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A Very Compact Hybrid Amp - Page 142

post #2116 of 2213

hey forsakenrider!  double checking the setup voltages would be a great start.  Your voltages are way off.  The e12 is probably tripped and will never turn on.

post #2117 of 2213

I dont think it was a spark, I was running with an 8416 tube and they light up when first powered on, The led seemed brighter then normal but it was just a flash, and thats what caught my eye. I didnt see smoke or fire and didnt smell anything off.


First off my wall wart is reading 31.9vac, Im not sure if its always read that or is thats new. I vaguely remember my HV being on the higher side but everything else being correct before, so It was probably always that.


all my measurements before were WRT SG


The LV supply is 0.8v, That cant be good.

post #2118 of 2213
Originally Posted by forsakenrider View Post
The LV supply is 0.8v, That cant be good.


Nope, not at all.  If you can, probe the points right after the rectification on the LV.  Your plate voltage is way too low, should be ~80V.  The CCS for the tube (opamp) should have ~2.5V on it's pins (in and out). 


Test the voltage after the 24V reg, C1P or C2P leads would be a good point to probe on the underside.  If it's dead, test after the rectifier, and then test after the cap multiplier to see which building block is dead.  I would be surprised if the diodes fried, but I wouldn't be surprised if the reg or the cap multiplier died.

post #2119 of 2213

Yep, as holland says let's figure out / fix that LV supply first.  Doing that may fix the other voltages.  I guess its OK that your wallwart is high if its the same wallwart you've been using all along.


Like he said, lets see the Vs around your 24V reg.   Another place to probe test points is on the reg itself.  Again, see the Output, -/center and Input labeling here http://www.cavalliaudio.com/cth/main.php?page=boards and let's know what the input & output Vs are on the reg WRT its center pin.


Again as holland said, a weak link in the original BoM was Q1P... Originally a BC550 it was changed to stronger BC337.  If input V to 24V reg is low measure your collector & emitter Vs on Q1P.  All this WRT SG.    BTW, if you need a BC337 I've plenty & could post one to you.

Edited by cfcubed - 12/1/10 at 4:15am
post #2120 of 2213

The LV supply is 44.5v  (at c5p's +)


Q2P C=45 B=41 E=44.2

Q1P C= 45 B=44.4 E=0.2


So I guess its Q1P, I will have to look but I doubt I have any BC337


what could cause that? Did it just die eventually?

Edited by forsakenrider - 12/1/10 at 4:29pm
post #2121 of 2213

We saw some Q1P BC550 failures over time (within 1st 4-6 months?) & it became clear BC337 was a better choice there & we updated the BoM. 

Hotter caused earlier failure & w/your 24V reg having to pull down so many volts that's more heat.  Is that 32VAC under any load?  It should not be higher than 28VAC under load.


If you've a BC550 around you could put it in just to confirm that's all that's wrong.  If you've one of those TO92 paddle heatsinks around that would help it (probably why my 1st proto w/BC550 is still fine).  


PM me your address & I'll drop you a couple BC337s

Originally Posted by forsakenrider View Post

The LV supply is 44.5v  (at c5p's +)


So I guess its Q1P, I will have to look but I doubt I have any BC337


what could cause that? Did it just die eventually?

Edited by cfcubed - 12/1/10 at 4:56pm
post #2122 of 2213

I just plugged the wall wart in for a minute and it seems around 28vac after a minute. At first it dropped down to 24 and raised up it slowed around 28. I hope its not too extreme! I did run it for an entire day just before it died, maybe it was just its time to go...

post #2123 of 2213

Wallwarts shouldn't die like that.  I have mine on quite a bit.  It's my office rig, so it's on pretty much 10 hours a day.  28VAC is fine, but the rise is odd.  It could be your mains is dipping and rising.  That's not unheard of in older areas.

post #2124 of 2213

Thought I'd post this somewhere...  At the start, the prime CTH goal was a through-hole, full-featured hybrid amp in as small form-factor (case) as possible.   So some earlier ones were made w/small pots & stereo mini (1/8") jacks like my current avatar. 

Well those little jacks & plugs are really a weak spot... Mine started getting dodgy & I was using a hokey 1/4"/1/8" adapter for my new cabled HD600s.  So I took care of that tonight:




I'd pulled the 24V LV reg out & gave it that cool heatsink a while back as I'm a heatsink fan:)  The new wiring is more simple & shorter but did have to dremel that 1/4" jack a bit to fit.

So its up to the task again as my @ work amp & we'll see if I get a few more years out of it:)

post #2125 of 2213

That's a nice heatsink. :)  It must be a really tight fit now.

post #2126 of 2213

>  It must be a really tight fit now.


Not that tight, but maybe I'm used to packing things in.  The RCAs fit right where the stereo minis were & the Neutrik NMJ6HCD2 right over ICE & a couple other low comps.  Had to rotate the jack just so, shave a bit of "extra" plastic off it & cut off its (unused) switched pin leads (to avoid shorts to case top).  No big deal really & its solid & working fine.

post #2127 of 2213

We want inside pics!!\

post #2128 of 2213

You DA MAN! my CTH is up and running! sounds great as ever and even ALL of the hum is gone on low Z phones. I cant here anything at listening volume even on my Yuin OK2.


Now one more question, when it first happened I swapped out the dual colour LED for two single colour LED's, when I plug it in both come on (green and red) but red is the brighter of the two. When the E12 switches the green gets brighter and the red goes out. Is this normal?

post #2129 of 2213

Great its back & better.  Though I've never used individual LEDs, it seems odd that both would lite @ startup.  Looking @ "Lights" in the schematic:




I guess its possible a BC560 is spilling some current into the green LED prior to e12 lock.  But even my dual color LEDs look "funny" prior to lock, as if both colors are lit somewhat.  So I think its no biggie.


Being overly paranoid, if you've a safe way to measure it I'd just check that your DC offset is < 50mV or so after lock (OL/OG & OR/OG).


BTW I'll try to post pics in the next couple days of the inside work I talked about above.  Picture = 1000 words:)

Edited by cfcubed - 12/8/10 at 7:22pm
post #2130 of 2213

My offset is 7mv :) it was the last thing I checked.


I want a picture because I want to do the same as you for the 24v reg. Remember, I have those heat sinks too. That was actually the idea I had but there was talk about the longer leads effecting it so I never got that far...

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