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Author Topic: New 5X3 build no sound help  (Read 16105 times)
davohilts
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« on: February 19, 2011, 03:24:51 PM »

Hi, I just finished the 5X3 build and am getting no sound from guitar input, maybe just light distorted sound with full volume.  I've gone over the wiring and don't see anything loose or not soldered, and have gone over everything with a chopstick to no avail.  Here is what happens when I turn on the amp:
pilot lamp lights
as amp warms up it begins to emit a hum from the speakers while still in standby
once I switch from standby to play the hum goes away
plug in guitar to any jack and bet no sound at all.

any ideas of where to begin to trouble shoot?

thanks
Dave
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wyatt
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« Reply #1 on: February 19, 2011, 05:26:37 PM »

Well, if you went through it with a chopstick test probe, how close to the front of the circuit can you get and still get output from the amp?
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davohilts
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« Reply #2 on: February 19, 2011, 07:39:57 PM »

I put a signal tracer on it and I have signal throughout the circuit, pins 5/6 of 6L6's and I get signal at volume and tone pots and a weak signal at output jacks.  I do have hum also and it seems the 12AX7 amplies it.
When I turn on the power switch it is quiet until the gz34 heats up and then it starts to hum, when I turn on the standby to play the hum goes away for a bit but then comes back.  As I trace the signal occasionally I touch a spot and the hum goes away, then slowly comes back.
I'm missing two input jacks for channel 2 so the 2 feeds off the 68K resisters are not tied to anything but the 2 jacks from channel 1 are connected and the ground is tied to the volume pot.
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cmoore
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« Reply #3 on: February 19, 2011, 09:57:38 PM »

Are you sure you have your In jacks wired correctly.?
Do you know how to check them with an ohm meter.?
Best
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wyatt
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« Reply #4 on: February 20, 2011, 12:22:34 AM »

I put a signal tracer on it and I have signal throughout the circuit, pins 5/6 of 6L6's and I get signal at volume and tone pots and a weak signal at output jacks.  I do have hum also and it seems the 12AX7 amplies it.
When I turn on the power switch it is quiet until the gz34 heats up and then it starts to hum, when I turn on the standby to play the hum goes away for a bit but then comes back.  As I trace the signal occasionally I touch a spot and the hum goes away, then slowly comes back.
I'm missing two input jacks for channel 2 so the 2 feeds off the 68K resisters are not tied to anything but the 2 jacks from channel 1 are connected and the ground is tied to the volume pot.


Do you just not have the other jacks right now?

First thing is attach those 68K to Ground for the time being.

Not sure what jacks Nik uses, but on a traditional 5E3 build, you use switching jacks that ground the tip of the jack when not in use, its to reduce hum.  I doubt it will fix the big issue, but it may handle that hum.

Nik does a bit of disservice by not posting schematics (I[m sure he has his reasons), but the closet schematic I know is Weber's 5E3P (similar to the 5X3)... here it is for reference....note the switching jacks.

https://taweber.powweb.com/store/5e3p_schem.jpg
« Last Edit: February 20, 2011, 12:25:01 AM by wyatt » Logged
davohilts
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« Reply #5 on: February 20, 2011, 11:01:28 AM »

I'm waiting to get the additional jacks in the mail.  Can't find any in town.  I believe I have the two I have installed wired correctly but don't know how to test with an ohm meter.  The other leads from the 68K resisters I have taped off in the chassis.  Should these be tied to ground until I get my additional jacks.
Thanks guys for your help, I know i'm not giving you much help by explaining what the issue is.  I've built a couple of amps from kits, an 18watt and a Deluxe Reverb.  I've been building this one with my son and between the two of us we have really created a problem here.  He wants to use it in a show on Thursday and we have been rushing to finish it and you know what happens when you rush.....
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wyatt
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« Reply #6 on: February 20, 2011, 12:53:05 PM »

I'm waiting to get the additional jacks in the mail.  Can't find any in town.  I believe I have the two I have installed wired correctly but don't know how to test with an ohm meter.  The other leads from the 68K resisters I have taped off in the chassis.  Should these be tied to ground until I get my additional jacks.
Thanks guys for your help, I know i'm not giving you much help by explaining what the issue is.  I've built a couple of amps from kits, an 18watt and a Deluxe Reverb.  I've been building this one with my son and between the two of us we have really created a problem here.  He wants to use it in a show on Thursday and we have been rushing to finish it and you know what happens when you rush.....

Ground those 68K's, even simply with Alligator clips for the time being and check the affect on the hum. 

But my guess is the hum is coming from wherever your input problem is.

Insert a cord in one of the jacks, power does not have to be on.  And check connectivity from the other cable end...make sure the sleeve is connected to ground and then make sure the tip is connected through to the input (checking on the leg of the correct 68k resistor is fine).

