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A Very Compact Hybrid Amp - Page 132

post #1966 of 2213
After a long time away from this I've finally ordered some desoldering braid and a solder sucker, to start disassembly to work out whats gone wrong with my CTH.

Back a couple of pages I'd ordered a new C10P having reversed it, that's now fitted and I read 117v between TB+ and SG (thanks cfcubed ) so that now looks sorted so it's just my LV stage, and it looks like sachu posted debugging steps only a couple of posts ago - I may have a new amp for the weekend
post #1967 of 2213
Quote:
Originally Posted by suicidal_orange View Post
<snip> that's now fitted and I read 117v between TB+ and SG <snip>
That voltage is 10 volts too high I believe compared to specs..will need to see if the rest of the voltages check out once you have the LV section figured out.

Quote:
Originally Posted by suicidal_orange View Post
I may have a new amp for the weekend
Good luck.
post #1968 of 2213
> That voltage is 10 volts too high I believe compared to specs.

It may be just that his A/C adapter is running a little high, which is fine (e.g. one of mine does 27VAC+ under load). The HV cap specs have plenty of headroom for this.
Note though that sachu sure knows his way around CTHs so we'll see
post #1969 of 2213
Thanks guys, this theme of ~10% too high seems to be continuing - removed the 7824, replaced Q1P and Q2P just to be sure and it now measures 41V to pin 1... same for both SG and OG so seems there is a short somewhere? Back to the magnifying glasss No smoke though?

Now to show my noobness again, which is the BJT(s) to test? Sounds easy enough once I know
post #1970 of 2213
Quote:
Originally Posted by suicidal_orange View Post
Thanks guys, this theme of ~10% too high seems to be continuing - removed the 7824, replaced Q1P and Q2P just to be sure and it now measures 41V to pin 1... same for both SG and OG so seems there is a short somewhere? Back to the magnifying glasss No smoke though?

Now to show my noobness again, which is the BJT(s) to test? Sounds easy enough once I know
From my understanding of the circuit, the B+ has nothing to do with q1p/q2p or the 24v reg. The circuit on the top of the picture, that is where you need to find the error. Good luck! I need some luck as well with mine
post #1971 of 2213
DOn't worry about the B+ for now, you will only know if that is OK once you put the tube in. You may just end up running the tube hotter, which is not a bad thing really. Just make sure your LV section is fine.
Are you saying you are getting 41V on pin 1 wrt OG and SG?
post #1972 of 2213
Thanks devast, I have (had?) two problems with my build. I got excited at the prospect of listening to it and put in the last and biggest cap (C10P) in backwards, so that nearly popped. Replaced it and now C10P is reading 130V. if it wasn't for pin 4-5 still reading 12.7V (only .1V up on last time) I'd have suspected the multimeter...

Completely unrelated Q1P burnt out (nice melt hole in the side...) but no idea why. I've just had a lunch break and come back to notice that my creative lead work has connected Q1P to Q2P, but not to the circuit... Connected it and no change.

I'm not giving up this time, it will work!
post #1973 of 2213
Having been on for about 30 minutes pin 1 of the 7824 measures 42V to either OG or SG, if that increase means anything to anyone?

I still see no shorts
post #1974 of 2213
Another unhappy update

Decided to test the dodgy multimeter idea so put in a new battery. First test? Resistance between 1-2 on ICP. Shorted it, blew half the front off Q1P. Replaced that and decided on the safer voltage check - pin 1 to either SG or OG now reads 5.2v

Not sure I'm going to be able to sort this, I'm too careless
post #1975 of 2213
Quote:
Originally Posted by suicidal_orange View Post
Another unhappy update

Decided to test the dodgy multimeter idea so put in a new battery. First test? Resistance between 1-2 on ICP. Shorted it, blew half the front off Q1P. Replaced that and decided on the safer voltage check - pin 1 to either SG or OG now reads 5.2v

Not sure I'm going to be able to sort this, I'm too careless
Just my idea, but i think you blew q2p as well. I'd try replacing that as well.
post #1976 of 2213
Thanks Devast, you're probably right but it's not really going to help much - it didn't work even with both transistors in even when they didn't explode!

I've just removed, verified and tested all the caps and diodes in the LV section and they're all fine. Not sure how to test the 7824 but it's not even got hot enough to melt the thermal tape to the heatsink and wasn't in when I shorted it's pads so should be ok. So now to try and think what caused Q1P to burn in the first place.

I remember the LED being on before it burnt and never since, so I looked to see where the LED is - is this the "to lights" indicated on the right of the E12 schematic? I'll take the E12 parts out too if that's where the problem is...

Thanks again
post #1977 of 2213
So I've given up on being spoon fed (this is DIY afterall ) and actually read the test site. Removed and checked the resistors and cap in the rail splitter, all fine. Swapped IC1 with ICL - no change. Replaced all but the 2426 and I still have no joy, but no smoke either!

I guess the 2426 is a very sensitive part to be listed specifically in the guide? Guess I'd better buy a replacement...

I've just re-checked the resistances on the 7824 and now it reads 8.2 to the middle of the board (200k scale) and the outer isn't connected but has 2.66V across it. C10P now reads 116v, pin 4-5 in the tube 12.7V but 1-6 is back to 0V.

I'm close to just buying new parts for both the dead supplies, but that seems overkill...
post #1978 of 2213
Quote:
Originally Posted by suicidal_orange View Post
I've just re-checked the resistances on the 7824 and now it reads 8.2 to the middle of the board (200k scale) and the outer isn't connected but has 2.66V across it. C10P now reads 116v, pin 4-5 in the tube 12.7V but 1-6 is back to 0V.

I'm close to just buying new parts for both the dead supplies, but that seems overkill...
So. My ideas (i'm no expert):
12,7V on tube pin4-5 is ok if your switch is set for it, meaning your heater supply seems ok. Always measure the voltage to the SG. Pin1 of the 7824 to SG should read something like ~34V(30-38) or so, even when you have 7824 removed(I'd try measuring that pad while 7824 is removed). Pin3 should read 24V when 7824 is installed. If you got the first reading ok, then probably your 7824 is dead. I wouldn't worry much about the other tube pins until you can get the 24V functioning.
your C10P value seems ok as well i think.
post #1979 of 2213
Thanks again Devast, expert or not your help and encouragement are much appreciated

So I measured pin 3 to SG at just 2.7V. Removed the 7824 and pin 1 to SG reads 35.7V so that's where my problem is. So in your inexpert opinion do I buy a 7824 or 3 of them, expecting it to blow again?

EDIT: http://uk.farnell.com/taiwan-semicon...0-3/dp/7174071 <-This one looks to be suitable?
post #1980 of 2213
having a couple extra of the 7824s is handy.
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