Thanks Joe, I just put a few of those chips in my digikey cart - will include some adapter boards too.

I'm not sure I understand your need for the inverter? I see it has differential input, but don't you just ground the inverting input and send the signal to the non-inverting input? I get that it would be half the volume than if the diff input was used, but couldn't that gain just be made up in the pre-amp stage anyways?

Hey guys,
I want to build a tiny guitar amplifier and my drawer full of LM386's isn't cutting it. Are there any IC's that are currently manufactured that do at least 3W and are similarly as easy as the LM386 and ideally include some protection for overheating, etc? 

If not, maybe my best bet is to add a push-pull transistor output at the end of an opamp stage (like in the attachment) - but I don't know how I'd chose the resistor values or the transistors to get 3W safely.

Hey everyone,
I've been given a Peavey LTD 400 that isn't working, it has 40VDC on the output. I've taken every power transistor out and tested them (diode setting on multimeter) and they all test fine.

Attached is the schematic with all of the DC measurements I've taken around all of the other transistors. Since I don't know what the voltages should be, I'm hoping someone can help me narrow down where the problem might be.

Quote from: J M Fahey on March 03, 2016, 11:16:35 PM

QuoteThe amp is rated for 150W on the rear, rail voltages are +/- 45V and the internal speaker is 8 ohms.

Thanks 

+/-45V rails allow for 100W@8 ohms and 150W@4 ohms.

A couple TIPs (which I hoped  might fit) definitely are not enough so it looks you'll have to get the suggestedvreplacements.
Good luck.

If there is NO WAY to get them, at any price, then you may kludge a replacement but not before turning all stones.

As usual, forget EBay, buy either reputable supplier or improvise (with good parts, of course).

Thanks J M, what about MJH11019 and MJH11020 ?

Quote from: J M Fahey on March 03, 2016, 05:59:06 PM
1) how much power/ohms is the amp rated?
"150" might just be w model "number".
2) actual rails voltage?
3) actual speaker ohms it's driving now?

The amp is rated for 150W on the rear, rail voltages are +/- 45V and the internal speaker is 8 ohms.

Quote from: g1 on March 03, 2016, 12:04:41 PM
Yorkville switched to MJH11017 & MJH11018 in some of these models, that would be the best sub.
However, you should contact them and ask.  In the higher power amps like the 150, it may not work.  The spec of the original BDV66 was changed and subs for the later type can be trouble.  They actually had a mod to add an extra output device when repairing certain models that used the BDV66 & 67.  Don't recall if it was the 150B, 250B, or both?
Best to contact them, or gamble and keep your 66's and use the MJH11018 for the 67's.

Just got off the phone with Yorkville, and they indeed recommended swapping out for MJH11017 & MJH11018. Looking at Digikey, they only have the MJH11017 available. For complementary pairs, they have the MJH11019 and MJH11020 available. Specs seem to say the only difference is a 200V "Collector Emitter Breakdown" VS 150V for the 17/18. Would this be a suitable substitute or should I be looking for something else?

Would digikey 2SD2560-ND be suitable?

It seems as though this is a "Transistor Darlington NPN 150V 16A 200W" according to google.
I'm looking for a replacement (reassigning the pin-out isn't a problem) if anyone knows one?

This is for a Yorkville 150B whose speaker cord shorted out while playing.

Thanks guys!

I'm happy to say I got this going again! i ended up desoldering all of the transistors and testing them. Q16, the MPSA20 was toast. I put a 2N3904 in there and the amp fired up!

Hey guys,
I recently inherited a Legend A30 with some problems in the output section. It looks like repairs were attempted, some capacitors replaced etc. I've tried my best to troubleshoot the output section, but to no success since the whole situation is complicated because of the previous attempted repairs.

The output looks correct on the scope when there is no speaker load attached. As soon as a load is attached (speaker or dummy), the output quickly drops to be nearly silent. The only thing that comes out of the amplifier is highly gated sounding, and on the scope appears to be just the very tops of the positive peaks (but inverted) of the signal going into the power section.

Attached is the relevant part of the schematic (full schematic here: http://music-electronics-forum.com/attachments/24638d1376247077-30watt1_1.jpg ) and I've also shown a bunch of test points and the results of the scope measurements I made at each of those test points, both with the load attached and with the load disconnected. I also wrote up all of the transistors in this section and what they've been replaced by. The schematic is hard to read, so there's a question-mark next to a few. Also note that Q12 (D41ES ?) was replaced with an A706 and the pin different pinout looks to be correctly compensated for.

I hope the diagram helps, let me know if there's anything you'd like me to test.

Thanks again,