ceriatone jtm 45 kit

cmb · Post by **cmb** » Thu Oct 04, 2012 9:35 pm

have a ceriatone jtm 45 kit this is my first amp build . i couldnt find any instructions so i used metros but looking at the ceriatone layout iam finding alot of small (or mabey large?) differences so if anybody can help answer my questions i would appreciate it. first the indicator light in my kit is only a 6v light i already have it wired like metros 120v . 6v supposed to wirer to the heater windings would i be better off to find 120v lite or rewire? also ceriatone layout showes 1uf resistors beetween pin 4 &5 and 6&8 of rectifier tube socket. mtro does not.why ? Also ceriatone swiches are 6 pin (3 terminals on each side top to bottom).they are showing .047 resistor beetween top and bottom pin and a 100k resistor beetweenmiddle and bottom pins on the st5and by swich. why the differences and what will work best. the board came pre populated and wired off but everythig there looks pretty mutch the same except routed a little differently. also different a resistor from pin 5 of both power tube sockets (5.6k)to the front of the 1st 2 signal caps on the boardand a 1k resistor pin 6 of the left (v4 i think)to the board.hope someone can help answer these question . i hope i diddnt buy ajunk kit. i want it to be a nice peice when i am done andf want it to be as accurate as possible also dont want to fry it on accident .hope i havent asked too much at once any help woulod be appreciated , thanks

neikeel · Post by **neikeel** » Fri Oct 05, 2012 9:24 am

Welcome to the forum.

You have not bought a piece of junk, teh Ceraitone kits that Nik puts together are fine, they are not as good as the ones George used to do but as he does not do them any more....
The Mojo ones look ok and the Weber ones are ok but are at the 'value' end of the market.
http://ceriatone.com/images/layoutPic/m ... iatone.jpg
You have used some odd terms so I take it you are a beginner?
The items on the rectifier are diodes to help with poor quality GZ34s.
The switches are dual purpose so have extra poles (on/on capability as well as off/on).
The 0.047uF is a capacitor, that and the resistor are there to minmise off/on pops.
The 6.3v lamp is a direct hook up to the PT lugs of the heaters, or if they are wires, not lugs to the rectifier socket , same lugs as the heaters - do not hook it up as te 120v - it will go ffut!
The 5k6 resistors on pin 5 are called swamp resistors and are a good idea.
The 1k 2W between the board (from the screen supply) and screens drops the voltage a little to the screens, again eases the life of new prodcution KT66s. Early JTM45s had them with 470R screen resistors, alternatively you can use 1k or 1k5 screen resistors. I like the 470R and I do not use the 1k.

cmb · Post by **cmb** » Sat Oct 06, 2012 12:32 am

sorry about the odd terminology im so much a biginner iv had to retyp this reply 3 times because i keep loosing it im no computer whiz for sure. if theres a site ic ould go to help me learn more about resistors and capacitor and therre values concerning amplifiers that would be ahelp as im having more trouble understanding this than i thought i would. also more questions 6v lite wires to the yellow wires to the rectifier socket or the green to the heaters(im using metro pt and ot) . areb the diodes on the rectifier socet nessicary if i use a good quality tube , as are the ones on the standby sw as im not even sure if i have these.do the swamp and screen resistors affect thje sound of the amp to some degree or is this something i should worry about tweeking later thanks again

neikeel · Post by **neikeel** » Sat Oct 06, 2012 3:57 am

Usually the green wires are 6.3v to the heaters of output and preamp valves only.

The yellow wires are usuually the 5v heaters to the GZ34 rectifier only.

The lamp goes to a 6.3v pair.

No the cap/resistor across the switch are not vital, nor the diodes across the rectifier.

I strongly suggest you use some screen resistors (3w flameproof) and the swamps.

arledgsc · Post by **arledgsc** » Sat Oct 06, 2012 12:55 pm

No you did not buy a hunk of junk. Many people love Ceriatone and I built a couple myself. Ironically the Ceriatone amps are my favorites having spent countless hours tweaking them up for the best sound. But Neil is correct as they not quite up to MetroAmp quality - transformers (and their location) being the my #1 complaint. I don't particularly like the supplied Ceriatone kit wiring so my suggestion would be to obtain some proper top-coat wires. Ceriatone faceplates are very nice but be extremely carefully if you have to drill large extra holes. The faceplates are brittle and can easily crack when a drill is applied (personal experience!).

My biggest Ceriatone headache was on the JTM50. As soon as the Mains were closed I got low level hum out of the speaker. The hum persisted even when no tubes were installed. Turns out the output transformer was cross coupling magnetically with the power transformer. I tried a lot things to lower this hum including trying a different OT, mu-metal shielding, grounding, rewiring, etc. Nothing was effective until I physically moved the output transformer farther away from the power tranny (about 1/2"). It was a big job to relocate the transformer but now the amp is totally quiet. Really like the amp now but what a pain in the ass. The JTM50 is so customized I no longer call it a Ceriatone LOL.

