Seeking help debugging Ceriatone Bluesmaster 50

[mwdavis14]

Thanks. I checked with Nik at Cortisone to confirm ok to use slow blow. He says ok. I will be rechecking all connections and looking for bridging, and will test resistance as suggested as well, and will try power up with slow blow installed.

[martin manning]

Ask Nik to send TAG a check for helping him out. It's the least he could do.

[mwdavis14]

I changed over to the slow blow fuse, and while it now holds power, there is no sound whatsoever coming out of the amp. I've plugged into both channels (hi & low). Nada. No hissing, scratching, humming. Silent. Speaker & speaker cable are fine, as is the guitar. I measured the voltages and HV is present. I came up with the following readings:

225.8 at the 1st filter cap
454 at the 2nd filter cap
the other 3 caps on the power board read 454, 402 and 328.2
The two connection points on the main board leading to the PI trimmer read 237.5 and 247.
The other 2 main power points on the main board read 328.1 and 296.8

At the tube sockets I get the following
V1
1: 195.8
2: 0
3: 1.46
4: 3.48 vac
5: 3.48 vac
6: 197.7
7: 0
8: 1.47
9: 3.48 vac

V2
1: 199.2
2: 0
3: 1.89
4: 3.49 vac
5: 3.49 vac
6: 206.5
7: .3 mv
8: 1.77
9: 3.49 vac

V3
1: 247.0
2: 26.52
3: 42
4: 3.49 vac
5: 3.49 vac
6: 237.5
7: 26.62
8: 42
9: 3.49 vac

V4
1: 18.6 mv
2: 3.5 vac
3: 455
4: 453
5: -47.3
6: 454
7: 3.5 vac
8: 18.6 mv

V5
1: 18.2 mv
2: 3.5 vac
3: 454
4: 452
5: -47.3
6: 454
7: 3.5 vac
8: 18.2 mv

the readings listed above are with the tubes installed.

I double checked the grounds at the input jacks, and the vol trimmer. Test fine. Continuity is present. Anyone have any thoughts as to what this may be?

[talbany]

Telling an experienced amp builder I get no sound from my amp (what could it be) is really no different than telling an experienced mechanic my car won't start (what could it be?)
Answer..Allot of things!!

IMO..At the very least Ceriatone should post on it's website a very basic troubleshooting guide (Safety start up procedures) for each amp..Listing proper operating voltages (on Layouts) and other signal path test (jumper) points ,to help if it's customers run into these kinds of problems..?
Where's the Service Manual??

Good Luck!

Tony

[mwdavis14]

Thanks Tony. And believe me I do understand the problem in attempting to remotely diagnose.

I ran some additional checks on the signal path, taking into consideration the shielded cable runs. On the shielded cables running from the input jacks (both) and on the cable running to the master vol, I found that I HAVE continuity b/t the signal attachment and the shield ground point. None of the other shielded cable runs demonstrate this. It strikes me that this is a likely ground short shunting the signal to ground. Make sense?

[talbany]

Thanks Tony. And believe me I do understand the problem in attempting to remotely diagnose.

I ran some additional checks on the signal path, taking into consideration the shielded cable runs. On the shielded cables running from the input jacks (both) and on the cable running to the master vol, I found that I HAVE continuity b/t the signal attachment and the shield ground point. None of the other shielded cable runs demonstrate this. It strikes me that this is a likely ground short shunting the signal to ground. Make sense?

Measuring continuity is pretty worthless (vol,gain,level controls all go to ground)..
First things first
Test point #1

If the output tubes are bias and stable..

Plug a cable to your effects return jack (with the amp on!)..Touch the tip with your finger..Does the amp make a noise.. If so plug in a pre amp (signal generator) out from another device (run your guitar through it). How does it sound?..

If your getting something there you now know the problem is in your pre amp section..One section at a time!!

