Tube vs. Solid State Preamp
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From: Joerg on 3 Apr 2010 18:47 Michael A. Terrell wrote: > Joerg wrote: >> krw(a)att.bizzzzzzzzzzzz wrote: >>> On Sat, 03 Apr 2010 12:22:27 -0700, Joerg <invalid(a)invalid.invalid> wrote: >>> >>>> krw(a)att.bizzzzzzzzzzzz wrote: >>>>> On Sat, 03 Apr 2010 00:45:27 -0400, "Michael A. Terrell" >>>>> <mike.terrell(a)earthlink.net> wrote: >>>>> >>>>>> Jim Thompson wrote: >>>>>>> But they _do_ rectify... just not as efficiently. >>>>>> I've seen quite a few tube PA amps that picked up CB radio, and >>>>>> police radios into the UHF Mobile band. Some small churches freaked out >>>>>> when a police call came through the speakers, at full volume during a >>>>>> church service. >>>>> Probably not the tube doing the rectification, though. Usually a corroded >>>>> wire/contact in a mic was the culprit. >>>> Depending on the sermon topic and the nature of that police call it >>>> could be a fitting reminder of the consequences of sin :-) >>> For communion do you serve coffee and doughnuts? ;-) >>> >> No, those are for _after_ worship services, even for deputy sheriffs in >> attendance :-) >> >>>> But FM rarely gets in. AM radio from low flying aircraft is another >>>> matter. Ham radio as well but since they use SSB most of the time that >>>> will sound more like Charlie Brown's teacher ... wah-wa-waah ... >>>> ouuah-wah-wah-waaah. >>> FM wouldn't be as obvious. Wouldn't FM just put a DC bias on the mic circuit? >> Yes, that's why I don't quite understand how police radio could have >> gotten in there unless it was through a wireless mike link. > > > How many wireless mikes did you see in small churches in the '50s > trough the '70s? > You hadn't said 70's but I did see wireless mikes back then. Here I must confess that I rarely went to church in those days. But we used them at school events, at the town hall, and so on. Once as a kid I was a helper during some council meeting ballot. They handed me a wireless mike to announce results. I felt real important when they gave me that thing :-) > Any AM detector can demodulate FM via 'Slope Detection'. > .... _if_ there is a rather steep filter in front of it. That would have to be a real coincidence. -- Regards, Joerg http://www.analogconsultants.com/ "gmail" domain blocked because of excessive spam. Use another domain or send PM.
From: Michael A. Terrell on 3 Apr 2010 23:13 Joerg wrote: > > Michael A. Terrell wrote: > > Joerg wrote: > >> krw(a)att.bizzzzzzzzzzzz wrote: > >>> On Sat, 03 Apr 2010 12:22:27 -0700, Joerg <invalid(a)invalid.invalid> wrote: > >>> > >>>> krw(a)att.bizzzzzzzzzzzz wrote: > >>>>> On Sat, 03 Apr 2010 00:45:27 -0400, "Michael A. Terrell" > >>>>> <mike.terrell(a)earthlink.net> wrote: > >>>>> > >>>>>> Jim Thompson wrote: > >>>>>>> But they _do_ rectify... just not as efficiently. > >>>>>> I've seen quite a few tube PA amps that picked up CB radio, and > >>>>>> police radios into the UHF Mobile band. Some small churches freaked out > >>>>>> when a police call came through the speakers, at full volume during a > >>>>>> church service. > >>>>> Probably not the tube doing the rectification, though. Usually a corroded > >>>>> wire/contact in a mic was the culprit. > >>>> Depending on the sermon topic and the nature of that police call it > >>>> could be a fitting reminder of the consequences of sin :-) > >>> For communion do you serve coffee and doughnuts? ;-) > >>> > >> No, those are for _after_ worship services, even for deputy sheriffs in > >> attendance :-) > >> > >>>> But FM rarely gets in. AM radio from low flying aircraft is another > >>>> matter. Ham radio as well but since they use SSB most of the time that > >>>> will sound more like Charlie Brown's teacher ... wah-wa-waah ... > >>>> ouuah-wah-wah-waaah. > >>> FM wouldn't be as obvious. Wouldn't FM just put a DC bias on the mic circuit? > >> Yes, that's why I don't quite understand how police radio could have > >> gotten in there unless it was through a wireless mike link. > > > > > > How many wireless mikes did you see in small churches in the '50s > > trough the '70s? > > > > You hadn't said 70's but I did see wireless mikes back then. Here I must > confess that I rarely went to church in those days. But we used them at > school events, at the town hall, and so on. Once as a kid I was a helper > during some council meeting ballot. They handed me a wireless mike to > announce results. I felt real important when they gave me that thing :-) > > > Any AM detector can demodulate FM via 'Slope Detection'. > > > > ... _if_ there is a rather steep filter in front of it. That would have > to be a real coincidence. The input is unbalanced, and not dressed for RF, so it will do slope detection. I used to put a ferrite bead and a 100 pf capacitor in old amps to make a low pass filter to keep all the RF from the usual triode input stage. A lot of the old amps ran the preamp at full gain, with the gain control after the triode. Some nasty designs, lifted right out of the RCA, GE and Sylvania tube handbooks. A 5W VHF or UHF commercial radio would knock some of them out of service at a quarter mile. -- Lead free solder is Belgium's version of 'Hold my beer and watch this!'
From: Robert Baer on 4 Apr 2010 11:49 Joerg wrote: > Paul Keinanen wrote: >> On Fri, 02 Apr 2010 10:51:59 -0700, Joerg <invalid(a)invalid.invalid> >> wrote: >> >>> The not so good ones usually hum. And badly engineered solid-state >>> ones (meaning a lot of them) go *POCK* when someone turns on a GSM >>> cell phone nearby. I am not a tube freak but I've never heard a tube >>> amp do that, even if the design was a bit screwed up. Because it has >>> no BE junctions. >> >> I have hunted down Radio Moscow from several tube guitar amplifiers. >> There was a large number of short and medium wave transmitters in the >> megawatt class across the border. >> >> Apparently the pick-up coil inductance and the cable stray capacitance >> formed a parallel resonant circuit that happened to resonate on one of >> the numerous high power transmitter. Often a quick fix was to use a >> different cable with different length, which apparently moved the >> resonance to a quilter place :-). Adding a resistor and capacitor to >> the input jack usually solved the problems completely. >> > > Well, in Europe propaganda stations from behind the former iron curtain > were huge in terms of power. Megawatts. In Germany the problem was Radio > Tirana. It was sad, they were blowing money on propaganda and > electricity while their people were barely scraping by and often didn't > have enough electricity. But that's what such political "systems" > ultimately do to people. > ....just watch OBAMAcare, etc...
From: Chris on 4 Apr 2010 00:19 > > Yes, that's why I don't quite understand how police radio could have > gotten in there unless it was through a wireless mike link. > If it was that long ago they were probably AM police radios. Chris
From: Michael A. Terrell on 4 Apr 2010 01:26
Chris wrote: > > > > > Yes, that's why I don't quite understand how police radio could have > > gotten in there unless it was through a wireless mike link. > > > > If it was that long ago they were probably AM police radios. I wasn't alive in the '30s. -- Lead free solder is Belgium's version of 'Hold my beer and watch this!' |