sb220 plate volts

[ke7trp]

Decided to wire up the SB220 yesterday.  Using SSB more and more since there is NO AM on 75 that I can hear. Put the SB220 back inline and wired it up for 220 volts.  In my shack, I have a 60 amp 220 volt line comming in.  This branches out to two 220 volt 20 amp plugs.  The kind of plug most amps use. This way, I can run my transmitter on one and an SSB amp on the other.

I noticed that this 60 amp plug has 248 volts across it.  The plate volts on the SB220 is 3300.  This SB220 has the harbach, caps, Diode board and meter board installed by myself.

I wonder what my Filiment volts are   Probably cooking my poor 500s.  Since its these tubes are instant on.. I have been shutting it off alot.  If I walk out of the room or I know I am not going to talk.  I wonder if thats actualy harder on it?

C

[W2PFY]

Better open it up and test the filament voltage. Most tubes are rated for 1/2 volt above or below the rated voltage. Better low than high. I don't know if the 200 has a stand alone filament transformer but if it does, it will be somewhat more easy to reduce the voltage to a proper level. 3-500's are very expensive to replace, even more difficult to find NOS from Eimac.

[ke7trp]

Yeah. It has a seperate fil trans. I think I better test it. Its almost 250 volts on this line. I have a dozen 3-500s. But these are perfect old eimacs with full output. I need to start looking for a big 220 volt variac at ham fests.

C

[KM1H]

It wouldnt take much of a bucking transformer to get the input down to a safe level for the filaments.

Either a 15A secondary 240V for everything or a 2A 120V just for the filament xfmr. Anything in the 10-15V area would be OK.

Carl

[Steve - WB3HUZ]

Or a small Variac. The higher plate voltage is probably good (assuming the PS caps are OK). THe 3-500Z will put out quite a bit more power as you move up the 3 kV scale.   

It wouldnt take much of a bucking transformer to get the input down to a safe level for the filaments.

Either a 15A secondary 240V for everything or a 2A 120V just for the filament xfmr. Anything in the 10-15V area would be OK.

Carl

[KE6DF]

For the filaments only, you could probably use a power resistor in series with the primary of the filament tranny.

As a side effect, the power resistor method also gives you a soft start on the filaments as they draw much more current when cold.

This wouldn't work for the plate transformer, however, as it would screw up regulation big time.

[ke7trp]

Yeah.  This one has the Harbach caps, Big diodes and metering board. The Grids are also Grounded.  Its showing 1508 watts on the Power master meter with 113 watts Drive on tune up.  I run it around 600 to 800 watts for rag chewing.

I just had an alarming experience.. LOL.. I was tuning up the thing on 40 meters since I moved about 50 KC and I saw a huge flash.  I let off and searched around behind the tuner. I found that a wall wart cord had fallen across the OWL!  That wall wart was off, Its part of my audio rack. However, The wire burnt to a crisp!  There must be huge voltage across that OWL!

Lucky for me, nothing is destroyed but the presonus preamp that the wall wart was plugged into.. Its done..  I unplugged it and through it in the garbage. I always make sure that nothing is hear that line. In fact there is only about 4 inches of it in the shack. The tuner is right at the point of exit.. But somehow, I knocked that wire loose and it fell down there over the OWL.

DOH!

C

[KD6VXI]

Clark,

Instead of a variac for station control, see if you can find a SOLA constant voltage conditioner...  Something like we used 'back in the day', in IT days.

With them, you get a nice sinewave output, at whatever voltage you want. 

Some people running large tubes (handled) use these on their fils.  You could probably run your entire 'legal limit' station off one......  Or, if all your equipment has sep fils xformers, have a filament bus, and a 220 bus for plate / etc.

The nice thing about the SOLA is, you don't have fluctuation with current draw like you do on a variac.  The variac, when you set it up for full voltage at idle, drops fils voltage on key...  And your tube gets cooler.  If you set it where the fils voltage is correct keydown, then when it's idling, it's too high.

You can also throw a couple small value power resistors in the filament xformer leads.  Not necessary, though, since the SB220 has a current limited fils xformer.

Cheapest way, variac.  Best = SOLA.

