Ceriatone 36W mods?

[George61]

I would have posted this at 18watt.com but there are a lot of members on 18watt.com that are highly opinionated and this seems to be a much more affable group.

I am fairly new at amp building and my first amp was a Ceriatone 36W EF86, which is a double-bubble 18W with a TMB channel and an EF86 channel. I considered the project a success because the amp actully works but I made some mistakes. The amp is a bit fizzy.

The biggest mistake is my can of worms lead dress. I was going to rewire the connections to the turret board with 20 AWG solid core wire. The turret board came prewired with Teflon mil-spec wire. I was also planning on replacing the output transformer with a GDS/Heyboer 36W. I was also going to replace the coupling capacitors with Sozo Vintage capacitors. To try to tighten up the bass a little I was considering a 90R and 2200uF cathode resistor and capacitor for the EL84's. I was going to eliminate the circuits that don't work; half-power and negative feedback.

I considered gutting the amp and converting it to a Richie Hall 36W TMB but I like the EF86 channel and would like to get this amp to work a little better. My Ceriatone is very close to the mid 60's British Invasion/San Francisco electric-folk clean chimey sound that I am trying to get. My sealed speaker cabinet was not a good choice but the Scumback speakers (M75 and H75) were. I have started to acquire parts to build a Trainwreck Rocket copy but I want to try tinkering with my Ceriatone.

Does any of this sound like a worthwhile thing to do?

Thank you,
George

[Cliff Schecht]

I don't get what you are trying to do. Do you want to rebuild this into a TMB 36W amp or were you considering converting it to a Rocket? You want to keep the two channels?

Sounds like most of the stuff you are tweaking are things that may not need tweaking (or are upgrades, not necessarily fixes per se). Sozo caps and a Heyboer output transformer probably won't magically turn your amp into a great sounding unit, you might be having circuital issues that need addressing first..

FWIW we love to see pictures around these parts .

[M Fowler]

I would just clean up the wiring making everything solder good, short leads and look good.

The half power setup works very well in this type of amp, I have done that in three amps so I can help you sort that circuit out. It should have a 50R or 60R power resistor for 36w setting and another power resistor larger to make up the 130R to 150R different for running on 18w setting and the bias resistor is wired common to both settings. I think I used 62R and 72R in my amps. But going up closer to 150R total for 18w would be better.

The fizz your hearing could be that the amp is not bias correctly.

Mark

[Cliff Schecht]

The fizz your hearing could be that the amp is not bias correctly.

Mark

Or a leaky coupling cap, a bad solder joint, a bad tube, etc.. Could be lots of things.

[M Fowler]

Yup you got that right Cliff

[Gibsonman63]

I would agree with Mark. No matter what else you do, you need to clean up the lead dress, so you might as well do that first and see where you are. Check your bias and roll some tubes through the amp. Even tubes of the same brand and type can sound very different. The other huge tone shaping thing to try is different speakers and/or cabinets. Then you can approach the rest as fine tuning.

[George61]

I don't get what you are trying to do. Do you want to rebuild this into a TMB 36W amp or were you considering converting it to a Rocket? You want to keep the two channels?

What I am trying to do is get my Ceriatone to work a bit better and maybe learn something in the process. I considered converting my Ceriatone to a "Richie Hall Plexi" but I decided to skip that because I don't want to lose the EF86 channel. The Trainwreck Rocket project is a totally seperate amp from scratch.

The half power switch may work but it is of no interest to me as I am primarily interested in the clean tones the amp is capable of. In fact, the amp doesn't have enough power for me. Actually the amp may have enough power, it may be more accurate to state that the amp doesn't have enough clean headroom for me.

[Phil_S]

Show us a picture or two of the inside. Maybe someone will spot an obvious problem.

I would not be quick to replace the teflon jacketed wire with #20 solid. It is quite likely that you can work with what you have. Besides that, #20 is rather large and may prove to be impractical in other ways. It is a bit harder to solder well, for one thing, as it sinks more heat. You might also be making a mess of things when you apply heat (soldering iron) to remove the existing wire.

One other possibility is that the 18W family of amps is known to sometimes suffer from fizz for no obvious reason. I suggest you go back to 18watt.com and search for the Paul Ruby buzz fix, which is done with zeners on the PI, if I recall correctly.

[George61]

The other huge tone shaping thing to try is different speakers and/or cabinets.

