New build 1969 Super Lead

[wpaulvogel]

Here’s the amp. This is the one I was asking about the heavy filtering. I’m amazed at how it sounds. Finished it tonight, started it yesterday, wow! It has the 470uF pair in series. Not stiff though. 465 volts on the plates at idle. I was afraid it would have 490 and I’m glad it’s lower. Testing tomorrow. Wendy is ready to see me tonight. Here’s some pictures.

[pompeiisneaks]

A thing of beauty is a joy forever

Nice!

~Phil

[wpaulvogel]

Got it mounted up in the cab today.

[burger]

Would love to hear it.....clips please!

[wpaulvogel]

I don't know if this will work.
https://soundcloud.com/vogel-instrument ... t-les-paul

[Colossal]

Super sweet build. I swore off 100W Plexis but you sir are not helping my willpower. How do you find the attack and clarity with the stiffer filtering? Is there still chewiness? What choke did you use? Looks like a 3H 100R or so.

[wpaulvogel]

It's a Heyboer C1999 copy, 3H 100R. The amp isn't stiff at all, I have a Metroamp JTM50 with Marstran transformers and it's stiffer than this 1oo watt. The power supply on the 100 sags down about 65 volts from idle to full power, even with the 235uF filters. The 50 watt only drops about 35 volts. I love them both and they are different animals indeed. I expected them to behave opposite.

[Roe]

the 100w amps often sag from ca 480v to 380v. The important thing is that they should sag below 425v or so, given a 1.75k reflected primary impedance and el34s

[wpaulvogel]

Roe, now that you say it, it went from 470 +\- volts to 395 +\- volts and the screen to something like 365.

[Colossal]

Roe, now that you say it, it went from 470 +\- volts to 395 +\- volts and the screen to something like 365.

Paul,

Is this with the amp plugged into a load and a signal at the input?

Thanks,
Dave

[wpaulvogel]

Colossal, yes
I had it testing with a 16 ohm dummy load, signal from a generator and watching it on my scope with a meter on pin 3 of the tube socket.

[pdf64]

Colossal, yes
I had it testing with a 16 ohm dummy load, signal from a generator and watching it on my scope with a meter on pin 3 of the tube socket.

Yikes, hope some sort of attenuating probe was being used, as there's massive kVac on the plate of an inductively loaded, overdriven power tube. I found that out the hard way, with the wreck of my first Fluke, 35 years ago, before I got my head around the back emf thing.

Maybe the resistive load prevented the degree of back emf that occurs with a regular inductive speaker load.

Plus just probing a power tube plate, especially pentode like EL34, can send the amp into oscillation; which itself may likely put the aforementioned kVac on to the meter.
Hence I suggest never to probe a power tube plate, without taking some mitigation, eg removing the phase splitter tube.

[wpaulvogel]

I only use a resistive load when doing tests for plate voltage. I’ve never had a problem with it yet. I’m not going to test with a speaker because the impedance is not stable or for better terms, I have no idea what it is at different frequencies.