--Shane

[ke7trp]

They are super expensive.. We need to find some at a surplus house somewhere   No more unlimited IT budget for me. Back in the day, I could order 20 of those and not even need a PO

I will ask mike to walk through Apache reclimation. He lives close by.  Maybe they have them. 

The amp lived through the shorted OWL.  Just talked AM on 7293 with the 220.  250 watts. Runs nice and cool.  Good reports.

Shane, While I have you here.. When I key the foot pedal with no Drive the standing current is .15  Is that normal? Seems high to me.. I thought my old SB221 that you worked on was more like .8

C

[W2PFY]

I need to start looking for a big 220 volt variac at ham fests.

I would just use a smaller variac to control the filament voltage. A few extra volts shouldn't hurt the tubes as long as they are not drawing too much resting current. somewhere I read that triodes in class B should have an idle current of 2/3 the total plate dissipation for the least amount of harmonic distortion.

[KD6VXI]

I know what you mean about budgetary constraints.....  Stupid people getting us all used to having open credit cards!

The one I worked on we did up a bias board using 'string of diodes', and tapped it to have it biased deeper class B, because it was an AM amplifier..  SSB was of no use.  50 mils a tube (on the high tap) is about the lowest you want to go to have any linearity out of the tubes.

100 mils a tube is about normal, or 180 would be fine, too.

I just read an email from a guy where they ran 20 volts of bias on the SB220!  NO idle current.  He said the distortion on SSB was so bad it made the amp unusable.

Tube brand, and how abused they are will also have an effect on the standing current.

--Shane

[KD6VXI]

Clark,

In addition, Carl has a mod to prevent your bandswitch from going out to lunch...  Small cap across 2 terminals on the switch....

I'd have to go through emails to find it, maybe he can chime it in?


--Shane

[ke7trp]

You guys got me worried so I checked the fil volts. 5.75 volts idle. 5.25 under key at 400 watts AM.  I think this is ok dont you guys?

C

[W2PFY]

5.75 is way too high. You'll pay the price of a short life tube.   You need to lower it. Your only .25 volts short of 6 volts. Do what you want but I would NEVER run a tube filament voltage that high. Just trying to help, not trying to admonish you

[KB2WIG]

C,

The Eimac data sheet has the  '500  at 5.0+/- 0.25......   so I'd say yer too high.

Click on the following.

http://www.umich.edu/~umarc/station/docs/3-500z.pdf


klc

[ke7trp]

Yeah.. We new I was high..   With almost 250 volts at the wall   To me a half volt is not that bad..  Hmmm.. Variac or resistors?

C

[ke7trp]

Wow.. Came back in room.  Fil volts 5.1 now.  Plates way down.. around 3k.  Power at wall is down.  Its 108 outside and every AC unit in the entire hood is on full bore..  including my 6.5 tons   Maybe I have nothing to worry about. 

We are supposed to run programable thermostats here.. I bet these people have them set to cool the house down at 3PM so when they get home from work, The house is cool. Thats what I used to do when I had to go to the office every day. 

  I cant make legal limit anymore 
C

[Jim, W5JO]

I have to ask, are you using the proper meter?  Does the meter read true RMS?  In other words, are you absolutely sure of the reading?

[ke7trp]

I am using a Fluke DVM.  I ran in the next room and got my second meter, it reads the same

C

[KM1H]

The reason I mentioned a bucking xfmr just for the filament is that it is the cheapest solution if you have to buy it. Ive seen new overstock at $2 for a 12V @ 2A unit on mail and internet flyers. Plus it is small enough to mount under the chassis.

With all the AC on and still 5.1V that will soar later. The 3-500 works very well at 4.7 to 4.8V. You can fine tune it with a Variac until the power just starts to drop and then increase it .1V Just my 22 cents adjusted for taxes, inflation, and health insurance

[Superhet66]

C,
If your in a tract development and share one large step down instead of individual pole pigs it might explain part of the line voltage issue.

After a renovation here at work we ended up sharing a common x-fmr and our comm. gear and back up generator board has been screwy ever since. The utility tapped in on the high side as a compromise.

As you pointed out, daily use cycles throw the E all over the place.
The large "community" x-formers have a very wide range of taps to choose from if you ever get a look inside. The voltage chosen is a guesstimate/crap shoot that often takes place before the houses are even built.  

