Ceriatone Bluesbreaker. No voltage to preamp tubes. Help humbly requested.

[camsna]

Hello fellas. My name is Cameron and I really need help. My dad and I have spent a bunch of hours building his dream amp — a Bluesbreaker (the whole family saved up and pitched in to do this for him). I’ve built other amps successfully (5E3, low power Twin), but this one is giving us real trouble and I don't know where to begin. I’m desperate and we’re truly, sincerely grateful for your help in getting this up and running.

It’s a Ceriatone Bluesbreaker kit. We’ve quadruple-checked our wiring against the layout and we installed the Lar/Mar PPIMV. We’ve obviously done SOMETHING wrong, but can’t figure it out. We finished the build and started testing (based on TubeDepot’s JTM45+ kit testing procedures). There are, so far, two problems:

1) We’re not getting 500ish volts (we’re getting ZERO volts) to either + terminal of the can cap and
2) our preamp voltage readings are mostly wrong. Our preamp readings are ( - connected to chassis, power and standby switches ON, recto and preamp tubes installed):

V1
   1: -0.5
   2:
   3: 0
   4: 3.3 AC
   5: 3.3 AC
   6: -0.5
   7:
   8: 0
   9: 3.3AC

V2
   1: -0.6
   2
   3: 0
   4: 3.3 AC
   5: 3.3 AC
   6: -0.5
   7: -0.6
   8: 0.1
   9: 3.3 AC

V3
   1: -0.5
   2
   3: 0.4
   4: 3.3 AC
   5: 3.3 AC
   6: -0.5
   7:
   8: 0.4
   9: 3.3 AC

Basically, everywhere we'd expect to see some DC on the preamp tube sockets, we're not seeing any DC. Where do I start? Humble apologies for the rookie mistakes you’re BOUND to notice.

Thanks so much. I really look forward to getting my dad's amp up and running!

---
Cam

[sluckey]

What voltages do you measure on the big tubes? Some of the voltages on the rectifier will be AC voltages. What voltage on the standby switch and HT fuse terminals? Are the rectifier filaments lit?

[camsna]

What voltages do you measure on the big tubes?
Haven't installed the power tubes yet. But I got 490VDC on rectifier pin 8.

What voltage on the standby switch and HT fuse terminals?
490 on both.


Are the rectifier filaments lit?
Seem to be.

[camsna]

Rectifier tube voltages:

   2: 490
   5: 350 VAC
   7: 350 VAC
   8: 490
   2 to 8: 5 VAC

I have holy crap diodes installed between pins 4&5 and 6&7.

[camsna]

Thank you!

Does that mean that I shouldn't be looking for 500v on that cap? (I'm seeing 0V...)

Or does it mean that that cap isn't getting fed?

[sluckey]

Haven't installed the power tubes yet.

Don't need them. I still want to know what voltages are on the sockets. It will help to know exactly what is getting voltage and what is not getting voltage.

[camsna]

Don't need them. I still want to know what voltages are on the sockets. It will help to know exactly what is getting voltage and what is not getting voltage.

Okay! Standby...

[camsna]

First of all there seems to be more than one ceriatone layout for that amp.  Could you verify which layout of Nik's you are using?
June 2014

If there is no voltage on the capacitor terminal the choke wiring may be the issue
Checking now!

[camsna]

GUYS! BLOWN HT FUSE!

Going to get a new'n. Standby!

[sluckey]

Hey Steve, in the layout above what is that unmarked switch next to the bias terminals?

That is a pentode/triode switch.

That doesn't make sense if you had voltage on the power tube sockets.

He never posted any voltages for the power tubes.

I don't like that schematic. It has a mod with an extra tube for tremolo. Wonder if his has trem?

[camsna]

ALRIGHT! Fuse replaced! We've got power to that cap again. Whew!

Here are the new tube voltage readings. Power tubes are NOT installed. Preamp tubes and rectifier ARE installed. I'm suspicious of V3.


V1
   1: 209
   2:
   3: 1.66
   4: 3.2
   5: 3.2
   6: 200
   7:
   8: 1.66
   9: 3.2

V2
   1: 170
   2
   3: 1.1
   4: 3.2 AC
   5: 3.2 AC
   6: 315
   7: 171
   8: 172
   9: 3.2 AC

V3
   1: 365
   2
   3: 6.8
   4: 3.2 AC
   5: 3.2 AC
   6: 366
   7:
   8: 6.8
   9: 3.2 AC

V4
   1:
   2: 3.2
   3: 470
   4: 470
   5: 0
   6: 470
   7: 3.2
   
V5
   1:
   2: 3.2
   3: 470
   4: 470
   5: 0
   6: 470
   7: 3.2
   8:
   


V6
   2: 490
   5: 350 VAC
   7: 350 VAC
   8: 490
   8 to 2: 5 VAC

[camsna]

(Amp doesn't work yet. DO have the trem version.)

