Input regarding possible mods

[jckid649]

I have had several issues with my ceriatone build from day one.

The first of which is that the gain is way too hot and the distortion unusable past 7 on the volume.

Secondly mine is far too boomy (bass heavy). Even when I dial the bass to 0 it is still too thick. Even cutting coupling cap values has had little effect on this.

Overall it is also too harsh and not the creamy woman tone that I want. I met a tech from California that I shared the build guide, layouts, and schematics with and asked his advice. He was quite shocked and perplexed with some things in the schematics that he thought didn't make a lot of sense.

First he noticed the tone stack resistance being 2.25 meg was way too hot effectively "slamming" the signal. He suggested possibly reducing the value of the bass and treble pots to as low as 250k for more subtle control over the tone and reducing the excessive gain that I'm experiencing to a more manageable level.

Also he suggests jumpering the middle tab and unused outer tabs of the middle pot and bass pots (each individually, not together) to prevent mid range bleed and create a cut for each of the tone controls (providing more control over each tone pot).

The next thing was the 500pf treble cap and choice of 500pf/100pf bypass. He states that it makes no sense to have the treble cap at 500pf since it pre-sets the roll off. He suggests going down to 250pf for the treble cap stating you will never even be able to use it all with that anyway.

He also said that the 82k plate resistor in the PI should be upped to around 91k since 82k may be to harsh of an offset/imbalance.

Also nix the 10k cath and make it a 1.5k just like the first stage but drop the cathode cap at the second stage or if you feel frisky keep the cap and/or play with the cap value and add a 100k pot between that cathode set and ground to form a variable gain control.

He also talked about throwing in a 10k resistor between pin 2 and the volume pot on the first stage and another 10k resistor between pin 2 and the 150k resistor on stage 2 (can't remember what that was supposed to do). He also suggested changing the slope resistor to 150k as well.

He states that bias should be 44ma at 70% for the EL34's.

Has anyone tried or know if any of these changes have been done with good effect? Ideas or opinions would be appreciated.

[John_P_WI]

Most of the mods mentioned are rather heavy handed and you will lose the character of the amp. I'm not going to look up the Ctone scheme, but a lot of gain can be dumped after the 2nd gain stage with the 150k to ground on the conventional scheme. There are lots of ways to be more subtle and keep the character. I for one would question 44ma for 70% dissipation without knowing the exact plate voltage.

[M Fowler]

Is your Express using Ceriatone transformers?

I had a Ceriatone Express and it was an aggressive loud amp for sure but still all Trainwreck.

The mods your tech suggested have been done before and schematics can be found on this forum and was recently posted. I think there are 15 different schematics or more.

The problem is your building something not Trainwreck when you change out pot values etc.

[xtian]

First priority should be to get the gain under control. As John said, use the voltage divider to reduce gain to a manageable level.

First he noticed the tone stack resistance being 2.25 meg was way too hot effectively "slamming" the signal.

I've never heard this idea before. Any merit?

[jckid649]

Most of the mods mentioned are rather heavy handed and you will lose the character of the amp. I'm not going to look up the Ctone scheme, but a lot of gain can be dumped after the 2nd gain stage with the 150k to ground on the conventional scheme. There are lots of ways to be more subtle and keep the character. I for one would question 44ma for 70% dissipation without knowing the exact plate voltage.

The board layout is identical on the ceriatone layout and 70% was at 395v.

What other suggestions would you give in contrast. I've basically parked my build in a corner and it's not being used because I've not been able to get it the way I want it.

[jckid649]

It is indeed using the ceriatone trannys. I've been considering getting some from RJ to see if that improves the quality of the sound.

If John is referring to the 150k at R7 to ground mine does have that.

[geetarpicker]

Truly your tech does not sound familiar with the Trainwreck circuit.
If your amp has way too much bass with the knob off it truly sounds like you have some build errors. As far as coupling caps changing the single .002 cap up or down will usually have quite an effect on the low end.

[M Fowler]

https://tubeamparchive.com/files/wreckxpr.pdf

[jckid649]

Truly your tech does not sound familiar with the Trainwreck circuit.
If your amp has way too much bass with the knob off it truly sounds like you have some build errors. As far as coupling caps changing the single .002 cap up or down will usually have quite an effect on the low end.

