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#1
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Kenwood TS-820s finals.
Good day all!
I've been having some problems with my 820s. It was fine for several years and then I had a flashover in the finals. This may have been due to a faulty ground on a "UHF" coax connector. Have replaced the finals with 12 volt 6146B's (putting the heaters in parallel of course). However although it now works, its effeciency is damned awful. When it is loaded up to give 60 watts RF into a dummy load the dissappation in 6146 anodes makes then glow cherry red!!! Now my info tells me that the 6146B is rated at 30 watts anode dissappation per tube (total 60 watts) so based on my 50 odd years of electronics wouldn't expect a red hot anode at anything like the theoretical 66% efficiency. Yes, I have replaced the anode coupling cap (with an appropriate 3Kv rf type) checked all the tube voltages set up the neutralisation and tried the rig on all bands to ensure that the padding caps are OK. Same result! My thinking is that my 6146B's may be in poor condition. Unfortunately My old Heath valve tester does not do a very good job on big power valves so although it says they are OK I don't really trust it. So far I can't locate any parasitics up to about 120 MHz either. Anyone had a similar problem? I am getting so fed up with it that I'm thinking of running with 1x6146 and building a small linear amp ~400watts to drive the antennas. Regards Cliff Wright ZL1BDA ex G3NIA. |
#2
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Kenwood TS-820s finals.
Hello,
On 28 Ago, 07:05, cliff wright wrote: Good day all! I've been having some problems with my 820s. It was fine for several years and then I had a flashover in the finals. This may have been due to a faulty ground on a "UHF" coax connector. Have replaced the finals with 12 volt 6146B's (putting the heaters in what exactly are "12 volt 6146B's" ? 6146B have 6.3V heater. What tube are you using exactly? 73 Francesco IZ8DWF |
#4
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Kenwood TS-820s finals.
On 28 Ago, 11:59, (Geoffrey S. Mendelson) wrote:
wrote: what exactly are "12 volt 6146B's" ? 6146B have 6.3V heater. What tube are you using exactly? There were several variants with different heater voltages. I once bought a bunch of them cheaply at a hamfest. If you were building your own rig and could set the heater voltage, they were well worth the price. yes, I remember, but afair they had different "names", surely not marked as 6146B. 73 Francesco IZ8DWF |
#5
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Kenwood TS-820s finals.
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#6
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Kenwood TS-820s finals.
Roger (K8RI) wrote:
6146W IIRC No. They are ruggedized versions of 6146A's. Still have the same heater voltage (6.3) as regular ones. Note that they are NOT the same as 6146B's however in a TS-820, it may not be noticable. Geoff. -- Geoffrey S. Mendelson, Jerusalem, Israel N3OWJ/4X1GM IL Voice: (07)-7424-1667 U.S. Voice: 1-215-821-1838 Visit my 'blog at http://geoffstechno.livejournal.com/ |
#7
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Kenwood TS-820s finals.
Roger (K8RI) wrote:
On Tue, 28 Aug 2007 03:16:06 -0700, wrote: On 28 Ago, 11:59, (Geoffrey S. Mendelson) wrote: wrote: what exactly are "12 volt 6146B's" ? 6146B have 6.3V heater. What tube are you using exactly? There were several variants with different heater voltages. I once bought a bunch of them cheaply at a hamfest. If you were building your own rig and could set the heater voltage, they were well worth the price. yes, I remember, but afair they had different "names", surely not marked as 6146B. 6146W IIRC Nope. A 6146W is just a ruggedized version of a 6146B. Same pinout, voltages, everything. I have two of them in my Kenwood TS820S, replacing S2001s. http://www.rfparts.com/tubeapp.html Bob. |
#8
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Kenwood TS-820s finals.
Geoffrey S. Mendelson wrote:
wrote: what exactly are "12 volt 6146B's" ? 6146B have 6.3V heater. What tube are you using exactly? There were several variants with different heater voltages. I once bought a bunch of them cheaply at a hamfest. If you were building your own rig and could set the heater voltage, they were well worth the price. In a commerical radio, e.g. the 820, they were of absolutely no use. Geoff. The tubes in Question are a pair of 6883B's. According to all my data they are identical to the 6146B except for a nominally 12.6 volt heater rating, and a tiny increase in interelectrode capacity (about 1%). They were often used in high power (~60 watt) HF "bush" radio telephones in NZ until recently, both in SSB and AM modes. So they are relatively common here. I pulled the covers off the final to check after your posting. Since the 820S actually runs the 6146B heaters in series from 12.6 volts there should be absolutely NO reason why they couldn't do the job with a simple heater rewire from series to parallel. They are physically identical to a 6146B externally. Hope this clarifies the situation. Regards Cliff Wright ZL1BDA |
#9
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Kenwood TS-820s finals.
On 28 Ago, 13:11, cliff wright wrote:
Geoffrey S. Mendelson wrote: The tubes in Question are a pair of 6883B's. According to all my data they are identical to the 6146B except for a nominally 12.6 volt heater rating, and a tiny increase in interelectrode capacity (about 1%). They were often used in high power (~60 watt) HF "bush" radio telephones in NZ until recently, both in SSB and AM modes. So they are relatively common here. I pulled the covers off the final to check after your posting. Since the 820S actually runs the 6146B heaters in series from 12.6 volts there should be absolutely NO reason why they couldn't do the job with a simple heater rewire from series to parallel. They are physically identical to a 6146B externally. Indeed the 6883B is like a 6146B with different heater voltage. Then either these tubes are bad or you have another problem on your radio. Check antenna TX/RX relay and antenna socket connector. I had an FT-102 with antenna socket with an intermittent solder joint and it caused all sort of problems. It seems that you already checked all voltages on the tubes, but it might help to know what you exactly measured on the various grids and anodes, both in RX mode and in TX (idle). Do you observe any variation on the idle current of tubes when in TX mode with no mic input? When these tubes fail usually they have an ever increasing idle current and there's little to no way to stop this current to increase. 73 Francesco IZ8DWF |
#10
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Kenwood TS-820s finals.
"cliff wright" wrote in message ... Good day all! Have replaced the finals with 12 volt 6146B's (putting the heaters in parallel of course). However although it now works, its effeciency is damned awful. That should work fine. When it is loaded up to give 60 watts RF into a dummy load the dissappation in 6146 anodes makes then glow cherry red!!! Does maximum power out perfectly coincide with the dip in plate current? What is the quiescient plate idle current in SSB? What is the grid drive current when tuning? Are you using a terminating type dummy load wattmeter, or an inline wattmeter to an antenna? What is the plate current when tuned for 60 watts output? Yes, I have replaced the anode coupling cap (with an appropriate 3Kv rf type) That wouldn't be a likely cause.,, checked all the tube voltages set up the neutralisation and tried the rig on all bands to ensure that the padding caps are OK. Double check you coax jumper cables for problems, unsoldered shields, etc. Sometimes simple solutions to difficult problems elude us. Peter k1zjh |
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