nice sweet bass and balanced left and right. During recap made a big mistake by switching wrong polarity (mistake on a diagram) on the power supply board causing system to get dead. Thanks Gregory for pictures and Kevzer for advise it was fixed. Found 8 dried caps. I used regular NICHICON caps from Newark. Tried to keep the same parameters with closest voltage available from Newark. Now enjoying Joe Walker. Sounds much better then before.

rpoli2518 said:

During recap made a big mistake by switching wrong polarity (mistake on a diagram) on the power supply board causing system to get dead. Thanks Gregory for pictures and Kevzer for advise it was fixed. Found 8 dried caps. I used regular NICHICON caps from Newark. Tried to keep the same parameters with closest voltage available.

Click to expand...

True, there are mistakes on the schematics, and there are 'some' caps in backwards. Best to study the schematics and use a digital camera to take 'before' photos for reference. If a cap is in doubt, you could measure the voltage across it. Like a fool I sold a perfectly good VTVM with high impedance probe a few years ago!

Which caps were dried out? and how were they dried out? What is the criteria for tagging a cap as dried out?


Replacement caps

There are various ways of choose replacement caps.. that is whether to upgrade them or simply replace them. I typically use all Nichicon, and in the 2013 Update.. probably went overboard with FG. But it can't hurt. Here's a little chart made by cutting and pasting 'flows' from Nichicon spec sheets. Suppose it should include VR and VZ general purpose series.




IMHO the Fine Gold (FG) are a good choice for the audio path. The FG series has small size, wide voltage range and plentiful supply. KZ are marketed as Premium. I upgraded some of the Power Supply and voltage rail bypass caps (where feasible) to KZ, even recapping with KZ soon after the first replacement. This isn't a lecture or sales pitch for caps, but is posted to discuss recap strategies. We [in the group] are always looking for and exploring new 'best practice' methods for maximizing performance of and preserving Mc gear. :thmbsp:


-Greg

After almost 3 weeks I've got huge distortion from the left channel. I checked board 045810 which is monitor amplifier. I found one of the power transistor PNP MJ3237 open. Checked the rest of the board and didn't find any bad resistors, diodes or caps. Don't know what was the reason for transistor to die. What is the best substitute for these MJ3237 and MJ3247. They are TO66 shape. Thanks

Hello !

132-197 = NPN = MJ3247 = 132-227 = TIP41B
132-198 = PNP = MJ3237 = 132-228 = TIP42B

You can trust me because these transistors are used in C34V in the monitor amplifier too .

C33 and C34V use exactly the same board ! :thmbsp:

clinic-audio said:

Hello !

132-197 = NPN = MJ3247 = 132-227 = TIP41B
132-198 = PNP = MJ3237 = 132-228 = TIP42B

You can trust me because these transistors are used in C34V in the monitor amplifier too .

C33 and C34V use exactly the same board ! :thmbsp:

Click to expand...

The TIP are TO220 right? So you have to cut the collector leg off? Is that right?

error

Hello Kevin !

The TIP are TO220 right? So you have to cut the collector leg off? Is that right?

absolutly !

see my picture :yes:

oooops ! forget the picture !

here it is !

Yea the to66 case style are long gone......don't forget to order some micas to insulate the tips from the heat sink.

Won't be long until we will be needing to use to220 for all the to66 case style Mac used.

What do you think about this substitute?
Motorola posted it as a direct replacement.
132-197 MJ3247 = NPN => MJE15030 or MJE15028
132-198 MJ3237 = PNP => MJE15031 or MJE15029
Is it a better choice then TIP41B and TIP42B?
Thanks

Mac engineers chose the TI devices over the then Motorola devices......

c_dk said:

Mac engineers chose the TI devices over the then Motorola devices......

Click to expand...

On Newark I found instead of TIP41B and TIP42B > TIP41C and TIP42C.
Difference only 80v with 100v. Is it ok?

clinic-audio said:

Hello Kevin !

The TIP are TO220 right? So you have to cut the collector leg off? Is that right?

absolutly !

see my picture :yes:

Click to expand...

Hello,
Do I need to short bolts (collector line) holding Q1022 NPN MJ3247 to replace it with TIP transistor?
C34V amplifier board is the same as C33 with different parts.
Is it getting better sound after upgrading/replacing MJ...s with TIP...s or even all transistors on the board?

Hi fellows,
Would like to thank you all for your help.
Now its up and running and sounds even better then before. I replaced MJ3247/MJ3237 with TIP transistors as you advised. Much more clear, no humm like before.

rpoli2518 said:

Hi fellows, Would like to thank you all for your help.
Now its up and running and sounds even better then before. I replaced MJ3247/MJ3237 with TIP transistors as you advised. Much more clear, no humm like before.

Click to expand...

Good to hear you got it sorted out. It would have been best to start a new thread with the issue. No complaints though, the view count went way up.


-Greg

Images in this thread have been restored, there may still be a few missing but I'm on it.

There's still trouble with the External Processor jacks, where they are shorted until an RCA plug is inserted. Could be from too much internal scrubbing.

Otherwise it's working fine.

Did a power test on the C33 monitor amp a few weeks ago and it was making in excess of 25 Watts, both channels. The side of chassis where the heat sink is mounted got pretty warm from continuous CW power!


-Greg

Gregory, I hope you are still out there, and hope you will respond to my request. I just completed rebuilding a blown channel on the C33 monitor amp. Among the damaged components was the bias adjustment pot, which I replaced. I set it to roughly the same position as the old one, but would like to set the bias on both channels before returning the unit to the customer. I see in this thread that you made these adjustments. I have downloaded several copies of the schematic from different sources, and they all have a portion of the bias instructions cut off! How frustrating! I wonder if you could let me know where to measure the voltage, and what is the correct voltage to adjust to?
Thanks!!
John H.

johnhoef said:

Gregory, I hope you are still out there, and hope you will respond to my request. I just completed rebuilding a blown channel on the C33 monitor amp. Among the damaged components was the bias adjustment pot, which I replaced. I set it to roughly the same position as the old one, but would like to set the bias on both channels before returning the unit to the customer. I see in this thread that you made these adjustments. I have downloaded several copies of the schematic from different sources, and they all have a portion of the bias instructions cut off! How frustrating! I wonder if you could let me know where to measure the voltage, and what is the correct voltage to adjust to?
Thanks!!
John H.

Click to expand...

The answer is at the BOTTOM of this post: https://audiokarma.org/forums/index.php?threads/c33-update-project-2013.494086/page-5#post-7376337

See in the photo and caption marked-up and reposted below, the bias setting is 5 mV and is measured "between the resistors" where you see circular yellow lines indicating the end loops of the two side-by-side resistors, each channel.

Click to expand...

-Greg

Gregory,
Thank you very much for responding so quickly! I had studied the schematic, and figured the voltage would be measured between the emitters of the output transistors. Thanks for confirming that. Indeed, we are adjusting the quiescent current flow through the output transistors. Considering the 5mv across .44 ohms, this translates to 11.4ma of current through the output transistors.