Sidebar Sidebar
  • You can now help support WorldwideDX when you shop on Amazon at no additional cost to you! Simply follow this Shop on Amazon link first and a portion of any purchase is sent to WorldwideDX to help with site costs.
  • Click here to find out how to win free radios from Retevis!

Heathkit sb-200 refurbishment

dozerman

dozerman

hello, its me again
Dec 16, 2013
186
36
38
milan tennessee
The wife bought me a heathkit today for my birthday. The unit is in really good shape cosmetically. Still has a few original caps, some replaced. Someone put new 1/2 watt resistors in place of the 30k 7 watt, smh... and that board had been hot. I've seen replacement power supplies online, are those a reasonable replacement? Is there a keying circuit that can be put in place of the pedal? Is there a reputable source for replacement parts? Thanks for any help
 

https://harbachelectronics.com/product-category/heathkit-sb-200-sb-201/

I have used these boards and found them to be very well done...
I have used many of his kits to repair various amplifiers.
Keying circuit?
Those amps were made to be controlled by the HF transceiver's switching circuits...
RF keying would require another circuit board with that ability...
Where to purchase?..and how to make that happen?
Sorry can not help with that.
All the Best
Gary

Good info here: http://www.crompton.com/hamradio/heath/sb200/sb200.html
 
not sure if this is what you are looking for, but it is a video of how to make an RF keying circuit.


there used to be a couple of online tutorials on how to set one up, but they seem to be gone.
LC
 
BJ radionut said:
https://harbachelectronics.com/product-category/heathkit-sb-200-sb-201/

I have used these boards and found them to be very well done...
I have used many of his kits to repair various amplifiers.
Keying circuit?
Those amps were made to be controlled by the HF transceiver's switching circuits...
RF keying would require another circuit board with that ability...
Where to purchase?..and how to make that happen?
Sorry can not help with that.
All the Best
Gary

Good info here: http://www.crompton.com/hamradio/heath/sb200/sb200.html
Click to expand...


Yeah I've been researching online and found several of his products and mods for these amplifiers. I'm going to order one of the supply boards. I also saw mods like soft start and hard key?? Unsure of what those are. Thanks for the help!
 
loosecannon said:
not sure if this is what you are looking for, but it is a video of how to make an RF keying circuit.


there used to be a couple of online tutorials on how to set one up, but they seem to be gone.
LC
Click to expand...



Yeah I didn't know if someone had a circuit that could be used in place of the foot pedal. Or if I could incorporate the pedal into my mic somehow. Keying a mic and remembering to mash a pedal is like rubbing my head and patting my stomach while chewing gum. I'm gonna forget to do it lol.
 
loosecannon said:
yep, that circuit will do it.

it will sense the RF coming into the amp, and key the relay.
LC
Click to expand...


A question.. would this need to be built on a circuit board? Obviously to keep it neat. And I'm assuming you would connect to the incoming so-239 then the relay. It can't be that simple, I'm missing something..
 
just saw that the relay in that amp is 120v coil, which means you'd have to replace it with a 12v relay, and then find somewhere inside the amp to get the 12v from.

sorry i didn't pay more attention before posting that video.
This mod can be done, but if you are not already adept at working on tube amps and the like, then it's probably above your pay grade.
LC
 
With the Soft Key module added which transforms the 120v to 1 volt dc just having a spare normally open set of contacts in mic or radio would serve the purpose to key amp.
All the Best
Gary

The SK-201 safely acts as an amplifier interface to your modern transceiver to the Heathkit SB-200 or SB-201. This unit is mounted inside the amplifier and transforms the negative 120VDC key closure to approximately 0.7VDC at 1.5mA. Without it you run the risk of severely damaging the keying circuit in your transceiver.

https://harbachelectronics.com/shop/heathkit-sb-200-sb-201/sk-201-soft-key-keying-interface/
 
  • Like
Reactions: Shadetree Mechanic
As BJ has already said, but I will say it again - Harhach!

Replace the power supply module - https://harbachelectronics.com/shop/heathkit-sb-200-sb-201/pm-200-replacement-power-supply-module

Add a soft-key interface - https://harbachelectronics.com/shop/heathkit-sb-200-sb-201/sk-201-soft-key-keying-interface

An alternative to the Soft-key would be a keying interface like the ARB-704
http://www.ameritron.com/Product.php?productid=ARB-704

Replacement tubes are available at RF Parts.
https://www.rfparts.com/tubes/tubes-572b.html
 
  • Like
Reactions: Shadetree Mechanic
Just got the Harbach power supply in today and in the amp. Got the board with the soft start and it was nice not seeing the tubes blasted instantly when I powered on. I let it idle a while to be sure of everything before I keyed and began to tune. Knowing next to nothing about this amp, aside from reading online what kind of drive it needed, I started with a dual final 939. Keying 15 on high swinging 50 pep. Swr between radio and box was good. A very quick tuned netted 550 pep. but the plates were cherry. So I let it idle a while. The plates cooled somewhat but not totally. Like they were working not idling or the bias was way off. Are the two trimmers by the band selector the bias?
 
Back side of tube sockets should have some 33 ohm 5watt resistors attached to the grids.
those have been known to get opened due to being over driven,

Check the resistance of those resistors.
 
Also worth noting is that amp was optimized for SSB usage at 1200 watts PEP INPUT...OK that in mind...At 50% efficiency that is 600 watts max PEP OUTPUT on SSB on the best bands normally 80/40m...20m and up that is reduced, with 10m normally producing the least output.
NOW if looking at the specs, CW(carrier) mode is 1000 watts INPUT at 50% duty cycle...So with this in mind on 10/11m AM service MAX drive should produce at best 400 watts PEP OUTPUT...If the tubes are CHERRY RED your over driving the amp.
If you want those tubes to last any length of time.:ROFLMAO:
The Bias is fixed by the supply board...MAX Plate current with ZERO drive should read about 100 mA on the meter...if the idling current is correct.
When driven correctly GRID current should not reach the the top of the GRID current scale except on Highest PEP peaks...normal voice peaks should be about 75% of scale...So keep this in range and the amp will give good service and clean signal. No one will hear the difference from 350-400 watts PEP and the 500+ PEP you are showing presently.
The tuned slugs are the INPUT tuning (SWR between radio and amp) and if showing good there as stated, there is no reason to adjust.
Try this operation and see if tubes run cooler and return to normal color very quickly(slightly Pink at most) after you unkey.
All the Best
Gary

EXTRA info:
The original Heath PA bias circuitry was routed through the antenna relay and the key line would ground this line with a small value resistor. This applied a high negative voltage to the tubes in standby(-120v...I think) and hopefully gave about 90ma of operating current in transmit. It was not variable. It also applied a high negative voltage to the key jack which is not compatible with the solid-state keying in modern rigs. I used the original bias winding rectified and filtered with a resistive voltage dropping network to give about -58 volts of standby bias. In transmit the relay on the control board switches the negative regulator in parallel with the standby bias with a 47 ohm resistor to ground. This shunts the -58 supply and the operating bias becomes just the adjusted output of the negative regulator. The regulator circuit has a pair of diodes in series in the output. This raises the minimum adjustable level getting it down close to zero volts. It also limits any backward current flow from the standby bias supply into the regulator.
http://www.crompton.com/hamradio/heath/sb200/sb200.html
https://forums.qrz.com/index.php?threads/sb200-amplifier-neutralization.242729/

And Wavrider is Dead on, in regards to the Grid resistors changing value!(y)
 
Last edited:
  • Like
Reactions: Shadetree Mechanic and wavrider

dxChat
Help Users
  • No one is chatting at the moment.


      Top Bottom
      Back