Ceriatone Forum

Most folk here seem interested in altering the sonics of this wonderful amp in one way or another.
For those that don`t feel inclined or experienced to get involved with a soldering iron, there`s still plenty of scope to play with shaping the OTS tone character.
This does include removing the chassis from the cab, but that`s no big deal.
Just keep in mind being safe around internal components & electricity...!!!

Locate the small cap on the back of the master volume pot.
There`s diagrams elsewhere on this forum that shows the layout of this amp.
Snip one side of the wire from the cap very close to where it is soldered to the master vol pot. This easy mod will even out the highs at lower vol levels & works very nicely..!
The mod can be easily reversed with a hot iron, but chances are you`ll probably stick with it clipped as the results are pleasing.

The 12AX7 pre tubes that come stock in the OTS can easily be substituted
with compatible tubes of lesser gain factor & warmer character.
I personally do like a 12AX7 in the first position (V1) but find the stock JJs produce a very focused  but narrower band of tone in (V1).
I like a Blackface clean tone and a 12AX7LPS (Long plate spirial) in (V1) does the job nicely for producing a broader & warmer sound for the clean channel.

With the O/D channel, a 12AX7 (V2) drives the amp with a hard edged tone that alot of people on this forum seem to be trying to tame one way or another.

Substituting the 12AX7 for 12AY7(60%) of the 12AX7 gain factor, or even a
12AU7 (20%) really warm up the O/D channel nicely, but these lower gain tubes also allow for more scope when fine tuning and dialing in your prefered O/D tone.

This is where the internal gain trim pot needs to be adjusted to suit.
Most folk on this forum seem to agree the best O/D tones come from the trim pot being set somewhere between  9 o`clock & 11 o`clock positions.
(Keep in mind this is with a 12AX7 in V2)

When using  lower gain pre tubes like the 12AY7 & 12AU7, the trim pot will require adjusting up to compensate for the subsituted tubes lesser gain character.
This is where the fun starts and a 12AY7 will probably require a small lift in gain on the trim pot, but you have more scope to find your sweet spot/s.
The 12AU7 will require even more gain adjustment to compensate, but once again
you`ll have a broader range of gain to play with and both these two tubes are much warmer sounding to me.

I`ve just tried a 12AU7 with the trim pot set way up in the 3 o`clock position & that was VERY GOOD. The level & ratio knobs worked together with a broader range for fine tuning your overdrive tone & with more flexability to the user.
If anything, I think the tones are more D-mble like & less of a narrow band gain tone from the use of a 12AX7.
12AX7s are good in the right application, but the down side is the high gain factor
drives harder and can often sound grainy.

I can recommend trying these easy mods, especially if your looking for more
D-mble than Marshall, as i would assume most of us here, are..!

I have tried a 5751 in (V2) but feel it sounds less warm than the 12AY7 or 12AU7.
It was a bit sterile to me.

I hope this might be of help to those looking to experiment and achieve different tones.
Cheers.

All good points, and the easiest thing to try even if you are happy to jump in with a soldering iron. I've had amps in the past that really didn't do it for me with 12AX7's in but sub-ing those for a 12AY7 or 5751 has transformed the tone..!!

Many Thanks for you tone tips. I have a later one from Nik that has the zucker mods but it is more gain and not as clean as I would like. ???  I think I will give your suggestions a try. It sound great with my Les Paul but I am having a harder time with the Strat Tones. I really do not want to alter it too much. Do you have any before and after sound clips?

Thanks,
Danny

Too much gain, try a "weaker" valve in V2 (5751 or 12ay7) see what that does for you...worked for Stevie!!

This is a great topic!!

I have a small problem I want to put forward. It seems I get a nasty (fizzy) endge on my OD when I turn up the gain. Even more so when I use humbukcers. I have the latest lay-out. My OD trimmer is set at about 11 o'clock. (I also use the Kleinulator)

I don't realy need a very high gain. Sounds very nice set at 4. But still it's a shame it starts to sound bad when I turn it up. maybe this is common with this amp?

One more thing. Would it be bad to use one tube of a different barnd? I have JJ's, they don't make the LPS tube as far as I can tell.

Cheers
Steven

 

You can use any brand of valve. Some have different audio properties than others

Based on whats been noted here I'm going to try every variant of the 12a_7 series in V2. I've currently got a 5751 in the there and prefer it to a ax7. Maybe an ay7 will be better still! I'm very glad I moved the OD trimmer to the rear panel, It really would be a pain taking the chassis out of the case very time.

