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[KD7TWW]

The bad
Band switch. What cleans up these, please? Would it be worth it in the long to get to Scubbin down? Switch contact cleaner? Or should I not worry about the tarnish/bluing and not mess around because it's so old. Or jus us DE-Oxit and be done?
I've not run the unit since the new P/S rebuild (new to me scenario). and checking everything and dotting my eyes and crossing my T's. BTW the band switch wafers have turned to a *Purple color. The camera does not show that Thanks 73 https://www.qsl.net/kd7tww/SB200/DSCI0211.JPG

P.S. I cant fine nobody that will test 2 572B in Boise for me? Nobody, even A-Gem (Caldwell) cant test em. A-Gem is the largest Wholesale Electronics in Idaho I think?

[WA2CWA]

Put some deoxit on a Q-tip and just wipe the contacts, exercise the switch several times, then wet with water another q-tip and wipe the contacts, use a heat gun or hair dryer to expedite the drying. Using the 572's in a rig is probably the best way to test them. My original 572's have been in my SB-200 since it was built in 1969.

Pete, wa2cwa

[G4AON]

Silver plated switch contacts oxidise, it’s normal. Even “new” switches that have been in storage discolour over time.

Use a non residue switch cleaner, rotate the switch and it will clean. Don’t be tempted to use switch cleaner which contains oil, yes it minimises future oxidation, but dust accumulates on it making a real mess.

Your amp looks to be very clean, I had an SB200 several years ago, nice amp if a little sluggish on c/o.

73 Dave

[K4PF]

You can test a 572B in any tube tester that will test an 811.  Just use the 811 settings.  Most emission type tube testers won't do a gas test, though.
To test for gas, look for color in-between the elements of the tube when it is energized with HV in the amplifier. 
Color at the interior surface of the glass is OK (actually indicates a hard vaccuum). 

73

[KD7TWW]

"look for color in-between the elements of the tube when it is energized with HV in the amplifier. Ok, I'll do that...
Thank you Ed and all that posted their reply's regarding the band switch and I'm going to ask my local Wholesaler now if he can test 811's with his Hicknok 600 Thanks for the help, Ho ho 73 

You can test a 572B in any tube tester that will test an 811.  Just use the 811 settings.  Most emission type tube testers won't do a gas test, though.
To test for gas, look for color in-between the elements of the tube when it is energized with HV in the amplifier. 
Color at the interior surface of the glass is OK (actually indicates a hard vacuum). 

73

[K4PF]

A Hickok 600 can do a gas test.  It's better to discard a gassy tube
before plugging it into the SB-200 for a 'trial by fire'..
The Hickok gas test is based on adding or removing
a high-value resistor in series with the control grid
while monitoring plate current. This is a push-button test
with the Hickok.
A tube with acceptable gas will not have much of a shift
in plate current due to the presence or absence of the added resistor.
Hickok says less than a one-division increase on the transconductance
scale means the tube passed.

73

[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 quantity to ( KEMET 270uF 450 caps. I've never seen 6 Heatkit Original Equipment caps get so bad and dried out!

(Operation) My thoughts are with 120v service and portable operations with a Chinese gen set for power. This unit will be my portable rig only. I like the lower bands, 10m and 2 meters.
(Tubes) As I was told, only a few hours of service (on the 572B) I have yet to test these pair still.
2. 6x 100K 5W Bleeders. Found 4 that were shot, 2 open
3. 16x New 1n5408 Rectifiers. Saved 2 old OEM diodes for the front meter bypass cross diodes
4. Put 2 cross diodes on the meter circuit
5. Added a Resistive circuit for an amplifier slow turn-on the circuit when Operated with a low voltage/current situation. The circuit comes with a front-mounted 10A 250V Toggle bypass switch. Engage-Bypass 2x 25 ohm 25-watt Ceramic wire wound resistors wired in-line. Wired 120v after the push button resettable fuses. I live in an apt, so cant use an outside attennas
6. Harabach Softkey SK-201 installed. Tested and works.
7. Lifted/Removed the PT HV Transformer to service. Installed 2 sleeves of High Temp Heat shrink tubing to the secondary output HV leads and a few sleeves of HS to Grn Fillment leads. Sealed up PT with Hot (chinese snot) Glue inside.

Delicate cloth HV HT wires will never fray again.

8. R&R 2 mfd and 20 mfd BIAS caps
9. Back of Chassis R&R 33 Ohm R21 and R22. Out of Tolerance
10. Re-added one each .02 1kv caps to the Ant and Alc connections in rear of chassis. Both where removed for some reason??
11. Added a cool mod. A Push-Pull 100k Lin pot for the SWR pot (r13). So I can disengage amplifier (barefoot) (bypass switch-pull) when I go 100 watts and a wire or QRP, barefoot? Pull to disengage. The pot was Pricey $$$ but a quality par $40 shipped!
12. Replaced many wire(s) and solder wicked wiring. R&R HV cable to a high-grade 10 KV red jacketed cable.
13. New 46 ohm Parasitic suppressors,
14. 1x 100 puff c26 blocking cap. It was cooked and checked open.
15. Front meter sticks. Moves slowly.      (Still to do)
16. R&R Original Fan motor. Replaced with a Bathroom plastic 4-bladed fan and motor. It works okay but not great. I'll update as I go along.
17. Added 12v DPDT Relay for control of both keying circuits
Thanks so far. 73, Vince

The bad
Band switch. What cleans up these, please? Would it be worth it in the long to get to Scubbin down? Switch contact cleaner? Or should I not worry about the tarnish/bluing and not mess around because it's so old. Or jus us DE-Oxit and be done?
I've not run the unit since the new P/S rebuild (new to me scenario). and checking everything and dotting my eyes and crossing my Ts. BTW the band switch wafers have turned to a *Purple color. The camera does not show that Thanks 73 https://www.qsl.net/kd7tww/SB200/DSCI0211.JPG

P.S. I can't fine nobody that will test 2 572B in Boise for me. Nobody, even A-Gem (Caldwell) cant test em. A-Gem is the largest Wholesale Electronics in Idaho I think?