Need help chupa 50

[Batman8]

Got amp to learn on That said had bias trouble .. Rebuilt bias 2 bias pots 4 caps diode resistors. Still was not working well ,,put new tubes in and bias got away from me -90 mv ...Smoked 2 resistors 1 cap ...put new parts in , everything worked biased up perfect on both tubes Turn standby on still bias ok .. But know it cuts in and out ...filament voltage was3.3 on one side and 7.3 on other side so put in new pt still goes up and down in volume.. Please don't say read and not solder... I am doing this to learn and do things my self. Just had heart op lots of time ,this I enjoy just need a few pointers. What's next to check I have can filter caps two 50-50 500 volts or could it be op transfomer thanks

[Phil_S]

Glad to hear you are on the mend from your surgery. IMO, this is an excellent recovery project.

When measuring filament voltage, the normal way is to measure across the two connections at the tube socket. For example many octal tubes connect the filaments at 2 and 8. Place one probe on pin 2 and the other on pin 8. You should see around 6.3V. It isn't clear if you are seeing 10v or 3V or 6V from what you report. Try doing it this way (using the appropriate pin numbers for the tube.) Tell us what you find.

Cutting in and out nearly always means there is a weak or cold solder or a wire that wasn't soldered at all. It can also be a poor ground connection, but that is really the same thing. When things heat up under operating load, the weak connection opens up and that is where the cut in/out happens.

Post some pictures. Maybe someone will notice something.

[M Fowler]

For example many octal tubes connect the filaments at 2 and 8.

That should be pins 2 and 7.

[Phil_S]

For example many octal tubes connect the filaments at 2 and 8.

That should be pins 2 and 7.

Oops!

[Batman8]

Thanks guys..I put in new pt voltage in filaments 3.3 on all tubes,and 2 wires off of pt to a terminal that goes to all filaments on tubes meter on orange and brown 3.3 ac volts. If I test the brown and orange off the pt one at a time brown shows 7.3 orange 3.3 dont know if this is a problem .....Made new bias circuit and now hav two bias pot , in standby with no tubes in I can bias up better than before ,turn standby to on amp works but goes up and down volume wise and over all bad sound cuts out ...help what do I test next cap cans or output transformer Four weeks after heart op still feel the shits but I am alive intill I get shocked ha ha Thanks for help you guys are keeping my mind bussy If you go to ceriatone web site it is a chupa 50 but the guy who made it did not follow the layout so that is really making things harder I am learning as I go along but it would so cool to get this amp to work like it did before I messed things ,, but reading will only take you so far

[martin manning]

What PT do you have in there now? Can you post or link to a wiring diagram for it?

[Batman8]

Hey thanks.... Pt is a classic tone 690 volt ct 150 ma Red & red wire.... 6.3 volts ct.05 ma model 40-18023 The output tranny goes out of range on my meter?? On plate voltage ,hits 400 then meter goes to 0 dont want to buy ot if not needed the new pt did not help I will try to give pics

[Batman8]

Sorry 5 amp on 6.3 off heater wire on pt

[martin manning]

Per the Classic Tone data sheet, Brown is the CT of the filament winding, and should be grounded. Black and Orange go to the filament lugs of the tube sockets, and you should see ~3.2VAC from either one to ground.

[Batman8]

Thanks I drew a diagram of the the terminal and took a photo.so I hooked it up like the last guy . I do get the correct voltage with brown to ground all my volt readings and bias numbers are dead on but I must have blown something else ....but the first reading with the pt that came with the amp was 3.3 on orange and 7.3 on brown ,how could it have worked at all ... Could the new pt be shorted if I pulled good numbers at the tube filament pins the tubes glow how they should and did not before, Not shure what to check next the amp still cuts in and out but thanks for help I think if I posted a day before I might have the pos working I wont bug you guys any more but how about one more check point

[martin manning]

Your voltages are dead-on with respect to to what? Do you have a schematic with voltages listed for this amp? In the Ceriatone layout the PT is shown as 325-0-325, and you are using 345-0-345... That means your DC supply voltages should be ~28V high with the same line voltage.

I also see that the first tube's filament is powered by regulated DC from a 5VAC winding, which your new PT (40-18023 per above) doesn't have. Can I assume that you are running that filament from 6.3VAC along with all the others?

I suggest that you get a line voltage measurement, a complete set of voltages to ground from all tube pins, and voltages to ground from the positive terminals of all of the power supply filter caps (5 places), and post them here.

Sound cutting in and out is often due to a bad solder connection or component in the signal path, but let's be sure that the power supply and idle voltages are reasonable.

[M Fowler]

Chupa 50 voltage chart attached.

[Batman8]

Thanks will do soon as I feel a little better went back to hospital 3 days 2nites fluid on back of heart o well things to do Monday
Cool thanks

[Batman8]

Thank to every body that helped.... Replaced transmormer, 4 caps, 5 resistors, rebuilt power supply, three wires hooked up wrong don't know how it worked at all,but had fun and learned more from amp garage than reading or school ...Sounds good for ceriatone ,$ 450 on eBay it worked ok but too much noise and now I really know how a amp works not bad for a old man next trainwreck kit so I am sure I will be back thanks to all