Will I need to rebias the amp after changing tubes?

Not pre-amp tubes, no.

If you take the chassis out and place it carefully on some supporting blocks, you are then in a position to access the internals.
Connect the chassis up to your speaker cab and away you go... it`s time to experiment.
Just remember though... (amoung the enthusiasm to explore tone).... the amp is alive when plugged in and turned on...!!!   Always be very cautious.!

With the chassis sitting supported & the tubes facing down.. (the same way it is mounted into the head cab) you can easily locate the internal trim-gain pot and adjust as you go.
It will always pay to switch the amp off before putting your small flat-head screw driver in there to adjust the gain trimmer.

It is also very accessable to change the pre tubes in this position, but once again switch the amp on standby & then off at the main to change any preamp tubes.

This way you can try new pre tubes of your choice, fire up the amp & try things.... shut it down again & adjust the trimmer as required.
Fire the amp back up and away you go to repeat the proceedure until you`ve fine tuned to a point that you`re happy with.

Always be careful and take your time when dealing with the amp internally.

I would suspect a 12AY7 will be the one for most guys looking for that warmer, less grainier tone.
12AY7s are usually it little more expensive than a 12AU7, but with the extra gain value it has and the warmth it supplies, it should help you achieve a more refined O/D channel tone with (in my opinion) more D-mble like character.
But you should also try a 5751 as tone is very subjective and you might just love what the 5751 has to say..!

Sovteck does a 12AX7LPS & this is the only sovteck tube i`ve ever liked.
The character of the LPS is warmer than other 12AX7s and a little more open sounding and vintage toned.
Good for (V1) i feel.

You just might be surprised at the difference a change of pre-tubes can bring.

Cheers & goodluck with your tone quest.

Thanks for putting that in simple terms with easy instructions. ;) I suppose I am like many folks here that has never worked much with the internal parts of an amp. I appreciate the words of caution about the voltage when opening up the amp. This has been very helpful advice and I will change the tubes and tweak the trimmer and see what that does for me. I am not trying to copy anyone tone because we all know that is in the fingers but I do like the clairity and sweet overdrive of Robben Ford and Tomo Fujita.

I looked at some information on 12AY7 tubes and there seems to be some differences in the types of Tubes. For example, The GT 12AY7 says that there is only a slight drop in gain where the EH 12AY7 decribes a much lower drop in gain with smoothness. Please let me know what 12AY7 you recommend?

Thanks,
Danny

Where does the 12AT7 fall in relation to the 12AX7 - 12AU7?  And in relation to the 5751?

Just to be sure, if the OTS is tubes up & you're looking at it from the back (tubes "in front", OT/PT "in back"), V1 is furthest from the pwr tubes, V2 is in the middle, and the tube closest to the pwr tubes is the PI?

Thanks!

V3- is closest to the power tubes. This is the PI.(Phase invertor)
V2- middle tube. Overdrive channel pretube
V1- is the furtherist away from the power tubes...or firstt tube in line.

12AT7 tubes are often found in blackface fenders & used for functions like the P.I. or somewhere in the reverb driver or revcovery stage... but not so much as a tone generator.
I have tried 12AT7s in other amps before & think these are never as warm or alive sounding as the likes of the 12AY7.
You could try one but i think you`d probably be wasting your time in the OTS as this amp really asks for 12AX7s or very similar tubes.

The stats for most 12AY7s shouldn`t vary too much. I don`t think you should get too concerned about one brand of 12AY7 to another.
Just get hold of something decent like the EH or similar and try one to see if you like tne sonic result..!

I`ve tried all these tubes at one time or another in different amps & the 12AY7 is a really good choice for tone character, warmth and the ability to still have enough gain to deliver.

The 12AY7 is actually about (45%) of the 12AX7s 100% gain factor.
I had written earlier that it sits at 60%, but need to correct that.
The 12AT7 sits at 60%
5751 70%
12AU7 20 %

I've done a lot of adjusting with my Zucker version amp and it's pretty well dialed in for my Strats (Lollar Blackface p/ups) and my Les Paul (WCR American Steel set). 

See if any of this is helpful.

I have the stock Tung Sol RI 6l6GC tubes which sound fine to me.  For years I have biased my Fender amps at around 32 to 35ma with good results.  The Weber Bias Charts and others recommend as high as 46ma or so for an amp with 450v plate voltage which is what my OTS reads.  I would suggest that you bias to somewhere between 35ma to about 40ma rather than to the hottest setting.  Mine sounds good to me all through this middle range.  For now I'm leaving it set at 40ma.