Another issue is how far down the feed you are.

Lots of nice, big, buzzardly analog Volt meters out there, mount one where you can see it swang. Or go Figital and program it to yell at you when a preset is exceeded.
It sounds like you have things under control, except for the wall wart execution  

                                    blah blah blah...    D.
 

 

[K5UJ]

I wondered about the fil.v. with my amp which also uses pair 3-500zg.  I noticed lately my service v. is up around 122 to 123 on each side.  I looked at the schematic of my Sparta 701 to see how they handled the fil. v.   

Now, the Sparta 701 is a 1 KW AM rig running two pairs of 4-500A, one for modulator and one for PA.  Each pair has its own fil. supply transformer to deliver 10 v. 20 A for each pair.  So the fil. v. is different from the 3-500 but the concept applies.  Everything in the 701 runs off 230 v. firstly, including the two fil. transformers so they each have that for primary (with several taps from 220 to 250).  The rig has one filament meter, 0 - 15 v. AC wired in through a dpdt switch so it can be switched from modulator pair to PA pair (although that part is unnecessary for the amp) and the meter tap is right across the cathode pins of one of the tubes in each pair at the pins. 

A 100 W. 0 to 5 ohm rheostat (a big ohmite ceramic wire wound pot) is in series with one side of the primaries of the two filament transformers to adjust the v. drop on one 115 v. leg before it branches out to the two primary sides.  That's the filament supply adjust.  So, I'd say if you are concerned about your filament v., you need to set up a permanently installed filament meter (which I think should be stock in all manufactured amps), and figure out the v. drop needed to cover the range supply v. fluxuation and get a rheostat in series with your filament supply transformer primary (it also doubles as a inrush inhibitor if that is a problem; may not be with small low current transformer) and you can dial in your voltage every time.

I imagine if you go out and buy one of those big pots they are kind of expensive but I saw some at Dayton in the flea market so you may find one at a hamfest.  You can get the value of R you need by putting one you find in series or || with a fixed value. You could also replace the stock transformer with one that has multiple primary taps or use an auto transformer with multiple taps to get you close to the 5 v. so the pot can be adjusted to get you right on it.  Hopefully with the right combination you can power up the amp and tweak the pot every time to get it right.

Rob   

[K5UJ]

This is the kind of thing I'm talking about however in this particular case you'd have to put a fixed value resistor in parallel to get it down in value.  probably not that big a deal and gives you an idea....

http://cgi.ebay.com/ws/eBayISAPI.dll?ViewItem&item=360262984687

[WD5JKO]

Instead of a variac for station control, see if you can find a SOLA constant voltage conditioner...  Something like we used 'back in the day', in IT days.

With them, you get a nice sinewave output, at whatever voltage you want. 

   I look fondly at old ferroresonant technology. They are old school, but have their place. They do however run hot, make noise, and the output is NOT sinusoidal. The output due to the saturate-able magnetics is more of a "quasi-square" wave. This means the peak is squished (no 1.414 X RMS). A peak reading AC meter will measure these low; you need a RMS type voltmeter. Most Sola's I've seen have a wide range input, and a fixed output at about 118 vac.

   I do like the series rheostat idea although it is rather lossy. Also take Carl's buck transformer idea and make it variable with a tapped transformer with a rotary switch. Clark, any chance you got a Lionel train power pack (the ones with AC output)? 

Jim
WD5JKO

[ke7trp]

The Transformer is right out side. I live in a Cul D sac.  The trouble is that its one 50 for 5! homes.  It was replaced a few years back so at least its new.

I have a big RCA power line monitor. It has a big needle.  It shows 127 at night and down  to 115 or so during the middle of the hottest part of the day.   So power is pretty good here but all those AC units running full bore when its 110 outside takes its toll.

For now, I just leave the amp off.  If I want to use it, I turn it on and talk.  Since its instant on, I dont need to idle the thing. 

This has really made me look over my entire shack power system.  I wanted to make a Visio Drawing of the power lines and do some analasis. But Visio is expensive.  I wonder if there are some cheap or free alternatives?  I have a feeling its time to run another line in. 

C