new build is now happy

[Luthierwnc]

Sounds like you have already isolated it past what I'm going to recommend but there are two safety items that if done incorrectly would also blow fuses. The first is using an undervoltage MOV on the on-off switch.

The second is checking the polarity on any flyback diodes you have running from pin 3 of the power tubes to ground. One time I spaced (it does occur) and put one of those assemblies in backwards -- colorful, to say the least. There were two of them in series and shrink-tubed so I couldn't see the anode stripe. I thought I remembered which end was which.

I think you are on the right track by starting at B+1 and adding nodes as you go. One time I got a faulty filter cap that had me poking and prodding for a couple hours. While the rail wires are off, you might see if any of the caps are conducting DC. Good luck, sh

[dcribbs1412]

Thanks Luthierwnc
not using the MOV or flyback diodes
but will keep in mind for future builds

Thanks again

Darin

[ToneMerc]

B+ Voltages?

Also, what brand/type of output transformer are you using?

I only see two leads terminating from your "power in" jack, there shoud be three.

1. PI ground (nothing is connected to that board eyelet)
2. Master
3. PI input coupling cap

[dcribbs1412]

ToneMerc,
will check voltages
OT is the MC 40-18026 100 watt
as far as the 123 connections you listed
I will check and report back ASAP

Thanks

Darin

[dcribbs1412]

I checked voltages B+3...476V, B+5...450V
no tubes with OT B+ disengaged...
as far as

I only see two leads terminating from your "power in" jack, there shoud be three.

not sure what you are seeing

1. PI ground (nothing is connected to that board eyelet)

your right..not sure as far as the layout goes(183 ver11) how to use this eyelet?

2. Master

not sure what your asking

3. PI input coupling cap

again not sure...Sorry ToneMerc I will keep looking...sometimes it takes me awhile to get it.

inspected the power tubes again looking for any wiring problems...nothing seems out of the ordinary...
I checked pin 3 and all have continuity to ground...
not sure how to proceed from here...
as always comments are greatly appreciated

Thanks


Darin

[ToneMerc]

I checked voltages B+3...476V, B+5...450V
no tubes with OT B+ disengaged...
as far as

I only see two leads terminating from your "power in" jack, there shoud be three.

not sure what you are seeing

1. PI ground (nothing is connected to that board eyelet)

your right..not sure as far as the layout goes(183 ver11) how to use this eyelet?

2. Master

not sure what your asking

3. PI input coupling cap

again not sure...Sorry ToneMerc I will keep looking...sometimes it takes me awhile to get it.

inspected the power tubes again looking for any wiring problems...nothing seems out of the ordinary...
I checked pin 3 and all have continuity to ground...
not sure how to proceed from here...
as always comments are greatly appreciated

Thanks


Darin

Eyelet-normally that's where the presence circuit tail ground is connected, back to the send/return jacks ground. 183 is wired that way, that eyelet is just not reflected on the layout. There should be 3 wires terminated at the send/return jacks which travel toward the front of the chassis.

Per layout

1. a ground ( black)
2. The Master pot , term #2 (red)
3. .02 PI input cap (brown)

I attached my #183, you can see 3 leads leaving the send/return area.

Nevertheless; the important question is, at the junction of the 390 ohm resistor and 1uF cap, is there a wire connected to ground? If not, there needs to be.

If V4-V7, pins 3 have continuity to ground, that's a no-no and will certainly blow a fuse because when you close the standby switch B+ is being dumped to the chassis.

I'm going to assume that the output transformer center tap(white wire) is still disconnected. Next, totally electrically isolate the OT primary from the circuit. Thus, desolder the red and blue primary wires from power tube pins 3.

Check all three primary leads for continuity to ground. If any of those have continuity to the chassis, it's solved.

TM

[dcribbs1412]

Just want to start by sincerely apologizing to all...
for having for lack of a better term "poor workmanship" on my part.
When I went to check the OT as suggested by ToneMerc(which checked out OK BTW)
I found a Pin 2 filament wire of a power tube laying against pin 3...