I have used Weber Bias Rites for years and I like them because they are easy to use and they show both the plate voltage and the bias.

With the Bias adjusted, set the Volume (far left) to about 7.5.  Right between 7 and 8.  Set the Presence to 8.5 or a little less.  Up to this point the Presence control adds harmonic distortion by decreasing negative feedback.  At this point and above it begins to add treble and very subtle adjustments in this range can help get the kind of edge you want on your OD.

Get as close as you can to what you are looking for by adjusting the Presence and then leave these settings alone while you adjust further with the OD trimmer inside the amp. 

I marked where mine was set when I got it and then turned it all the way down (toward the back of the amp).  Then I set the OD Level control on the front of the amp to about 2 (pointing straight over to the left) and the OD Ratio all the way up.  You will have no volume in the OD channel while the trimmer is down like this.   The idea is to turn the internal trimmer back up until your OD volume matches the Clean volume when you switch back and forth.  I end up adjusting it as low as possible but up just enough so you can hear some drive in the OD channel and the OD volume at this low setting still gets at least as loud as the Clean channel.  Mine ended up at around 9 to 930 which is a bit lower than where it was when I got it.

Now adjust so you have the sound you want on your Clean channel and the drive you want on your OD channel.

I get a nice cleanish overdrive with Strats at low drive settings all the way to heavy drive with a Les Paul and the OD Level all the way up (backing the ratio down accordingly).  I usually end up in the low to mid drive area personally but this set up gives a wide range of useable settings.  You can easily shift the range toward higher gain and hotter bias if that's your preference. 

Experimenting like this will also give you an idea about how the different controls work.

Thanks for the info, Bluestone.

I'm currently using a JJ 12AX7 in V1, a NOS JAN 12AT7 in V2, and a NOS 5751 in the PI position with JJ 6L6s.  Sounds good with the internal trimmer around 10:30.  I'm very happy.

BTW, the Speaker Warehouse ET65 (their version of the venerable Celestion G1265) sounds REALLY good with this amp.  I have it housed in a supposed Fuchs 1x12" closed-back, front-ported cab.  I gotta take some pics of this rig!

Hey guys sorry to ask a dumb question but do I change all 3 of the preamp tubes?

Dumbleseeker, I wouldn't say its necessary, however, if you decide to invest in one or two NOS tubes, why not go the whole way, right.  If you're buying new tubes, EH, JJs, etc, nah, just buy the specific tube(s) you need & leave the other(s) in there.

If you're replacing power tubes, however, yeah, you should replace them in pairs (or quartets) with matched set(s). 

Best of luck!

Thanks for the advice. I ordered my tubes from www.torresengineering.com. I will let everyone know how it turns out. :)

O.K. here is an update. I put in 3 new EH 12AY7 and now have excellent clean tones and more headroom with my strat. Now I getting closer to the sound I am looking for.  8) Do I really gain much from snipping the cap on the volume control?

Did you have to take the gain trimmer up a touch to compensate for the 12AY7 in V2..?
I clipped one side of the cap on the master just as a trial.. and do think it helps to smooth the tone further especially at lower volume settings.

O.k.- I think I will snip the cap on the volume as I have read several people say they have experienced smoothier tone at lower volumes. I have not  moved the trimmer yet. What do you have yours set at? 

with a 12AY7 it`s set at about 11 o`clock position,.. but that`s with PAF type humbuckers. Single coils may need a touch more. It all depends on weather you think you`re getting the right kind of tone and gain.
A 12AY7 in V1 position didn`t have quite enough juice for me,. that`s why i went with the LPS 12AX7.  More of a rounder, vintage type tone from the LPS over the JJ12AX7.

Great Information! I think I am just going to have to play it more to decide on the gain. I have read alot of information on 6L6 tubes. Their seem to be a wide array to choose from. The JJ's I got from Nik sound good-just not sure if there is something better? Some people seem to think that the preamp tubes make the most difference and that the power tubes are only noticable at higher volumes. What are your thoughts?

Preamp tubes make all the difference in the world tonewise.  Not so much with the different brands of 6L6's.  There is a difference, but you really hear it experimenting with different preamp tubes.

Jim

Quick question, when setting the OD trimmer, which side are you looking at?  I was looking towards the inputs (the side with the arrow), but read somewhere on here that it was actually the other side that was 'correct'.  Thanks!