With that said for a first amp just build it up with some well thought through changes (if any). You will gain a lot of valuable experience and promise you will be pleasantly surprised by the results. Don't fully judge the amp until it settles in and then think about getting some better valves as your first tweak. Mods are pretty easy once the amp is built and you have some experience. Good luck with your build and this forum is here to answer any questions. Scott

neikeel · Post by **neikeel** » Sat Oct 13, 2012 11:01 am

He seems to have disappeared.

We were nice to him were n't we?

cmb · Post by **cmb** » Sat Oct 13, 2012 9:44 pm

no i havent dissapered. have been busy at work also spending alot of time over at the cave working on my amp.i have no internet over there . and its hard to be in too places at once. my build is together but im having some issues hope you guys can help. got everything completed and went through the preliminary tests as according to metro istructions.everythig powers up ok no blown fuses or anything like that. all voltages seem to be within limits on all valves but cant seem to get a bias reading, mabey its my multimeter? you measure in dc millivolts not amps right? no noises or humms or anything like that. this probably wasnt smart but i plugged into it with the bias set cold and sound comes through but it is very quite on 6 or 7 as in no volume very soft this thing should rip my head off on 7 right? im going over later to check all wireing and solder connections again, but i think iv looked it over pretty good but am going to go over it as many times as it takes i guess.if any one can think of anything to check or where to start trouble shooting let me know any help is appreciated as always.by the way neil and scott you guys have been very helpful and i appreciate it thanks again clint

toner · Post by **toner** » Sat Oct 13, 2012 10:35 pm

cmb wrote:...but cant seem to get a bias reading, mabey its my multimeter? you measure in dc millivolts not amps right?...

If you are using 1 ohm resistors to measure bias (most likely, as the Ceriatone layout includes them), yes, set the meter to DC millivolts and connect the meter common (ground) lead to the chassis and the positive lead to pin 8. Make sure the amp is in "play" mode (not on standby) with a speaker load connected.

Regarding the low volume, it's hard to say but a common error is using a 470k resistor on the PI cathode (connects to V3, pins 3 and 8 -- in between two 1M resistors). It should be 470 ohm (yellow-violet-brown), NOT 470k (yellow-violet-yellow). Not sure if that's your issue but it's worth checking.

cmb · Post by **cmb** » Sun Oct 14, 2012 12:49 am

im sure the 470 ohm that connects to pin 3 v 3 is right . ceriatone uses brown resistors so the browns are vere hard to tell by my eyes but im 98% sure it is the right one . checked all my wiring and solder connections again tonight and once again cant find anything out of place or a bad connection. checked my voltages again and wrote them down they seem alittle high now that i recorded them but dont think they are to far out of specs. here they are v1 p1-210; p3-1.7;p6-203;p8-1.7 v2 p1-154;p3-1.2;p6-317;p8-164 v3 p1-235;p3-45.3;p6-220;p8-45 v4 p3-455;p4-453;p5negative 51;p6-455 v5 p3-455;p4-454;p5negative 51;p6-455 ( sorry about listing these like this hope it not to hard to understand was going to try and make a nice neat chart but my computer skills are somewhat lacking) voltage at standby sw is 450 with the standby on. bias voltage as icould read it tonight was about 30 mv witth the pot about 3/4 of the way up and it wouldnt go any higher . going to get a different multimeter this week and test bias again. still no volume.could i have got a bad set of tubes ??? how would i know? would that explain the funky bias? .seems like i keep coming up with more questions than answers tonight.

thanks to everyone again clint.

toner · Post by **toner** » Sun Oct 14, 2012 3:30 pm

If your readings are accurate, the bias is around 52% so it's not too far off and shouldn't cause the lack of volume. You'll probably need to change a bias resistor to get it in range but don't worry about that yet.

I assume your heater voltages are okay since you omitted them.

Something else must be going on. I doubt it's a tube but that's always a good place to start. Try swapping in a different 12AX7 in V1, then V2, V3 and see if it has any effect.

Post some pictures and someone may spot something.

cmb · Post by **cmb** » Sun Oct 14, 2012 6:31 pm

i will try to get some pics on here as soon as i can thanks again clint

arledgsc · Post by **arledgsc** » Mon Oct 15, 2012 10:23 am

Now your are getting down to the fun part. Pictures would be very helpful. Measure the 470 ohm resistor in the circuit after bleeding the power supply caps. Verify the phase inverter long tail pair 10K ohm resistor is connected to the Presence pot. This should be completed with a wire on back of the pre-wired Ceriatone board (see the layout for location). Also verify the ground connection to the Presence pot. May also be something else upstream from the phase inverter so let's see some pics.

I think it is wise to verify the bias voltage readings with another meter. Sometimes lesser quality meters have a hard time accurately reading this voltage. I notice the Ceriatone bias pot value is 50K ohms where 25K is standard. Once the adjustment range is found 50K ohm will make the adjustment courser meaning small tweaks make larger bias changes. The 56k ohm resistor preceeding the pot sets the range. But first things first. Let's locate the problem.