That said I loaded up with tubes and fired it up only to have
the bias way off... after switching off standby the tubes go blueish followed by a crackling/frying noise... fuse blows...using 3A SloBlo
not sure what is causing this new development.

again sorry for this long drawn out soap opera of a build...

Again any comments /suggestions are greatly appreciated

Darin

[heisthl]

use a light bulb in series with one side of the power cord. Even a 40 watt bulb is big enough (limits the current to roughly 0.4 amps).

[alvarezh]

Darin, glad you are getting there, soon you will be done, your problems do happen to some of us once in a while.

Heisthl has suggested twice (Structo has also) to use a light bulb current limiter. If you don't have one, do build yourself one. Parts only costs about $10.00 and you can get them all at your local hardware store. It's one of the most useful tools you can have for the money. Not only good for troubleshooting but for forming your caps as well. It only takes about an hour to build, complete instructions here:

http://tubenewbie.com/light_bulb_current_limiter.html

BTW, I use a plastic box on mine, wires could get loose with time and touch the enclosure because they are usually held by screws, safer with a plastic box IMO.

@Heisthl: Love your amps, hopefully I will have you build me one in the (very?) near future!

[dcribbs1412]

Thanks alvarezh
really appreciate the link...
I will get the parts and build it ASAP...and report back

Heisthl has suggested twice (Structo has also) to use a light bulb current limiter.

I need to read and follow what the more experienced builders write
because I am a tube newbie
For some reason this build is making me nervous...maybe the fact
it's 100 watts (my first big amp)..finding myself being very cautious.
relieved the PT and OT are not fried.
hoping to shake the walls soon...

Thanks

Darin

[Chris G]

Thanks alvarezh
really appreciate the link...
I will get the parts and build it ASAP...and report back

Heisthl has suggested twice (Structo has also) to use a light bulb current limiter.

I need to read and follow what the more experienced builders write
because I am a tube newbie
For some reason this build is making me nervous...maybe the fact
it's 100 watts (my first big amp)..finding myself being very cautious.
relieved the PT and OT are not fried.
hoping to shake the walls soon...

Thanks

Darin

Hi Darin,
They make me nervous as well!!!
Here's an electricians trick, Keep one hand in your pocket!!!!
(or away from the amp if your checking it while it's live......
Thanks
Chris

[Structo]

Here is another diagram of a light bulb limiter.
You can get fancy and put a switch on the hot side before the light bulb if you wish.
But notice how the light bulb is on the hot (black) side of the circuit.
Try a 40 watt light bulb first. I some times use a 25w bulb if I am not sure of an amp. That limits it to less than 250ma.

So when you first power up with this light bulb inline the bulb will kind of flash brightly then go down to a low glow.
That is normal and is the filter caps charging.
So if that is what you get without tubes you can now install tubes and try it again.
Remember any time you have power tubes installed you need to have a speaker load connected.

It should do roughly the same thing again.

If it passes the light bulb test then you can take the limiter out of circuit and try it with a guitar plugged in and hopefully it will work.

[img:800:618]https://lh3.googleusercontent.com/-ufJU ... imiter.jpg[/img]

Here is my version, very simple but effective tool.
I used a metal junction box with a ceramic light bulb socket on top.

[img:400:300]https://lh4.googleusercontent.com/-S9_T ... G_0114.jpg[/img]

Hope this helps!

[dcribbs1412]

Thanks Chris G
I make a point of working in a safe manner( one hand in one out when live)
I've been bitten a few times in the past...
the few amps I've built all seem to have there own character(my wife thinks
I'm strange when I talk about computers having certain attitudes...I work
in IT or TJ(Technology Janitor) as I call it)
this one just seem to want to be an intimidating from the start
I hope it translates to tone with an attitude

Thanks for the tips


Darin

[dcribbs1412]

Thanks Tom
this will come in handy


Darin

[dcribbs1412]

Got my limiter done
pulling out the power tubes I noticed one with something
rattling around inside...bummer don't have extra
can I run it with 2 tubes?
or should I get another set
any suggestions?
BTW no flash on start up with limiter 25 or 40 w bulb?

Thanks

Darin