Toshiba SC-335 Sporatic DC at output

I agree with Jon, not that important to match the gains in the output stage.

Your hFE are on the low side tough. What transistors do you use?

using fja4313 and fja4213 transistors. I put in 3.3K parrelled to r9 and r10 and dc is down to 2mV and -2.3mV. My offest has been set as well and I am just installing final drivers.

Done. Dc is -3.3mV left and -4.2mV right. I am extremely pleased with those numbers and can do a little more fine tuning later on, but for now listening to a little Black Sabbath on vinyl.

Thanks for all the help everyone. It was a great experience for me and I am extremely happy with the quality that I am hearing right now.

ecluser said:

The most probable cause is mismatched transistors in the differential input stage.

They are the two small (2SA841BL) transistors, identified as TR1, 3 in the Right channel, and TR2, 4 in the Left channel.

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I have a SC-335 that I've owned for years, that I finally retired in 2005, due to the popping/frying bacon noise in the right channel that others have mentioned. The other day, just for fun, I pulled the 335 and my old pair of EV Sentry 100a Studio Monitors out of the closet, to replace a pair of Tannoy Actives that normally reside in my office, but are temporarily out on a project. I checked for DC on the outputs, and both channels won't even deflect the needle on the 250 mv scale. However, once the bacon frying/popping starts, it will deflect +/- around 20mv. I'm guessing the differential inputs (2SA841BL's) are due for replacement. I've had no love finding a direct replacement, and the only substitution I can find is the NTE NTE234. Does anyone have any better suggestions than the NTE's? I've heard negative comments about some of the NTE stuff, so any recommendations would be much appreciated. Thanks!!

First step is to clean the -20dB muting switch.

You will need matched (close hFE matching) transistors in the differential stage. If your meter can measure the hFE of transistors, pull out the actual 2SA841 and try to find the best match between them. It may solve your problem.

For substitution of the original, I would use:

2SA970(BL), 2SA1084(E), 2SA1085(E), 2SA872(E), 2SA1015L (GR), 2SA1048L(GR)

If you can't measure the hFE, a dual transistor like the 2SA798 may be your best option. I don't remember if this dual transitor is easy to fit on the board.

ecluser said:

For substitution of the original, I would use:

2SA970(BL), 2SA1084(E), 2SA1085(E), 2SA872(E), 2SA1015L (GR), 2SA1048L(GR)

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Hello

Can you recommend a source? Digikey, Newark, Mouser, etc. don't show a return on any of those numbers. The 20db pad switch is the first thing I checked and DeOx'ed, although I pretty much knew by the type of noise it was making that it was beyond a simple switch cleaning. I don't have a way of metering hFE. The little thing still sounds great, in between it's bouts of bacon frying. I bought it from a pawn shop in 1988, and it ran 24/7 (except for thunderstorms) all the way until 2005 when it got noisy. BTW, the noise is starting to become apparent in the left channel too, so I'll be replacing both sides. Thanks for the advice!

The choice of transistor is great. The ones I suggested are good low noise high gain transistors but you can use almost any other transistor you can find. The popular 2SA733 will work, and is no so bad. In fact, if you don't have a way to measure the hFE, you must use a dual transistor. Keep in mind that it is the most probable cause of your noise but it may be something else.

Did you try to remove the input capacitor and see if you have the noise?

ecluser said:

Did you try to remove the input capacitor and see if you have the noise?

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No I haven't had a chance to open it back up, but that will be the first thing I check when I go back in. I'm still unable to find a source for those part numbers, I would be grateful for any suggestions.

I finally got around to opening the Toshiba back up, and went ahead and put a pair of the NTE NTE234 on the left channel. (TR2 and TR4) It has solved the sizzling bacon noise. Based on my very crude RS voltmeter, I'm getting about -12 mv across the original unchanged right output, and about -30 mv across the left output with the new NTE234's. Sonically the unit sounds fine, although the left channel is showing signs of bacon sizzle like the right channel was. I swapped in the NTE's as a diagnostic step, and I know I need to get a VOM that will let me measure hfe. I would still be very grateful if someone could point me to a source for the components recommended by ecluser. Again, thanks so much for the advice!

Next Day Update:

I went ahead and did the right side with NTE234's, since it was already opened up. I've had the amp on all morning for about 5 hours, and it is dead quiet, running cool, and sounding good. I ran it up to full power last night on the Sentry 100A nearfields, and let it thump for a couple hours right at it's limits, and it's nice and stable. However, as I had been warned, the NTE's aren't matched very well. After being on all morning, and occasionally playing music, I'm getting -50mv on the left channel, and a whopping -70mv on the right. I have ordered a multimeter so I can compare hfe on pairs and try to get the mv readings back down where it belongs. In the meantime, I found a lot of 20 Toshiba 2SA970(BL) transistors on eBay, of all places, so I'll be replacing the NTE's with those. 20 of them should be able to get me 2 pairs that match pretty closely. If anyone is needing some, drop me a PM. Again, thanks for the advice!

