blown speedball

[pro_crip]

I got my speedball stuffed and installed last night with only 1 slight problem, I was getting a hum in 1 channel. Not enough to stop me from listening and what I heard I liked. Since I had some free time today I thought I'd try and solve that hum problem. The first thing I did was pull the CBS 5814 and swap in a GE 5814, that killed the hum and microphonics problems I was having. I then did some tube rolling to find a combo I liked. First, out came the 7236 (to my ears not a bad little tube) and in went the 421a (to my ears a great little tube . Then I tried a 12bh7 in for the 5814, which had a muddy sound, to my ears at least. So I popped the 5814 back in. Unfortunately I left the volume turned up and when I repowered the crack I got a loud pop in the right channel and only got sound out of the left. Thinking I had just fried my new 650's, I tried some 570's I had laying around. Luckily I only had sound out of the left with the 570's. I propped the plate up, with the power on, and saw that the led's on the big board (spacing on the name at the moment) only lit up on 1 side, I'm assuming that's the left side. I'm also assuming the right side is fried, is that a correct assumption? If so, how do I fix it? All new componentry on that side or do I start over with a new board? Thanks for listening.


Rich

[JC]

Caveat: I don't know any of this for a fact, since I don't have Crack.

But, it seems to me from what little I know that the "big board" probably serves the "big tube".  So, I think I would try resistance and Voltage measurements in that vicinity to see what you can learn first.

[Doc B.]

Yup, sounds like the load blew on one channel. You could try replacing the TIP50, 2N2222A and the LEDs on that side of the board. You will want a solder sucker to clear the pad holes after you pull the dead parts, so you can easily insert the replacement parts before you solder them. Another tip - cut the body of the old TIP 50 off its legs, then remove each leg from its solder pad individually instead of trying to heat and wrench out all three at once. Usually end up ripping some traces if you do it that way. Trust me - I've wrecked PC boards just about every way imaginable!

Eileen will be in the office a bit later this afternoon, and she can help you get the replacement parts you need.

[pro_crip]

Thanks for the tips doc, they worked just fine. A quick update, after re-stuffing the board and plugging it back in it turns out that I blew my 421a. One channel at least. That was a $100 lesson, make sure all strays are taken care of. I used stranded wire to make the hookups and the B+ connection had a stray strand that went where it shouldn't have, hence the pop and blown tube. At least it gave me a chance to bypass the output caps with some commie surplus teflons. The 7236 and 12bh7 combo is working nicely. Thanks for listening.

Rich