The Amp Garage Light Bulb Current Limiter

[Colossal]

Very cool, Martin. Thanks, as always, for all you do for this community. I have learned and continue to learn a lot from you. You and everybody else sharing great ideas, layouts, schematics, and experiences are why our community is great and continues to stand the test of time. You are a true gentleman and a scholar (but I use gentleman somewhat loosely )

[ChopSauce]

You guys make me feel so cheap ...

I'll admit this is a deluxe model, but it was entertaining to build and a pleasure to use.

BTW, the 2x EL34 amp draws 720 mA at 120V (no limiter, no signal), 430 mA at 99.8V with both 60W bulbs on, and 290 mA at 77.8V with one. By comparison, a 100W 4x 6L6 D-clone amp draws 1260 mA at 120V, 550 mA at 83.1V with both bulbs on, 340 mA at 60.8V with one (glowing quite brightly operating on 59 VAC). I highly recommend the power meter, which can be had for $25 or less. It comes alive at around 42 VAC, so it's working fine for the 100W amp/60W bulb case.

We sure don't have the same needs ...

[martin manning]

Inspired by sluckey's Volt/Amp/Watt meter addition to a Variac, I've added one to my Bulb Limiter II, which is typically plugged into a Variac. This meter module has a bright color display, and is attached to the limiter box. Only a matter of minutes to install. The Kill-A-Watt device I have been using for this purpose works ok, but its monochrome display is hard to read, and flipping through the screens is annoying.

Switching the bulb limiter to bypass, the display shows the Variac output, but not all the way down to zero volts. The description of this unit on Amazon says it operates from 80-300V, but the one I received is a 40-300V model per package markings, and indeed it turns on at 40V. It might be possible to connect the meter power supply upstream of the limiter bulbs so it would come alive at a lower DUT voltage (per sluckey's mod), but it didn't want to come apart easily, and it seems to work well enough as it is.

Video showing operation powering up a 100W amp with all tubes installed. Main power on, then standby to play: https://www.youtube.com/shorts/joEk_DKBOK0

[xtian]

This is awesome, Martin!

Can you show photos of the wiring inside, and show what you've used for the input and output AC plug/socket?

[xtian]

Here is a quick shopping list from Amazon:

DROK AC multimeter https://www.amazon.com/gp/product/B09998YBHW
Square plenum box https://www.amazon.com/gp/product/B003A2GWX4
Square work cover https://www.amazon.com/gp/product/B005JC6PLW
2 pack toggle switch/output https://www.amazon.com/gp/product/B07WS31L87
Socket-to-bulb adapters https://www.amazon.com/gp/product/B07LDMP1LX
Extension cord https://www.amazon.com/gp/product/B002HWMY9E

[martin manning]

Under the hood shot. The meter I bought is this one: https://www.amazon.com/DROK-Frequency-E ... 1XHKQ&th=1
The 120V electrical hardware can be bought at the local Home Depot or whatever.

[lonote]

Inspired by sluckey's Volt/Amp/Watt meter addition to a Variac, I've added one to my Bulb Limiter II, which is typically plugged into a Variac.

I recently bought a variac & after seeing this thread, I thought I would borrow both of these ideas (adding a panel meter & incorporating it into a new light bulb limiter) before it ever went into service. If I didn't do it now, neither thing would have likely happened.


I ended up with a really nice Powerstat from the 70s(?) off Ebay for less than one of the new Asian units would have cost. I had forgotten how nice stuff was built back in the day.

Anyway, I decided to leave the variac alone & add the power meter to a base along with the limiter outlet & to include a switch to switch between limit & line (variac adjusted) modes. I did Sluckey's "zero" mod to the panel meter, which works perfectly. https://sluckeyamps.com/misc/Amp_Scrapbook.pdf

The base is 1/2" ply with speaker cabinet paint, about the size of a shoebox & just big enough for two double gang boxes & the power meter. Lots of lights, switches & read-outs. Just missing the flux capacitor...

Variac limiter base.JPEG

[Mars_Amp_Repair]

Hello folks,
I know this post is older, but thought I'd throw in my 2 cents.
Attached is the bulb limiter I built for all my techs when I had my shop. It employs a single pole switch the throw the bulb in the circuit as well as a main power switch that is a DPDT variety. The DPDT ensures that the DUT will be completely isolated from the line when it is shut off. As you can see it is constructed of standard plastic electrical boxes that are relatively cheap to purchase. I used the 'cut-in' boxes as they sat flush at an angle.
Installing wall plates make it look clean & allows easy attachment of the labels you can see on them.
Being that the boxes & the keyless bulb fixture are attached to a piece of 2x6, allow it to be attached to the bench making it easy to push & pull the AC plugs out of it with one hand.
The unit is then plugged into the Sencore PR57 Powerite Variac/isolation unit so that you are protected as much as possible.
Just thought I'd throw that in...probably should have thrown it out (;- )'
Glen

Bulb_Limiter.jpg