"MNACE" <[EMAIL PROTECTED]> made an utterance to the drakelist gang ---------------------------------------------------------------------- I had a TR4-C that had a very dirty slide switch that Garey talks about (the one that switches between plate current and power out). I actually (very very carefully) took it apart, cleaned the contacts, re-assembled, sprayed with deoxit, and all the meter problems went away. The other option would be to replace with a new slide switch.... 73, Mark N5KAE
----- Original Message ----- From: "R. Ton" <[EMAIL PROTECTED]> To: <[EMAIL PROTECTED]> Cc: "Drakelist" <drakelist@www.zerobeat.net> Sent: Sunday, April 16, 2006 4:14 PM Subject: RE: [drakelist] TR-4C transmitter troubleshooting > > "R. Ton" <[EMAIL PROTECTED]> made an utterance to the drakelist gang > ---------------------------------------------------------------------- > Great idea, Garey... > > With my meter set as low as it'll go, I'm showing about 0.3 mV across > the shunt resistor in transmit. This thing isn't drawing any current > at all! In receive, I'm getting a cathode voltage of about 155V and > a plate voltage of about 754V. The 754V plate reading is the same > as my AC-4 under no load. In transmit, there is no change in plate > voltage, but the cathode voltage goes to zero. > > According to the schematic, the cathodes are grounded via the T/R relay, > the 2 ohm shunt resistor, an RF choke and a 15 ohm resistor (one 15 > ohm resistor for each tube). Even through the 15 ohm resistor, I'm > showing 0V on the cathode in transmit. > > Wierd. This would sure seem to indicate that the finals aren't > conducting at all. Still, very weak on my tube theory here -- > could a grid condition cause this? I'm showing a good -60V on > pins 2 and 6. > > I was also thinking that a 1 watt, 2 ohm resistor should be able > to handle about 700ma without cooking. When I got the rig, this > resistor was burned in half. Maybe it's time to pull the tubes > and see if anything is rattling around inside? :( > > Is my thinking halfway straight? :) Hoping like heck the plate > current meter isn't shot -- I have a feeling those are hard to > get. > > Thanks again everyone! > > 73, Rob (KFØRT) > > > > -----Original Message----- > > From: [EMAIL PROTECTED] > > [mailto:[EMAIL PROTECTED] Behalf Of Garey Barrell > > Sent: Sunday, April 16, 2006 9:57 AM > > To: R. Ton > > Cc: Drakelist > > Subject: Re: [drakelist] TR-4C transmitter troubleshooting > > > > > > > > Garey Barrell <[EMAIL PROTECTED]> made an utterance to the > > drakelist gang > > ---------------------------------------------------------------------- > > Rob - > > > > OK, a little more information..... > > > > When the 2 ohm meter shunt resistor opens up, the Final cathode current > > is routed through a "slide switch" mounted up on the LOAD capacitor > > shaft, (activated by pushing in the LOAD control,) a series resistor > > that is selected at test, (mounted on the slide switch terminals,) of > > typically ~200 ohms, and the plate meter. It wouldn't take much > > current to damage that resistor and/or meter with the shunt resistor > > open. Or if the slide switch contacts are not closing properly in the > > "out" position of the LOAD control. > > > > Perhaps your finals are drawing idle current, it's just not showing on > > the meter!? Measure the voltage drop across the meter shunt resistor. > > 100 mA should read 200 mV. > > > > By the way, if you're not used to working on tube gear, keep in mind > > that 650V (OR 250v) BITES! An AC-4 bleeds down pretty quickly when > > turned off, but only your meter knows for sure before you stick your > > fingers in there! > > > > 73, Garey - K4OAH > > Atlanta > > > > Drake B & C-Line Service CDs > > <http://www.k4oah.com> > > > > > > > > R. Ton wrote: > > > Thanks to all (!!) -- more coming when I get a chance (life is > > getting in > > > the way of fun right now). > > > > > > So far, I've had the chance to change out the relay -- the ONE > > spare part > > > I had on hand. No difference. The rig does go into transmit > > when switched > > > to CW mode (no key plugged in). Both relays respond and the > > receiver mutes. > > > I just noticed this AM that the .025 plate current reading I > > get is there > > > even with the power off. Meter moves about a needle's width > > when put into > > > transmit and the S-meter reads about 7-8 in transmit -- may be > > another clue? > > > > > > And thanks for the hollow-state theory Garey. It's been a > > REALLY long time > > > since I've worked on any tube gear, but it's slowly coming back > > to me. :) > > > > > > I'll be digging some more in a bit here and will report back. I'll also > > > see if I can catch the technical net this afternoon. 