![]() You will still need output device bias, but with a triple EF it can be confined to the first stage of the darlington and still have “acceptable” crossover distortion. If you use them, the output stage can be run fully class B. Predrvers may be a really good idea here. The 11015’s are fine up to +/-40 - but not much higher. Bump it up to the 38 volt range (wont need more than 40) and you’re more likely not to come up maddeningly short at 90 or 95 watts. The only issue is whether you can get the 28.3 volts peak off a real transformer supply. Even single C5200’s do fine down that low. The 11015 has a decent amount of gain at 8A because it is a 30 amp device not 15. The 11015 is good for 4A at 40V, which is plenty for 4 ohms (But not 2). If the supply is actually +/-35V the trannies only need to see high current at 35V (any more volts And the current will be dropping rapidly even into a zero power load). The person that popularized the DCsoa rule for output transistor survival was AndrewT. Also easier to drill one hole, not 3 holes precisely lined up.Ībout the drivers, a sansui z3900 has 560 ohm resistors in emitter of the drivers. If you don't have the MJ15015/16 yet, On is charging ~$10 for any to3 package. Even MJ15024/25 has only 5 amp one pulse soa rating. You need more than one pair OT for 150 w. MJ15015-16 has 60 v one pulse soa of 3 amps. Crown D150 with single OT pair also was rated for that wattage. I've used a single MJ15003 pair for 75 watts on +-35v, originally 40636 (2n3055 selected for more Vce). The output transistors are emitter followers, don't need a lot of gain. Triple output gain (with predrivers) is for 3 or 6 pairs of output transistors. Q11 BD139 should be big enough to drive the drivers Q1 Q2. Dyna got compensation wrong in 1966, the "TIP mod" about 1972 straightened that out. ![]() Allen originally had a relay to disconnect the speakers at power up, which performed the RF block function until the contact became unreliaible at 30 years of age.Ĭalculating compensation to the feedback is over my head. I had to install the 14 turns parallel resistor in an Allen organ amp to keep AM sports talk radio out of the Sunday service. Dyna had 11 turns wire around the 2" diameter speaker caps, which worked. Put 14 turns 20 ga wire around a china marker or AA battery (removed) near the output jack, parallel a 3 watt 10 ohm resistor. The feedback line in from speaker to Q7 is a good way to inject radio interferance into Q7. Costs $.07 consumer products can't afford that. Paralleling the adjustment pot with a resistor or diode is good practice. The current adjustment should not fail open or short if the wiper loses contact. Yes, VAS Q5 should be on heatsink with the output transistors. For survivability look at Peavey & Crown schematics. +-35 is a little lightweight for 150 w if you are driving 8 ohm speakers. Somebody now deceased said OT survivability was predicted by DC SOA. If you don't have any highs you can get away with TIP41c/42c. To drive that much base you need something bigger than BD139/140 IMHO. ![]() You want 150 w you need a pair of output transistors, even TO3. My dynaco ST120 was cheap but it came with them. Lots of cheapo consumer units put no heat sink on the driver. Sakis, who ran a repair agency in Peraius for the beach bar trade, said darlington output bar amps blew up a lot more often than ones with separate driver transistors with their own heat sinks.
0 Comments
Leave a Reply. |
AuthorWrite something about yourself. No need to be fancy, just an overview. ArchivesCategories |