Author Topic: Ab763~ ish build no sound (Read 13647 times)

sluckey · « **Reply #50 on:** July 12, 2016, 07:54:20 pm »

Much better answer. 20K is what it should be. If you stay online for a few minutes and respond with me in a timely manner, we can probably fix this or at least find out what the problem is pretty quickly. Can you do that?

silat · « **Reply #51 on:** July 12, 2016, 07:55:43 pm »

Yeah I can hang on here but I noticed it went down to about 17. k something from 20.

sluckey · « **Reply #52 on:** July 12, 2016, 07:59:04 pm »

Is the white band on the diode connected to the 100K resistor?

silat · « **Reply #53 on:** July 12, 2016, 08:01:12 pm »

Yes the white band on the diode is on same right leg of the 100 k resistor .

sluckey · « **Reply #54 on:** July 12, 2016, 08:04:56 pm »

After you post a response start refreshing your browser about every 10 seconds. We can almost have a real time conversation if you do that.

Disconnect the two wires that are soldered to the right side of the diode.

sluckey · « **Reply #55 on:** July 12, 2016, 08:08:13 pm »

Why did you log off?

silat · « **Reply #56 on:** July 12, 2016, 08:08:30 pm »

Ok it is disconnected.

silat · « **Reply #57 on:** July 12, 2016, 08:09:09 pm »

I did not log off???

silat · « **Reply #58 on:** July 12, 2016, 08:11:06 pm »

My browser takes me outside of the thread after I post back to the beginning of the forum. I have not logged off.

sluckey · « **Reply #59 on:** July 12, 2016, 08:25:40 pm »

Go to your profile, modify profile, look and layout, and change so you return to the message after replying.

silat · « **Reply #60 on:** July 12, 2016, 08:28:15 pm »

Ok I fixed that part of it on my profile.

sluckey · « **Reply #61 on:** July 12, 2016, 08:33:14 pm »

Measure the dc voltage on the right side of the diode.

silat · « **Reply #62 on:** July 12, 2016, 08:34:42 pm »

-6 VDC.

sluckey · « **Reply #63 on:** July 12, 2016, 08:38:04 pm »

Is the negative lead of the filter cap connected to the diode and the positive lead connected to ground?

silat · « **Reply #64 on:** July 12, 2016, 08:40:13 pm »

That might be it. I have that backwards.

silat · « **Reply #65 on:** July 12, 2016, 08:41:12 pm »

I am going to change that now.

sluckey · « **Reply #66 on:** July 12, 2016, 08:42:48 pm »

OK. Then reconnect the two wires you disconnected and measure the voltage at the right side of the diode.

silat · « **Reply #67 on:** July 12, 2016, 08:54:36 pm »

I am now at -25

sluckey · « **Reply #68 on:** July 12, 2016, 08:57:55 pm »

Progress finally. OK. You need to decrease the value of that 100K resistor. Take it down to 82K, 68K, or 62K, or 56K. One watt is big enough. We're looking to have about -40vdc on the right side of the diode.

silat · « **Reply #69 on:** July 12, 2016, 08:59:30 pm »

Ok it will take me awhile to find one

sluckey · « **Reply #70 on:** July 12, 2016, 09:03:51 pm »

That's OK. I've gotta go to bed. You know what to do now. When you get about -40V on the right side of the diode you can move the voltmeter probe to pin 5 of an output tube. You should be able to turn the bias pot from one end to the other and change the voltage on pin 5 from about -20v to about -40v. That's the goal.

Post what you do and I'll pick it up again tomorrow morning. Night, night.

silat · « **Reply #71 on:** July 12, 2016, 09:12:10 pm »

Thanks Sluckey!

silat · « **Reply #72 on:** July 13, 2016, 07:06:26 pm »

-36 DCV with 1w 56K that is all I can do because that is all I have. I had to send my wife over to the next town and all they had were 68 K and 56K 1 watt.

sluckey · « **Reply #73 on:** July 13, 2016, 07:28:44 pm »

-36 may be OK. Set the bias pot for maximum negative voltage at the 6V6 pin 5. What have you?

silat · « **Reply #74 on:** July 13, 2016, 07:35:36 pm »

-30 VDC

sluckey · « **Reply #75 on:** July 13, 2016, 07:47:12 pm »

OK. Put your tubes in and see if it smokes or plays.

