Ceriatone Forum

Hi I'm new so go careful  :)

Just finished the Overtone HRM and have no output through the preamp. Power amp is working through return.

Voltages I have (UK) are as follows, some a little off and I can't see for looking where the problem might be.

ANY help is greatly appreciated...

Voltages:

Pin     1               2              3                 4                  5                 6                   7                8           

V1     200                          1.8                                 3.1                                      0
V2     212                          1.7                                 3.1                                      0
V3     297                           57                                 3.5                                     37
V4    0                             450                319            270                442                                  0
V5    0                             450                319            270                442                                  0


OT CT 455
HT 268 if I'm checking in the right places...

Any suggestions ?  the pin 8 of zero volts looks strange on v4 and V5 but the power amp does work. Pin 1 & 8 are tied so zero on both of those on V4 & 5....
I have some dirty pictures  : see below...

note the V4-5 was taken during the build but I think its ok - shows the build...

I assume V4 and V5 are your Power Tubes.
Pin 3 seems normal.
Pin 4 seems pretty low. Should be closer to 450.
Pin 5 should be -VDC.  Something like -45VDC.
Pin 8 should not be Zero.  Should be milli volts.  Perhaps something like .035 VDC.
Does that make sense to you?

Pin 3 is plate voltage.
Pin 4 is screen voltage.
Pin 5 is bias voltage.
Pin 8 is your plate current across what I assume are 1 ohm resistors.
Are these 6L6 power tubes?

Hi Hired Hand...

Yes the V4 & V5 are 6l6wgc from TAD.

Remember I can get output from the power amp by feeding the return of the loop and while I have not tested that bit in any real depth
it seems to work.  There is VERY low output from the regular hi input on the amp - just discernable.

Problem seems to be in the preamp section somewhere and I need a clue where to look.

Ill check these voltages again presently against what you have said and repost the results on here.

thanks for your help.

I have checked again the voltages.

They are as follows:

Voltages:

Pin     1               2              3                 4                  5                 6                   7                8           

V1     200                          1.8                                 3.1                                      0
V2     212                          1.7                                 3.1                                      0
V3     297                           57                                 3.5                                     37
V4    0                             452                319            -25                442                                  0
V5    0                             453                319            -38                442                                  0

I don't particularly get a reading on the pin 8's of the V4 and V5. It could be me - especially if the voltages should be extremely low.

I have also posted some pics of the chassis for scrutiny by anyone....

Just need a pointer where to check....

thanks


tonym

I really have not looked at any of your pictures.  But from your chart it seems like you have B+ problems with your screens, they should be much closer to your plate readings, and you have bias problems.  Your bias voltage should not have that disparity, the two readings should be very close to equal. Also, you need to have a meter that will read milli amps between the cathodes and ground.

I now have bias at 34.7 and 35.3 for V4 & V5

Is that bias voltage on Pin 5?  Those should be negative numbers.   But they will be meaningless if you cannot read the plate current on Pin 8.   You need to find out, from some of the other guys who have built this amp, what kind of voltage they have on their screens.  Yours seem very low to me, but I have never been in one of these amps.

Hi,

The bias voltage was measured with a biasmaster from TAD. After ajustments that is what I got on the meter - hence the reported reading from the bias master (uses sockets under the tubes to get the measurement). After adjustment those were the figures I got.

I also got on pin 8 of V4 & V5 71.7 mv and 70.8 mv respectively.

Not sure how to get everyone to read this?

thanks

tony

This is getting a little confusing.



Bias voltage refers to the -VDC (negative) that is on Pin 5.  But you say those numbers are positive, and that you are reading them from a "bias meter". 
Bias voltage is normally read with a DMM.
A bias meter would normally read plate voltage (pin 3) and plate current on pin 8.
What concerns me is:
1.  You are getting positive bias voltage on Pin 5. (34.7 and 35.3)
2.  You are reading approximately 70 milli amps (71.7mv and 70.8mv) and have a plate voltage of  450 volts (452 and 453).  That is pushing those 6L6 tubes really hard (about 31-32 watts).
3.  Your screen voltage just seems way too low to me.   You are dropping well over 100 volts across the screen resistors.  Can you verify the value of one of those?  I do not think you should not have enough screen current to drop more than 5 volts.