This may be a big factor that I am overlooking. I have two 100W Scumbacks as I was going for maximum clean headroom and I use the cabinet with higher powered amps. Could it be that I am not getting any cone breakup and that is adversely affecting the overdrive sound? My Mesa-Boogie likes high power speakers. Tonewise, the Scumback's blow my beloved EVM-12L's out of the water. The Scumbacks are much smoother. This vintage British amp thing seems to be a whole new ballgame.

[Gibsonman63]

The other huge tone shaping thing to try is different speakers and/or cabinets.

This may be a big factor that I am overlooking. I have two 100W Scumbacks as I was going for maximum clean headroom and I use the cabinet with higher powered amps. Could it be that I am not getting any cone breakup and that is adversely affecting the overdrive sound? My Mesa-Boogie likes high power speakers. This vintage British amp thing seems to be a whole new ballgame.

Very possibly. You might try a more effecient speaker. It could be that the speaker isn't breaking up, but you have to push the amp into distortion to get any level out of it. Check the effeciency rating of your speakers to be sure. I have a Scumback in a 1x12 cabinet. I have noticed that the speaker seems to be loosening up and sounding better over time, even though I had the break in done at the factory.

Personally, I like the Jensen gold-backs for clean and chimey, but there are others.

Bug your friends. Try every cabinet you can get your hands on.

[Cliff Schecht]

The other huge tone shaping thing to try is different speakers and/or cabinets.

This may be a big factor that I am overlooking. I have two 100W Scumbacks as I was going for maximum clean headroom and I use the cabinet with higher powered amps. Could it be that I am not getting any cone breakup and that is adversely affecting the overdrive sound? My Mesa-Boogie likes high power speakers. This vintage British amp thing seems to be a whole new ballgame.

Very possibly. You might try a more effecient speaker. It could be that the speaker isn't breaking up, but you have to push the amp into distortion to get any level out of it. Check the effeciency rating of your speakers to be sure. I have a Scumback in a 1x12 cabinet. I have noticed that the speaker seems to be loosening up and sounding better over time, even though I had the break in done at the factory.

Personally, I like the Jensen gold-backs for clean and chimey, but there are others.

Bug your friends. Try every cabinet you can get your hands on.

I love how my Rocket sounds through my 1x12 closed back alnico SRO cab. I've had similarly pleasant experiences with 12L's. EV speakers tend to be (relatively) flat throughout their response and therefore will really reveal what an amp sounds like (as opposed to what a speaker sounds like through the amp). If your amp sounds harsh and shrill through EV's, then your amp is harsh and shrill..

Then again I think everything sounds good through that SRO .

[George61]

You might try a more effecient speaker. It could be that the speaker isn't breaking up, but you have to push the amp into distortion to get any level out of it.

Efficiency is not a problem. The cabinet is very loud. At about 2 1/2 on the volume where the amp starts to break up the amp is very loud. At 5 on the volume the amp is in the vicinity of the threshold of pain but the tone is fizzy. I may be exaggerating on that threshold of pain thing. This whole post is actually pretty much moot as I use the amp at a volume of 1 1/2 to 2 and it works pretty good there but I am new at this and this is my first amp that I built and I am trying to learn. Somewhere I went slightly wrong on this build.

A factor I forgot about is starting at about 8 on the volume the amp starts to squeal. Someone told me to try adding a bottom cover to the chassis. Not that I would ever turn the amp up to 8. If I want distortion I will use my Mesa-Boogie. My Boogie has that 90's chainsaw sound that I like.

[Weathered]

My guess is that if you have squealing at that point on the volume, you've got parasitic oscillation somewhere in the amp, which may be contributing to the fizz you hear.

I would double check the lead dress and see if that clears up the problems before going whole-hog into mods. I would also be sure to learn about lead dress before starting on a Wreck, since they are very sensitive to proper lead dress.

[M Fowler]

Well I tried to help with 18w/36w switching but you blew that ideas off, no problem not really needed, But I have to ask what is this all about?

considering a 90R and 2200uF cathode resistor and capacitor for the EL84's

Why 90R?

Mark

[Colossal]

I agree with Weathered that since your lead dress is suspect, your amp is probably suffering from oscillation. But I would also offer that you may also have crossover distortion in the output section. Without trying to introduce to many changes at once which will only serve to confound your efforts, first thing would be to clean up the amp. Get your lead dress dialed in and then re-evaluate the tone before changing anything else such as coupling caps or the output transformer. If you still have the fizz after your makeover, then you can consider your options.