[cfcubed]

With 37VDC in & not getting 24VDC out, my guess would be (another?) bad 7824. Unusual, as I've had many (maybe close to a dozen) through my hands & never hit or had a bad one.
Assume you assured center pin is ground/SG & it sounds like the 7824 is only passing 3V of its incoming 37V. Which is bad.

 

[aphexii]

So I was going through the parts list and noticed a couple items were no longer in production and/or out of stock.

If I list them here, would anyone be able to help me find suitable replacements? Still fairly new to DIY (this is my 3rd build), so I don't want to buy the wrong thing

 

[cfcubed]

> If I list them here, would anyone be able to help me find suitable replacements?

This thread was targeted towards tweaks to CTH, prospectively for SQ improvement, and tube rolling experiences. I think it best to bring necessary parts substitution & debugging over to the "A Very..." thread. Unless its something in progress like s_o's debugging...

WRT "simple" parts (resistors, caps) substitution, the builder could/should compare spec sheets of spec'd parts vs those they can source to ID a sub. Watching physical size limitation (esp. height limit on big caps like C10P) while reviewing pics of completed PCBs if they must go bigger. And sticking as close to spec'd value as possible & respecting ratings. After going through that process hopefully we'd be down to very few part subs needing assistance / review here.

 

[suicidal_orange]

> Assume you assured center pin is ground/SG

eh...

I checked my legwork and ground wasn't connected. Sorted that, plugged it in and released smoke instantly from another Q1P. It was on for less than a second, so no damage elsewhere (hopefully)

Having previously checked the caps and diodes where am I looking next? Disconnect pin 3 and see if I get 24V? I've only got one spare Q1P left so don't want to blow it up if it's inevitable...

 

[Henmyr]

Quote:

Originally Posted by cfcubed /img/forum/go_quote.gif Default R18s = 100R & they were incorporated for reducing gain to give more useful range on volume control, not for the purpose of altering output impedance. It may be possible that the R18s could save your OB from errant Line-In/Line-out swaps as well (mines survived that a few times). @ work I use partial markl-modded D2000s w/Siemens tube & 100R R18s to good effect. Erikzen's CTH is set up similarly & he's used / enjoyed his modded D5000s w/this.

There's been a lot of talk about damping factor lately (A low output impedance from an amplifier seems to be desirable). Do a high R18 reduce the damping factor in a way that the sound would be better if one were to short the R18?

I'm thinking about adding a switchable R18 of 0R and 100R, would that be a good idea or is there nothing to gain by this? The volume would have to be lowered from the source a bit instead.

 

[cfcubed]

Quote:

Originally Posted by suicidal_orange /img/forum/go_quote.gif I checked my legwork and ground wasn't connected. Sorted that, plugged it in and released smoke instantly from another Q1P. Having previously checked the caps and diodes where am I looking next? Disconnect pin 3 and see if I get 24V? I've only got one spare Q1P left so don't want to blow it up if it's inevitable...

> Disconnect pin 3 and see if I get 24V?

Yes, after replacing the newly blown Q1P please only attach pins 1 & 2 of 7824 to PCB. Then measure V between it's 3rd pin (output) & gnd/SG. You should get 24VDC in this no-load test (just proving PS portion in attachment).
If you do then I think you need to:
1) find a way to simulate a decent load (between pin #3 & SG) to proof LV circuit through 7824,
2) if you 7824 drives a decent load, then problem seems downstream of reg - something drawing way too much current.
Sorry for the difficulties you are having.
 
Note: if a big pic of some cable shows below its this forum software screwing up    Because this post has NO attachments.

 

[suicidal_orange]

I mess things up (if I'd done it right in the first place it would work) then be stupid (not checking my wiring) and you apologise, cfcubed? I know it's rude not to accept, but I can't. I'm just sorry for wasting your time and really greatful for the support

Anyway, in the absence of any false load I've just listened to a couple of minutes music through my Voyager amp being powered by the CTH, is that enough to call the 24V OK? I'd like to think so...

 

[suicidal_orange]

Can anyone help me with determining my current sucker?

I've nearly finished markl'ing my new cans and would like an alternat amp for them (much like the Grado's they've replaced the gain on the canamp is just too high!)

 

[suicidal_orange]

Final bump for assistance before I post a "FS/pay to fix" for this - I can't even find a full schematic of the amp to work out what's using this LV supply so no chance of fixing it

 

[sachu]

huh? schematics are up on the cavalliaudio website. See link in my signature.
 
What exactly are you having problems with?

 

[suicidal_orange]

Thanks sachu, I've looked on the website and it has schematics for the four parts but not the whole thing showing how it fits together - unless I'm blind?  After all the stupidity I've displayed in this build it wouldn't surprise me, it's my third and final project (the second was also a failure - SMD isn't fun)
 
I have 24v coming out of the 7824 powerful enough to run a portable amp at decent volume without clipping but if I connect it to the PCB Q1P burns, slowly.  Any idea what's sucking the 24v so hard that it dies?

 

[sachu]

you need check further up the chain. I would say replace all buffer and rail splitter transistors at one go and then try it out again

 

[naamanf]

Quote:

Thanks sachu, I've looked on the website and it has schematics for the four parts but not the whole thing showing how it fits together - unless I'm blind?  After all the stupidity I've displayed in this build it wouldn't surprise me, it's my third and final project (the second was also a failure - SMD isn't fun)
 
I have 24v coming out of the 7824 powerful enough to run a portable amp at decent volume without clipping but if I connect it to the PCB Q1P burns, slowly.  Any idea what's sucking the 24v so hard that it dies?

Have you verified the value of R1P?
 

 

[suicidal_orange]

 
Quote:

I would say replace all buffer and rail splitter transistors at one go and then try it out again

Damn.  No spare MPSA42's and not enough 337's, and farnell now have a £20 minimum order.  Has to be done though, when I get time.  Thanks for the help - you were banned first time round!
 
Quote:

Have you verified the value of R1P?

1003F, measures 100.2k on my multimeter - no quick fix for me

 

[sachu]

let me dig through my parts bin..i have some MPSA42s you can use..but the 337s..and 327s i will have to look.