Bottlehead Forum
Bottlehead Kits => Legacy Kit Products => Tode => Topic started by: TubeTim on January 20, 2014, 07:36:07 AM
-
Well, my luck ran out... Was able to build a Mainline that worked at first power up. For the Tode, it didn't go so well. The EL84 tube did a nice Sparks show internal to the tube. I figure that tube is toast - and any further testing with that tube is futile - Correct?
A missed solder joint on a ground connection was likely the cause.
BTW what does Tode mean? Google search didn't help. Not a musician, so the meaning escapes me.
Thanks
Tim
-
"Tode" was derived from "pentode", as both the tubes in the Tode are pentodes.
If you ended up discovering a funky joint, you can try powering on the Tode again with the same EL84. It can be shocking and somewhat magnificent to observe how much abuse certain tubes can take!
-
Thanks for the explanation of Tode.
I don't have a guitar (building this amp was for fun) therefore I don't have a proper input device. So, with a 2 wire jack plugged in and the 2 wires shorted to each other (input grounded), the sparking EL84 settled down. It is however mighty hot, to hot to touch. The feedback is set to 'creamy'.
I realize tubes get hot but this bad boy seems a bit to much. Maybe I'm to used to parts that run on 1.1 V-DC.
Removing the input short, one can touch the input lead and hear a nice 60 cycle hum, as expected. The brake works as expected with hum getting louder / softer based on brake setting. The input is mighty sensitive and I wonder if anyone can suggest an input device to use to test? Maybe a line-out dropped thru a 10:1 voltage divider?
The voltage readings on the back terminal strip are:
1 - 0
2 - 0
3 - did not measure
4 - did not measure
5 - 414
6 - 0
7 - 0
8 - 0
9 - 207
10- 414
11 - 300
The AC power shows 119.3 V-AC on meter. Terminals 3 & 4 I couldn't not probe comfortably.
Do these voltages look in the ball park?
A 1.6k resistor is between terminals 5 and 11, we have power in said resistor =
V2 / R = 1142 / 1600 = 8.122 watts.
That is within the power limits but that puppy sure gets hot also. Also the 560 ohm 5 watt resistor gets to hot to touch. Maybe I'm to used to micro-power stuff....
I'll order up a new EL84 just to be on the safe side.
Many Thanks for your help!!
Tim
-
Yeah, you're in the ballpark.
Yes, the resistors get hot. They are inside the chassis so that you won't touch them ;)
-
The input is mighty sensitive and I wonder if anyone can suggest an input device to use to test?
How about a guitar player?
Electric guitar pickups put out about 250-500 mV. You could also try a dynamic microphone or an electronic keyboard.
-
Hi Doc B,
I didn't think I knew any guitar players but a buddy of mine just happened to mention he played and agreed to give it a go. Will also try the dynamic mic. For some strange reason I'd like to build a Crystal radio and give it a go thru this amp.
Thanks for the info about a guitar pickup. This is very good to know.
Attached is a (rather poor) image of the front portion of the Tode. It was a fun kit to build and not particular difficult.
Will I hate myself for routing the A-C filament wires in parallel with the signal wires from A to B tube? The filament wire is shielded so it should be okay, but???
Best Regards,
Tim
-
Took The Tode to a friend who has several guitars and agreed to test the new amp. He plugged one in and nadda. Absolutely no sound. I knew that couldn't be right as I could touch the tip of the input on the test bench and hear AC hum. Luckily he had a second sound cord, plugged it in and beautiful sounds! They commented how clean the amp sounded. It's also loud enough to use in a small bar gig they thought. We only had it cranked up 2/3 of the way too.
Tim
-
...
It can be shocking and somewhat magnificent to observe how much abuse certain tubes can take!
I have done some reading about tubes. If one searches for 3cx800A7 you'll eventually land on a Ham Radio ops page who knows a lot of the care and feeding of these tubes and their big brothers. At $1k a pop they take good care of them. Some of the tubes, (3-500Z) they say to run slightly cherry red to act at the 'getter' function.
After reading about these, your are absolutely correct, the tubes can take a lot of abuse. Being hot to the touch is not even close, of course.
Now have to figure out how to drive a 3cx800A7 with the Tode and get 800 watts out.
TiM