Ceriatone Forum

Hi
This is my first post here.
I know just a little bit about electronics and tube amps and would like to do some mods to my Ceriatone amp.
I have a 50 W HRM that I would like to add a sagresistor to the Powersupply. I've searched the forums for instructions on how to do it and I can't find any that are clear enough for me.
I'd be very happy if someone could post the layout for the amp with the sagresistor in the right spot:-)
What kind of resistor do I need?

I'm also interested to know if it´s a major mod to rebuild it to Bluesmaster HRM specs?

Cheers!
/Thomas

Changing your amp to bluesmaster specs shouldn't be too hard. You just have to change the PI and the tonestack.

Thanks for the reply boldaslove6789!

I guess I just have to read up on the layouts then:-) I've printed them out today and tonight I'm going to take a closer look at them.

Could anyone give me a hint on the sagresistors whereabouts.

cheers
/Thomas

Sagresistor: it is a resistor instead of a choke. Somewhere between 300 and 500 ohm. You have to use a 5w power rating resistor.

erwin_ve: a sag resistor is NOT a resistor in place of a choke. a resistor CAN be used in place of a choke transformer, and is used in certain designs, like on my Sovtek, for example. In either case the choke transformer or choke resistor, depending on what is being used works kinda like a built in line filter to help clean up the power signal a bit.

The sag resistor the OP is referring to is most likely what Nik is building into my HRM BM 50 watter which will be a resistor placed on the center HT lead coming out of the power transformer, which will help simulate having a tube rectifier. on mine this will be able be switched in and out.


Gregg

Thanks for the replies. I think it's as plasticvonaband says.

Excuse me for asking a stupid question, but which one is thecenter HT lead?

(http://i161.photobucket.com/albums/t216/hoffe_68/HRM-50W_crop.jpg)

/cheers
Thomas

We're basically thinking the same. Both ways you have sag. Both are connected to the Ht lead. Yes you're right it's not the only way.
For the sake of the non-technical TS, he will benefit with a approach were there is a simple swap, instead of adding or drilling something in the existing layout.

Btw the difference between a choke or a choke resistor is noticable at band volumes as sag in favor of the choke resistor. Not only line filtering.

Thomas - it's the one between the 3.15v wires, marked 0.

Thanks!
What's the best placement for the resistor? And what kind of resistor do I need?
Would it be the best to attach a terminalstrip to the chassis next to the PT? Or just solder the resistor to the star ground and attach the PT wire to the other end?!

I have a couple of 10W ceramic resistors (100, 150 and 200 ohms). Would I be able to use them?

@erwin_ve: Do you mean it's easier for me to swap out the choke?! Isn't that what they call the Robben Fordmod? But I also heard he is using a choke now. The Robben Ford sound is not something I'm trying to emulate, I'm leaning more towards John Mayer's sound. And yes I know, he's using SSS for his cleans with now sag what so ever I guess, but I like an amp to have a little squish:-)   

That's the filament wire; if you put a resistor there, it probably will burn.

The one Gregg is talking about is probably the one between the 345 wires.
I would be reluctant to use it, because you raise the ground potential. With a shared CT grounding for the filaments you'll risk hum. But then again I'm not a EI.

@Hoffe; you wanted sag. I didn't mention Robben Ford. I'm trying to help you, not turn your amp in #102. Btw I don't like a sag resistor in this amp unless you play at small room levels.

@erwin_ve: Thanks for the advice. Yeah you didn't mention Robben Ford:-) But I read another thread were they switched the choke for a resistor and called it the Robben Ford mod so it was just an assumption from my side, no hard feelings:-)

I just play at home at the moment so a sagresistor would be a blessing, but maybe on a switch so I could take it out of the circuit when playing on larger stages.

Could I use the groundswitch that is not used in the HRM to mount the resistor?

cheers
Thomas

You're absolutely correct, I had misread the email I recently got from Nik about this very thing.

I should probably stay out of technical discussions about these amps - they're not really my area of expertise.

Hoffe,  It is indeed center tap between  the HT feeds coming out of the transformer (the 345 volt lines) that is used for the sag resistor. As far as value goes, i don't know as i haven't gotten the amp yet. Nik is setting mine up to use the ground switch to switch the resistor in an out of line.  Putting the resistor in my amp was actually Nik's idea. I had asked him if there was a way to add a tube rectifier and be able to switch between the tube and SS rectifier, but since there is no 5 volt tap coming out of the transformer used in the overtone series, it isn't possible.

hope this helps!

and sduck, didn't you build your HRM? That makes you WAY more qualified than me!  ;D

Well yes, but that doesn't give me the right to get my nose in technical matters like this. Especially if I get one small detail like this wrong! I may have built one fully functional guitar amp, but I'm not nearly on the same playing field as some folks here who have been messing with these things for years.

However, if you visit the modular synth forums, I'll be more than happy to help you troubleshoot your DIY synth problems - that's my actual area of (some) expertise!  8)

Yes you can use the groundswitch. However you have to take care with the wiring. If you're crossing other wires(like filaments) you have a serious problem.

here's how nik wired mine...