AC30C2 help

[shawn w]

forgot last night to have you ohm all the PA tubes pins to ground also, so put the - on chassis, and ohm each socket pin, tube side, to ground.  something in your PA is drawing way more current than design spec'd.

do you  have a 5k 10 watter, maybe 2 10k 5watters you can put in parallel laying around?  how bout 20 - 100uf 400+vdc caps?

once you get those measurements, put all 4 tubes back in (NO power) and ohm from B+1 to ground (right side of R120 pg3)

***EDIT*** make sure you indicate ohms, K ohms, Meg ohms, guessing your 3.2 is really 3.2K?

Yes, measurements are in K. I'll check all those pins and let you know what they read. I don't have any resistors oe caps like that, but I'll pick some up.
shawn

[shooter]

I'll pick some up.

everything we've done so far is "on the cheap"    If you have a local place, try for a 5K 10 to 20w, 20w preferable (2 10k 10watters works also).  I use one for PS load testing.   

hopefully you're having fun 

[shawn w]

I'll pick some up.

everything we've done so far is "on the cheap"    If you have a local place, try for a 5K 10 to 20w, 20w preferable (2 10k 10watters works also).  I use one for PS load testing.   

hopefully you're having fun 

I ordered (2) 5k 10 watters and (6) 100uf 600v capacitors. Should be here Weds. Yes, i am having fun and learning a lot. I'm a bit of an information junkie, so this is right in my wheelhouse. Thanks again for your patience and expertise.
shawn

[shawn w]

forgot last night to have you ohm all the PA tubes pins to ground also, so put the - on chassis, and ohm each socket pin, tube side, to ground.  something in your PA is drawing way more current than design spec'd.

do you  have a 5k 10 watter, maybe 2 10k 5watters you can put in parallel laying around?  how bout 20 - 100uf 400+vdc caps?

once you get those measurements, put all 4 tubes back in (NO power) and ohm from B+1 to ground (right side of R120 pg3)

***EDIT*** make sure you indicate ohms, K ohms, Meg ohms, guessing your 3.2 is really 3.2K?

I checked those pins on all four tube sockets and here's the results-
Pins 1,6&8 i didn't get any reading from at all
Pins 7 & 9 the results were moving all over. I couldnt get a steady reading
2 - .186
3 - 51.9
4 - 108.5
5 - 108.5
Thanks
shawn

[shooter]

2 - .186

Ohms, kilos, psi ?

Re-measure 7 & 9, and watch close, the #'s should be raising, then maybe max out at something close to open.

[shawn w]

2 - .186

Ohms, kilos, psi ?

Re-measure 7 & 9, and watch close, the #'s should be raising, then maybe max out at something close to open.

Checking today #2 settled in about .256m ohms. All #7 pins went to ol, except tube #6. It stopped at about 111k ohms. Pin number #9 did the same. All stopped at about 111k ohms.
shawn

[shooter]

measure;
pin 3 to ground on all  4 ( I know, we did it, just once more )

Find J29, 35, and 36 connected to OT, take a pic, draw a pic, then unplug 'em,  and ohm the CT (where j35 went) to each "end" (where 29 and 35 36 went)

did your resistor come in?

[shawn w]

measure;
pin 3 to ground on all  4 ( I know, we did it, just once more )

Find J29, 35, and 36 connected to OT, take a pic, draw a pic, then unplug 'em,  and ohm the CT (where j35 went) to each "end" (where 29 and 35 36 went)

did your resistor come in?

Pin 3 measured 51.5-51.6 ohms. Just to be clear, I'm unplugging those terminals at the board and measuring resistance from one terminal on the board to the other? So clamp on J35 spade and touch on 29 and 36?
Thanks
Shawn

[shooter]

Just to be clear

you're measuring the transformer those wires go to, one lead on CT, then the other measures each end, in a good world they should be about equal in value.

[shawn w]

Just to be clear

you're measuring the transformer those wires go to, one lead on CT, then the other measures each end, in a good world they should be about equal in value.