I have unfortunately addressed all the lead dress issues that have been previously suggested by others on the site and have reduced caps to the lowest levels I could without sacrificing tone and it's still too bassy. Not to mention that the gain is completely unusable past 7 or 8 on the volume dial. The amp is a little harsh but decent overall yet it just breaks up way too early.

[M Fowler]

Might just have to use lower gain preamp tubes. I'm quite sure I was using 5751 in V1 & V2 and 12AT7 in V3.

I even changed the OT primary between 6k6 and 5k2 to try tame it.

[jckid649]

Might just have to use lower gain preamp tubes. I'm quite sure I was using 5751 in V1 & V2 and 12AT7 in V3.

I even changed the OT primary between 6k6 and 5k2 to try tame it.

I did play with the 6k6 and 5k2 primaries and I think I ultimatly felt that the 5k2 was a little tamer.

I have a RFT 12ax7 tested for low microphonics at V1, a 7025 at V2, and a NOS GE 12ax7 at V3. I have considered trying the 12AT7 mod that I've read about.

[geetarpicker]

Double post...

[geetarpicker]

Typically the sweet spot on a TW volume knob isn't dimed or even much passed 7.

It's not a Marshall plexi where dimed is the norm. Yes it may seem strange to have an amp that sounds like it's fully cranking when only on 1/2... That said many folks build these amps with pots that ramp up WAY more quickly than the pots Ken used, and that can be a problem with what to expect from the controls. On my '85 Express for example it's almost still clean on 1/2, and from 7 to 10 there is a lot of gain left to go. A good volume pot taper in these amps would be a 1 meg pot that only reads about 100k at half rotation. Same goes for all the audio taper pots in the amp, and even the tone controls can add a ton of apparent gain if they come on really quick and are effectively cranked when they visually appear to be at modest levels.

I'd suggest unhooking your volume pot from the circuit and measure it's value at different settings to see what sort of taper it actually has even if it is labeled "audio" taper.

Truly though I'd double check your build before you start modding. I expect either there are some errors, or you simply were expecting something way different than these amps are all about.

[jckid649]

Typically the sweet spot on a TW volume knob isn't dimed or even much passed 7.

It's not a Marshall plexi where dimed is the norm. Yes it may seem strange to have an amp that sounds like it's fully cranking when only on 1/2... That said many folks build these amps with pots that ramp up WAY more quickly than the pots Ken used, and that can be a problem with what to expect from the controls. On my '85 Express for example it's almost still clean on 1/2, and from 7 to 10 there is a lot of gain left to go. A good volume pot taper in these amps would be a 1 meg pot that only reads about 100k at half rotation. Same goes for all the audio taper pots in the amp, and even the tone controls can add a ton of apparent gain if they come on really quick and are effectively cranked when they visually appear to be at modest levels.

I'd suggest unhooking your volume pot from the circuit and measure it's value at different settings to see what sort of taper it actually has even if it is labeled "audio" taper.

Truly though I'd double check your build before you start modding. I expect either there are some errors, or you simply were expecting something way different than these amps are all about.

I have to respect your opinion since you are one of the rare privileged few who both knew Ken and actually possess original TWs. I suppose my ear is somewhat deceived in its expectations by the highly compressed YouTube audio. I'm sure my lead dress Iisn't perfect but it's as good as I could get and I've totally eliminated all the major issues people have with noise, oscillation, and general uncontrollability.

It is possible that some of my issues aren't as big as I assumed. Perhaps some tube swaps or different speaker/cab configuration may yield an entirely different animal. I am running it as a 1 X 12 combo with 1 65 watt Scumbag and SED winged Cs in the power section and the 12 ax combination that I mentioned above.

The only thing that perplexes me is the excess bass despite all the mods mentioned here.

[geetarpicker]

Sorry if I was a bit harsh in my prior reply. It just struck me SO odd for an Express to have too much low end with the bass knob off. That really makes me question something may have been missed and I'd truly search high and low throughout before I'd start any mods. Like I mentioned you also might want to check your pots, because if you have pots that come on too quickly a basic setting of all knobs on 1/2 could be totally different and much gainier than expected. For example if one built a TW with linear taper pots you would probably need to have the volume, treble, and bass pots set on just "1" to get the same sound a TW running slow analog taper pots with everything on 1/2. Slow taper meaning about 10%, where "1" on the dial would be about 100k or 10% of the full 1meg value.