7.238 @ > > 2000Z, right? > > > > > > Thanks again everyone! > > > > > > 73, Rob (KFØRT) > > > > > > > > >> -----Original Message----- > > >> From: [EMAIL PROTECTED] > > >> [mailto:[EMAIL PROTECTED] Behalf Of Garey Barrell > > >> Sent: Sunday, April 16, 2006 8:41 AM > > >> To: Drakelist > > >> Subject: Re: [drakelist] TR-4C transmitter troubleshooting > > >> > > >> > > >> > > >> Garey Barrell <[EMAIL PROTECTED]> made an utterance to the > > >> drakelist gang > > >> ---------------------------------------------------------------------- > > >> Hi Kevin - > > >> > > >> Expertise is just experience clouded by memory! :-) > > >> > > >> I don't think I've ever come across a PAIR of finals that "lit up", but > > >> wouldn't draw at least a couple hundred mA if they had the DC > > potentials > > >> applied to them. In fact, I can only remember one tube that > > was "open", > > >> but lit. I still think it had a broken weld inside it!! :-) > > >> > > >> But then I've been wrong before. A favorite med school phrase, "when > > >> you hear hoof beats, think horses, not zebras" comes to mind! > > >> > > >> Hopefully Rob will get it fixed in spite of my help and let us know the > > >> truth!! > > >> > > >> 73, Garey - K4OAH > > >> Atlanta > > >> > > >> Drake B & C-Line Service CDs > > >> <http://www.k4oah.com> > > >> > > >> > > >> > > >> kbgluxford wrote: > > >> > > >>> kbgluxford <[EMAIL PROTECTED]> made an utterance to the drakelist > > >>> gang > > >>> ---------------------------------------------------------------------- > > >>> I certainly don't have Garey's expertise or long experience, but I did > > >>> have a similar problem on one of my TX4 transmitters recently. I > > >>> changed out the PA tubes and the problem disappeared. > > >>> > > >>> 73 > > >>> Kevin > > >>> VK3DAP / ZL2DAP > > >>> > > >>> Garey Barrell wrote: > > >>> > > >>>> Garey Barrell <[EMAIL PROTECTED]> made an utterance to the > > >>>> drakelist gang > > >>>> > > ---------------------------------------------------------------------- > > >>>> Rob - > > >>>> > > >>>> You don't mention anything about "keying" the transmitter. You have > > >>>> to "key" the Push-To-Talk (PTT) of the microphone to switch it to > > >>>> transmit to see the idling plate current. You should hear the relay > > >>>> click when it closes. > > >>>> > > >>>> If the final tubes have plate voltage, screen voltage and filament > > >>>> voltage, and the cathodes are returned to the negative pole of those > > >>>> supplies, they WILL draw plate current! The grid voltage is the > > >>>> only thing that keeps them from drawing AMPS of current in the > > >>>> presence of the other voltages. > > >>>> > > >>>> There are two RF chokes in series between the +650VDC supply and the > > >>>> plate caps of the tubes. There is a 15 ohm, 1W resistor in series > > >>>> with each of the final tube cathodes to another RF choke, through the > > >>>> meter shunt resistor, and then through a relay contact to ground. > > >>>> > > >>>> 73, Garey - K4OAH > > >>>> Atlanta > > >>>> > > >>>> Drake B & C-Line Service CDs > > >>>> <http://www.k4oah.com> > > >>>> > > >>>> > > >>>> > > >>>> R. Ton wrote: > > >>>> > > >>>>> "R. Ton" <[EMAIL PROTECTED]> made an utterance to the drakelist gang > > >>>>> > > ---------------------------------------------------------------------- > > >>>>> I'm finally digging into a TR-4C I bought used some time ago. It > > >>>>> "worked > > >>>>> fine" when it was shipped here, but I haven't been able to get any > > >>>>> power out > > >>>>> of the transmitter. It at least oscillates -- I can hear it on a > > >>>>> receiver > > >>>>> in the same room. > > >>>>> > > >>>>> Starting at the beginning... > > >>>>> > > >>>>> The manual says to adjust the bias on the AC-4 so that the plate > > >>>>> meter reads > > >>>>> .1 amp. This is with the sideband switch counter-clockwise and the > > >>>>> xmtr > > >>>>> gain all the way down. The meter seems to read about .025 in > > >>>>> receive and > > >>>>> goes up just a little when the rig is switched to CW. Adjusting the > > >>>>> bias > > >>>>> has no effect on the plate meter, but it does indeed adjust the bias > > >>>>> voltage. Setting it to -60 volts is no problem, but I'm unable to > > >>>>> get any > > >>>>> "real" plate current no matter what I do. Any ideas? > > >>>>> > > >>>>> I haven't done anything to the radio since I got it except spray the > > >>>>> switches with Deoxit D5 and replace R45 (2 ohms -- plate meter shunt > > >>>>> resistor!!). This resistor was fried in half. > > >>>>> > > >>>>> What am I in for? > > >>>>> > > >>>>> Many thanks in advance! > > >>>>> > > >>>>> 73, Rob (KFØRT) > > >>>>> > > ---------------------------------------------------------------------- > > Submissions: drakelist@www.zerobeat.net > > Unsubscribe: [EMAIL PROTECTED] - unsubscribe > > drakelist in body > > Hopelessly Lost: [EMAIL PROTECTED] - help in body of message > > Zerobeat Web Page: www.zerobeat.net - sponsored by www.tlchost.net > > ---------------------------------------------------------------------- > > > > ---------------------------------------------------------------------- > Submissions: drakelist@www.zerobeat.net > Unsubscribe: [EMAIL PROTECTED] - unsubscribe drakelist in body > Hopelessly Lost: [EMAIL PROTECTED] - help in body of message > Zerobeat Web Page: www.zerobeat.net - sponsored by www.tlchost.net > ---------------------------------------------------------------------- > ---------------------------------------------------------------------- Submissions: drakelist@www.zerobeat.net Unsubscribe: [EMAIL PROTECTED] - unsubscribe drakelist in body Hopelessly Lost: [EMAIL PROTECTED] - help in body of message Zerobeat Web Page: www.zerobeat.net - sponsored by www.tlchost.net ----------------------------------------------------------------------
