SB200 Linear Amplifier - Capacitor & T/R Relay Replacement

[@Grimstash]

Fortunately you are one of the lucky ones that could source a harbach relay. They do no longer carry or have replacements, still looking.

[@macpowas316]

Original relay is a P&B KA11DY 110VDC.

[@noakeswalker]

I had to look up this Heathkit linear - amazing that you could buy this for nearly 20 years back in the day. Great to see one being overhauled a bit.

[@9Z4Y]

hi thanks for this video, I need to change my relay and Harbach is out of stock, where else can I get a relay of a similar value for my SB200? any advice would be helpful please

[@PeopleAlreadyDidThis]

The original Potter & Brumfield relay had the same wires running from the moving contacts to terminals on the frame. The Heathkit assembly instructions had you cut these wires from the terminals, shorten to length, and solder the cut ends to the input jack and SWR bridge. In fact, the “old wires” you replaced were the original relay wires. I surmise this was done to keep the wires short and inductance down. That’s a guess...it might just have been convenient. The resistor is wired in parallel with the relay coil, lowering the total DC resistance. This was to set the grid bias for the tubes during transmit, as they are wired through the relay coil. Harbach’s relay has a different coil resistance, necessitating a different parallel resistor to set the bias voltage.

[@mefedler]

Thanks for the great historic insight.

[@macpowas316]

Two things, the resistor you said was in series with the coil of the relay is actually in parallel with it (part of a voltage divider) and when the original relay was installed they cut the wires off of tabs on relay and soldered them to input connector and SWR bridge. The wires were left connected to arm of relay.

[@johnmuise1785]

Question for you - (great video by the way). I'm replacing the TR relay in my old AEA LA-30 amp - same connection type on the original relay. The plastic cover had two holes "drilled" into the top of it for the RF in and out wires - so the two tabs at the top go directly to the RF connectors on the amp - and not internally wired to the bottom tabs like your new relay (and mine). So the question is . . . I'm guessing they did this originally to keep the RF kind of separate from the other DC wires etc. at the bottom of the relay. The downside to that (in my experience) is that if you don't solder from the RF connectors "just right", you can put stress on the actual relay contacts carrying RF and they stay open all the time. So I LIKE the way you are doing it - with all wiring at the bottom of the relay - but did it work well ? Was there an issue with the internal wires of the relay going from the top tabs to the bottom contacts or did everything just work well with all wiring at the bottom of the relay now ? THANKS ! de John VE3YUL

[@Ibelieve218]

I have the heathkit sb-200 complete with manual I just drilled out the rca and replaced it with so-239

[@jimpruett424]

This is my first amplifier I just received a heathkit sb 200 it needed a tube and I have that installed, it has a toggle switch on the front to key it, shouldn't I hear the relay clicking when keyed

[@mefedler]

The SB200 did not originally come with a toggle switch on the front. Either the original on/off rocker switch was replace with a toggle switch or maybe a second switch was added to enable the amp to be put into stand-by mode by turning off the tube filaments. You should hear the relay click when the amp is keyed through the RCA socket (Antenna Relay) on the back of the amplifier.

[@Ibelieve218]

where you get the relay and part number thank you

[@mefedler]

I purchased the relay along with the needed resistor from Harbach Electronics. The part number is RY-200.

[@cpgoef6]

Did you have any issues going from the old 150V capacitors to the 250V capacitors?

[@mefedler]

No issues seen using 250V capacitors.

[@cpgoef6]

I just completed the install and I haven't seen any issues as well!! Thank you!!

[@TI3WTI]

I´m considering to get one SB200, can you please post where did you bought replacements (Relay, etc). Thanks for thr detailed video ! 73, and "pura vida" William/ Ti3WTi

[@mefedler]

I purchased the relay along with the needed resistor from Harbach Electronics. The part number is RY-200. The relay was not available the last time I checked.

[@richardbaker1729]

Where did u get the new capacitors and what was the part number for them

[@mefedler]

Harbach Electronics

[@richardbaker1729]

@@mefedler ok ty

[@robertmeyer4744]

got the same one.I had to change out the power supply bored. relay as well. changed bnc to so-239. using Taylor 572/b tubes. works great. I do also have a SB-201 does not have 10 meters. I just purchased a SB 220. 2 / 3-500-Z tube amp. Ampex tubes. just need power supply Board and doorknob cap. it is working but plate volts drop off a lot .burned green resistors on power supply. red cap in tank circuit soft .getting new parts .came across this video looking for SB 220 power supply replacement and soft start relay.

[@dambuster6387]

I think that the fan is not pushing enough air I have fitted a much larger fan , cut a large hole in the chassis fitted about 4 inch fan much better. I fitted some Chinese tube,s a waste of time lasted 3 weeks going to mod it with Russian GI 7B and they are cheap as chips better than those Chinese rubbish.

[@edschaff6291]

i found a muffin fan n a little thinner and quieter that moves move air. fits underneath chassis. doest ror like full size fans.