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[KD7TWW]

Good evening where ever you are in the small world? Hi hi. Boise, Idaho. Home of the Dropping Potato!
I have a new to me SB200 I recvd about 60 days ago. I'm just now getting ahead of upgrading/repairing this unit. SB200
Pics https://www.qsl.net/kd7tww/SB200/
MY main reason here & question is? I've done as much as what was recommend by my other Hams and my own personal experience which is not much on RF Equipment and online? But I do have a pretty good understanding of electronics and learning as I go about HV amplifier units like this and slimmer ones. So Right from Wrong works well with me in my head for repairs. I don't botch, Hi Hi.
I could never afford something this nice in my lifetime. I am a General btw. I am hoping to learn more about HF amplifiers. And I'm on the lookout for another BONE stock unit, BTW.

Hoo hoo. What's been done so far:

1. Upgrade p/s. Increased Capacitor Quaintly to 8 KEMET 270uF 450 caps. I've never seen 6 Original Equipment caps get so bad and dried out My thoughts are with 120v service and portable Operations with a Chinese gen set. This unit will be my portable rig only. I like the lower bands, 10m and 2 meters. Tubes as I was told only had a few hours of service (572B) I have yet to test those pair still.
2. 6x 100K 5W Bleeders. 4 were shot, 2 open
3. 16x 1n5408. Saved 2 old for the front meter
4. Put 2 cross diodes on the meter circuit
5. Added a slow turn on circuit with a front mounted toggle bypass switch. 2x 25 ohm 25 watt Ceramic wire wound resistors. Wired 120v after the push button fuses. I live in an apt
6. Harabach Softkey SK-201 tested and works
7. Removed the PT HV Transformer out and installed 2 sleeves of High Temp Heat shrink tubing to the HV leads and Grn Fillment leads. Sealed up PT with Hot (chinese snot) Glue. Delicate cloth wires will never fray again.
8. R&R 2 mfd and 20 mfd caps
9. Back of Chassis R&R R21 and R22. Out of Tol
10. Re-added one each .02 1kv caps to the Ant and Alc. They where removed for some reason??
11. Added a cool mod. A Push-Pull 100k Lin 6mm shaft, for the SWR pot (r13). So I can disengage amplifier (Pull2 bypass switch) when I want to go 100 watts and a wire or QRP? Pull to disengage. Pot was Pricey $$$ &X&X^&..!
12. Replaced many wire(s) and solder wicked wiring. R&R HV cable to a high grade 10 KV cable.
13. New Parasitic suppressors, 100 puff c26 blocking cap. It was cooked, checked open.
14. Front meter sticks. Moves slowly?
15. R&R Original fan and motor. Replaced with a Bathroom plastic bladed fan and motor. It's works okay but not great (wanted to try it). I'll update as I go along. Thanks so far. 73, Vince
P.S Am I missing something here? Hey Heathkit Gurus
https://www.qsl.net/k/kd7tww//Canadas%20New%20Class%20of%20Amateur%20Radio%20License.html

[KD6VXI]

Start a Heathkit amplifier in CW mode.  No need for a step start. 

If you insist on a step start, a resistor and a relay is all that is needed.  Automatic step start.  Wire the coil of the relay or contactor on the transformer side of the step start resistor.  1 47 ohm wirewound resistor is all that is needed.

Use a simple IRF640 and 2 resistors.  Soft key done.

Replace all the resistors in the amp.  Use metal film for this.  Most are way out of tolerance, and flameproof is better.

If the metering circuit uses more than .5 volts across it then throwing the diode (you only need one) across the meter will effect accuracy at the higher end of the meter.

I don't know what you mean by the lower bands of 10 and 2 meters.  Your amplifier has zero hope of ever operating on 2 meters.  Maybe I'm missing something?  10 meters is the upper band of HF.  2 meters is VHF.

Those BROAN bathroom fans usually pump a LOT more air.  I had to slow mine down with resistors in each lead (I didn't have the resistor I needed to slow it down, but I did have a pair that where half the value!!!).  Without doing this it sounded like a jet taking off.

The 572B is an instant on tube.  With a step start wired in the circuit the bypass / operate switch is nonsense.

Any capacitor should check 'open'.  At least until the cap is charged up, then it will slowly move an analog meter to the right.

Move the meter adjustment back and forth.  Put a cotton swap of DeOxit on the meter adjustment screw.  This usually frees stuck meter assemblies.

I would have replaced the bleeders with 200K or slightly higher.  But that's just me.

There is more than one way to skin a cat.  I still don't understand why people spend money on the 'harbach' stuff unless their PC boards have disintegrated to the point they are unviable.  The original boards and circuit has lasted decades.  I get it that it's cool to "did the harbach mods", but what did they net you?  A few watts of imperceptible increase in Pout?  Increased safety for the end user?  What am I missing here?  (I've asked this question before and never got an answer, only agreements).

Replace all the resistors.  Replace all the electrolytics.

The SB200 is a good amp, it should provide you with many years of service.  If you can find CETRON tubes, snap them up.  They will outlast you and I, probably put together.  The Chinese tubes of today, not so much.

--Shane
WP2ASS / ex KD6VXI 

[K8AXW]

One thing you might want to check:  Heath made a bandswitch change sometime during the SB-200 run. The original had a switch wafer connection that was very close to metal at ground potential. 

Mine arced over (I'm assuming during a klutz moment) and destroyed a ceramic wafer.  Fortunately, I was able to find a suitable replacement wafer.

My original assembly manual was yellow.  I found the Heath wiring change in a tan assembly manual. 

If you're interested in the details, let me know.  If your assembly manual is tan, chances are you have the newer model and you're OK.

Otherwise you have gone through what I call the "Heathkit Amplifier Upgrade Syndrome."  Most of it unnecessary. But, that's one of the beautiful things about Heath amps.  They invite tinkering!

As one pointed out, the resistors and electrolytics should be replaced.  The relay circuit that activates the amp should be modified to accommodate modern transceivers. I made one mod....a front panel STANDBY/OPERATE switch.  Although the 572Bs are "instant on" I couldn't stand turning the amp on and off repeatedly.   

Al - K8AXW

[KD7TWW]

Was the Band switch Black or white with silver contacts? I have the White model and it looks great. Then put my eyeballs close and looked over the contacts, those look great as well. I do mods because it makes me feel better and I think mentioned that I will be portable and I said I live in an apt. So a 3500w Gen set and 120v. And no, I'm not on the band wagon either for this or that..., I overbuild like most hams do. Just because.
73

One thing you might want to check:  Heath made a band switch change sometime during the SB-200 run. The original had a switch wafer connection that was very close to metal at ground potential. 

Mine arced over (I'm assuming during a klutz moment) and destroyed a ceramic wafer.  Fortunately, I was able to find a suitable replacement wafer.

My original assembly manual was yellow.  I found the Heath wiring change in a tan assembly manual. 

If you're interested in the details, let me know.  If your assembly manual is tan, chances are you have the newer model and you're OK.

Otherwise you have gone through what I call the "Heathkit Amplifier Upgrade Syndrome."  Most of it unnecessary. But, that's one of the beautiful things about Heath amps.  They invite tinkering!

As one pointed out, the resistors and electrolytics should be replaced.  The relay circuit that activates the amp should be modified to accommodate modern transceivers. I made one mod....a front panel STANDBY/OPERATE switch.  Although the 572Bs are "instant on" I couldn't stand turning the amp on and off repeatedly.   

Al - K8AXW