SB220 Rebuild

[@Saltshaker762-KF4LBG]

Im attacking a SB-220 while watching your content... Thank you for sharing what you have experienced with your refurbishment project... 73 de KF4LBG

[@captlarry-3525]

Very ill advised to use the chemicals suggested here. DEoxitD5 for all contacts, pots and tube pins, burnishing tool if need for relay contacts, triflow and paper towel for xfrmr laminations, tri-flow or other penetrating oil on switch and pot sfts, but keep it out of the pot. deoxit but no oil on variable caps.

[@MrMuppetbaby]

I hoping to see how you oiled the fan, I suspect mine needs a little love as it's been 30 years since it's been oiled at least. Still works but why take a chance? Maybe you could just mention how you did it as I don't see a hole for that. ALso Alex, is that solder wick you are using to ground your grids? That a good idea if so I think. Thanks, Tod KJ6H

[@wc4988]

hi Alex, Just wanted to know how the SB-220 project turned out ? I looked at your other videos but seen no part 2

[@alexwa2bmb743]

Hello WC : Thanks for your kind attention and comment!! I ended up replacing the High voltage transformer. The Hammarlund transformer is an exact replacement. I fired it up without incident and I am still using it daily. The output tubes are not 100% but all in all everything worked out fine. I was trying to do this on a shoe string budget. Well that did not work out the transformer alone was $300.00 OUCH !!!!!! I did not do a second video my point was to make a safety video with a few trouble shooting tips. If you intend on working on one of these little beasties. PLEASE be Careful .

[@louw1qjparascondola821]

Hi Alex, just a couple of words about your SB-220 project. I want to commend you on your admonishment to those buying an amp on Ebay or any other venue where you do not see your purchase in operation. I agree that you should NEVER just plug it in and go. You must do as you suggest and look over the entire amp and visually inspect it for an obvious imperfections. I also highly recommend since someone buying a vintage piece of gear like this do the very minimum updates to it immediately if it has not already been done. That would be new filter caps and bleeder resistors. Secondly I HIGHLY recommend the Harbach rectifier replacement board and NOT messing with the original. The Harbach board does away with the Zener diode, adds 3 amp rectifier diodes and meter protection. It is cheap enough and a quick build and install compared to revamping an old board. Years ago I realized that revamping an old board is a waste of time and you don't have as good a product as a new Harbach design. The parasitic set up that was in there was not stock but that design can be seen in some vintage amps and do work. The original design is very effective, a simple 2 watt 47 ohm carbon resistor and 3 turns of #16 or #14 silvered wire around it is best. No other design works any better than the original. The ones you made are incorrect, they may work but I do believe you have far too much inductance on them. Any 2 watt carbon in the neighborhood of 47-56 ohms with 3 turns of wire around it is best. Stay away from Nichrome. I did not quite understand how you determined that your primary of the power transformer was shorted, you did not elaborate on that and I wonder if you should have another look at that. Perhaps I missed your explanation. Cleaning the relay is also a good thing and the time should be spent on doing that. Grounding the grids is another good thing although it does increase the gain of the tubes and care must be taken when loading. The stock transformer has a built in impedance and a step start is not a requirement however some feel more confident with it and it can't hurt, toss a coin if you are undecided on that. A soft key is a MUST. The Harbach soft key unit is well worth the money and as far as I am concerned a MUST have. You can bet that over 50% or more of modern radios will be destroyed by the 120vdc the SB-220 relay needs to switch. Here again, the cost is minimal and the reward is huge compared to repairing the keying circuit in a new radio. Once again, cleaning the meter function switch is another good idea. One major observation I have made over the years which is quite troubling is the frequency that I see bad band switch contacts on these amps. I have owned or repaired upwards of 500 SB-220/221 Hl-2200 amps over my 45 years of working on them and unfortunately about 7 out of 10 amps I see have at least one bad band switch contact. Those odds are pretty bad, so don't be surprised if you see a bad contact. Often times the amp still works because the contacts are redundant and one may still be good but now has to handle twice the current. Lastly, once all your renovations are completed you should as you suggest bring the amp up slowly with a variac, first with no tubes to check that all your work was done properly and see if all systems are go with no tubes. Once you have confirmed all is ok then put the tubes in and once again bring the amp up on variac slowly, put the meter in grid position, start bringing up the HV, watch the plate and grid meters for ANY movement UP OR DOWN, if you see any meter movement you have a tube problem so stop right there and determine which tube is making the meters move. If all is OK keep bringing up the HV and now keep an eye on the tubes themselves and see if you can see any signs of gas. You will see a violet hue inside the tube if it is gassy. Again, if you see gas, STOP. Probably time for new tubes if they are gassy. You could try to getter them, that may or may not work depending on how badly they are gassy. Personally I replace gassy tubes and make decorations out of them. Some mildly gassy tubes will only show gas when excited with RF, they may getter with use but may also arc and cause some damage. So how are you doing with this project? Lou W1QJ

[@alexwa2bmb743]

Hi Lou sorry I was not able to respond sooner sometimes life gets in the way! I want to thank you for your comments. I would like to argue with you but I can not. I am a disciple of W8JI . I should have mentioned in the article my intention to make this a cheapo / experimental project. That is the reason for trying the loop parasitic suppressor. Also why I did the refit of the old rectifier board. What I might add I also replaced the 5.1 volt Zener diode with a higher wattage unit. By the way I do use the Harbach stuff I am a fan!! The reason I did not use any this time is because I recently finished another amp and as it turns out all the Harbach parts I bought cost mre than the amp. So I decided the next amp project will be done on the cheap as an experiment. But the power transformer started sputtering and snapping as I slowly brought it up. So much for doing it on the cheap!!!! Well 300 bucks later it is up and running. The only arc problem I experienced was when I accidentally miss tuned the amp. But no harm was done.Thank You so very much for your kind attention and for keeping me honest. Best Wishes Alex WA2BMB

[@gmw1964z]

The harbachelectronics.com updates work the best for this amp.

[@alexwa2bmb743]

Greetings: Thanks for your comment. I am a Harbach fan also. But as they say there is more than one way to skin a cat ! But why anyone would want to skin a cat is beyond me!! Sorry Kitty

[@macp8854]

You should post an email address on QRZ. I repair amplifiers and have repaired over 400 SB-220/1s in my lifetime. Would like to compare notes.

[@alexwa2bmb743]

Dear Mac: Thanks for you interest. I have listed my personal Email on QRZ. Sorry it has taken me soooo! long to answer. My computers all went south on me and a death in the family had side lined my ham radio stuff. I would welcome an exchange of info with you. I am afraid next to your experience my exploits would not be very helpful to you but I am at your service. Thank You for your patients .