Bottlehead Forum
Bottlehead Kits => Legacy Kit Products => Paramount => Topic started by: Rob C on November 06, 2023, 09:21:13 PM
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Hi, Rob here. Newbie kinda. I have some questions. The mje350 transistor and LED on the 4c snapped into smoke tonight. Could old age be the reason? Is there a usual reason? I really dont push the amps, it's for late night listening. Any insight is appreciated. It's labeled cc525 mje350 Mar. Will I be ok with any mje350? I have 2 extra leds. what is the led part number? Thanks a lot!
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It's labeled cc525 mje350 Mar. Will I be ok with any mje350? I have 2 extra leds. what is the led part number? Thanks a lot!
you can reach out to Queen for another MJE350. I believe any of the variants should be OK - AFAIK. This is the part number for the LED:
https://bottlehead.com/product/hlmp-6000-leds-combo/
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This is not going to help you problem , I just have a question. What is the tester you are using in the 3rd picture? Thanks.
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The MJE350 would be expected to fail from a driver tube failure taking the collector to ground. It's possible that if you replace it, the LEDs, and the 2N2907 that your amp will come back to life. If it doesn't, then we will have to explore some options to get these up and running again.
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The MJE350 would be expected to fail from a driver tube failure taking the collector to ground. It's possible that if you replace it, the LEDs, and the 2N2907 that your amp will come back to life. If it doesn't, then we will have to explore some options to get these up and running again.
Ok thank you. LEDs meaning all 4? 2? Or the one? Also did you mean the mje350 or 2n2907a or both?
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This is not going to help you problem , I just have a question. What is the tester you are using in the 3rd picture? Thanks.
Hi drok transistor tester. I modded mine. I don't like the lead clamp so I opened and soldered 3 wires to 1 2 3 and added clips.
https://www.amazon.com/Transistor-DROK-Capacitor-Capacitance-Automatic/dp/B01MS1FOYM/ref=asc_df_B01MS1FOYM/?tag=hyprod-20&linkCode=df0&hvadid=642146280909&hvpos=&hvnetw=g&hvrand=17795736675563495445&hvpone=&hvptwo=&hvqmt=&hvdev=m&hvdvcmdl=&hvlocint=&hvlocphy=9003472&hvtargid=pla-906476891433&psc=1
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Replace the LEDs on the side with the MJE350 that's blown. Replace the MJE-350, 2N2907, and 2 LEDs, then see what happens. 50/50 that gets you back in business.
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As I recall, the zener string can die if something else craps out. You can check each zener diode for resistance, before firing it up. (Check both polarities; one should conduct but the reverse should not.)
Unfortunately, the soft-start retrofit kit is long out of production.
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And obviously replace the driver tube? Is the 12at7 or 300b the diver? I prob should know that.
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The 12AT7 would be the potential source for an issue like this.
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PJ is right on here. When an LED explodes violently on a Paramount board there is most often a zener or two taken out in the zener string as well. Definitely check them for shorts and replace any blown ones before firing it up. I can't say that we came up with a definitive cause for this condition, but we have seen it happen a few times over the past 15+ years.
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Man, I saw the MJE350 and thought this would be the B side of the C4S, but now seeing the 90.9 Ohm R1, this is the A side!
Yes, PJ is correct. You probably have a 75V zener diode or several that are shorted out, just pull them all out and replace them. The MJE350 needs to come out and be replaced by an MJE5731A with the metal tab facing the opposite way. The LEDs get replaced, as well as the 2N2907. When this is sorted out, be sure to go into your other Paramount and replace the MJE350 on the A side with an MJE5731A.
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Oh right, MJE350. Pushing the limit at startup voltage. Just finally gave out after so many years. 5731A is the way to go.
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Good to know. Thank you. can I buy what I need from BH?
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This is not going to help you problem , I just have a question. What is the tester you are using in the 3rd picture? Thanks.
Vid of mod
https://youtube.com/shorts/MYkKOiIVswk?si=34S0M_MqxVvbeCf4
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MJE5731A looks discontinued. Recommend a sub? Think ebay has genuine?
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Nicely done with the mod, thanks for sharing.
I bought some transistors on eBay once for my Foreplay and they crapped out after a month or so. If you do all that work I would spend a few more bucks and order from a reputable seller even if shipping is higher in the end than the parts.
