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Replacement electrolytics
I have just re-capped the power supply capacitors in a DX-40 with 40uf 450 VDC
Aluminum Electrolytics from NTE Electronics in New Jersey. I have noticeable hum on the carrier. Measuring the ripple voltage with a 10 Megohm ac coupled meter shows 2.3+ volts [average/rms ... non-sinusoidal] on the 600 vdc line and 1.2 volts [average/rms ... non-sinusoidal] on the 300 vdc line. It appears the RS of the capacitors is way too high. What manufacturer or brand are others using with success? Does MOUSER carry suitable replacements? If so, what brand/style? Other sources? TIA DD, W1MCE |
Replacement electrolytics
Dave wrote:
I have just re-capped the power supply capacitors in a DX-40 with 40uf 450 VDC Aluminum Electrolytics from NTE Electronics in New Jersey. I have noticeable hum on the carrier. Measuring the ripple voltage with a 10 Megohm ac coupled meter shows 2.3+ volts [average/rms ... non-sinusoidal] on the 600 vdc line and 1.2 volts [average/rms ... non-sinusoidal] on the 300 vdc line. It appears the RS of the capacitors is way too high. Your ripple values look ok to me. They calculate out to be under 1%. (0.4% rms) You probably have a problem elsewhere, such as a heater-cathode leak, or short. -Chuck |
Replacement electrolytics
How do you know you have hum? Are you listening on a local receiver? If so it could be a form of "tuneable hum" caused by the AC in the house wiring modulating the received signal. If you have a good scope, try looking at the waveform directly; any hum will show as modulation riding on carrier. The amounts of ripple you're seeing are very minimal, as others noted... Pete |
Replacement electrolytics
Is this hum on am or both am and cw. If it is only on am, then it would be
int he audio chain and not the power supply. Colin K7FM |
Replacement electrolytics
Dave wrote:
I have just re-capped the power supply capacitors in a DX-40 with 40uf 450 VDC Aluminum Electrolytics from NTE Electronics in New Jersey. I have noticeable hum on the carrier. Measuring the ripple voltage with a 10 Megohm ac coupled meter shows 2.3+ volts [average/rms ... non-sinusoidal] on the 600 vdc line and 1.2 volts [average/rms ... non-sinusoidal] on the 300 vdc line. It appears the RS of the capacitors is way too high. What manufacturer or brand are others using with success? Does MOUSER carry suitable replacements? If so, what brand/style? Other sources? TIA DD, W1MCE Dave, Although I concur with the thoughts of others replying, FYI, I use the Xicom series of electrolytics from Mouser with success on virtually all projects that have been recapped, transmitters and receivers. |
Replacement electrolytics
COLIN LAMB wrote:
Is this hum on am or both am and cw. If it is only on am, then it would be int he audio chain and not the power supply. Colin K7FM No ripple on the audio power buss [400+ vdc. 0.001 vac] This bus has a RC filter of 20K and 20 uf. It is clean. It is in both the AM & CW mode. So, it has to be the rf string where the +600 is common to the two 6CL6s [series connected] and the 6146. I'm beginning to suspect heater/cathode coupling/short in one or more of those tubes. I gave my scope away about 5 years ago ... :-( I have an EE degree and 40+ years of design/management experience, so a little trouble shooting is not a problem for me. But, I have no capability to measure capacitor ESR. Well, I'll keep playing. Thanks for suggestions. DD, W1MCE |
Replacement electrolytics
thanks
K3HVG wrote: Dave wrote: I have just re-capped the power supply capacitors in a DX-40 with 40uf 450 VDC Aluminum Electrolytics from NTE Electronics in New Jersey. I have noticeable hum on the carrier. Measuring the ripple voltage with a 10 Megohm ac coupled meter shows 2.3+ volts [average/rms ... non-sinusoidal] on the 600 vdc line and 1.2 volts [average/rms ... non-sinusoidal] on the 300 vdc line. It appears the RS of the capacitors is way too high. What manufacturer or brand are others using with success? Does MOUSER carry suitable replacements? If so, what brand/style? Other sources? TIA DD, W1MCE Dave, Although I concur with the thoughts of others replying, FYI, I use the Xicom series of electrolytics from Mouser with success on virtually all projects that have been recapped, transmitters and receivers. |
Replacement electrolytics
Dave wrote:
I have just re-capped the power supply capacitors in a DX-40 with 40uf 450 VDC Aluminum Electrolytics from NTE Electronics in New Jersey. Who makes them? NTE does not make capacitors, they rebadge them. I have noticeable hum on the carrier. Measuring the ripple voltage with a 10 Megohm ac coupled meter shows 2.3+ volts [average/rms ... non-sinusoidal] on the 600 vdc line and 1.2 volts [average/rms ... non-sinusoidal] on the 300 vdc line. It appears the RS of the capacitors is way too high. What manufacturer or brand are others using with success? Does MOUSER carry suitable replacements? If so, what brand/style? I have been using the Panasonics from Digi-Key for years with no problem. Always go for 105'F types, even for lower temperature applications. The BCC ones are fine also. I am surprised you would have any issue with the NTE ones, though... even the cheapest caps today have better ESR than the caps of the sixties. I might look elsewhere first, like a bad rectifier. --scott -- "C'est un Nagra. C'est suisse, et tres, tres precis." |
