Ceriatone HRM 50 Build - HELP NEEDED!!!

[The_Nuge]

I just measured pin 7 again: When I switch from standby to operate the voltage increases from approx -0.3V to approx 2 Volts...

Es

[martin manning]

Connect the black meter lead to chassis ground (the star ground near the input jacks, say) and probe with the red one. Check the voltages on V1 again, and it sounds like inspecting the input jack wiring is a good idea. You can get a usable multimeter for not too much money, and it would be a useful tool if you are going to tinker with amps.

[Structo]

Glad to see you are making progress.

Once you get it working properly, you should look over your lead dress.
Which means how the wires are routed to and from connections.

Here is a great build by member UltraHookedOnPhonix.
Although this is not a HRM amp, the wiring is what we are looking at.

I think we all strive to imitate this great wiring but most of us fall short.

But it should act as a guide to inspire you for better lead dress.

See how the wires on the preamp tubes are run down to the chassis floor and to the pins,
keeping the wires short as possible.
This can make the amp much more stable and keep the noise floor low.

[The_Nuge]

That suede 183 and it's wiring does look very nice!
I'll try improving my wiring once the amp works properly

Es

[The_Nuge]

Hi!
I didn't get anything done yesterday - mainly because I went on a 5 hour motorbike ride with my colleagues after work! Good fun too

Couldn't find a 470pF cap, but did find a 560pF which I'll fit instead of the 47pF tomorrow. Also, I couldn't find a 470 Ohm 1/2W resitor, so I'll use two "bigger" 1/4W ones in parallel to make a ~390 Ohm one.

First in the to-do list though is checking the input jacks and I'll re-solder the V1 socket.

More tonight!

Es

[The_Nuge]

Got a few things done:

Pilot light: put a 470 Ohm resistor in - heater voltage didn't drop, but the pilot didn't light up. So I too it out, with the result that the voltage doesn't drop and the pilot works too!

Cap on V1: replaced the 47pF with the 560pF which should put me closer to the 470pF on the diagram.

Input jacks: Took those out. The shield on the "HI" wasn't connected to ground very well!

Test: Hooked the amp up to a 2x12" and plugged in... The amp works! Both inputs and all of the knobs "do something". Still some problems though:

Sometimes the amp goes quiet - usually after adjusting the volume - and then comes "back on" when I hit a chord hard. As if there's bad connection? Also the same volume knob is extremely noisy when you turn it... So I pulled it and am now in the process of re-wiring that, including the shielded cable that runs from it to V1.

Will post again tomorrow!

Es

[bluesfendermanblues]

Got a few things done:

Pilot light: put a 470 Ohm resistor in - heater voltage didn't drop, but the pilot didn't light up. So I too it out, with the result that the voltage doesn't drop and the pilot works too!

Cap on V1: replaced the 47pF with the 560pF which should put me closer to the 470pF on the diagram.

Input jacks: Took those out. The shield on the "HI" wasn't connected to ground very well!

Test: Hooked the amp up to a 2x12" and plugged in... The amp works! Both inputs and all of the knobs "do something". Still some problems though:

Sometimes the amp goes quiet - usually after adjusting the volume - and then comes "back on" when I hit a chord hard. As if there's bad connection? Also the same volume knob is extremely noisy when you turn it... So I pulled it and am now in the process of re-wiring that, including the shielded cable that runs from it to V1.

Will post again tomorrow!

Es

Sounds like a faluty volume pot maybe due to overheating of the pot's lugs. Try to resolder og change the pot....

[The_Nuge]

Hi again,

I had the volume pot out, cleaned it with contact spray and re-wired it completely.
I also re-checked the connections at V1 and made the following measurements:

On "Operate", no input, all pots turned to "0":

V1 (Sovtek 12AX7):

Pin 1: 191 VDC
Pin 2: 126.5 mV DC
Pin 3: 20mV DC
Pin 4: 2.97 V AC
Pin 5: 2.97 V AC
Pin 6: 88.44 V DC
Pin 7: 3.10 V DC
Pin 8: 29.6 mV DC
Pin 9: 2.97 V AC

V2 (TAD 12AX7):

Pin 1: 195.15 VDC
Pin 2: 0 V DC
Pin 3: 1.79 V DC
Pin 4: 2.97 V AC
Pin 5: 2.97 V AC
Pin 6: 35mV DC
Pin 7: 0.2 mV DC
Pin 8: 1.6 V DC
Pin 9: 2.97 V AC

V3 (Tube-Town 12AX7):

Pin 1: 300 VDC
Pin 2: 32 V DC
Pin 3: 53 V DC
Pin 4: 2.97 V AC
Pin 5: 2.97 V AC
Pin 6: 308 V DC
Pin 7: 34.5 V DC
Pin 8: 53 V DC
Pin 9: 2.97 V AC


When I plug in a guitar, both inputs now do what you'd expect them to, and the knobs and switches also seem to do their "thing".

When playing quietly, like single notes and picking very lightly, all appears OK. However, if I really pluck the strings hard or play a chord, there is a sudden very loud pop and an increase in volume! I think this is most dominant on the clean channel.
Help! I can't really think of anything to check - I've probably checked the V1 wiring 20 times.

Cheers

Es

[xtian]

The voltages on V3 seem way too high.