silat · « **Reply #76 on:** July 13, 2016, 07:47:50 pm »

Ok doing it now.

silat · « **Reply #77 on:** July 13, 2016, 07:58:19 pm »

It had a loud squeal. Until I changed it to normal it played and then I had a fire on pin one of the 3rd 6v6. I unplugged it.

silat · « **Reply #78 on:** July 13, 2016, 08:06:09 pm »

Looks as though I could have possibly had a bad wire on pin 4 that grounded against the 6v6 and caused the fire and it looked like it came from pin 1 but it was not it just happened to be above it.

sluckey · « **Reply #79 on:** July 13, 2016, 08:08:59 pm »

Disconnect the NFB wire from the speaker jack. It's actually the wire between the OT 8Ω tap and the board on the weber layout.

I have no idea about the fire on pin 1 of a 6V6, except to say, we're probably just looking at the tip of the iceberg. Click on the link in my signature line and follow instructions to verify your amp is wired correctly. I'm out of time tonight. Maybe someone else can fill in and work with you.

silat · « **Reply #80 on:** July 13, 2016, 08:20:10 pm »

It was pin 3 not pin 1 sorry about. 3 is the plate I think?

silat · « **Reply #81 on:** July 13, 2016, 08:22:07 pm »

Thanks Sluckey for your help.

sluckey · « **Reply #82 on:** July 14, 2016, 06:45:03 am »

You need to replace that tube socket if there are signs of burning on it. I would replace it even if I could not see any burn signs.

Then disconnect the NFB wire. Does the amp still squeal?

silat · « **Reply #83 on:** July 14, 2016, 07:39:56 am »

I unhooked the Neg feedback and it stopped squealing, but it is really distorted and will only play in the normal channel with lots of distortion. No clean whatsoever.

sluckey · « **Reply #84 on:** July 14, 2016, 07:54:21 am »

Quote

I unhooked the Neg feedback and it stopped squealing

OK. That means the phase of the NFB signal is reversed. To correct it, swap the OT plate leads that connect to pin 3 of the 6V6s. Then reconnect the NFB wire.

The other problems could be almost anything. Click on the link in my signature line and follow instructions to verify your wiring is correct.

silat · « **Reply #85 on:** July 15, 2016, 08:17:39 am »

For the next few days I am going to be really busy so I will not be able to touch the amp...

sluckey · « **Reply #86 on:** July 15, 2016, 08:25:48 am »

We'll be right here whenever you can get back to it.

silat · « **Reply #87 on:** July 28, 2016, 11:42:24 am »

Well I have good news

It is working great on the vibrato channel but the normal channel is still distorted and not very loud. After I figure out the problem with the Normal channel we should be good with it.

silat · « **Reply #88 on:** August 01, 2016, 10:57:44 am »

Hey does anyone have any idea how many watts this thing is when it is all said and done? I still do not have much sound in my normal channel for some reason. The Vibrato channel plays awesome. I have a -35 on the bias now down from -41.

silat · « **Reply #89 on:** August 01, 2016, 11:29:32 am »

I am thinking it will be around 20 maybe 25 watts?

sluckey · « **Reply #90 on:** August 01, 2016, 12:06:23 pm »

Quote from: silat on July 28, 2016, 11:42:24 am

Well I have good news It is working great on the vibrato channel but the normal channel is still distorted and not very loud. After I figure out the problem with the Normal channel we should be good with it.

Can you tell us what you did?

silat · « **Reply #91 on:** August 01, 2016, 12:34:53 pm »

I just did what you told me and traced down everything finding a few wires that were cold soldered on some of the pins tracing with yellow marker. It sounds really good on the vibrato channel, but the Normal is really low almost no sound. I traced it too and looked at the inputs and they seem to be correct.

sluckey · « **Reply #92 on:** August 01, 2016, 02:58:56 pm »

The normal channel is very simple. Only one tube. Keep at it. You'll find the bug. OH, and you can use the VIB channel as a comparison.

silat · « **Reply #93 on:** August 02, 2016, 04:51:50 pm »

Got the normal channel fixed now. Sounds great. It was a bad tube. I just looked it over and everything was correct. My only last resort was trying another tube and that did it. I am now done. I am going to build a cabinet now.

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Author Topic: Ab763~ ish build no sound (Read 13647 times)