Burnt 1st ic in vox ad30vt

[mountianjustice]

So i managed to put 260vdc throough the input of my vox. Neddless to say it cooked the first ic. Looki g at the schematic i tried injecting signal at pin 2 pin 7 and pis 2-7 in parallel. With mixed results it worked but was noisy and on the higher gain models it would oscilate and squeal. Then i tried at r88 and it workec great. Now my dilema is put this 15 cent single transistor boost stage in and be done or put a 6sn7 running at 260vdc in there. The tranny boost has adjustable gain so once its in there i can dial it in just like it was. The 6sn7 sounds great its really clean and its another tube in the signal path.

[Enzo]

I assume you are also building a complete power supply for that 6SN7?

really, just replace the op amp you blew and have the amp back stock if that is all that is damaged.   This amp is basically a computer, there is one tube in it, but the tube is running on only 15v, so it really isn;t adding a lot of real "tubiness".   If you want to feed a tube preamp into the input of the amp  fine, but adding one tube in the amp signal path won't remove its "computeriness".

I don't know how you got 260v onto this board, but if it was around the input, make sure you didn;t kill either half of the dual diode on the input:  WD1.  If one side shorted, you will have 15v sitting on that C1 input cap, and that will distort your signal for sure.

[mountianjustice]

Wd1 is at +15 on one side and -15 on the other the voltage to ic1 checks ot ok i just dont think i can feplace the ic being that its so small. The 260vdc was from the 6sn7 preamp i was building i had the input to the amp on two loose leads and it contactec the bottom of the tube socket. im not trying to turnmit into a tube amp but given the choice of a real tube 1st stage or a single tranny boost stage im just wonderjng what others would do. Im pretty sure replacing the ic is not an option as i dont think i could solder those tiny leads.

[Enzo]

Then take it to someone who can.  We call those small parts "surface mount" in that they solder right to the top of the board rather than have legs going through holes.  It is a soldering skill that anyone in the business has to know these days, as surface mount - often just "sm" - is everywhere.

There is a product called CHip Quik that really helps.  You can use that with a hand soldering iron.  there are also of course commercial surface mount soldering equipment.  if I had stayed in the repair business another few years, I would have invested in some of that gear, but a I was retiring, I just used ChipQuik and my regular irons, and it worked out.

Here is a video, he does it without the ChipQuik, but I prefer to use it.
https://www.youtube.com/watch?v=3NN7UGWYmBY

I won't lie to you, my first one or two of them came out pretty clumsy.

Yes, the two ends of that dual diode will be 15v, just as long as the center pin is not 15, you are OK there.

[mckayprod]

That's a great video!  I had no idea the rework guys could do stuff like that.  It CAN be done!  I think I'll get a few different sizes of tips and some of that liquid flux and start doing more surface-mount work.

[Enzo]

It is a skill, like any other skill, you just have to start and get some practice.