Seeking help debugging Ceriatone Bluesmaster 50

[mwdavis14]

I'm on my second time through trying to fix this amp and am at a loss. I'll give you the history briefly, and then where I stand presently.

I finished build, which was done slowly and by the book. Went through power up w/bulb limiter w/o issues. Hooked up guitar and speaker, and there was a horrible scratching w/the vol pot and only clean tone with limited volume. Bias voltage reading was also low. Maxed out only got 23 mv. Came to discover that the vol pot was bad, and I had used too much solder when hooking up V1 and V3, and had blocked some of the pins so those two tubes were not working. Purchased new vol put (CTS) and new tube sockets. Pulled those items and hooked everything back up. Double checked continuity across everything w/DMM. All checked out. Power up w/bulb limiter again w/o issues. All tubes heating properly, no sockets blocked this time. Bias voltage remained low as before. Hook up the guitar and........ Nothing. No sound. Not a peep.

Anyone have an idea of where I go from here to debug this thing?

I'm in the process of measuring all voltages at each pin for the valves and will post separately. I have posted this on the ceriatone forum as well, but as yet have had no replies. Would very much appreciate any insight that you all may have to offer.

Thanks,
Mark.

[Darkbluemurder]

Bias voltage reading was also low. Maxed out only got 23 mv.

Mark, what did you actually measure here - the raw bias voltage at pins 5 of the power tubes or the voltage drop across the 1 ohm cathode resistors? 23 mv as bias voltage would cause severe red plating of the power tubes. If the amp has 6L6s you should have 40 to 55 volts (not mv) there.

I'm in the process of measuring all voltages at each pin for the valves and will post separately.

Good idea. Any voltages that may be off will pinpoint to potential trouble sources. It would also be beneficial to post a picture of the amp's inside.

Cheers Stephan

[rogb]

Bias voltage reading was also low. Maxed out only got 23 mv.

Mark, what did you actually measure here - the raw bias voltage at pins 5 of the power tubes or the voltage drop across the 1 ohm cathode resistors? 23 mv as bias voltage would cause severe red plating of the power tubes. If the amp has 6L6s you should have 40 to 55 volts (not mv) there.

I'm in the process of measuring all voltages at each pin for the valves and will post separately.

Good idea. Any voltages that may be off will pinpoint to potential trouble sources. It would also be beneficial to post a picture of the amp's inside.

Cheers Stephan

A negative value for bias- just to clarify.
Measure the output at the bias board just to be sure.

[mwdavis14]

Here are the pin voltages (measured w/the tubes out - 50w amp):

V1 1: 211 mv
2: 0
3: 0
4: 3.58 v
5: 3.58 v
6: 200 mv
7: 0
8: 0
9: 3.58 v

V2 1: 222 mv
2: 0
3: 0
4: 3.58 v
5: 3.58 v
6: 211 mv
7: 0
8: 0
9: 3.58 v

V3 1: 241 mv
2: 0
3: 0
4: 3.58 v
5: 3.58 v
6: 229 mv
7: 0
8: 0
9: 3.58 v

V4 1: 0
2: 3.59 v
3: 218 mv
4: 219 mv
5: -46 v
6: 222 mv
7: 3.59 v
8: 0

V5 1: 0
2: 3.59 v
3: 218 mv
4: 219 mv
5: -46 v
6: 222 mv
7: 3.59 v
8: 0

With the exception of the heaters, all readings are in DC. "mv" is not an error, that is what the DMM is measuring.

Bias readings from original post were taken from the bias measurement points, which have a resistor. The pin #5 voltage reading referenced above is taken directly from the pin socket. I currently have no idea how to measure bias at the board, but will read up on it and try to post that.

Pictures to follow as well. Hopefully someone can help me here.

Could this be a transformer or choke issue? As I stated in original post, this build was done slowly and very meticulously. Continuity exists across all points. I have traced all wiring to the board positions to double check continuity, and all of that checks out. Layout strictly followed Ceriatone's posting. There are a couple of mods, but these were standard Ceriatone mods and followed Nik's layouts to the letter as well.

[martin manning]

All we can get out of that is that the filament and bias voltages look ok. You need to put all the tubes in and repeat.

[bcook]

You should still have 200+vdc on pins 1 and 6 of the preamp tubes. Measure at each resistor junction in the power supply also, right to the rectifiers.

[ToneMerc]

These builds are complex compared to other builds, thus everything is suspect. Thus, you need to leave the mindset that it is not a wiring issue, with these builds more often than not, it is a wiring issue. However, troubleshooting this is no different from a Fender Champ.

Like Martin stated, your AC and LV bias is verified, but where is your high voltage DC? I would install only the preamp tubes first.


PHASE 1

1, Verify high DC voltage at rectifier board output.
2. Do you have HV DC output at the standby switch?
3. Do you have HV DC at the first filter cap bank (K)
4. Do you have HV DC at point ( L), the last filter cap on the main power board?

If you don't have HV DC at these points, there's no use probing the rest of the amp yet.

TM

[martin manning]

You should still have 200+vdc on pins 1 and 6 of the preamp tubes. Measure at each resistor junction in the power supply also, right to the rectifiers.

Nothing on the power tube plates either... I'm guessing the standby is off.

[rogb]

As well as checking for DC on the power supply board, if it is present at the stated points L and M, check to see if there is DC on the main board where I have circled.
Good luck

[mwdavis14]

Thanks much everyone. I'll do these checks, and recheck voltages w/the tubes installed, and re-post the results w/pics.

[mwdavis14]

There is no high voltage DC anywhere. With all tubes installed, readings are almost all NEGATIVE DC voltage, and in mv only. I get a reading of -198mv at the standby switch. 12 mv at the mains switch. First two filter caps read -98mv and -197mv respectively.

At the tubes, V1 reads:
1: -209 mv
2: -258 mv
3: 23.3 mv
4: 3.59 v (AC)
5: 3.59 v (AC)
6: -208 mv
7: -.5 mv
8: 4 mv
9: 3.58 v (AC)

(similar for V2 & V3)

V4 & V5 are identical:
1: 0
2: 3.59 v (AC)
3: -184 mv
4: -186 mv
5: -39 v
6: -189 mv
7: 3.59 v (AC)
8: 0

Measured voltage at the bias board and it read -53v

FWIW, as the tubes are installed for these readings, I checked voltage w/my DMM probe at the connection point for wires running to each tube pin, w/the other lead to chassis ground.

This makes no sense to me. Hopefully someone out there can help.

[mwdavis14]

BTW, both standby and power switches are on for these readings.

[martin manning]

Check the ground path from the HT center tap "0" on the PT between 345 and 345, through the fuse (got fuse?) and to chassis ground, and grounds on the large filter caps. If those are all good, check DC voltage at K, both sides of the choke, L, M.

[Structo]

Where in "the united states" are you located?

Might be someone close that can troubleshoot it for you....

[mwdavis14]

I am in NJ (Princeton area)

Pics of the amp will follow as soon as they are uploaded for access