Both mod decks are hooked up to the RF deck all the time. They both get high voltage, but I only turn one on at a time. Both are driven by the same 120 watt 8 ohm power amp, into LS output transformers (right and left channels), as is the 811 mod deck in the pp 812 rig. All the transmitters should sound the same, since the same audio feeds them. The 4x150 (or 4cx250b) sounds best, in AB1. Yes, lots of current, 500ma at 1000 or 2000 volts, 250 ma each tube.
I have tried just two 100TH tubes, different plate voltages (variac in power supply), yet it just never sounds as clean as the 4x150 deck. I can also run 100TL tubes, and tried them, same sound. People over the air cant hear a difference, they say, but its quite audible in the mod monitor. My voice is also lop sided, but not as much as yours! I get the best peaks on the 813/4x150 combo, I don't know what the actual reading is, as the pep wattmeter only goes up to 2000 watts, and I have to guestimate by how hard the needle slams into the stop, but expect its not much over 2500 watts at 600 watts carrier. If I was to run the rig at 2000 watts pep, would anyone know or care that I was exceeding the power limit (by a little bit)??? In your case, I would try to limit the positive peaks, say equal to the negative peaks, and run about 90% modulation. This will give good audio percentage and a strong carrier. Positive peaks are good, but I don't think they are effective on the air, if you have to limit the negative mod and the pep. better to make sure you go 90% negative at least, and whatever positive, lower is better to keep it under 1500 watts, although I doubt the FCC truck will pull up outside the house if you go over 1500 watts pep. If you ran 10,000 watts pep, someone might notice eventually, but they really should pay more attention to the intentional interference on the bands. I personally don't think they pay any attention to anything other than blatant abuse over a long time, and even then, they seem to play games, warnings, going to court, etc. I think offensive people should have their equipment taken and a hefty fine, there seems to be no way to self police the ham bands, how can I find out who is causing problems and drive way down south to have a 'talk' with someone? I did track down Ron boot (anyone remember him?), go over his house, and confront him face to face. He was a foul mouth, and talking tough to me over the air, so I went over his house (parents house) on my motorcycle, rang the bell, and asked him if he was ready to go at it. He turned REAL nice and gave me a tour of his shack (junk). I told him, I know where you live, and can come back anytime day or night, and although I am mellow and tolerant, I can pound your face if I get pissed enough. The FCC had gone after him somewhat, with zero results, so I personally don't worry about going slightly over 1500 watts pep. Brett N2DTS > > My voice is so lopsided; it has peaks 2 squares pos on the scope > for one square down. I've tried it on many scopes direct > from many good > microphones. When connecting the same mic to the rig, a 600 watt > carrier output yields 5400 watts PEP output just as the carrier is > pinched on the 100% negative cylce. If I switch the polarity of the > microphone it all goes downward and pinches the carrier with > only a PEP > of about 700-600 watts. I was very careful to maintain the linearity > and phase of the audio all the way through to the output of the > modulator so that in the old days when we ran 1KW input and got 800 or > more out of the high efficiency finals the PEP was 3 squared > for me not > 2. I am now toying with the idea of reversing the phase of > the mic and > increasing the carrier to about 1200 watts to yield 1500 PEP, just to > see how it works that way. Same amount of sideband power just more > carrier. It probably won't sound as heavily modulated nut I wonder if > it will take out more noise and make diode detection cleaner. > > About your modulator decks, do they each have there on modulation XFMR > or is the modulation XFMR common to both. As for the different sounds > for each one, there may be many variables I am not aware of. I assume > the quad 100th modulator is AB2 of B and requires some driving power > where as the 4X150 are probably AB1. so there may be different driving > techniques. I don't know what the peak current capability > for either of > those tubes is for a given drive voltage. I used quad > 4CX300s once for > modulators and boy did that thing have the current swing > capability, and > in AB1 even. The sockets were a bear though. I had to make adapters > with octal plugs on them. I was given the tubes and have no idea what > the real socket even looks like. I now use quad 813s in AB1 although > they will do AB2 just fine. They just never draw and grid current at > the low level we run them these days. I run about 2500 volts on the > plates and 800 on the screens setting the bias to idle total cathode > current of about 100 ma. They show just a tiny little color on the > plates. > > John, > WA5BXO > > > > -----Original Message----- > From: [EMAIL PROTECTED] > [mailto:[EMAIL PROTECTED] On Behalf Of Brett Gazdzinski > Sent: Tuesday, November 25, 2003 2:33 PM > To: amradio@mailman.qth.net > Subject: RE: [AMRadio] Re: Modulation transformer ID and repair > > Well, the 813 rig seems to be clean in the audio > department, and gets nice positive peaks, over 130% positive, > and I can get 2500 watts pep out of a 600 watt carrier, but > will try a bigger audio cap and see if it sounds better... > > When I run the push pull parallel 100TH deck, the audio does > NOT sound as clean, its not bad, its just not as clean as the 4x150a > mod deck. > Resting current and plate voltage does not seem to change the sound, > I tried various settings and so on. > > Brett > N2DTS > > > > > _______________________________________________ > AMRadio mailing list > AMRadio@mailman.qth.net > http://mailman.qth.net/mailman/listinfo/amradio
