18 watt TMB?

[chuckb]

Hey guys, I just finished wiring up a 18 watt tmb using ceriatone layout. Ihave power but no sound at all. I took some voltage check and here are what I have.

Rectifier- pin 1= 267vdc
pin 3= 362vdc
pin 7= 267vdc

!2ax7 -v1- pin 1=136.9 vdc
pin 6=135.6vdc
pin 3&8=0.995vdc

v2-pin 1=162vdc
pin 6=167vdc
pin 3&8=121vdc

v3-pin1=136vdc
pin 6=258vdc
pin 3=0.959vdc
pin8=136.6vdc

EL 84 v4&5-pin7=252.9vdc
pin9=337vdc
pin2=ovdc
pin3=11.5vdc

I'm not really sure what's going on here and any help would be greatly appreciated.

Chuck

[chuckb]

Anyone?

[Jazz P Bass]

A schematic would be nice.
Even the layout would be better than nothing.
My first impression (not knowing what is hooked up where) is V2 pin 3 & 8.
Why is the voltage so high?

[big_teee]

http://www.ceriatone.com/images/layo...Bceriatone.jpg
Do you get a pop on the speaker when you read voltages across the Turret board.
If not I would look at the OT and Power out wiring.
If you do get a pop, I would head back toward the input jacks.
Like Mr Bass said a Schematic would be nice.
Good Luck,
T
**
I agree pin 3 should not be that high, and you probably don't even have B+ that high in the amp.
It is probably 3.62V instead of 362v.
That is the cathode and has a 820 Ohm resistor to ground.
It should be low voltage.

[chuckb]

http://www.ceriatone.com/images/layo...Bceriatone.jpg
Do you get a pop on the speaker when you read voltages across the Turret board.
If not I would look at the OT and Power out wiring.
If you do get a pop, I would head back toward the input jacks.
Like Mr Bass said a Schematic would be nice.
Good Luck,
T
**
I agree pin 3 should not be that high, and you probably don't even have B+ that high in the amp.
It is probably 3.62V instead of 362v.
That is the cathode and has a 820 Ohm resistor to ground.
It should be low voltage.

Yes, I've re-checked the voltages on pins 3&8 of v2 and the reading is 74vdc on both. When i was checking pin 7 of the power tubes i did get a small stactic noise coming from the speaker, but it was only when the meter lead touched it. Here is the layout from ceriatone website.. I have nothing on the inputs or output jacks whatsoever.

Chuck.

[big_teee]

Here's a schematic I found on the Weber Site that may be pretty close.
You can compare it to your layout.
http://taweber.powweb.com/store/6m18tmbh_schem.jpg
T

[chuckb]

Yes, I've re-checked the voltages on pins 3&8 of v2 and the reading is 74vdc on both. When i was checking pin 7 of the power tubes i did get a small stactic noise coming from the speaker, but it was only when the meter lead touched it. Here is the layout from ceriatone website.[ATTACH=CONFIG]17578[/ATTACH]. I have nothing on the inputs or output jacks whatsoever.

Chuck.

Hey guys, I now have vol,although its very low,on the tmb input. still nothing on the hi and lo inputs.
at least I have something!
Chuck.

[loudthud]

There was a report in another thread that the jacks on a Ceratone layout had different terminal locations than those commonly available. With the power to the amp off, plug a guitar cord into the high input jack. Measure the ohms from the tip of the fee end of the guitar cord to pin 7 of V1. It should be 34K ohms. Now ohm from the tip of the free end of the guitar cord to the ground (sleeve)of the guitar cord. It should be 1 megohm.

[chuckb]

There was a report in another thread that the jacks on a Ceratone layout had different terminal locations than those commonly available. With the power to the amp off, plug a guitar cord into the high input jack. Measure the ohms from the tip of the fee end of the guitar cord to pin 7 of V1. It should be 34K ohms. Now ohm from the tip of the free end of the guitar cord to the ground (sleeve)of the guitar cord. It should be 1 megohm.

Yes, Thanks for your reply. I have lots of volume now , It turned out that two of the 470k resistors were only 470ohms. It's loud now but I got some aweful ground hum going on,seems it's connected to the master vol though. When the master is increased the hum gets louder.also hum with the preamp volume as well. I'm figuring a ground loop issue but it's sure hard to isolate it.

Chuck.

[big_teee]

Marshalls are notorious with that ground loop hum.
Make sure that the Preamp ground is only connected on one end like the diagram.
Also You could have a Noisy 12AX7.
Sounds like your well on your way!
T

[hasserl]

The 18watt TMB amps are notorious for being noisy, lead dress is critical in them, as is shielded leads.

[chuckb]

The 18watt TMB amps are notorious for being noisy, lead dress is critical in them, as is shielded leads.

Yes ,it would seem that way. I have that loud hum whenever i turn the master volume up. I've check and re-check every lead and solder joint and I still can't isolate the problem? The sound is much like when you have your guitar lead plugged into the amp without being plugged into the guitar and when I turn up the master volume it gets louder.The ground buss is fine and all grounding points seem to be ok as well.I checked to see if i had a grounf loop anywhere and nothing. this one is frustrating! I have sheilded wire on all inputs,and volume controls,I checked the proximity of the B+ in relation to the preamp leads,also tube sockets,tubes etc,still nothing. It seems to originate around the master vol and the Tmb vol. i checked to see if I had made a mistake in wiring the pots but it's how it should be. Anything else I can try?

chuck.

[big_teee]

Yes ,it would seem that way. I have that loud hum whenever i turn the master volume up. I've check and re-check every lead and solder joint and I still can't isolate the problem? The sound is much like when you have your guitar lead plugged into the amp without being plugged into the guitar and when I turn up the master volume it gets louder.The ground buss is fine and all grounding points seem to be ok as well.I checked to see if i had a grounf loop anywhere and nothing. this one is frustrating! I have sheilded wire on all inputs,and volume controls,I checked the proximity of the B+ in relation to the preamp leads,also tube sockets,tubes etc,still nothing. It seems to originate around the master vol and the Tmb vol. i checked to see if I had made a mistake in wiring the pots but it's how it should be. Anything else I can try?
chuck.

Did you try different Preamp tubes?
Try pulling different preamp tubes.
Does the other channel make noise or hum?
I've read that putting a Choke on the B+ also helps.
T

[chuckb]

Did you try different Preamp tubes?
Try pulling different preamp tubes.
Does the other channel make noise or hum?
I've read that putting a Choke on the B+ also helps.
T

Yes , I've pulled the preamp tubes one by one replacing them with new tested ones .The other channell makes noise as well.

chuck.

[loudthud]

Check this thread: http://music-electronics-forum.com/t16362/ . It has tips on finding the source of hum. Try the standby switch test.