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davohilts
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« Reply #7 on: February 20, 2011, 02:41:20 PM »

grounding the 68k's didn't help on the hum. I checked the input jacks and they work as they should. I get signal undistorted to the 12AY7 but the sound out of the 12AX7 is overdriven and distorted.
the grounding on the pot side is sort of strange I think.  The schematic doesn't show any direct grounding, everything seems to be connected to the 16uF caps w/out a direct to ground connection. I might try adding a ground here to see if I can get rid of some hum.
the weber schematic seems like a better layout with a bias adjustment.
i don't see a bias adjustment capability with the 5X3 circuit.
How would I adjust the bias on the 5X3?
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davohilts
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« Reply #8 on: February 20, 2011, 06:03:57 PM »

okay, I added a ground to the circuit because the grounding scheme on the layout didn't ground the big resister and cap, they were not grounded. When I added the ground the amp sprung to life!  The hum is gone and the guitar input goes through and all knobs work.  Now my issue is that although I get good throughput on the signal the amp sounds more like a deluxe not the super deluxe. It is not loud enough to play along with a drummer.  I'm disappointed because I have a deluxe reverb that is louder.
Any ideas as to what to do the get more out of this amp?
Thanks,
Dave
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wyatt
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« Reply #9 on: February 20, 2011, 06:06:20 PM »

okay, I added a ground to the circuit because the grounding scheme on the layout didn't ground the big resister and cap, they were not grounded. When I added the ground the amp sprung to life!  The hum is gone and the guitar input goes through and all knobs work.  Now my issue is that although I get good throughput on the signal the amp sounds more like a deluxe not the super deluxe. It is not loud enough to play along with a drummer.  I'm disappointed because I have a deluxe reverb that is louder.
Any ideas as to what to do the get more out of this amp?
Thanks,
Dave

What speaker and what are your B+ and plate voltages?
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davohilts
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« Reply #10 on: February 20, 2011, 09:19:23 PM »

good questions!
my speaker is a newly reconed JBL D120F 8 ohm
my OT is from Weber (same one used in the 5E3P)
voltages for B+ on 16mfd filter caps are 427, 392, 280
Pin 1:  12AY7 = 140v
Pin 6: 12 AY7 = 86v
Pin 1: 12AX7 = 188v
Pin 6: 12AX7 = 228v
Pin 3: 6L6 = 428v same for each one

thanks
Dave
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wyatt
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« Reply #11 on: February 21, 2011, 04:27:03 PM »

okay, I added a ground to the circuit because the grounding scheme on the layout didn't ground the big resister and cap, they were not grounded. When I added the ground the amp sprung to life!  The hum is gone and the guitar input goes through and all knobs work.  Now my issue is that although I get good throughput on the signal the amp sounds more like a deluxe not the super deluxe. It is not loud enough to play along with a drummer.  I'm disappointed because I have a deluxe reverb that is louder.
Any ideas as to what to do the get more out of this amp?
Thanks,
Dave

You mean the places on Nik's layout where it shows a green line going to "X" and "X" being the Ground lug?

Yeah, that's the problem with layouts, they make certain omissions based on assumed common knowledge and that you would have the schematic available.  They really are for assembly instructions and not troubleshooting.

As for the current crisis....

Use Weber's bias calculator to figure out your dissipation.

The 5X3 and 5E3P differ in the bias.  The Weber uses fixed bias to get about ~35 watts, the Ceriatone is cathode bias, and should give around 25 watts (of top of my head). 

If you are getting low output, it may just mean tweaking the bias resistor for more dissipation.

Which 6L6GC's are you using?  You can figure many Chinese and the Tesla for 30 watt tubes and assume Russian tubes are 25 watts max. dissipation.

If the recone was done right, you should have a very sensitive 103db speaker in there.  So, you should be getting more output than you are implying.
« Last Edit: February 21, 2011, 04:36:33 PM by wyatt » Logged
davohilts
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« Reply #12 on: February 21, 2011, 05:06:52 PM »

Okay, I've been working on the amp again as I was able to buy a couple of input jacks from a repair place that was open today.  I installed the 2 input jacks and that has improved my sound and volume very much.  The plate voltage on pin 6 of before I connected the second pair of inputs was 86v and now is 140v. There must be some connection thru the jacks that was missing. 
I get a good sound now although compared to the Bell Pacemaker PA head I modified which uses 2 6L6 power tubes, this circuit doesn't have near the same amount of power.
We built the cabinet out of canary wood and we were expecting this thing to blow our sox's off but it is a little dark and not as loud as my Magnatone MP1. I'm using a pair of Silvertone 6L6's which test good until the JJ 6L6's arrive. I will check into the bias issue and report back what I find out, not too sure what the silvertone tube manufacturer was. The bias thing has always seemed mysterious to me so this should be a good learning experience.
I appreciate the help.
Dave
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wyatt
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« Reply #13 on: February 21, 2011, 06:51:28 PM »

I bet it's a matter of weak power tubes.

As for tone, dark is the Tweed Deluxe vibe.

Some people buy Tweeds and clones assuming they are getting that classic signature "Fender Tone" in cooler clothes.

Tweed Tone is midrange heavy, with big, loose bottom end and the high-end rolls off very early (earlier on the smaller amps), and they generally break up early, a side-effect of the midrange and low-voltage preamps.  Tweeds are really part of the Marshall family of amps tone-wise.
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davohilts
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« Reply #14 on: February 21, 2011, 08:57:27 PM »

By a little dark, I mean cotton in ears dark, even dark for a deluxe in my opinion.
the schematic called for a 270 ohm 10 watt cathode resister and all i could find was a 250 ohm 10 watt resister. I went through and ran the calcs on the weber site and got the following:
2 tubes, 32.5v across cathode resister, 250 ohm resister actual, 403 volts across cathode and plate of 6L6's, giving me a calculated 25 watts plate dissipation per tube and an approximate plate current in each tube of 62 milliamps.
There you go.  Now what if I went to a 200 ohm cathode resister?  That should kick up my plate dissipation to around 31 watts, is this the direction I should go or does that set the bias too hot?
Thanks,
Dave
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