Heathkit SB-220 unpowered walkthru and thoughts.

Mono Banded, 10 meter only, Heathkit SB-220 unpowered walkthru only. This one all the Ham bands except for 10 meters have been removed on both the Input and Output, and the Band switch has been replaced by a variable Tune cap for the input. Hence, you Tune the Bandswitch for the lowest Input SWR. This amp has the small Harbach relay 'Soft Key' PCB and the Harbach HV/Bias PCB. I originally thought the HV/Bias PCB had soft start on it, but looking at the Harbach site just now as I am writing this, that HV PCB updates the HV diodes, Bias, and Metering, but it does not have soft start on that board and this one doesn't seem to soft start at all. However, this amp uses a voltage doubler for the HV and the original cap bank doesn't have a ton of capacitance anyway. Hence, though Soft Start is a good thing, with this amp being a voltage doubler and being somewhat underpowered anyway, it doesn't really need soft start. With 500z amps with more robust power supplies like Henry or Drake, I think soft start is almost a must. SB-220's are decent KW amps, but try to do more and then you will start having problems. Underpowered transformer, just adequate capacitor bank, just barely adequate Tune and load cap voltage rating. Weak voltage doubler circuit, especially with the underwhelming cap bank. Undersized wiring and no cooling for the tube pins. IMHO for this to be a good powerhouse amp, all this needs to be addressed.

[@eugenioschneiderpithan]

Everyone is now a valve teacher, RF decks and co!

[@joesitter20101]

Ahhh. Excuse me but, those black "capacitor" looking things on the incoming AC lines are NOT Capacitors at all. They're actually a Varistor made by Matsushita (Panasonic). A Varistor is an over-voltage surge suppressor. In this case the Varistors were used to inhibit the entry or exit of voltage surges on the AC line. You see, a Varistor is essentially out of the circuit, having zero effect until such time as the voltage across its' terminals exceeds a specific level. The two V14201 devices on the ends for example, will allow up to 130VAC to pass unabated but will turn to a SHORT circuit if the voltage ever tries to exceed 340VAC. It will start to conduct like a resistor at about 180VAC. The device in the center is rated at a significantly higher voltage, probably two times or 260VAC. Voltage surges are typically transient so that these things seldom catch on fire but in extreme cases they can (and are supposed to) do just that. Whenever a Varistor is used you should always install them away from anything else that's flammable so they don't start a fire. It's not a capacitor. It's a Transient Voltage suppressor. The trade name is "Varistor".

[@tramdr]

Good Job.

[@RL-521]

Tramdr, what are you seeing that indicates that this amp is strictly 10/11 meter? Also thanks for these vids, explains a lot for someone who'd like to build amps one day.

[@rocklickranch2804]

I enjoyed the information in this video Doc. You and I tried to buy the same L4B last year at the Hamvention. I ended up finding a mint one last week and just had the Harbach mods done to it so I can use my 7300 with it.

[@tramdr]

Very nice! I should have offered more for that one in Dayton, but it was early. I came back later and it was gone.

[@keithweiss7899]

Back in the 70’s there were a lot of channel 6 guys who bought the 220. But the power supplies were not up to long transmit times. They had to rest a fair percentage of time. So my friend used to specialize in doubling up their power supply’s to prevent failure. He stayed very busy building those amps!

[@KO4L_Lloyd]

How did the amp workout for you? I had one given to me but it will need going thru and ALL the caps and resistors changed. Not sure it's worth it?

[@tramdr]

kzbin.info/www/bejne/haDJeHaKmsl6hM0

[@minibikemadman]

can't forget amp supply... 3 3-500zs..with heavy duty parts. all PD transformers. I love my lk550.

[@tramdr]

Agreed.

[@danieljohnson8437]

I love, School. Thank you.

[@DoctorCalabria]

Great explanation. Thanks. Coming from an audio amp world, these look mighty scary!

[@tramdr]

Glad it was helpful!

[@vu3mes]

Good video..informative you know.

[@tramdr]

Glad it was helpful!

[@itsonlyme9938]

I have a SB 200 cost effective and simple the only trouble now is the tubes are made in China and the quality is very doubtful. I have reversed engineered mine and fitted GI6B ceramic pulse radar tube and 50 watts of drive will give 800 watts output. They are very cheap at the moment.

[@tramdr]

4cx800's were my tubes of choice. However, they have got expensive and harder to find.

[@jeffalessi]

Remember Boys, Girls And Sports Fans, High Voltage Might Keel You. Thats Right "Keel" You Faster Than Lying Down In Front Of A 100 Ton Freight Train.

[@tramdr]

Agreed and Thanks. I should have stressed this a lot more.

[@roger552fl5]

Excellent video I have one in mint condition

[@tramdr]

Very cool

[@WokeYtube]

last year passed 3 sb220 linears thru my hands and only objection i have is = ground those grids, plate coil is not good enaugh, 125volt on TX relay is TOO MUCH, and am misses plate and load reductions to tune easier, for rest is buletproof linear. I use QB3,5-750 tubes inside and work just fine 👍

[@tramdr]

Grids not grounded, correct. Plate coil not enough correct. 125 on relay, correct. No plate and load reductions, correct. Rest is bulletproof, incorrect. Undersized Transformer, you missed. Voltage doubler on HV, you missed. Undersized tune cap, you missed. Undersized load cap, you missed, Undersized band switch, you missed. No cooling of tube pins, you missed. Zener diode for bias, you missed. Meters not diode protected, you missed.

[@benjaminmeadows1380]

Seen more sb220 s than drake's

[@tramdr]

Yes, because they are a lot cheaper.