Some inside pics would be nice.
I´ve got one here and someone made a mess of it, worst diy tweaking I´ve ever seen.

Got me a second set since the first one were abused in every way(holes drilled trough the front plate and such)
This is a very clean set, apart from pilot lights needing replacement and some minor detailing. The sc-335 have had one of the 2sd718 replaced with a 716? but it plays fine anyway. I need new drivers for the old one, it has the sizzling bacon noise in the left channel.

Nevermind the THX badge on the bottom one, it´s just to cover up a nasty drill hole.

Does anyone here know what the Toshiba's Tuner (ST-335MKII) display bulb's value's are? Voltage, Amps, Wattage,size, etc.?

**EDIT: I forgot to mention that I had already checked the bulbs themselves and they are very small with no markings or any other information on them to give me an indication. I'd really hate to buy a service manual just to replace two small bulbs. These two bulbs are smaller than mini size bulbs and each have two wires attached to both of each bulb with what appears to be a very small amount of heat-shrink to secure the wires to the bottom of the bulbs.

I do belive they are 8V 50mA. Blue wires and blue´ish glass?

IsakAlexande said:

I do belive they are 8V 50mA. Blue wires and blue´ish glass?

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Yes!
Each having two blue wires attached and the bulb having a light blue-ish tint.

That is a good description of them.

Please, no disrespect meant here but how were you able to know the values (voltage & amperage) of these bulbs?

Last question: Would you happen to know off hand where I can find these?

Hey, thank you so much for your help I really do appreciate it!

I might have the models and bulbs confused. Lol

I´ve already sold these so no way of checking either.

Toshiba 335MKII Series

It appears that Toshiba audio products are rarely talked about or mentioned but anyway since this thread has to do with Toshiba well I just wanted to show my Toshiba 335MKII System. This system and I go way back to 1980 (believe it or not, CD's were just being talked about and in its infant stage). During the winter of that year I remember my brother and I walking through a high end department store (back when department stores used to sell electronics, it no longer exist, were bought out) kinda in a rush and I just happen to spot this fantastic looking stereo system that just stopped me in my tracks! This particular 'black' Toshiba System, set up, was awesome looking back at that time. Right then and there (I didn't even have to think twice about it) I bought it!
The system consisted of the following: Original Rack cabinet (had Toshiba labeled on it) for all audio components to fit perfectly stacked, Turntable (which I still have), Tuner ST-335MKII, Pre-Amplifier SY-335MKII, Power Amplifier SC-335MKII and the matching cassette deck (can't remember the model number) which, back then, was sold seperately if wanted to match the system which of course I bought.
A pair of 3-way, wood grain speakers (not huge or very large but big and good enough to kick out them sounds and on each middle part of the woofer the brand name 'TOSHIBA' was on them. Cable's, connectors, etc. everything that I saw with it I took!
Now that I look back at it all, over a period of time, I foolishly got rid of the cassette deck, the rack style cabinet and the speakers. Man, kick myself for doing that, I wish that I would had kept everything!
The only original parts that I stayed with are what you see in the pictures (and of course the turntable which is boxedup and stored away). I had the Tuner ST-335MKII, Pre-Amplifier SY-335MKII and the Power Amplifier SC-335MKII stored in boxes for years now. A couple of months ago our boombox was giving out that we used for tunes out in our back patio. I remembered about the Toshiba three piece system, take it out of storage, hook up everything turn it on and still kicking! Only thing though is the receiver's display lamps/bulbs that display the dial settings are out which I currently am trying to find and replace.
Recently on Craigslist someone is selling the exact same three piece 'black' Toshiba set (same model 335MKII series) and of course I bought it.

Mono OK

Hello AudioKarma,
I've read this thread with interest. I picked up a Toshiba stack, including SC-335 and SY-335 from auction quite cheaply.

Couple of issues.
1) One channel is completely silent when the switch is set to stereo. On the mono setting both channels output OK.

2) No voltage from the blue cables from the transformer to drive the lamps.

3) One meter meter needle never moves.

When testing the 688/718 pairs one was giving different readings to the rest so I've replaced all four last night. No change.

Any suggestions what to look at next. I did take some measurements and voltages matched the schematic fairly closely.

If you guys like the SC-335 amplifier, try the SC-665. They're available cheaply on eBay, and 65 watts instead of 35 makes for a really nice sound. I have mine running from my SY-335 preamp, and it matches exactly. Looks just like a SC-335, but so much more headroom! (Especially with my somewhat inefficient speakers). The SY-665 preamp is a thing of beauty... if I can ever snag one off of eBay I'll be a happy man. They keep going for WAY more than I'm willing to spend.

Charles.

Any suggestion for an equivalent part for the M8513A-R diodes?

http://www.perfectelectronicparts.c...513A-R&mfname=AMERICAN+MICROSEMICONDUCTOR+INC

guys need a hint on this amplifier .. changed the resistors r41 and r42 since my relatives swam ... set it to 110 ohms ... or, all the same, set it to 100 as according to the scheme?