Jump to content
Gibson Brands Forums
Sign in to follow this  
TWANG

test help...

Recommended Posts

6V6 all done..

no standby or other controls except vol and NFB on R/pot.

 

light bulb tester connected. tubes out. speaker plugged in.

 

turned it on. wasn't looking at the bulb right away..but.

it apparently didn't light up.

 

nothing happened but I thought that was odd. so I shut it down.

 

whats' the exact procedure then..

light should glow.. then dim.. then test voltages?

they'll be wrong but I should be able to test ok.. I suppose..

 

??

not sure never did it!

Share this post


Link to post
Share on other sites

okey dokey. sure I put one in..

but I'll look.

otherwise I've got it right though.. bulb should light up and dim..

may as well jump back on it..!

Share this post


Link to post
Share on other sites

well..

tested again.. no light at all.

slight hum from speaker. volume turning no effect on that.

neg. voltage at each end of r10

then shut it off.

 

???

put tubes in disconnect bulb tester. or does this indicate something?

Share this post


Link to post
Share on other sites
well..

tested again.. no light at all.

slight hum from speaker. volume turning no effect on that.

neg. voltage at each end of r10

then shut it off.

 

???

put tubes in disconnect bulb tester. or does this indicate something?

 

OK please don't get pissed at me...but are you sure you wired the light bulb tester correctly? If it's not in series with the hot leg that could be your problem?:-

Share this post


Link to post
Share on other sites

Yewww. Negative voltage? Not good. Pull those tubes outta there. Disconnect the OT, put the limiter back in and see if it's still weird. And check your diodes!

 

Gil...

Share this post


Link to post
Share on other sites

I'm pretty darn sure.. had the cont. tester right there.

even remember testing it and looking right at the diagram.

but.. I'm gonna to test it right now.

I've done dumber things!

brb

Share this post


Link to post
Share on other sites

Ok.. right according to the diagram.. with the third lug pointed down.. and both plugs facing me..right side to bulb to right side..

and so forth.. all tests fine.

 

bulb out signal stops at socket.. tests from socket to each end correctly.

 

I feel that's right.

 

NFB on pot..

is this it?

I have 5K5W cement block.. *didn't have a 10K at 5W so I used a 5K*

from R9 to 5K5W..to wiper of 50K pot, left pot lug looking from the back of the pot, to the 8ohm tap,

right lug to ground via a wire because I haven't got a hole for the pot yet.

Share this post


Link to post
Share on other sites

Well, with the NFB resistor between R9 and the pot, and the pot connected to your OT,... all that 5 watts of voltage on your OT tap is hitting the pot directly. That's not real good for a 1/2 watt pot. I tried to tell ya to put the resistor between the pot and the OT tap, but nooo! I bet ya grounded it too. :-

 

Gil...

Share this post


Link to post
Share on other sites

yeah I did. backwards! damn and we just talked about that.

well I'll go reverse it.

tubes were out.

yes it wasn't in the chassis so I ran a wire to the star ground.

good grief.

Share this post


Link to post
Share on other sites

Check the pot out with your ohm meter to make sure it's still doing what it's supposed to be doing. When it's disconnected, of course. Don't ground any solder lugs on it next time. None. Nada! Zip! The pot's metal housing you can ground just for noise abatement, but it probably won't be be needed. That's a hot signal, and you don't want it dumped to ground.

 

Gil...

Share this post


Link to post
Share on other sites

ok.. do you want me to disc. the ot.. since there weren't any tubes in it to start with.. I don't know if that makes a difference..

 

the nfb then is: R9 to wiper left lug looking at back of pot to tap?

 

the ground wire had come off! so it wasn't grounded.

Share this post


Link to post
Share on other sites

the pot is ok.

do I test the amp without the ot first?

the nfb then is: R9 to wiper left lug looking at back of pot to tap.

 

luckily, I have another 7.5Kot if need be. hope the pt is ok.

nothing lit up or warmed up or buzzed.. just a very soft hum from the speaker.

Share this post


Link to post
Share on other sites

If you've got the NFB corrected, leave the OT in and just fire it up. If it looks good, try it with tubes. If not, disconnect the OT and try it again.

 

Gil...

Share this post


Link to post
Share on other sites

same deal. no light at the bulb. soft hum from the speaker.

so I'll disconnect the ot..

but what am I looking for here.. just the bulb to light and dim as per usual?

if it does that, then I put in the new ot.. and test again..

and from there I put in the tubes and test that way.

then get rid of the bulb and try her out..

eh?

Share this post


Link to post
Share on other sites

Yep. That's the plan.

 

The current limiter light bulb's there just to take the heat long enough to shut down gracefully in an emergency. If the light dims as expected, you can get to measuring voltages. When the voltages look reasonable, you take it to the next level, and test again. Once the power supply is functional and you can get it up and running with tubes, and the voltages are mostly okay, and the amp's making tone (even if it's also humming or squealing like a pig gremlin), you can then unplug the light bulb limiter, and fire it up for some serious voltage measurements of the sort that you would write down to plug into the bias calculator, for instance. But let it have 20 minutes for the tubes to get good and warm. After that, you can bop rail ferrets and tweak the tones to your heart's content. =P~

 

Gil...

Share this post


Link to post
Share on other sites

Duuuh dum...

 

 

Duuuh dum dum...

 

Dum dum, dum dum, dum dum, dum dum, dum dum, dum dum, dum dum,

 

buh do dooooo! =P~

 

Gil...

Share this post


Link to post
Share on other sites

got tired and went to bed.

still wouldn't test though pot was ok..

will pull the OT and do it again, today.

Share this post


Link to post
Share on other sites

Yeah, do tell. We're all on the edge of our seats waiting for the conclusion of this cliffhanger.

Was is the OT? Or those pesky gremlins again?

 

Gil...

Share this post


Link to post
Share on other sites

Here's where I got lucky.

The ground I connected to the star ground from the pot, was never connected.

 

so. I pulled the ot anyway..

I checked every single connect point throughout the board.

 

took a deep breath.

and same results. no light.

tested bulb in another lamp. again! yep, fine.

 

So I said.. Dexter works.. brought him to the bench.

NO LIGHT.

 

I swear to you the bulb test device is perfect.

all continuity works fine. It should simply light up.

 

In fact, I just finished. so.. you tell me.

should I just put tubes in it and test it the old fashioned way?

Share this post


Link to post
Share on other sites

Join the conversation

You can post now and register later. If you have an account, sign in now to post with your account.
Note: Your post will require moderator approval before it will be visible.

Guest
Reply to this topic...

×   Pasted as rich text.   Paste as plain text instead

  Only 75 emoji are allowed.

×   Your link has been automatically embedded.   Display as a link instead

×   Your previous content has been restored.   Clear editor

×   You cannot paste images directly. Upload or insert images from URL.

Loading...
Sign in to follow this  

×
×
  • Create New...