Hello Phil. the 8877 Chinese jobs sell for about 650.00 and the Imac for
1400.00 or there abouts that is what Alpha sells them for as I remember.
You had a lot of experience with amps sounds like. I built my own amp with
4 811 tubes and they sure were rugged I thought. I used to tune for max
smoke but they sure did the job.. 73
Ed K7UC
----- Original Message -----
From: "Phil Scovell" <[log in to unmask]>
To: <[log in to unmask]>
Sent: Sunday, August 15, 2010 9:01 PM
Subject: tuning Tubes
> All the many years I ran tube amps, I did as basically is being suggested.
> I always first tuned at low input power to the amp. I often began, with a
> new amp, by someone, even if it were my young children reading the meter,
> got someone to give me the meter readings to get a feel for presets before
> tuning. In some cases, more times than not, I had to even explain to the
> person how to read the meter because nothing was digital back in those
> days.
> Once I repeated everything several times, band to band, I marked the front
> panel near the tuning knobs with anything, such as strips of clear vinyl
> tape we all use for Braille labeling etc. I normally only needed two
> pieces
> of marking tape because all other bands, 80 through 10, were very closely
> set to those pieces of tape, that is, to one side or the other. Once
> satisfied with all readings, grid current, voltage, and milliamp readings,
> in other words, once I knew my settings, I just preset the knobs and band
> switch, plugged in a little power, quickly peaked everything with the tone
> device I had back then, and dropped the carrier briefly to give the tubes
> a
> rest, although I normally didn't bother once I became familiar with the
> presetting of the controls, and then punched it with 100 watts of drive
> and
> found I only had to tweak the settings for a couple of seconds before they
> were at maximum. One day, when using my old Heath Kit Warrior amp with 4
> 811A tubes, quite rugged tubes, of course, I popped all four of the
> bleeder
> resisters across the top of the tube caps. This seemed to occur with that
> amp, and those tubes, once every 4 years. Talk about stink. Those
> resisters took weeks before the smell in the room finally went away. I
> had
> a friend who used to work for heath kit and was good with amps of all
> types
> but he would bring the new resisters over and solder them back over the
> tube
> caps. He tuned the amp on the air and before he did so, he was very
> adamant
> that they blew because I took way too long to tune up the amp. He had
> suggested this a half a dozen times that day and even before he came to
> replace the coil resisters. I kept telling him, that wasn't the problem,
> but you know how sighted people get some times about such issues. So, Bob
> cranks up the amp, driving it with 100 watts output from my Omni D, and
> while he was tuning, he caused the tuning condensers to spit, that is,
> ark.
> I said nothing but smiled big time to myself because with that amp, I
> never
> made the tubes spit during tuning because the carrier was never driving
> the
> amp for more than 3 or 4 seconds after presetting the controls. So, Bob
> has
> his good watt meter in line and I asked what the output was because a
> friend
> had pulled out two plug in tube shaped diodes someone had put in for the
> built in power supply and wired a circuit board in to the power supply and
> it pushed up my voltage, under load, up another 200 volts. He reported
> exactly 700 watts output. I said, Ok now Bob, turn everything off, that
> is,
> drop the carrier. Then detune all the controls, even the band switch to
> another band, mess up the loading control, the tuning capacitor, and
> everything. He did so,. He got up, I sat down, preset everything,
> snapped
> on a full 100 watt carrier without using even low input at first, and was
> done in 3 to 4 seconds. Bob said, "I can't believe it. You tuned it way
> faster than I did and without arcing it and I can see. I laughed. By the
> way, I used 4 811A tubes in that amp for years and replaced them about
> every
> 4 years during a period of years when I was super active on CW and I
> always
> ran the amp on CW about 90 percent of the time. The rest was on sideband.
> I'd run the 811A tubes down till they would show about 425 watts of output
> before replacing them. One time, when I replaced them, I pulled the old
> tubes, because they were beginning to ark occasionally, and when I shook
> the
> tubes, I could hear pieces of the plate that had burned off bouncing
> around
> the tubes and yet those 811A tubes still kept working. I've run amps with
> 572B tubes and the SB220 with a pair of 3 dash 500z tubes and I tuned them
> all the same way. I tried buying, from a contest friend, one of his amps
> which was the Henry 2K4. During contests, they got 2,000 watts output for
> the full 48 hours of the contest on phone or CW. After I had paid him
> some
> money down, a friend called me up with an amp with 3 811A tubes that
> Ameritron was making back then and when I saw how small the thing was, I
> decided, screw that big amp, my contest and big DX days are long gone so
> gave up the big amp for the little one. I know you can push 572B tubes
> more
> and get more output but based on my personal experience, and that of
> friends, they don't last as long and they are a little touchier when
> tuning.
> If you really take care of 3 dash 500Z tubes, and I'm talking about
> contesting and running thousands of hours of operation time, they will
> last
> 10 and 11 years. In all the years I ran the SB220, and I pushed it hard
> and
> always ran it in the highest voltage range even when you weren't supposed
> to
> do that on CW but could do so in side band, and I would run, with 100
> watts
> of drive out of my Omni, 1200 watts output on 20 meter CW, I never had to
> buy new tubes. It's a good thing as much as those dumb 3 500 tubes cost.
> So just get a single 8877, rung 5K output all day and all night, and when
> the tube eventually goes about 10 years later, it will cost you 1200 to
> 1600
> dollars to replace is all, hahaha.
>
> Phil.
> K0NX
|
