Vibro Champ Clone new build needs help

[ampgaragemc]

Hello, I'm new to posting in the forum but have read quite a lot here. I started a VC project and with all I had read, it seemed best to make a couple mods. Like keeping the signal ground separated from the power ground. Also adding a filter stage before the first B+. It's not a kit since I ordered all my own parts, which was not easy and I'm sure I got some things wrong. I wanted the 6087 to hit a 20uF first then drop voltage a little. I added a 20uF outside of the multi-cap can so I could isolate the ground.

Anyway, I'm at the stage where I first turned it on with a dim bulb limiter and hoped for best. Right now, I've only put in the 6087/5y3 and tested voltage in a couple places. I hope someone can tell me if my idea of how to wire it up was correct. My voltages are not what I expected. I have no experience building an amp but want to learn. Up until now, the most I've ever done was to maybe change tubes. I hope it makes sense because I'm not sure how to ask the right question.

mc-VibroChamp-voltage.PNG

mc-vibroChamp-build.jpg

[xtian]

Hi and welcome.

You don't say what voltages you observed or why you're concerned.

[ampgaragemc]

I put the voltages on the diy layout file--

[sluckey]

Anyway, I'm at the stage where I first turned it on with a dim bulb limiter and hoped for best. Right now, I've only put in the 6087/5y3 and tested voltage in a couple places. I hope someone can tell me if my idea of how to wire it up was correct. My voltages are not what I expected.

If you want believable voltages get rid of the dim bulb limiter and plug the amp straight into the wall. Then plug in ALL tubes. Now you can get some believable voltages... if you made no wiring errors.

[B Ingram]

... I've only put in the 6087/5y3 and tested voltage in a couple places. ... My voltages are not what I expected. ...

Ohm's Law: Volts = Current x Resistance

The "Volts" above is the voltage dropped across resistances in the amp, which can only happen if current is drawn.

Right now, there are no tubes in the amp, nothing pulling current through any resistance, so:
Zero milliamps Current x any Resistance = Zero Volts Dropped ------> The same B+ is measured everywhere


Plug some tubes in, you'll get some voltage-drop. But after you're sure no magic smoke is being let out, plug the amp into regular power, because the dim bulb limiter will make the voltage drop too low to be realistic.



I'm saying all the same things Sluckey already said, but simply connecting some dots to explain why he said it.

[ampgaragemc]

Thanks for the info. I finished wiring the input, then started it up and it had a high pitch that was trying to run away. I switched the OT primary polarity and that went away. It sounds pretty good and clean. Very slight buzz. Tremolo sounds good so far. I have not pushed it into breakup yet. I wanted to post the voltages so maybe someone could tell me how close it is to being right.

6087 pin 8 - 381v
B+1 - 366v
B+2 - 357v
B+3 - 334v
6v6 pin 3 - 353v
6v6 pin 4 - 355v
6v6 pin 8 - 334v

Any advice on what to check or adjust is appreciated.

[martin manning]

Voltages look ballpark, B+1 is 10V high, as are 6V6 pins 3 and 4, but 6V6 pin 8 should be ~20V. Maybe a typo?

[ampgaragemc]

You're right, it was a typo, thanks - 6v6 pin 8 is 20v.

So, I should increase the 330-3W resistor to drop B+1 a little more? I suppose that would drop all the other B+ too. I want to check plate dissipation as soon as learn about that.

Rectifier and power tubes are pretty hot to the touch, but not red plate, just a glow.

[martin manning]

Vk/Rk = 20V/470 ohms = 0.426A cathode current
Ia x Va-k = 0.0426 x 0.95 x (353-20) = 13.5W plate dissipation (estimating plate current at 95% of cathode current)
It’s a bit high but if you don’t see red plating it should be ok. A JJ 6V6S with its 14W Pa max would be fine.

[ampgaragemc]

I replaced the 330R on the B+ with a 470R. Voltages came down a little. These are at idle:
B+ - 377v
B+1 - 356v
B+2 - 346v
B+3 - 324v
Pin 3 - 344v
Pin 8 - 19.7v
In your formula, where does the 470 ohms from? Were you saying I should use a 470 ohm at B+?
Amp is way loud and I don't get much breakup. I wouldn't mind a little more brown sound.

[martin manning]

I see a 470 ohm cathode resistor on the output tube. Just using Ohm's law to get cathode current.
You now have 19.7/470 * 0.95 * (324-19.7) =12.117 W
Looks good!

[ampgaragemc]

Thanks for your help