Tony

[mwdavis14]

I realized that I had the master vol pot set at zero when I tested it, which would shunt signal to ground. Turning pot away from zero removed the ground on the cable run to the master volume, so it appears that the issue there was the setting of that pot rather than an issue w/the cable. I also realized that I was testing the input jacks w/o a cable inserted, which would naturally ground to keep the amp quiet when nothing was plugged in. Plugging a cable in removed the grounding issue. So, in short, none of the shielded cables appear to be the problem. This is really frustrating.

[mwdavis14]

Thanks Tony. I do have a bias issue. I understand that the bias reading per tube at the bias points should be able to reach 35 mA or more. However, when I test bias via the test points, I get the following readings (high-low across the sweep of the pot):
3.5mv to 24.8 mv.

I am not able to get the bias reading any higher than 24.8.
The bias pot is a 10kL pot, as per spec. The resistor affixed to the pot is a 15k, also per spec, and tests true.

I tested the diodes on the bias board and they test fine. I also checked the resistor on that board, and it tests true to spec. The bias tap off the PT is rated 60v, but reads 62.4 vac at the board connection. The B+ secondaries from the PT are rated 345, but I measure 360 where each connects to the board. At the bias pot, i read the following at each of the 3 connection points on the pot (labeled L-R as viewed from the rear of the pot)
L: - 38.8 v (DC)
center:-48.5 v (DC)
R: 63.3 v (DC)

The tubes being run are a new set of TAD 6L6GC, supposedly matched pair.

I will run the additional test which you suggested. Thanks for the help. This is an incredibly frustrating process!

[martin manning]

Voltages look ok except you need to run the bias up to about 35mA. Given that, no sound from the output probably does mean a break or unintentional grounding in the signal path.

Tony, if you write a nice paint-by-numbers build and troubleshooting guide, I'm sure Nik would be more than willing to post it on his site for his customers ;^)

[talbany]

Mark
Don't worry about that for now (don't have time), you just need to change the bias range resistor..You should still be getting sound out of the amp set @ 24ma..

Tony, if you write a nice paint-by-numbers build and troubleshooting guide, I'm sure Nik would be more than willing to post it on his site for his customers

;



Tony

[mwdavis14]

Tony,
I ran the test you suggested. Plugged a cable into the effects return jack with the amp on, touched the tip with finger... NADA. No sound at all. Despite this, ran phase 2 and plugged in a pre amp signal generator, guitar, etc. Predictably, no sound.

[ToneMerc]

Mark
Don't worry about that for now, you just need to change the bias range resistor..You should still be getting sound out of the amp set @ 24ma..

Tony, if you write a nice paint-by-numbers build and troubleshooting guide, I'm sure Nik would be more than willing to post it on his site for his customers

;



Tony

Exactly, change that resistor to 22-24K or so.

TM

[talbany]

Tony,
I ran the test you suggested. Plugged a cable into the effects return jack with the amp on, touched the tip with finger... NADA. No sound at all. Despite this, ran phase 2 and plugged in a pre amp signal generator, guitar, etc. Predictably, no sound.

So now you need to get that working first!!.. Go back over the layout and double check everything from that jack back to the speaker jacks and make sure every connection is wired properly and soldered well.. Also don't rule out a bad set of tubes..Screen voltages should be several volts lower than the plates..

Posting some good pics of the output section will certainly help other here spot something mis wired...Help us help you!

Good Luck!!

Tony

[mwdavis14]

Should there be continuity on the impedance switch b/t the set point of contact (4 ohm, 8 ohm, etc.) and the speaker output jack? It appears to me that this is the final signal out connection point. I have no continuity reading here. Possible I have a bad switch?

[mwdavis14]

Nik @ Ceriatone advises that there SHOULD be continuity across the impedance switch to the speaker out jacks. I get nothing when I test mine. In any position. There is continuity across the wire connecting the switch to the speaker jacks however. There is really very little going on here as best I can tell. Connections b/t the various ohm taps from the OT and the switch with a rotating contact point. I've attached a pic of mine as wired, which matches to the pics on Nik's site. Is there anything obviously wrong here?