So measuring from the J35 wire to J36 wire,  get 17.3 ohms. From J35 wire to J29 wire I get 17.5 ohms. I haven't been to the post office, but I'm sure my caps and resistors are there.
shawn

[shooter]

get 17.3 ohms

I went hunting for "typical DCR" because 17.3ohms seemed low, about right for hummm pop, 

from these 2 threads and notes I have  100 to 400 seems a "normal" range, anyone wanna weigh in?

http://el34world.com/Forum/index.php?topic=14479.msg137295#msg137295

http://el34world.com/Forum/index.php?topic=18909.msg194096#msg194096

[shawn w]

get 17.3 ohms

I went hunting for "typical DCR" because 17.3ohms seemed low, about right for hummm pop, 

from these 2 threads and notes I have  100 to 400 seems a "normal" range, anyone wanna weigh in?

http://el34world.com/Forum/index.php?topic=14479.msg137295#msg137295

http://el34world.com/Forum/index.php?topic=18909.msg194096#msg194096

I think you may be correct. I did some looking, too and most are 100+ ohms. That and the variance from one side to the other seems to be larger than a couple tenths. Maybe a dead short in it?
shawn

[sluckey]

Try this...

[shawn w]

Try this...

I build one of those and give it a shot.
Thanks
shawn

[shawn w]

So I built the test light. I went from J35 to J29, J35 to J36 and even J36 to J29 and didn't get any flashes or light out of the bulb. I did get a noticeable pop out of the speaker each time it was connectected. So bad transformer?
Thanks,
shawn

[shooter]

So bad transformer?

Until proven otherwise, I think you're correct.
popin fuses means "short"  They can be easily found with enough current and voltage 
the more better way is to use ohms, not enough ohms indicates lots of current, without really plugging it in, make sense ?  You happen to have an inductor problem, which doesn't play quite the same, so extra testing

[shawn w]

So bad transformer?

Until proven otherwise, I think you're correct.
popin fuses means "short"  They can be easily found with enough current and voltage 
the more better way is to use ohms, not enough ohms indicates lots of current, without really plugging it in, make sense ?  You happen to have an inductor problem, which doesn't play quite the same, so extra testing

Awesome!  So a new transformer it is. Thanks to everyone for working through this with me.
So the next question is, what brand of transformer? There seems to be quite a few different ones available. If I want that "older" A.C. chime, is there one preferred?
shawn

[sluckey]

So I built the test light. I went from J35 to J29, J35 to J36 and even J36 to J29 and didn't get any flashes or light out of the bulb. I did get a noticeable pop out of the speaker each time it was connectected. So bad transformer?

Read the instructions for that tester. You cannot have speakers connected while doing this test!

Keep in mind there are a few sneaky things that can invalidate your test. If there is a load on any
winding, those loads will eat the inductive kickback and the neon will not light up. You’ll think you
have a bad transformer but you might not. If the transformer is a power transformer, watch out for
connections to filament windings or solid state rectifiers. If it’s an output transformer, make sure the
speaker is not connected and there is no minimum load resistor on the output jack or diode from plate
to ground, as is found in some amps.

[shooter]

noticeable pop

 
It was late, I was .................

[shawn w]

noticeable pop

 
It was late, I was .................

So I did the test again, with no speakers hooked up. Same results. No flash, no light.
Thanks
Shawn

[shooter]

Same results

Cool, then you gotta decide where next.  there are still a few "free" things, like verifying preamp DC volts and AC signal, if that plays out it makes the tranny cost/benefit scale tip 

(btw, I was kicking myself for missing a nugget in reply #68)

[shawn w]

Same results

Cool, then you gotta decide where next.  there are still a few "free" things, like verifying preamp DC volts and AC signal, if that plays out it makes the tranny cost/benefit scale tip 

(btw, I was kicking myself for missing a nugget in reply #68)

My inclination is that it's the tranny. Low ohm reading and no light from the test would indicate to me that it is bad. I'm going to order a Classic Tone and put it in. If you feel that we should check the other things, too great. I'm all for learning more!
Oh, don't kick yourself. I read the instructions, but in my limited experience misinterpreted what it said. It's why I always try and provide as much information as I can. So someone can catch me! (;
shawn

[shawn w]

New transformer in.  Same problem. I lit the main power, all power tubes glow lightly. Turn the standby switch to rock n roll, light comes on, hum from the speakers and it pops the fuse. Anymore ideas?
Thanks again for all the help.
shawn

[pompeiisneaks]

It's been a while on this thread, but to me that sounds like something is drawing too much current to ground.  You've got some kind of short.  Have you tried connecting a multimeter to ground on continuity mode and touched all of the power rail and tube anode areas to ensure nothing in the power side has a direct route to ground? 

also photos of things as they are now will make some of this troubleshooting a bit easier. 

