Hoffman Amplifiers Tube Amplifier Forum
Amp Stuff => Tube Amp Building - Tweaks - Repairs => Topic started by: dbray6714 on December 11, 2016, 01:34:33 pm
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:BangHead: So I have finished my build of a 2204 Ceriatone (JCM800). When I went to fire it up, none of the tubes lit up. I have 3.24V individually on each side but zero across. By no means am I an expert on amp building but I have built some in the past and fortunately I never had any issues with those. This is the first one where I need to troubleshoot so any help or suggestions would be appreciated.
Plate Voltage is 474V.
Fuses are not blown.
No accidental grounding (that I can find)
Speaker Load in place
Pilot Light operates
Thanks...
Don
{edit- fixed bang-head icon syntax - PRR}
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Welcome.
> none of the tubes lit up. I have 3.24V individually on each side but zero across...Pilot Light operates
So where would 6V come from? Brown wires out of the PT. Actually, since the pilot light works, you probably have 6V *across* the pilot light. (or is it 3V dim?) Next step seems to be the red wires running toward the tubes. Is one not connected, or both connected to the same brown feed?
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Brown from PT going to Pilot Light. Red wires from Pilot to tube sockets. No loose wires, shorts or such that I can see or find.
Feeds from Pilot are separate.
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The brown wires and red wires need to connect DIRECTLY to each other at the pilot lamp. May I suggest you run the brown wires DIRECTLY to pins 2 and 7 of the first power tube. Then use small wires from pin 2 and 7 to the pilot lamp resistors.
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Looks like that PT has a heater CT (black) but it looks like the 2 PT brown heater wires go to the pilot light then there's a resistor between 1 of the PT fly lead brown heater wires and 1 of the red heater wires?
If so what's that series R for?
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That resistor is supposed to limit the current to the pilot lamp. But he has it wired wrong. As it is, the resistor is in line with the entire filament string.
(http://www.ceriatone.com/ceriatone/wp-content/uploads/2016/09/JCM800_2204Ceriatone.jpg)
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I think I see what you mean. The Resistor should be on the Brown PT wires and not the Heater Wires. Didn't even think of that.
Ok - let me change that around tonight.
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Connect like this...
However, I would prefer to put the brown wires DIRECTLY on the tube socket.
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I can certainly do that. If I may ask though - why do people want the heaters to the tube socket first? Is it just to avoid any other components in the way or...?
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A lot of people don't care. Fender build about a gazillion amps with the PT wires going first to the indicator. But the Fender lamp socket is considerably beefier than that little lamp you have. There's something substantial to support the heavy wires.
But your socket is too flimsy IMO to support those heavy filament wires. Especially since you will also be soldering two wires to the unsupported end of that even more flimsy resistor.
The octal tube sockets will provide a very secure mounting for the heavy filament wires. Then you can use tiny wires to run from the first socket up to the indicator lamp.
When I build something, every resistor and cap will be supported on both ends. I don't believe in the 'flying' lead connection. And I certainly would not rely on the unsupported end of a half watt resistor as a solder point for two wires that will be carrying several amps of current.
You've built a nice amp. Don't cheapen it with a flimsy connection for your heaters. Make it road worthy.