New build tw

[Batman8]

Have no guitar signal at all just hum.all caps & resistors checked same values as when put in. No fuse blown or any thing smoking.. Biased up ok 40 mv ... Suspect valve one 12ax7 super loud hum with4 great different tubes all did the same how can I tell if I messeed up tube socket? And to check filament voltage ?? Pin 2 to pin 7 or pin 2 to ground pin 7 to ground ect tube 1 hit it and it sounds like as loud as if you taped a mic on a big pa system I did this build after open heart surgery . Very shakey on solder at first think I put too much on number 1 tube socket it was hard to put in a tube.... How to test socket if I messed it up ?? Please help I am so close

[Zippy]

Troubleshooting?

From your description, I'd suggest you power it down, drain the caps, then check for continuity around the V1 socket. It certainly sounds like you might have dribbled a solder short in there or otherwise neutered the socket.

You might consider just swapping out the socket if you find the readings are wonky. That would be far easier - and safer - than trying to get all the solder out of the wrong places.

[M Fowler]

I use old tubes in the sockets when I solder to prevent solder dripping into the sockets.

[Phil_S]

OK, slow up a bit and I"m sure folks will help you sort this out. Is this your first build?

+1 on what Zippy says.

Building on that, help us figure out a few things.

Do you have filament voltage on all sockets? Filaments are AC volts so set your meter for ACV. For the 12AX7's, one probe on pin 9, the other on pin 4 or 5. Pins 4 & 5 should have a jumper that connects the two. For the power tubes, filament voltage is on pins 2 and 7. I like to use clips, which help to get a reliable reading. It can be difficult to hold steady, and you don't want to slip on a live chassis. You should see about 6.3VAC at each tube socket.

After you confirm good filament voltage, give us a set of DC voltage readings for all the other tube pins. Include readings for the + side of each filter cap (except the bias cap). The black probe to ground, the red probe to the socket pin. Post this information.

When you probe for DC volts, do you hear a pop or static at each pin? If you do not, that suggests where the problem lies. Tell us what you find.

Check the wiring on the input jack. You may have it wrong. See the picture.

[Batman8]

Yes it's first complete build ...Filament voltage Good on all tube 3.3 to ground on all 6.6 on pin to pin. Stoped voltage checks waiting for new 9pin tube sockets .... In a few days I will get back. But it sounds like a short hoping it just a socket I checked all caps &resistors to specs I did before build really want this to work out ,I have a cab being made by this cool cabinet maker in Tennessee. This guy makes a maple cab that looks like nothing I have ever seen in a amp cab

[Batman8]

Got voltage v1 12ax7 pin 1 260 volts pin 3. 2 volts heater pin 4 6.6. Pin 6 296 volts pin 8 0 volts. Pin 9 6.6. Expected 1 210 volts 3 2 volts 4 6.3 volts 6 182 volts 8. 1.5 volts 9 6.3 volts V2 pin one is expected 267 volts. Actual 300 and climbing The rest of v2 and v3 are as expected. Same with v4 and v5 all good b+ all good v1 seems to be messed up
...... .?? Any help. Thanks all

[martin manning]

Zero volts on V1 pin 8 (cathode) likely means that it is missing its ground. Pin 4 (and 9) voltage to ground should be half of the filament supply voltage since there is a grounded center tap.

[Phil_S]

Got voltage v1 12ax7 pin 1 260 volts pin 3. 2 volts heater pin 4 6.6. Pin 6 296 volts pin 8 0 volts. Pin 9 6.6. Expected 1 210 volts 3 2 volts 4 6.3 volts 6 182 volts 8. 1.5 volts 9 6.3 volts V2 pin one is expected 267 volts. Actual 300 and climbing The rest of v2 and v3 are as expected. Same with v4 and v5 all good b+ all good v1 seems to be messed up
...... .?? Any help. Thanks all

You aren't making it easy for us older guys to read It this what you are saying?

Pin: Actual; Expected
V1 12AX7
p1: 260; 210
p3: 2.0; 2
p6: 296; 182
p8: 0; 1.5

V2
p1: 300+; 267

Really a full set of readings, and not "b+ all good" is how to get real help.
Saying that is like telling your doctor you pulse is OK. He still wants to put his finger on your wrist and see for himself exactly what it is. There is more to it than meets the eye.

Your run away voltage on V2 p1 may be from a variety of things. Without a voltage chart, it's a WAG. Help us help you. It would be extremely helpful if we knew the B+ supplying the 300+ runaway.

My WAG is that you don't have proper bias on that section of the triode. Cause? Ida Noe.

[Batman8]

Here goes. V1a anode 260 volts... Cathode 2 volts ... Heater 6.6 vac pin 5 jumper V1b anode 295 volts. Cathode 0 volts. Heater 6.6 vac. Expected 210 .1.9. 6.3 . 182 . 1.5 . 6.3 . V2a. Actual Anode300 volts. Cathode 3 volts . Heater 6.6 volts . Pin 5 jumper . V2 b. anode na . Grid na . Heater 6.6 vac.... Expected 287 .. 2.8 .. 6.3 ..vac .. 6.3 vac... V3a actual anode 210 volts .. Grid 25 volts .. Cathode 38 volts .. Pin 5 jumper ..v3b anode 202 volts .. Grid 24 volts ..cathode 39 volts .. Heater 6.6 vac ... Expected. 190 .. 25 .. 38 .. 6.3 .. 193 .. 27 .. 39 .. 6.3 vac.. V4 actual heater 6.6 vac .. Anode 386 volts .. Screen 377 volts bias -33 mv ..heater 6.6 vac .. Expected 6.3 .. 415 .. 397 .. -33 .. 6 . 3 vac .. V5 el34 heater 6.6 vac .. Anode 415 volts .. Screen 397 volts .. Bias -33 mv .. Heater 6.6 vac..... Expected 6.3 415 .. 397 .. -33 .. 6.3 vac .. Mains 120 B+1 387 v .. B+2 391 v .. B+3 319 v .. B+4 299v .. B+5 310v .. Bias -40 mv.. Expected 120 v 420v .405v.. 317v .. 298v.. 310v... -35 to -45 mv bias mv ... Best to my understanding thanks V1a anode 260 and v1b anode 296 and v1 b cathode is what I see wrong and don't know how to fix. Thanks

[menger66]

Is the cathiode resistor for v1 pin 8 grounded as it should be? how about pix?

[M Fowler]

Voltage is too high at V1 so make sure you have the wiring of the B+ correct.

Also, based on your voltages given V5 doesn't have correct readings only expected values in your post.?

Mark

[Batman8]

Pin 8 and pin 1 go to ground on v 4 and 5 el34 ..... .? V1 is 12ax7 pin 8. Goes to Pre amp board to 1.5k resistor The layout is on ampgarage drawn by Ron Worley ... Don't have camera for pics Iam a old fart , but I have gone over the layout for 3 days took readings on all resistors , cap ect.... First build very close if you can check layout and schematic on this site it is Ken Fischer 1990 revision ..... Francesca lots of pics. Thanks again

[menger66]

The 1.5k is it grounded? you reading 0v on pin 8 of v1 would imply that the 1.5k resistor is not connected to ground, and it needs to be.

[Batman8]

it is v1 the preamp first tube not the power tube and the resistor on pre amp board is ok

[ampgeek]

The flaky half of V1 may not be conducting. That could cause a zero volt condition at the cathode.

Can you swap in another tube and give it a go?

Good luck,
Dave O.