This seems to be the same the only difference that I saw is the Watt rating which is 50 instead of 40: MJE5731AG
https://www.mouser.com/c/?q=MJE5731A
But Paul will know better, in case I am wrong.
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I really appreciate all the help and knowledge. I could however benefit from a parts list. I could make one but I don't know the zener diode part. I'd assume there are different ones? Thank you.
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Good to know. Thank you. can I buy what I need from BH?
We no longer use or stock the 2N2907, so this is probably a better order for Mouser.
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MJE5731A looks discontinued. Recommend a sub? Think ebay has genuine?
https://www.mouser.com/ProductDetail/onsemi/MJE5731G?qs=sGAEpiMZZMv4z0HnGdrLjjK%252BdB6HHs0Yogi5zyayRfc%3D (https://www.mouser.com/ProductDetail/onsemi/MJE5731G?qs=sGAEpiMZZMv4z0HnGdrLjjK%252BdB6HHs0Yogi5zyayRfc%3D)
https://www.mouser.com/ProductDetail/Broadcom-Avago/HLMP-6000?qs=jT9z6tsiFNmh%2F1NRKSS5EA%3D%3D (https://www.mouser.com/ProductDetail/Broadcom-Avago/HLMP-6000?qs=jT9z6tsiFNmh%2F1NRKSS5EA%3D%3D)
https://www.mouser.com/ProductDetail/Central-Semiconductor/2N2907-PBFREE?qs=u16ybLDytRY%252BTMJ2a8Vx4w%3D%3D (https://www.mouser.com/ProductDetail/Central-Semiconductor/2N2907-PBFREE?qs=u16ybLDytRY%252BTMJ2a8Vx4w%3D%3D)
https://www.mouser.com/ProductDetail/Vishay-Semiconductors/1N4761A-TR?qs=8Acm1RElxHLZ6H5eAfHicA%3D%3D (https://www.mouser.com/ProductDetail/Vishay-Semiconductors/1N4761A-TR?qs=8Acm1RElxHLZ6H5eAfHicA%3D%3D)
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Thank you everyone!
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Ohm question. I have sonus faber concertino and concerto. Thoes are 6ohm. I assume there shouldn't be a problem there hasn't been for over a year. I have to look if the opt is wired 4 or 8. Which is recommended?
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Ohm question. I have sonus faber concertino and concerto. Thoes are 6ohm. I assume there shouldn't be a problem there hasn't been for over a year. I have to look if the opt is wired 4 or 8. Which is recommended?
"Which is recommended?"
I recommend the one that sounds better to you.
:^) Both are reasonable choices from a technical perspective. But they will interact differently with the speakers, and the differences will likely be audible.
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:^) Both are reasonable choices from a technical perspective. But they will interact differently with the speakers, and the differences will likely be audible.
Ok thought so, thank you. I've obviously googled it a bunch. I went to 4 ohms on the dynaco vta st120. I like it.
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Since I'm replacing both 12at7, I'm looking at matched JJ. Any reason not to?
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https://www.ebay.com/itm/285550720735?hash=item427c2636df:g:F4UAAOSwIwllPxzi&amdata=enc%3AAQAIAAAAwOasRtz9VYGFhb8On%2FTQl6dZNug4HvYW32NWrlSonhQ4eD3PQ1kljn2HQoQv%2Fztl%2Bumsq6ZYtOt255MYIk%2FiBbC30SGbQScHThyQB65ntWm%2B5AmunGgSoNWMWiySJeJuSeXG42hjqPrZ4MQACJQY2U2qCNKLiGSPzL0fhfpqxh%2B8nx4td5%2FohCOvJj4RRm%2FmavGbBX0efLt%2FdBhU%2F75c8afer%2FajUUft0VbEo21U%2B1FFfa9stl9ff9S7LoUZa9027Q%3D%3D%7Ctkp%3ABk9SR-jO1J_5Yg (https://www.ebay.com/itm/285550720735?hash=item427c2636df:g:F4UAAOSwIwllPxzi&amdata=enc%3AAQAIAAAAwOasRtz9VYGFhb8On%2FTQl6dZNug4HvYW32NWrlSonhQ4eD3PQ1kljn2HQoQv%2Fztl%2Bumsq6ZYtOt255MYIk%2FiBbC30SGbQScHThyQB65ntWm%2B5AmunGgSoNWMWiySJeJuSeXG42hjqPrZ4MQACJQY2U2qCNKLiGSPzL0fhfpqxh%2B8nx4td5%2FohCOvJj4RRm%2FmavGbBX0efLt%2FdBhU%2F75c8afer%2FajUUft0VbEo21U%2B1FFfa9stl9ff9S7LoUZa9027Q%3D%3D%7Ctkp%3ABk9SR-jO1J_5Yg)
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Nice find. Thank you. Bid is in.
