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Not if you want to use the original "D" shaft knobs. Filing/grinding the shaft is a laborious poor solution. Been there.

Something to consider, which would require revising the board layout, would be to use vertical mounted resistors. This would reduce space. Using 2 x 5 watt series resistors for each application (a total of 4 ) would further reduce heating while taking up less space.

Squared!

With few exceptions, i don't change out transistors that haven't failed. Joe has commented before that the 40412 operates outside of it's safe operating area. However it's 40 years old. I can say all of my series II amps that have the original control board still have the original 40412...

If you find that replacing the pots doesn't fix it, the issue is the front end transistors Q1-4.

Mouser also sells the mounting bracket.

My version of the 700II Manual , had limited information on the update to full comp. The 400II which I posted yesterday has more details.

I agree with Sniff on the silpads. No reason to go back to mica. With few exceptions, power transistors are run until fail. Yes, there are newer devices with slightly better characteristics such as safe operating area. When I test an amp I get it nice and hot and check the output case...

Do not plug the 400 in until the meters are secured. Then use the dim bulb test set to bring it up. Do not bother with the 4000 until you pull the bottom cover and fix a couple hundred cracked solder joints. Then fix all of the cracked solder joints on I/O jacks on the back.

Nope! Call me a butt head instead. You gotta get in line first.

That's all Spencer's gear. I provided the scope, signal generator and load bank. My definition of a science fair project requires a minimum of 5 instruments.

When I was a bench tech at Sound Values, they literally bought a semi load of crown amps that were pulled from MRI systems. The audio version was the MA10,000. The output would go down well below 1 ohm. It was a bridge amp that had 4 heatsinks for the outputs. As I recall each heatsink had...

At the risk of being labeled a butt head by critiquing a fine test set, it is desired to mount binding posts/banana jacks on 0.75" centers to accommodate adaptor plugs and test cables that use dual banana plugs.

The heaters are slightly less than 8 ohms. The cables have dual banana jacks on the other end. For 4 ohm testing, 2 cables are plugged in to each channel. Zoom in on the photo and you’ll see the area that melted.

The heating element works really good. If doing a 700 the elements would need to fully emerged in water. Otherwise they’ll quickly burn up. I V melted the plastic lid on the 5 gallon bucket.

If it's an electronic load, It's not likely to be purely resistive. Probably a high frequency switching device. If that's the case it wouldn't be good for testing amplifiers.

I've been using the bulb for itnitial power up for more than 40 years. Variacs don't provide any current limiting. The bulb never fails. The variac will allow a catostrophic failure.

I've got one. Picked it up at The Dayton Ham radio show 30 years ago. About to retire it as I bought the HP8903. Haven't got around to doing much with it. The 334 is pretty straight forward. You need a low distortion oscillator such as the HP 204. If you want to go real vinatge, pick up an...

I developed a triac board for the 700's that is controlled by the original power switch. The goal was to preserve the original power switch in the 700B's which are near unobtanium. In the development process I captured a lot of inrush currents at turn on. Typical peak current during the first...

I've got a Leader curve tracer I use for bipolars. I much prefer to look at a scope as opposed to numbers. Max collector voltage is only 100VDC but it has confirmed suspected transistor breakdown voltage a number of times on TO92 types Q1-4 on the 400/700's. I also use it to match transistors...