I emailed nik some pics after checking the board over and over.

The FAULT was one of the relays fitted in to it's socket the wrong way around.  :-[

A simple mistake that I simply could not see.

Yes the Biasmaster just shows a voltage (probably a - voltage) as a real voltage and for 6L6WGC they say 35 on the reading so I'm pretty much there on the bias I think.

The preamp now has output so I'll check the amp further now that 'relay short' has been found and let you guys know what I find next.

Actually, I'm quite happy about this build because up to now to get it all running I just turned the relay around and this was in fact my first amp build.

I am going to make a website with the whole story on there with a video of the whole build which I have documented since day 1.

Likely I'll show the voltage measurements when this amp is dead on and of course show any obstacles in the build etc.


The site is bought but not on line yet www.overtonehrm.com

Thanks for your help again...

Voltages:

Pin     1               2              3                 4                  5                 6                   7                8           

V1     200                          1.8                                 3.2                                     0
V2     212                          1.7                                 3.2                                     0
V3     297                           57                                 3.2                                    38.2
V4    34.5ma                    471              465            -50                466                                  as pin 1
V5    34.6ma                    468              465            -50                466                                  as pin 1

do these look better???

thanks

tony

What are your voltages on Pin 6 with V1/2/3?

erwin brings up a good point.
It looks like half of your pre tubes are not working.   You should have similar voltage on Pin 1 and Pin 6.
But other than that, yes, your voltage chart looks MUCH better to me now.  You did a good job of sticking with this. 
Well Done !!!

V1 is 216

V2 is 224

V3 is 306

all on pin 6

there was nothing originally....

 :P

PS - the bias master I used is here: http://www.tubeampdoctor.com/index.php?cPath=74

does a great job on most amps I use and it's quick and fast.

By the way - thanks all you guys for the very informative help on this forum.

Heres a photo of the offending relay.

It's really easy to get this the wrong way around - it fits both ways.

Spotted by Nik - I looked for hours  :(

But once I changed this the amp was basically running in less than 5 minutes except for lots of adjustments....

Anyway - see the pic....

These are pretty complex amps, with A LOT of components.  From your pictures, I would say you did a nice, clean job of assembly.  You really only had one big problem.  Glad to hear you are on Easy Street now.
Good Luck

Thanks Hired Hand I appreciate your comments - it was my first build....

But I am usually good with my hands...

But not as good as you with the voltages  ;)

Ill keep you all posted on this topic if I find any more stuff going on.

I had a 'funny' last night with the amp. After about 3 hours when it was hot the notes became distorted and I lost preamp output.

Im going to check forstly the tubes then for a dry joint - I suspect a dry joint. It was repeatable - I turned off for just 30 seconds and on again and the volume was back - for just a while while the amp heated again and then it lost the preamp (I reckon) volume again - distortion on the bass notes and then loss of output.


Ill let you guys know what I find for the record.

Here's the scenario so far and I'm running out of things to check  :-*

I had the amp running for about two hours and then got a fault where if you played hard and loud the first thing that happens is that the volume reduces as distortion (especially on bassy notes) is heard.

You then get an effect like there is no preamp (a signal is still heard but it’s like on low volume and no real preamp banging the signal out.)

I did the following:

1.   Changed all tubes one at a time and it made no difference whatsoever.
2.   Checked ALL grounding to the star grounds and all earths at the other end of the wires.
3.   Re soldered all tube socket wires irrespective of condition.
4.   Further ensured all grounds are tight and good.

When the problem exists (and it can remain if the guitar is not played but placed down) as soon as you try and check any voltage the signal returns (hence my thoughts on the grounding). My meter goes from whatever voltage to ground....

Voltages seem to be ok all round when I check them - but I guess they would be - the amp is working....