[JazzGuitarGimp]

Hi Nuge,

I skimmed over the three pages of discussion, looking for a link to your schematic, but I don't see one - did I miss it? If you have not posted it, it really would be a great help to everyone here who is trying to help you.

Assuming V1 is your first preamp tube (the one fed from the input jack), there is no possible way that 20mV on the cathode (pin 3) is correct. 30mV on the other cathode (pin 8) just isn't right either, nor is 3.1V on the grid at pin 7. All this is assuming the first two preamp stages are designed around the usual Fender / Marshall / Vox circuit topology. But none of us know this for sure without a schematic.

Cheers,
Lou

[vibratoking]

Lou, it's a Ceriatone HRM. Should be Dumble type values. I agree with you, those cathode voltages can't be correct.

Those preamps aren't biased correctly.

[The_Nuge]

Hi Nuge,

I skimmed over the three pages of discussion, looking for a link to your schematic, but I don't see one - did I miss it? If you have not posted it, it really would be a great help to everyone here who is trying to help you.

Assuming V1 is your first preamp tube (the one fed from the input jack), there is no possible way that 20mV on the cathode (pin 3) is correct. 30mV on the other cathode (pin just isn't right either, nor is 3.1V on the grid at pin 7. All this is assuming the first two preamp stages are designed around the usual Fender / Marshall / Vox circuit topology. But none of us know this for sure without a schematic.

Cheers,
Lou

Hi Lou,

Here's the schematic:
[img1274]http://niffko.com/g2data/gallery2/d/169 ... RM-50W.jpg[/img]

The voltage seem all over the place - as others have also told me!
When I measured those voltages an hour or so ago, I also measured 35mV on Pin 6 of V2. I was re-routing some of the wires slightly as they were touching the heater wires, and suddenly I was getting 208V at the same position...

I am considering rewiring the heaters "up in the air". Would that be a step forward?

Is there a list of what the voltages should be somewhere?

BTW, this is my first build and I obviously don't have much of a clue!

A general question: What does the LNFB switch between V1 and V2 do?


Cheers

Es

[Structo]

Hi again,

I had the volume pot out, cleaned it with contact spray and re-wired it completely.
I also re-checked the connections at V1 and made the following measurements:

On "Operate", no input, all pots turned to "0":

V1 (Sovtek 12AX7):

Pin 1: 191 VDC
Pin 2: 126.5 mV DC
Pin 3: 20mV DC
Pin 4: 2.97 V AC
Pin 5: 2.97 V AC
Pin 6: 88.44 V DC
Pin 7: 3.10 V DC
Pin 8: 29.6 mV DC
Pin 9: 2.97 V AC

V2 (TAD 12AX7):

Pin 1: 195.15 VDC
Pin 2: 0 V DC
Pin 3: 1.79 V DC
Pin 4: 2.97 V AC
Pin 5: 2.97 V AC
Pin 6: 35mV DC
Pin 7: 0.2 mV DC
Pin 8: 1.6 V DC
Pin 9: 2.97 V AC

V3 (Tube-Town 12AX7):

Pin 1: 300 VDC
Pin 2: 32 V DC
Pin 3: 53 V DC
Pin 4: 2.97 V AC
Pin 5: 2.97 V AC
Pin 6: 308 V DC
Pin 7: 34.5 V DC
Pin 8: 53 V DC
Pin 9: 2.97 V AC


When I plug in a guitar, both inputs now do what you'd expect them to, and the knobs and switches also seem to do their "thing".

When playing quietly, like single notes and picking very lightly, all appears OK. However, if I really pluck the strings hard or play a chord, there is a sudden very loud pop and an increase in volume! I think this is most dominant on the clean channel.
Help! I can't really think of anything to check - I've probably checked the V1 wiring 20 times.

Cheers

Es

If the dropping resistors are correct then I suspect either a bad tube or incorrect wiring.

Well, first of all, the voltages on V1 and V2 the preamp tubes is off,on pin 6.
You should have similar voltages on the plates (Pin 1 and Pin 6), in this case pin 6, on each preamp tube.
Should be 5-8 volts max different between the plates.

A mistake I made was getting the plate and cathode resistors backwards.

In other words, be sure the cathode resistor and cap is is connected to the proper side of the tube (plate).

So for an amp that has a 220K and 150K plate resistors make sure the corresponding cathode resistor is right. (3K3 and 2K2

I made this same mistake when I built mine.

[alvarezh]

Hi Nuge, here is a voltage listing from Ceriatone. It's for an OTS (Non-HRM) but it shouldn't matter.

All the best.

[The_Nuge]

I checked the voltages again - they're still off, so I've decided to redo the wiring aroung the valves.

I'm taking the heater wires out, and want to redo them last "in the air". Anything speak against this? Also, I have some copper non-tinned wire which I'd like to use - is that a problem? Getting the same silicon stuff ceriatone uses could be difficult.

Found another anomaly: the two 22M resistors at V1 aren't very close to 22m - the one off pin 7 is about 18-19M (the reading moves around a lot), the one off pin 6 is about 26M Could this be causing my problems? The 220k is close to spec.

Can I check the voltages without the heater wire connected, or doesn't that make any sense?

Cheers

Es