Metropoulos Forum

Crazy paint job on the bomb Phil! Did you get your EC-80 A units working for the "Eruption" dive?

Where did you get the choke? The bomb looks looks Freddy Kruegers sweater.

I actually had it painted like a giant 100k Iskra, but it looked stupid, so I went back in with some red. Now it looks like a Freddie krueger sweater, I just can't win! It's an opened ended project that bomb. The EC-80's still don't work, I've lost much of my energy for these things, but they are great for looking.
I've been looking for that choke for three years, so when one finally came up on ebay I offered the guy a ridiculous price and he ended the auction and very gladly took my money. I also bought a T 100 1471-263 Drake choke from the guy, I'm wondering if it is the same choke without the brackets. I need something to measure Henries.

What exactly did you type to find the ebay listing? I've never seen one.

And you probably will never see one, that is, in time before I grab it!! I'm kidding of course, I'll keep my eyes pealed for you. I typed "Marshall Choke." Here is the seller, he seems to have allot of this kind of thing.
http://www.ebay.com/itm/Vintage-Marshal ... 27dc3f0e5e" onclick="window.open(this.href);return false;

RED PLATING check list:

Measure the amp B+ voltage and bias voltage at pin 5 both at idle and at full output, when the tubes are red plating. These readings may help point us to the issue.

When using the Airbrake with older vintage amps, mismatching the load will be a safer way to operate. This will eliminate any overheating of the output transformer. For example, a Vox AC30 or vintage 100 watt Marshall should be run at 8 ohms through the Z Airbrake with a 16 ohm speaker load.

If only V4 red plates, just replace the 82k plate resistor in the phase invertor with a 68k. This will make the output of the PI driving V4 closer to the output driving V5. And should alleviate red plating altogether.

Did you read that pin from up top or underneath? The female pin is a little piece of metal rolled into a cylinder with a tab sticking out to solder to. I have see a few times the cylinder part is broken off the tab part, but both pieces stay in the socket body. That means the voltage is on the solder tab underneath, but the part gripping the tube pin is not connected to it. SO, busted socket pin. Rare, but happens.

Maybe also your ground connection on pins 1 and 8 has broken.

it is important for the voltage to get to pin 5, but it is equally important that the female pin 5 grips the tube male pin well enough to make electrical contact. Look down the hole, are the female pins spread? At least the pin 5 one?

Does it red plate when you're not playing through it, If it red plates all the time, either the grid leak resistor or the grid stopper resistor on that valve is blown open.

t's worth checking on the condition of the capacitor that bypasses the shared cathode resistor(s). A cathode resistor bypass cap that starts leaking reduces the voltage that the resistor produces as it gets leakier. In a cathode-biased amp, this would increase the current through the tube.

The simple thing to do is to pull out the cathode bypass cap. If the redplating stops, it was the cap, and a new one ought to fix it. unsolder one end of the cathode bypass capacitor and measure the voltage. If the cap is leaky (and effectively lowering the value of the cathode resistor), you might find the under-bias condition goes away. If so, replace it. If it is still red-plating, you've eliminated one of the most-suspect non-tube components and have a voltage to calculate current from.

Strat78 wrote:

JimiJames wrote:
2.2k ? What H choke ?

Those chokes with the brackets showed up between 69 and 72 going by 100w superlead pics at amp archives. I get conflicting accounts as to what they are rated, I think mine is 5Hy. Maybe someone can fill us in on what these chokes were.

nominally 3H, 110 ohms, 100mA

To sum up the 12xxx connection to the EVH first album tone, it's pretty simple at least for the songs played with the Destroyer. A 12series spec variaced down to around 60 to 70v going into a 4x12 of Black Backs. Super70's into an actual Echoplex (with slap-back) into amp and that's it. The overdubbed solo could have been JBL's on the original recording, but other than that I don't think they are relevant.
https://youtu.be/2nUDHm3r-pU

Strat78 wrote:And you probably will never see one, that is, in time before I grab it!! I'm kidding of course, I'll keep my eyes pealed for you. I typed "Marshall Choke." Here is the seller, he seems to have allot of this kind of thing.
http://www.ebay.com/itm/Vintage-Marshal ... 27dc3f0e5e" onclick="window.open(this.href);return false;

Looks like Trace Davis's ebay acc...
http://www.voodooamps.com/home/Home/tab ... fault.aspx" onclick="window.open(this.href);return false;

Strat78 wrote:

JimiJames wrote:
2.2k ? What H choke ?

Those chokes with the brackets showed up between 69 and 72 going by 100w superlead pics at amp archives. I get conflicting accounts as to what they are rated, I think mine is 5Hy. Maybe someone can fill us in on what these chokes were.

The one that Brian measured was 3.63 Hy.
http://www.marstran.com/Open%2520Frame.jpg" onclick="window.open(this.href);return false;

Strat78 wrote:Been laid up for many months without a knee in my leg, so to keep from going crazy, I have been building away. Here is the latest build which is a kind of tribute to Mark with my own spin. The clip is useless but it was the best I could muster in my condition. Oh, I get a new knee tomorrow so once again I'll be on the wings of opioids....see you all next year.

This amp sounds amazing! Nice work strat78!