Another thing I have noticed is that when you get the problem, if I lift the chassis slightly from one side (any corner) so as to flex the chassis the signal returns to good.

I can’t seem to see anything amiss and wondered if you guys have seen anything like this before…

I'm not sure what to check next? Maybe it's a faulty component? But where do you start?

The amp DID work ok for that first hour or so - but I guess with the heat and everything....


Scary  :(

OK to keep the thread up to speed here's what I did next:

I spoke with Nik who said that it could be the associated boards around the amp (power, relay etc) which have been overtightened - apparently if you tighten them too much then you can get a similar problem especially if you use too much solder on the connections - it 'blobs' through the tag on the board, creates a solder ball and proceeds to distort the board when you overtighten it!

However, after slacking off all the peripheral boards so they were loose, it made absolutely no difference..  :(

So, heeding what Nik had said, I removed (at least took the screws out) and checked the connections at the BACK of the boards one at a time. It is correct that you can get this solder build up - I found one on the rectifier board, but it was not causing any problems. I cleaned off the excess solder anyway.

But when I got to the relay board (the one that had the relay wrong way round) I saw a connection underneath (it looked perfect from above) the one with the red wire you solder to it from the main board - see my picture..  that had excessive solder under the board. This connection has a wire under the board that connects to something else and that wire was not a good joint. It looked perfect from above.


I resolderd that connector and cleared off the excess from the joint and rebuilt the amp boards to their original positions making sure I did not overtighten the boards.

AND IT WORKS!

At least for now - but I'm going to test the amp further and see if it hangs in there for a longer time. It worked last night for about 1 hour.

Lastly, Ill update this thread to help others - after all that's what this board is for....

I trust anyone reading this at any time will benefit from the insight of the build - and don't forget I'm developing a website www.overtonehrm.com which will show the build from scratch, it will go in to depth about things to get right and things which typically go wrong. It will cover the order of install (in my view) and it will show you on the amp what adjusters do what! Also voltages and any other quirky stuff with words, images and video of the head, the tail - the whole damn thing  ;) as they say.

If everything goes to plan there will be another post from me confirming the amp is good.

I always choose function before form.  I HATE under the board jumpers, connections, etc.   Unless it is guaranteed to cause oscillation, or some other type of problem, I put all components, connections, jumpers, on one side of the board.   I will never win any Harry Joyce awards, but who cares ?!!?!!?  I prefer to see everything, and not guess if something underneath might have fallen off, have cold solder, etc. etc.  I have a 1971 Marshall Super Lead, it has the preamp filter cap underneath the board.  It is not necessary to deal with that can very often.  But when you do need to..........
Anyway, that is how I feel about building under the board.   I would much rather look at a few extra wires, than a pretty chassis that plays hide and seek.
Good Luck with your video.

Hi Hired Hand,

You are exactly right. I have in front of me right now a JTM45 board from the boys in the USA and the wires are all on the top of the board but under the components - it would be much easier to solve the problems if the boards were made this way. But of course, the Overtone HRM is a much more complex amp in my view against the JTM45. It's all those little boards and some of the stuff is a little funny, like the solder balls that form if you use a little too much solder.

It was a real pain to find actually. The result was much the same as if that relay was not there (like when it was fitted the wrong way around) and you know what - even the wrong way around, or when the connection was bad after reversing the relay, it still worked for about 4-5 minutes for some reason. I never got to the bottom of why that was so. Someone will know...  but it won't be me  :)

Yes I reckon actually the website should be very useful for anyone building one of the HRM's. There's lots to get wrong if you're not careful, and lot's to get wrong if you are careful..  :D

Anyway.. thanks for your input throughout the time....

tonym

I have uploaded that video I was talking about to www.overtonehrm.com

This is playable with a free microsoft plugin.. (silverlight) - dont worry, if its not installed it will ask you....

The video is not designed for techies particularly - its designed for someone who wants an overview of what I did and shows how I fixed the problems later in the video.

It is in very high quality bearing in mind this is the internet and is hosted on my own servers...

enjoy (or not)  :)