Y'all. I found a 470k resistor that should've been a 470r.

Replaced it.

V3 looks oh so nice, now. Going to hook up the power tubes and keep testing. Standby!

[camsna]

Okay. So -- I'm back to where I started, but encouraged. Fixing that resistor value mistake brought V3 RIGHT to where it needs to be, and I'm happy about that.

But now, I plugged power tubes in and blew the HT fuse. Which is where I was when I started today, with a blown HT fuse after getting to the 'plug the power tubes in' part of testing.

What do you think?

[sluckey]

You have zero volts on pin 5 of the output tubes! Pull those tubes out and lay them aside until you have approx. -35v to -45v on pin 5 of each tube. This is the bias supply. Could be a problem with the wiring on the intensity pot.

DON'T PUT THOSE POWER TUBES BACK IN UNTIL THIS IS FIXED!

[camsna]

Roger that.

[camsna]

So! Intensity is wired correctly. I removed the PPIMV circuit and reverted the bias circuit to stock. Fiddled with the bias pot until I got -45ish on Pin 5 of the power tubes. Voltages on other pins looked good.

I plugged the power tubes back in and powered up. One or both of them is making an "I'm about to explode" squeaking/crackling noise. So I powered down. They were also doing that BEFORE when I was blowing HT fuses.

What's my next step?

[camsna]

Checked the voltage on pins 1/8 of the power tubes. They were 17mv (v5) and 28mv (v4) with the bias adjustment pot turned all the way down. In case that's relevant information... :-/

[camsna]

Alright. Here's where we're at.

First of all -- can't thank you enough for all the help!!!! I feel like we're getting closer!

It's the OT that's rattling, not the tubes. It sounds like it's about to take off. Super freaky. And the rattle/buzz changes intensity/pitch as I adjust the bias. It changes even more significantly as I turn the tone knobs up and down.

The bias reading between the tubes is at too much of a variance. And the disparity is worse as I turn the tone knobs. At some settings, the bias is within a couple MV (30mv/31.5mv), at others, one tube's reading is twice the other (36mv/19mv)!

So I think I'll do as advised. I'll check over the print very carefully; check every connection and see what I find. But if either of you fine gentlemen has any more ideas about where to look for the gremlins, I'm all ears!

[sluckey]

Before you dive in too deep just disconnect that wire labeled "X (16 ohm)" from the 27K resistor on the board. This is just a test. If the amp gets happy, then reconnect that wire. The actual fix is to swap the OT plate leads that connect to pins 3 of each power tube.

[labb]

OT making noise------You do have a speaker connected to the amp don't you.

[camsna]

Before you dive in too deep just disconnect that wire labeled "X (16 ohm)" from the 27K resistor on the board. This is just a test. If the amp gets happy, then reconnect that wire. The actual fix is to swap the OT plate leads that connect to pins 3 of each power tube.
Roger that!

You do have a speaker connected to the amp don't you.
Yes, of course!

[drew]

Photos!

[camsna]

Swapped the OT plate leads. Now the OT doesn't sound like it's trying to make smoothies.

Bias is still weird. Bias reading between tubes is too different.

Thanks again for the help so far, lads. Can't tell you how much I appreciate it!

[sluckey]

It's very possible that the output tubes have been damaged while the bias voltage was zero and the NFB was wrong. They were definitely stressed.

How does it sound?

[camsna]

I assume you are taking your bias readings at the bias test points.
Same disparity whether I test at the test points or measure at pins 8/1.

[camsna]

Doesn't appear to be any output. When I dime all the knobs, I don't get anything through the speakers; not even a hum or a hiss.

I Ordered a new set of tubes. They'll be here in a couple days. I'll re-check everything and install the new tubes this weekend and let you know how it goes!

Can't thank you all enough for all of your help!!!

[uki]

Photos!

QFE !

A picture say more than a thousand words !!

[camsna]

SHE WORKS, FELLAS!

One resistor value was wrong.
The Lar/Mar PPIMV was causing the HT fuse to blow
And, get this, the speaker cabinet was mis-wired (wrong half of the jack was wired, so when plugged in, it was dead!).

Replaced the resistor, removed PPIMV, rewired the speaker cab. BOOM! AMP!

Thanks for all your help!!!!