Thank you Dave for a masterful set of instructions. This whole thread has
been fun but throwing in unnecessary aftermarket devices complicates it all.
If the switch is a big worry just bypass it (or leave it on) and buy a 240
volt plug strip. I can't believe someone actually referred to
microprocessor functions. This is an amplifier straight out of the ARRL
handbook of the early 1960 but with a very nice transformer design and
parasitic suppressers that I have copied in building or repairing many dual
3-500Z amplifiers and have never had a problem unless the original builder
had really sloppy lead lengths and the antenna was a mess. I do suggest
buying a High Voltage probe for the DMM (mine is a Fluke rated to 6000 volts
bought off ebay for $60 or currently $160 brand new so you are not dependent
on the panel meter for troubleshooting.
Dave
W7VM
-----Original Message-----
From: Amps [mailto:amps-bounces@contesting.com] On Behalf Of Dave
Hachadorian
Sent: Monday, July 10, 2017 1:03 PM
To: amps@contesting.com
Subject: Re: [Amps] SB220 step start blows fuses - c'mon
C'mon guys, this is only an SB-220. It's a barebones amplifier with no
complicated protective circuits. It's easy to work on, since it was built
as a kit.
To troubleshoot this amp, you should need only one spare fuse.
Somewhere in the procedure below, the fuse will blow, and you will know
where the problem is.
First, remove the surge limiter circuit. It is a troublesome, unnecessary
item. Restore to factory configuration.
Disconnect the primaries of the plate and fil/bias transformer and see if
the fuse blows.
Connect the primary of the fil/bias transformer, with secondaries
disconnected, see if the fuse blows.
Connect the bias secondary of the fil/bias transformer and see if the fuse
blows.
Connect the filament secondary of the fil/bias transformer, with the tubes
removed. See if the fuse blows.
Plug in the tubes. See if the fuse blows.
Connect the primary of the plate transformer with secondary disconnected,
see if the fuse blows.
Connect the secondary of the plate transformer, with the B+ line to the
tubes disconnected. See if the tube blows.
Connect the b+ line to the tubes and see if the fuse blows.
It's a lot more fun to work on Tetrode amps with all kinds of digital and
analog protective circuitry!
Dave Hachadorian, K6LL
Big Bear Lake, CA
-----Original Message-----
From: donroden@hiwaay.net
Sent: Monday, July 10, 2017 5:50 AM
To: amps@contesting.com
Subject: Re: [Amps] SB220 step start blows fuses
Agree with Gary !!
Make a tester out of a garage light with a 300 or 500 watt halogen element.
( or pair ) relatively inexpensive and I always need an extra
light
when looking for things in my garage.
Don W4DNR
Quoting Gary Schafer <garyschafer@largeriver.net>:
> You don't have a big enough bulb.
>
> I use two 300 watt bulbs in parallel. 300 watt bulbs are about the
> largest you can find easily.
>
> I made up the bulb unit using a square electrical box and mounted two
> outdoor light sockets on it, an outlet and a regular house switch to
> short out the bulbs when I want to bypass the series bulbs.
> It works great for checking amps. It is really nice if you have an
> intermittent arc or want to let suspect capacitors cook for awhile
> with the amp is in standby as no harm is done if something arcs, the
> bulbs just light up bright.
>
> I sometimes plug the light bulb setup into a variac too.
>
> 73
>
> Gary K4FMX
>
>> -----Original Message-----
>> From: Amps [mailto:amps-bounces@contesting.com] On Behalf Of Warren
>> Volz
>> Sent: Sunday, July 09, 2017 9:53 PM
>> To: amps; gudguyham@aol.com
>> Subject: Re: [Amps] SB220 step start blows fuses
>>
>> I may shortly be looking to purchase a variac.
>>
>> After building a dim bulb tester this weekend I have a minor update.
>>
>> With 120V connected, the HV primary disconnected and one tube in a
>> socket (doesn't matter which I use) the 100W bulb in my tester lights
>> up bright. No fan and the meter lights aren't on. If I take out the
>> tube the fan and meter lights work. So I guess I have a shorted tube?
>> Would it be good to double check the DC/AC voltage on the filament
>> supply with the tubes plugged in? That would show any sags that might
>> exist.
>>
>> -Warren
>>
>> > On Jul 7, 2017, at 12:58 PM, gudguyham--- via Amps
>> <amps@contesting.com> wrote:
>> >
>> > I know I sound like a broken record but yes, a Variac is the way to
>> go. Especially with amps that can have power supply problems and
>> gassy tubes. You will hear the plate transformer groan and won't see
>> HV climbing on the meter if there is a problem in the PS long before
>> the smoke Genie appears. My Variac gets used daily several times
>> after doing ANY work on an amp. It's saved me loads of time fixing
>> blown parts that would normally occur if I had just turned an amp on
>> with problems. Best investment I ever made. 0-250 volts at 20 amps.
>> >
>> > Sent from AOL Mobile Mail
>> >
>> >
>> > -----Original Message-----
>> > From: Bill Turner <dezrat@outlook.com>
>> > To: Amps group <amps@contesting.com>
>> > Sent: Fri, Jul 7, 2017 12:34 PM
>> > Subject: Re: [Amps] SB220 step start blows fuses
>> >
>> >
>> > ------------ ORIGINAL MESSAGE ------------(may be snipped)
>> >
>> > On Fri, 7 Jul 2017 10:21:36 -0400, Mark B. wrote:
>> >
>> >> A variac varies voltage. It is not designed to limit
>> >> current.
>> >
>> > REPLY:
>> >
>> > At the very low end of its range, a Variac limits current just
>> > fine. I worked as a calibration technician at Tektronix for years,
>> > taking brand new scopes off the assembly line and powering them up
>> > for the first time. Believe me, a Variac is the only way to go with
>> > a unit which could have any number of problems at first. Over the
>> > years I powered up literally thousands of scopes this way and never
>> > a problem with current limiting.
>> >
>> > 73, Bill W6WRT
>> > _______________________________________________
>> > Amps mailing list
>> > <a href="mailto:Amps@contesting.com";>Amps@contesting.com</a>
>> > <a href="http://lists.contesting.com/mailman/listinfo/amps";
>> target="_blank">http://lists.contesting.com/mailman/listinfo/amps</a>
>> > _______________________________________________
>> > Amps mailing list
>> > Amps@contesting.com
>> > http://lists.contesting.com/mailman/listinfo/amps
>>
>> _______________________________________________
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>
> _______________________________________________
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DonR
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