Drake L4B amplifier modification with Harbach mod.

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This video is not a replacement for the written docs. It's just something you can watch and pause as you do your steps according to the documentation. I'm not going to tell you HOW to do it, just show you what it all looked like as I did it. Like a second opinion. I take no responsibility for the end results, your life, or any amp that doesn't work afterward.
As well as the documentation is written, here is a video overview of the steps and what I did. Note that I take no responsibility for anything going wrong. As I was, you are on your own, so read well, and take your time. Make sure everything is unplugged and discharged as is normal with any amplifier maintenance. Like a gun, always assume it is ready to kill you.

Опубликовано:

28 авг 2022

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Комментарии : 16

@nick14454 Год назад

Fantastic video. I picked up a used L4B not that long ago and have the harbach board sitting here waiting to be installed. I will have to come back once i'm ready! I'm waiting for 240 into my office before I play with it.

@DaveKelleyphotography Год назад

It is certainly a beautiful amp. It is the first one I've owned that have the big tubes in it. Legal limit is easy for sure. The mod wasn't as complicated as I expected it to be. I just triple-checked everything as I went along...and filmed it. The fan is quiet enough that I always reach back and touch the fan blades to make sure it is running. Have fun and let me know how it goes.

@nick14454 Год назад

@@DaveKelleyphotography Just got the harbach kit installed and I grounded the grids. Very happy with the results, I bought the amp with no guarantees it worked, so its exciting to see the tubes glowing and it keying. 1.3kw with it in ssb mode with a 100w cw tone. This will be a very fun amp, and a nice replacement to my Heathkit SB-200 which will now become the backup! Still waiting on power in the office and some diodes to protect the meters. Hopefully it'll be wrapped up this coming week!

@kastaways1259 8 месяцев назад

What does grounding the grids accomplish?

@hunt555fish Год назад

Great video Dave.I want to make the power supply mod and the soft start mod you have done.Did you have to do a bias adjustment after installing this board!Also where did you get the bound instruction manual for your install.I want to use the L4-B with my Icom7300 or my Yaesu FTDX10.Not sure what interface cable to use between the transceiver and the amp.I feel a little better about making this board install after watching your video.

@DaveKelleyphotography Год назад

Hi Ron. I actually have so many manuals around that I bind my own these days. When you order up the mod kit also order the little RCA jack to put on the back of the L4B. I haven't installed mine yet, but that should make it so you can easily just have an RCA to RCA cable go between your radio keying jack and the amp. The board takes all of the high voltage out of the situation so modern radios can key the amp without frying the radio. Still, I'd put a meter on the input of the amp to make sure the voltage is down to the limits of the radio. Generally 12 volts or less. I just picked a middle spot for the bias and it worked just fine. It sounds like you might be new to ham radio? In any case, as a reminder, that amp will kill you if given any chance at all. Don't reach behind the amp for anything once it's been on. That HV line can stay charged for a very long time even after it is off. Treat any older amp like a loaded gun. Even if you just unloaded it, assume it is loaded.

@kastaways1259 8 месяцев назад

Thanks so much for making this video. I see a couple people just leave the amp on and place a on off switch right on the 220 cable. Does putting in this kit eliminate the need for an external keying relay too ? Thanks

@DaveKelleyphotography 8 месяцев назад

This kit does three things. It does a timed power up were it does 120 volts for a second or so before a relay brings it up to 240. Saves the switch. It changes the idling bias so it isn't so hot just sitting there. And yep, it changed the keying circuit so you can key it with a modern solid state radio. Well worth the time and effort.

@AlbertMilliron 5 месяцев назад

Dave. I bought a keying rca to replace the original. When I took it apart looked like the .01 uf cap was across both terminals attached to the rectifier. When I looked at the schematic looked like the cap is supposed to go before the rectifier to ground and rectifier to center pin of rca cable. When you did your upgrade. How did you wire the rca key plug?

@DaveKelleyphotography 5 месяцев назад

That's actually something I didn't install, so I can't answer that. And I'm not very inclined technically. If in doubt, check with Harbach I guess. Sorry I can't give you an informative answer.

@GlassRF 7 месяцев назад

You're screwed when the guy you got the custom board from goes under and leaves you on your own with no parts now that you chopped the wiring all up. Dumb...

@DaveKelleyphotography 7 месяцев назад

I'm not sure what you mean. The board installs fine, and really makes the amp far more operable and cooler. If Harbach went out of business tomorrow, my amp is still working great. I've installed a lot of power supply upgrades from them and each one has worked perfecly.