This is from the Layout Thread.

 Re: Overtone Layout
« Reply #30 on: June 04, 2008, 03:58:05 PM » 

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Quote from: jerrydyer on June 04, 2008, 11:04:41 AM
The two trimmers on the main board get left alone? thanx 


The right hand trimmer on the main board is the one that controls the OD channel level and is the one you'll experiment with most. The PI trimmer (left hand end of main board) is set and forget The trimmer on the satellite board that contains the FET, controls the level for that input. Most owners don't use the FET input much but you might want to just set it to a sensible level and leave it, I have mine at 9 o'clock.

Right, I've read that whole thread, however:

http://ceriatoneforum.com/index.php?topic=552.msg4245#msg4245

In this thread, bluesfenderman says that we should be adjusting the trimmer from the OTHER SIDE (the trimmer is on the LEFT hand side of the board if you're looking at the chassis with the knobs closest to you). 

So, I ask again, first, can we all agree that if we're looking at the chassis with the knobs closest to us, that the "middle" trimmer, the left-most being the FET, and the right-most being the PI, is the OD trimmer?  If so, which side should we be looking at for adjustment purposes?  I look at the side with the arrow, at least one person disagrees with that.

Thanks!

Well, upon closer inspection, the arrow is visible on both sides of the trimmer (a fact that was lost on me due to the low light I was working in).

In either case, if I'm standing in front of the chassis, with the knobs closest to me, would I adjust the trimmer as if turning it clockwise turns towards the knobs, or as if turning it clockwise turns towards the back of the amp?

Standing with the chassis open upwards, with the knobs facing you the OD trimmer is second from the left (ie the middle, well it''l be in the middle which ever way you look at it!!). Now you have to adjust it with the screwdriver entering from the right, but read the clock face FROM the left.

If you use a long electricians insulated screwdriver and are very careful you can do this while its on and someone is playing a guitar through it. Turning the trimmer all the way to either end will tell you which is the 'low' end ie 7 o'clock. Once you understand which is the low end you can adjust it looking from either side. But be careful.

Thanks, Hywelg!

I have a THD Bivalve 30. It allows me to quickly change tubes without biasing and hence allows me to A/B tubes of all kinds.
My favorite 6L6s on a consistent basis are the JJ's. An extremely close second would be the Svetlana Winged C's (not SED). The Winged C's just are not as consistent as the JJ's. My main gigging amp for many years has been a '66 Super Reverb and I usually run the JJ's in it. I buy them and my JJ pre-amp tubes from Bob at Eurotubes. I highly recommended BOB at Eurotubes. I have also used TAD 6L6's in my Super Reverb. They sound very, very,  good, but they only last 3-6 months, for some reason. I also have a Fender Bassman clone that only sounds good to me when I am running the JJ 6L6s.

The effect of pre-amp tubes is far more noticeable. That said, you will notice a tone improvement with the right output tubes. Moreover if you have crappy output tubes, you are wasting your money on upgraded pre-amp tubes.

Bottom Line: I recommend the JJ's but do try a couple other and see what you think.

I must say that I was a little dissapointed when I first got my Overtone. :-\ Afterall, I had waited 13 weeks and mine did not sound like any of the clips I had heard. Little did I know that they all require some fine tuning. However, that is also what makes them great amps. They can be tweaked to your liking.  ;) I would suggest that anyone wanting to change their tone to try different preamp tubes. Huge difference!!!! I wanted cleans so I change all of them to EH Ay7. This created great cleans but not enough grind on the OD. One thought was to turn up the internal trimmer but decided against this. After reading a lot of information I decided to set the trimmer on 10. So in doing so I need to change more tubes. Now V1 has tung-sol 12ax7 ,V2 has 5751 and V3 has EH Ay7. Now it sounds killer and I am considering changing the JJ power tubes to SED 6l6GC. Many thanks to all of you who have guided me in my tone quest. It will never be over but I am getting closer everyday ;D

Very Interesting pre-amp set up. I will have to try that out. I would recommend the original Svetlana Winged C's rather than the SED's. SED bought out the winged C brand name  and they are not the same tube. The Svetlana Winged C's sre very musical.

I've had my OTS for a couple of weeks now and am trying different pre-amp tubes and speakers. The problem is I made the mistake of thinking the bias dial was an trimmer for the overdrive or what ever. I got some info here in biasing with a meter I have at home, and so if I can work that out I'll be able to set the bias. But I'm not sure exactly where the internal trimmers are and which ones to adjust.