~Phil

[shooter]

Same problem

sucks!
did you get a 5k 10w or bigger resistor?

If so;
remove R120 in the PS, page 3.  you want to put the 5K in parallel with c72.  You can do this by soldering a temp wire in the "right" hole were R120 came from, then clip one side of the 5k there, the other to end clipped to ground.
set your meter to Volts DC, clip the leads across the 5K.  when you're sure of the setup, power up, get a quick reading, don't leave power on for more than a minute.

[shawn w]

It's been a while on this thread, but to me that sounds like something is drawing too much current to ground.  You've got some kind of short.  Have you tried connecting a multimeter to ground on continuity mode and touched all of the power rail and tube anode areas to ensure nothing in the power side has a direct route to ground? 

also photos of things as they are now will make some of this troubleshooting a bit easier. 

~Phil

We checked all the tube posts to ground. Those results are posted earlier. I'm not sure if we checked the power rail? What would you like to see photos of?  I'd be happy to take some more.
Thanks
shawn

[shawn w]

Same problem

sucks!
did you get a 5k 10w or bigger resistor?

If so;
remove R120 in the PS, page 3.  you want to put the 5K in parallel with c72.  You can do this by soldering a temp wire in the "right" hole were R120 came from, then clip one side of the 5k there, the other to end clipped to ground.
set your meter to Volts DC, clip the leads across the 5K.  when you're sure of the setup, power up, get a quick reading, don't leave power on for more than a minute.

Yes, I did get some resistors and capacitors you mentioned earlier. I got 10watt 5k and 100uf 400v. I'll give that a shot and report the results.
shawn

[pompeiisneaks]

Ok here's an idea, it will cost another fuse, but put your multimeter on volts dc, and then connect to one of the resistors that  burned, like R101, that you've replaced.  Set the DMM to 'max' so it remembers the max voltage, and turn it on.  If the problem is still there, it may show you if that area is still getting a voltage level it shouldn't.  It should have 0 dc as it's a cathode biased amp, and won't have negative bias.  If it has anything there, something is leaking voltage towards it.  Also another idea would be to put a second one on the same 'max' setting but VAC and see if there's any ac on the line, (there should be some in an active amp, as signal, but this is test mode, so I'm guessing you don't have any.)  If you have a variac, it would make this a bit easier as you could keep the voltage lower so it's not drawing enough current to burn things up and blow the f use, but test for voltages around the board and report back what you're seeing.

If that still doesn't help, you may have to think about gutting and building a hoffman AC30 in there :D

[shawn w]

Hi,
It's been a minute or two. I stuck this project in the corner and left it there for a bit. About a month ago I thought I should do something with it, so I took it to Matthew Dawson in Portland,OR to have him look at it. What an amazing guy. He found a trace on the board that was arcing across, causing the whole issue. Some Dremel work to cut it out, little old school hand wiring and its works better than new! Thanks to everyone who contributed with ideas.
Shawn

[jojokeo]

It would be helpful for everyone if you could get a final picture of where the trace arc'd across and then made a note on the schematic and post that too. This would help everyone to see/know what happened where plus this might just happen to more of these amps down the line and could be a real time saver? I know I'm curious...


ps - these are some of the things that just can't be seen here troubleshooting remotely. But in the hands of many here likely it would've been spotted (perhaps almost immediately)? Visual & manual inspections cannot be overstated enough to the trained eye.

[shawn w]

I agree totally. According to Matthew, this "could" be a common problem because the traces are so close together. Hopefully my photo shows enough to make heads or tails of it.
Shawn

[sluckey]

Did you forget something?   

https://imgur.com/gallery/KwNPcnL

[shawn w]

I've been trying to get it to post lol. Thanks!
Shawn

[kr2p]

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