C33 Update Project 2013

[perryinva]

This is a great thread for information on substitutes and possible issues on the C33. Let me pay a little forward in case someone down the road reads this and has this issue & contribute a small bit.

I recently came across an annoying fault in one of my fully rebuilt C33s. (All new electrolytics and upgraded opamps in many locations). The left channel would occasionally (but consistently) experience a reduction in clarity and volume, regardless of the source. Investigation showed that regardless of which channel was sent to the Left output, the Left output was the issue, whether through headphones (on board amp) or output to an external amp. This eliminated a lot of possibilities for problem components. The problem was I could never reproduce the problem with the unit open on my bench to trace it out. But it always did it after about an hour of normal playing when installed in a system, closed in its case. Bottom line, it was the muting transistor after the LDR as part of the mute during start, a 132-170. It is practically the last component in the output chain. . I replaced the pair (to match) with P1087 (cross legs 1 & 2 to match the original) and all is great again. Transistor tester showed the left transistor bad/broken and the right as two equal diodes. But the tester shows the 1087 correctly as a JFET.

 

[johnhoef]

Reminds me of a unit I worked on a while ago. The fault would only occur if the cabinet was installed. Without the cabinet, it worked fine for hours. Of course, my first thought was a heat issue. So, I turned on the unit, and touched each suspect transistor with my soldering iron until the problem surfaced. Quite an easy fix. Easily verified with freeze spray, then soldering iron again.

 

[perryinva]

Well here’s the thing. I didn’t even know there was a gradual mute during start and apparently shutoff as well. So I assumed the noise I heard during turn on was normal. With the new transistor the voltage rise on turn on is slower than it was with the old ones, maybe 3 seconds vs 1 second.

 

[perryinva]

One more pay it forward. I bought replacement faceplate bulbs for the C33 from our own dwojo, (superb service, very well priced and great craftsmanship). The bulbs are 6.3V on a 5.3VAC source, held to the chassis with yellow grommets, which I assume were a gum rubber type when new. They are twisted wire leads soldered to pins in front of the chassis. At this age, the original grommets are stone hard yellow and fall apart when you remove the bulbs. I found that standard 10mm black rubber grommets are the correct size, as long as you add another wrap of heatshrink around the bulb base as Dave supplies them. The original bulbs all still worked, but were definitely blackened some in the glass after almost 40 years of use.

 

[psychoaudio]

One more pay it forward. I bought replacement faceplate bulbs for the C33 from our own dwojo, (superb service, very well priced and great craftsmanship). The bulbs are 6.3V on a 5.3VAC source, held to the chassis with yellow grommets, which I assume were a gum rubber type when new. They are twisted wire leads soldered to pins in front of the chassis. At this age, the original grommets are stone hard yellow and fall apart when you remove the bulbs. I found that standard 10mm black rubber grommets are the correct size, as long as you add another wrap of heatshrink around the bulb base as Dave supplies them. The original bulbs all still worked, but were definitely blackened some in the glass after almost 40 years of use.

Nice! thanks for the tip. Were the lamps LEDs?

 

[perryinva]

No, they are bulbs. Too much hot spot with any LED I tried. Original bulbs lasted 40 years, guess I can live with that!

 

[nbndtrain]

I found that standard 10mm black rubber grommets are the correct size, as long as you add another wrap of heatshrink around the bulb base as Dave supplies them.

This is good motivation to pull my c33 and fix a few things. May as well do bulbs as it's pretty dim. Where is a good place to find standard 10mm grommets? Does dwojo have them? After recapping, any other must do updates you recommend?

 

[perryinva]

Dave did say he has grommets that work but they are not included in the price, and he didn’t say that they were 10mm. I bought a kit of assorted “metric” grommets on Amazon for $7, to try different sizes once I had the bulbs in hand. There were 40 of the size in the kit, so more than I will probably ever use. I have nothing against LEDs, BTW, but it is just too time consuming and expensive to be the first to experiment with different ones. For instance, the warm white frosted ones from Comet Pinball to replace 1866 or 1847 bulbs in my MR-78 or MC2205 work and look exactly like incandescent but a needed touch brighter. And were inexpensive (like $0.70 each in a pack of 25)

But the warm white LED festoons I tried (not from Comet, they don’t carry them) for the tuner glass looked decidedly like neon crap. $$ down the drain. Tried to save a few bucks over buying new incandescent ones ($11 each for a pair w/shipping) but by the time you waste the effort & $$ on bad LEDs, you may have well just bought them.

The recap helps a lot. This is my 3rd C33, and results have always been excellent. Just be sure to use low leakage for any of the orange or yellow caps. Other than that, any repairs I did were from random failed transistors due to age. Even the monitor amp only required insignificant touch up of bias after cap replacements.