At that point the PT is quite hot to the touch so the amp ask the PT to deliver a good amount of current. I'm using an Heyboer Mojotone PT and an old 75 twin OT and the PT is oversized.
I think you could try to change the PT, Leo was cheap but more so for Ceriatone.
FWIW.. I've built quite a few 124 style and HRM's using Mojotone, Heybors/ MMag/ New Sensor, Marshall style 100w/ Music Man/ Used Fender Iron/
I've never had 1 run what I would consider hot..(Accept for a Dagnall) The rest ran warm to touch
IMHO when it came to transformers Leo didn't go cheap --Over spec--.. Many of todays transformer manufactures go by the same specs and even blue printed The Schumachers to get the same sound.. The Tweed Bassman OPT for the time was a serious transformer for a guitar amp..Still is..My 2 cents..
There are quite a few Ceriatones out there if it were a Transformer spec issue that would of showed up long ago.. That's not to say you couldn't have gotten a bad run..
Tony
" The psychics on my bench is the same as Dumble'"
Well, I may be wrong !! My point is that an heyboer has more "metal" to it than a classic schumacher and from my limiting experience rebuilding Fenders they tend to sound more stiff or hifi than a regular repro like magnetics. Living in Europe I'm used to build amps using Partridge type trannies and as for as weight and oversized is concerned these are way bigger than any Fender or Marshall classics (and I've got a lots of them).
Tweed amps used oversized for sure, I was talking about BF.
In my (first !!) Dumble style amp the PT is definetly hot after an hour or two, more than my others amps. I could put my hand on it for a second or two but not much more. Maybe because I use a bankok chassis and the power tubes are close to it.
No offense whatsoever, just wanted to share my point, I have already found that kind of issue on other amps and changing the PT for a proper current rating one solve the issue.
mojotom wrote:I may be wrong but on my newly build 124 the amp start to sound better when it's warm and even better when played for 30 mn or more. At that point the PT is quite hot to the touch so the amp ask the PT to deliver a good amount of current. I'm using an Heyboer Mojotone PT and an old 75 twin OT and the PT is oversized.
I think you could try to change the PT, Leo was cheap but more so for Ceriatone. It could be the PT not being able to supply enough current when hot (running for a while)
Where did you buy The heyboer?
Have any number for the tranny?
I need 230 Vac.
I also need a tranny to supply the relays 230Vac + 6v,0.
Any suggestions?
;)
mojotom wrote:I may be wrong but on my newly build 124 the amp start to sound better when it's warm and even better when played for 30 mn or more. At that point the PT is quite hot to the touch so the amp ask the PT to deliver a good amount of current. I'm using an Heyboer Mojotone PT and an old 75 twin OT and the PT is oversized.
I think you could try to change the PT, Leo was cheap but more so for Ceriatone. It could be the PT not being able to supply enough current when hot (running for a while)
Where did you buy The heyboer?
Have any number for the tranny?
I need 230 Vac.
I also need a tranny to supply the relays 230Vac + 6v,0.
Any suggestions?
Frankie, I suggest you verify the PT is really the problem. You have asked a lot of questions but doubt you have fully verified all the suggested areas of concern. Using your scope and meter are you convinced you have fully measured and compared all provided suggestions in both a working and volume drop state? (I doubt it) If not, then you may be chasing your tail. Again no disrespect meant but you need to fully test and verify before jumping to the next suspected area. Maybe creating a chart would help. I do hope you can get your amp(s) working. That all I'll say.
I agree you need to test everything before changing the PT, if everything seems right, no cold solder joints or leaky cap, etc then you coule think about such mod.
PT is Mojotone twin export tap.
I used a 10VA 6-0-6V for the relay (use on side only)
massygt6 wrote:I had an issue similar to yours that sent me mad for about two weeks...it was the shielded cable from the input to the first preamp tube...check it out.
How did you fix the problem in your amp, was the shielded cable broken, or did you go unshielded?
Earlier I changed the ceramic cap and resistor on V1b, It was not the issue either:( You can see the change on the picture. By the way this is not a Troll, even if we have some Trolls here in Norway. This is not!!
You do not have the required permissions to view the files attached to this post.
The 2 grid resistors V1A ... If those resistors are 22K each..That may not give you proper isolation and could carry some bleed back causing the drop.. A scope wold tell you..Looks like you have that on both amps
Tony
" The psychics on my bench is the same as Dumble'"
Structo wrote:They may be 47K, but why is there two shielded cables to V1a grid?
Yes they are 47k, and It is high and low input. (On the non hrm I have 22k and one input.) I did try other resistors just incase to eliminate fault on them, it was not them so I put them back again, cause the others I tried was not carbon.
I gather these amps were built by you or for you.
Shield problems can be a just small strand of wire on the end of the part with the heat shrink.
I did notice a solder glob in the photo on your V1b shielded wire?
Put a signal generator on the amp connect the amp to a dummy load and monitor the output. Watch for what the wave does.
You can get a sine signal from your pc or make a wave file of it and put it on a MP3 player if you need.
You will see something change in the signal, when the amp changes it's sound. Repeat(cool down/heat up) as you move along the signal the path. Not just into the input. make up some clips and inject the signal.Take your time.
Check all your DC rails with the scope as stated before it needs to be a straight line.
I have had power transformer problems with a ceriatone. These were not a sound issue but a failure on the heater circuit. I'm running on 240volts here in Australia.
I think you have a solder splatter, dry joint, small wiring glitch that is eluding you.
Have you tried the chop stick/insulated screw driver trick. Tap the wires around and see if you can induce the problem.
One other note you have hot glued the wires to the chassis, are you sure that there is not a small short happening there, as it heats up things expand and short?
That all I'll say.
