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sb-221 Question

N

North Texas Mudduck

Active Member
Apr 5, 2005
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got a sb-221 from a freind that can no longer operate it due to illness.
the sb-221 has 2 of the 3-500zg
i have a ft-950 at 100 watts on both fm and lsb
on fm radio keys 100 watts when i key the amp it tunes up to about 1100 to 1200 on this meter
then i flip to lsb same 100 watts i can only get 400 to 600 watts on a normal voice.
 

meter is a Swan wm-2000A in the rms mode
 

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Then I have to think that the meter is reading correctly and the average power is right for SSB readings. SSB is maybe 50% duty cycle and FM is 100% duty cycle so the two readings are comparable.
- 'Doc

... and just for grins. If he keeps running that power level in FM on that '221 he'd better start saving up for some tubes.
 
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Agreed with Doc. You cannot accurately measure pep with an average reading meter. In FM mode the carrier level is the same as the pep value but in SSB mode there is no carrier. The power level varies with voice levels and the meter is not fast enough to indicate instantaneous peak values without a true active pep circuit.
 
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Hmmmmm???
what can i do to get him to see the watts this thing is supposed to do on ssb
for some reason he wants it tuned on fm then he flips back to lsb
he said it had the graphite tubes and he said it might need more drive for the ssb part
but im thinking if hes tuning up on fm and has a driver inline he wont be talking very much longer on the box
 
If he has the operating manual you really should be following the tune up procedures in the manual. Guessing at it and hitting the amp with 100 watts FM is a sure way to fry something in that old amp.

And to measure the SSB PEP output you need a PEP reading watt meter. It's as simple as that.
 
North Texas Mudduck said:
got a sb-221 from a freind that can no longer operate it due to illness.
the sb-221 has 2 of the 3-500zg
i have a ft-950 at 100 watts on both fm and lsb
on fm radio keys 100 watts when i key the amp it tunes up to about 1100 to 1200 on this meter
then i flip to lsb same 100 watts i can only get 400 to 600 watts on a normal voice.
Click to expand...

North Texas Mudduck said:
Hmmmmm???
what can i do to get him to see the watts this thing is supposed to do on ssb
for some reason he wants it tuned on fm then he flips back to lsb
he said it had the graphite tubes and he said it might need more drive for the ssb part
but im thinking if hes tuning up on fm and has a driver inline he wont be talking very much longer on the box
Click to expand...


I thought YOU got it from him because he can no longer use it due to illness. :confused:

The amp has to be tuned with a carrier and that carrier can be AM/FM/CW or whatever produces a steady output level. Switching to SSB will make the meter read low simply because the meter cannot respond fast enough and peaks cannot be seen. A typical average responding meter will read as low as 40% of the true pep value depending on voice characteristics and meter damping (how slow the meter responds). All you can do to get the readings you want is to buy a TRUE peak reading meter or just spring for a cheap Dosy and tweak it to make you feel better. :D

OK on second look it appears that Swan WM-2000A does have an active pep circuit. It should read true pep levels. Is it plugged in and does the pep function work properly. It MUST have electrical power applied to measure pep.
 
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Don't worry about it. The amplifier is working just fine. If you really want to see what the amplifier is doing, look at it on an oscilloscope, that will tell the tale. The meter cannot physically keep up with voice peaks.

People on here seem to put too much stock on what their power output meters say on SSB.
 
WA8ZYT said:
Don't worry about it. The amplifier is working just fine. If you really want to see what the amplifier is doing, look at it on an oscilloscope, that will tell the tale. The meter cannot physically keep up with voice peaks.

People on here seem to put too much stock on what their power output meters say on SSB.
Click to expand...

I thought that as well and read an article here recently saying that an active peak reading circuit with a peak/hold does a better job at capturing true peaks.

So what happened with the OP?
 
WA8ZYT said:
Don't worry about it. The amplifier is working just fine. If you really want to see what the amplifier is doing, look at it on an oscilloscope, that will tell the tale. The meter cannot physically keep up with voice peaks.

People on here seem to put too much stock on what their power output meters say on SSB.
Click to expand...


Well that would be true if the meter was not a true peak reading type and was the type that simple placed a capacitor across the detector circuit to make the meter read a little higher in peak mode. Since the Swan WM-2000A does indeed have an active peak circuit it should read very close to the true pep value. With my Diawa CN-801H I see a big difference between average and peak readings.

Using an oscilloscope to measure power output is a PITA as you must first convert peak-peak voltage to something a bit more useful and then compute the power based on true load impedance which must be measured and not just assumed even if using a dummy load. Of course you could also use RF current meters and compute power but then again you are dealing with slow reacting analog meters.

Just get a true peak reading meter that works and you will be close enough and it's the easiest way.
 
359 said:
I thought that as well and read an article here recently saying that an active peak reading circuit with a peak/hold does a better job at capturing true peaks.

So what happened with the OP?
Click to expand...

hes been in and out sick for awhile and up had had a stroke
and unable to do much, going to be in rehab for awhile
and thats not looking good either
 

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