[Amps] Bring a SB-220 Back To Life.

Sun Jun 19 11:17:20 EDT 2016

When I made this posting ,  I was asking for whats everyone's thoughts 
were as to the best path to take to get this running again, with the 
minimal chance of destroying something.

 From what I have gathered by a lot of Googleing, This is what I think 
is the best way.

PLEASE! if you think something is wrong, or I should do something 
differently, or add something else PLEASE! let me know.

But this is what I have gathered so far.

Open it up of course, and Defeat the HV shorting thing.

Install a resistor in the HV line, I can not find the values of what 
this resistor should be.  Anyone?  And best placement location? And is 
it's intention to protect if I remember correctly the HV supply if some 
sort of a catastrophic failure with a tube should happen?

OK pull both tubes.

Make sure the HV connections to the tubes cant touch anything,

Power switch "OFF"

Voltage switch to the "LOW" voltage  ( CW/Tune Position )

Meter switch to the "HV" Position.

Now this amp, has some sort of a homebrew soft start system added.

Should I By-Pass it? Or leave it inline to add a bit of additional 
protection. The resistors can act somewhat like fuses, if something 
should be terribly wrong yes?

Now connect the power via the variac. Have variac set to zero volts.

Connect a HV probe and suitable meter to a convenient HV measurement 
location.

Connect another meter to the filament pins of one of the tube sockets.

Turn power stitch to "ON"

Extremely slowly start to raise voltage using the variac.

Monitor all three voltage meters.

I would assume that there will not be any plate current. No tubes, plus 
in receive position.

Now if something "IS" wrong, could there be an indication of plate current?

Same thing with Grid current? no tubes, so should be NO grid current true?

Would there be any way for grid current to appear at this stage?

Now, how slow should I take to raise the voltage?

Many talk about "Days" to "Form" the caps after being un charged for 
such a long time.

Eventually bring the line voltage to full value.

Now if anything should be wrong, what would I see? About all I am 
monitoring is the three sources of voltage measurements, and switch to 
the grid current if anything could be good to monitor there.

Now power down,  switch to the HV voltage to the "HIGH" lever the ( SSB 
) position. And do all the above again just to make sure all is well.

In a "Stock" 220, what should the HV voltages be in this situation?

And also the filament voltages? This would be under no load since no tubes..

Now after safely discharging all voltages, install one of the tubes.

Power up as above again all slowly.

Now should I power it up, with the HV connected to the tube right from 
the start? Or leave the HV off first and bring the tube up to full 
filament voltage slowly first? Now I am assuming that I will have to 
stop early with the variac, because the load on the filament transformer 
will be half of it's normal load since it is only one tube.

So should I bring the tube up with no HV first, and then later do it all 
again with the HV?

What if anything should I watch for? Like anything HV voltage wise? or 
grid current wise? etc?

Shut down again, make safe again, and do it all again with the second 
tube solo again.

If all seems good, shut her down, make safe and install the second tube 
and do it all again but with both tubes in now.

Once all looks good, now short the transmit jack and what should I see 
metering wise?

Now this amp will not show a "Idle Current" it has one of those ummm 
active idle current shut off circuits, so when simply putting it into 
transmit mode, the plate current meter does nothing.

Now slowly apply some power, what should I monitor closely?

I'm thinking of course plate current, and grid current.

Plate should slowly rise, and of course dip and all that with the tune 
and load controls usual tuning up stuff. But what should I see grid 
current wise?

I guess slowly bring up power and see what she does?

Thoughts, comments, additions, suggestions, anything?

Joe WB9SBD

Sig
The Original Rolling Ball Clock
Idle Tyme
Idle-Tyme.com
http://www.idle-tyme.com
On 6/15/2016 9:13 PM, Louis Parascondola wrote:
> I'm sure someone here has saved  one of my many emails on this 
> subject.  Can anyone post it.  Thanks
>
> Sent from AOL Mobile Mail
>
>
> -----Original Message-----
> From: Joe <nss at mwt.net>
> To: Amps group <amps at contesting.com>
> Sent: Wed, Jun 15, 2016 01:46 PM
> Subject: [Amps] Bring a SB-220 Back To Life.
>
>
> I have an old SB-220, That when it was running, ran like what? Holy COW!
> Long story.
>
> Anyway, I desire to being it back to life. It was last on the air in
> 1993. And has sat in storage places, and damp basements ever since.
>
> As a primer to the home-brewing of these other Amps I plan on making. I
> want to bring this girl back to life.
>
> I will shortly be installing the 220 power in the shack, and even have
> ready for it a 220 volt variac.
>
> So, I have discussed this with some others, and got several different
> theories on how I should proceed in bringing this back to life with the
> least possible chance of any damage.
>
> So what do all you pro's here say. step by step, what would you do if
> this was your amp. And you wanted to bring it back to life after sitting
> since 1993.
>
> Here is the story of how I came to own this amp, and it's,,, well,,
> uniqueness?
>
> http://www.qsl.net/nss/SB-220-Story.html
>
> Joe WB9SBD
> -- 
> Sig
> The Original Rolling Ball Clock
> Idle Tyme
> Idle-Tyme.com
> http://www.idle-tyme.com
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