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Once all the new components and tubes are in should I start the amp with a variac and take measurements or just turn it on with fingers crossed?
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On the mje350
1.emitter
2 collector
3 base
MJE5731g
1 base
2 collector
3 emmiter
So I will install backwards.
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The MJE5731G I ordered is 350v
There is an mje5731AG that's 375v and available.
Should I have ordered the MJE5731ag ?
https://www.mouser.com/ProductDetail/onsemi/MJE5731AG?qs=R2UZ7gjkEjIIBIrVFKMX3w%3D%3D
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Yes , the 375 volt will be more reliable. The higher voltage is the primary reason for changing from the MJE350.
If there were an even higher-voltage PNP transistor available, I would probably want to switch again.
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Either one will work adequately in the Paramount. The change is to buy a little extra tolerance to high voltage (the MJE350 is rated for 300V max) and to better handle the thermal requirements in that position.
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https://youtu.be/0LyUAwK985c?si=dsYMtSWcko1YbfEU
SUCCESS! YOU GUYS ARE GREAT! THANK YOU!
4 out of 5 diodes fried.
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The presence of the MJE350 in the original circuit was likely the cause of the fried zener diodes.
Don't hesitate to clip a little heatsink onto the 5731A down the road if you can.
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I will. I have mini ones that'll be perfect. All of them I suppose could benefit, even the power supply board? What's the best way to attach? Thermal paste and maybe thin tie wire twisted.
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I'm going to pick up heatsink glue
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I would just get some small clip on heatsinks for TO-220s. I wouldn't glue anything on or use thermal grease, that's pretty overkill for the application.
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I got nte425. Thermal Interface pad self adhesive.
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Something like this is fine:
https://www.digikey.com/en/products/detail/assmann-wsw-components/V8508A/3476148 (https://www.digikey.com/en/products/detail/assmann-wsw-components/V8508A/3476148)
If you need to take the heatsink off for future work, it's pretty easily done.
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Do any of the repairs I've done have an effect on the audio at all? Sonics, volume?
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No, you're just replacing broken parts with new ones.
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Heat sinks
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Should I replace all four mje350 on both boards in both amps?
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I would take the heatsinks off the high voltage rectifier diodes, as they dissipate nearly no heat. Likewise on the remaining MJE350 in the Paramount.
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I would take the heatsinks off the high voltage rectifier diodes, as they dissipate nearly no heat. Likewise on the remaining MJE350 in the Paramount.
Ok I will. I am also going to replace the old A side mje with mje5731AG on both amps. Also both on the center board in the foreplay. I will only heatsink the MJE5731ag on the B side only? . I assuming the MJE5731ag will work on both the A and B side. Any other prevention upgrades I should do?
Also, why in the manual ,A side calls for MJE5731a and B side mje350? Thanks.
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You want the 5731A on the A side where it's exposed to more voltage and cooks off a little more heat (in the Paramount). In the Foreplay, the center board just gets a little warmer than the outer boards and the 5731A will more gracefully handle the load in that position.
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how about the B side? I've installed the MJE5731a. On the B side. Can I put mje5731AG on both A and B?
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You can do that in the Paramount. I personally don't find it worth the risk of damaging a PC board that we don't produce anymore to do this, but it's certainly an option.
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So then I'll leave alone side A in paramount, but upgrade side B in foreplay center board?
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Yes, you are correct. For whatever reason, I remembered the higher current/voltage side of the Paramount C4S being the A side (a convention which we did adopt at some point), but it appears that the B side is where you want the 5731As. Such things happen on a product that hasn't been around in a while!
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Thank you