Bias zener substitute for Drake L4B amplifiers used for AM mode.

Description: This product probably deserves to have the safety-hazard disclaimer placed UP FRONT where nobody can miss it. Yes, the Drake L4B has deadly-hazardous voltages inside, possibly even after the plug is pulled from the wall. Proceed only if you possess proper safety training and high-voltage experience. By reading this sale description you hereby agree not to kill yourself attempting to install our product. If this is not acceptable, DON'T READ ANY FURTHER! Besides, if you do end up dead fooling with the inside of your Drake L4B, and your heirs sue me for wrongful death, I will immediately file a countersuit for three times the damages you seek, claiming breach of contract. You did agree not to, after all. Here is a way to reduce the heat load on the tubes in your Drake L4 or L4B linear amplifier. The amplifier was designed for zero-bias tubes, and if you use it for SSB only you probably don't need to add any fixed bias. It was built this way. It will work this way. On sideband. This is the same circuit board we sell to replace the 10-Watt zener diode in a Heathkit SB220. This version has mounting hardware meant to use in the Drake ampliifer. If you use this model for AM, the factory recommends you select the "CW/Tune" mode on the front panel. This reduces the heat load on the tubes to a safe level. Also reduces the output power. Naturally, the AM operator wants to use the amplifier at full power. The solder melts from the tubes' filament pins and then damages the socket spring contacts. Dern! An amplifier designed for sideband will run hot when it is delivering a carrier in AM mode. Placing this board into the cathode circuit will reduce the so-called "idle" current of the tubes, the current they draw from the power supply with no drive power applied. This keeps the tubes' heat load below the danger level so long as you keep the AM carrier level below a reasonable limit. And if you apply excessive drive power, you'll blow out your L4B whether this board is in place or not. Feel free. It's your money to burn, blowing it up with excess drive. Lotsa people do it. We also include a new 220uf 50-Volt cap shown in one pic to replace C33, the filter cap for the relay coil's power source. Odds are that your amplifier still has the original 100uf axial cap. It's too old, so you should replace it, as shown in one pic. There is no handy-dandy web page or YT video showing how to install it. Pulling one wire off the relay, moving it to our board and soldering a new wire where it came off is simple enough to explain with a few pictures. If you need more hand-holding than that, I suggest you hire someone who has the skills to avoid getting killed doing this. Killed, as in PERMANENTLY! There are NO RETURNS AT ALL FOR ANY REASON OF ANY KIND!No matter how good they sound. We ship no later than the second business day following receipt of cleared payment. I prefer USPS First Class. It's been VERY reliable and comes with tracking. I will insure it for the final sale price. IF YOU PREFER A DIFFERENT **USA ONLY** SHIPPING METHOD, CONTACT ME **BEFORE** YOU PAY! I will prepare a quote for the method you specify and send you an invoice for the corrected amount. This option is available to USA destinations ONLY! !!!! NOTE !!!!Shipping to destinations outside the US are by the Ebay GSP or Global Shipping Program. How much that will cost you is anybody's guess. Ask Ebay if you want to know. Maybe they'll tell you. They won't tell me. Maybe they should rename the "GSP" the "Global Secret Program". GSP ONLY!! GSP ONLY!! GSP ONLY!! No, I will NOT ship direct if you are outside the USA and its colonies. GSP ONLY!! GSP ONLY!! GSP ONLY!! If you know what it is and what it's for, you can decide if you want or need it. And if you don't know what it is, you probably don't need it. Trust me on this. All routine Ebay precautions apply. Scammers take your nonsense elsewhere. Please. Thanks for looking and happy bidding!

Price: 49.99 USD

Location: Louisville, Kentucky

End Time: 2023-10-22T02:29:53.000Z

Shipping Cost: 0 USD