Replacement electrolytics
Dave wrote:
I have just re-capped the power supply capacitors in a DX-40 with 40uf 450 VDC Aluminum Electrolytics from NTE Electronics in New Jersey. I have noticeable hum on the carrier. Measuring the ripple voltage with a 10 Megohm ac coupled meter shows 2.3+ volts [average/rms ... non-sinusoidal] on the 600 vdc line and 1.2 volts [average/rms ... non-sinusoidal] on the 300 vdc line. It appears the RS of the capacitors is way too high. What manufacturer or brand are others using with success? Does MOUSER carry suitable replacements? If so, what brand/style? Other sources? TIA DD, W1MCE I guarantee it's not the caps |
Replacement electrolytics
"Dave" wrote in message . .. I have just re-capped the power supply capacitors in a DX-40 with 40uf 450 VDC Aluminum Electrolytics from NTE Electronics in New Jersey. I have noticeable hum on the carrier. Measuring the ripple voltage with a 10 Megohm ac coupled meter shows 2.3+ volts [average/rms ... non-sinusoidal] on the 600 vdc line and 1.2 volts [average/rms ... non-sinusoidal] on the 300 vdc line. It appears the RS of the capacitors is way too high. What manufacturer or brand are others using with success? Does MOUSER carry suitable replacements? If so, what brand/style? Other sources? TIA DD, W1MCE Sounds like a earth loop..... |
DX-40
While we are on the subject of DX-40s, I have one with a problem
that's driving me nuts. In AM mode, just sitting at idle, the plate current pulses up about every second or so. The scope shows a pulse on the plate of the second 12AX7 audio stage. It's acting like some sort of relaxation oscillator. I've rebuilt the audio section to no avail. Anyone have an idea what the heck is going on? 73, Roger Remember the USS Liberty (AGTR-5) http://ussliberty.org/ |
DX-40
Roger D Johnson wrote:
While we are on the subject of DX-40s, I have one with a problem that's driving me nuts. In AM mode, just sitting at idle, the plate current pulses up about every second or so. The scope shows a pulse on the plate of the second 12AX7 audio stage. It's acting like some sort of relaxation oscillator. I've rebuilt the audio section to no avail. Anyone have an idea what the heck is going on? Have you tried replacing the 12AX7? -Chuck |
DX-40
Typically, this sort of thing is a form of motorboating. There are
a couple of ways it comes about. One is through power supply sagging as current in some stage starts increasing. The supply sags until a certain point is reached where the current in the affected stage decreases, and the cycle continues. It is very low frequency because the power supply filters are the resonant element. Another way it can happen is through grid leakage. Many tube stages of the low power sort have a resistor from the grid to ground that is supposed to keep the grid at a reasonable negative bias value. If that resistor is open circuit, or if the tube develops excessive gas, the grid, the leakage, and the coupling capacitor of the previous stage can get a relaxation oscillation thing going. A leaky coupling capacitor, such as C27, or C25 can do the same thing. Look at pin 7 of V4. Try paralleling a 1M resistor on that stage and see if it changes the rate of the motorboating. If it doesn't, try the grids on the 12AX7... and, of course, replace C27 and C25... -Chuck Chuck Harris wrote: Roger D Johnson wrote: While we are on the subject of DX-40s, I have one with a problem that's driving me nuts. In AM mode, just sitting at idle, the plate current pulses up about every second or so. The scope shows a pulse on the plate of the second 12AX7 audio stage. It's acting like some sort of relaxation oscillator. I've rebuilt the audio section to no avail. Anyone have an idea what the heck is going on? Have you tried replacing the 12AX7? -Chuck |
DX-40
Chuck Harris wrote:
Roger D Johnson wrote: While we are on the subject of DX-40s, I have one with a problem that's driving me nuts. In AM mode, just sitting at idle, the plate current pulses up about every second or so. The scope shows a pulse on the plate of the second 12AX7 audio stage. It's acting like some sort of relaxation oscillator. I've rebuilt the audio section to no avail. Anyone have an idea what the heck is going on? Have you tried replacing the 12AX7? -Chuck Yes....several times! I don't have a spare 6DE7 however. Roger -- Remember the USS Liberty (AGTR-5) http://ussliberty.org/ |
DX-40
In article ,
Roger D Johnson wrote: While we are on the subject of DX-40s, I have one with a problem that's driving me nuts. In AM mode, just sitting at idle, the plate current pulses up about every second or so. The scope shows a pulse on the plate of the second 12AX7 audio stage. It's acting like some sort of relaxation oscillator. I've rebuilt the audio section to no avail. Anyone have an idea what the heck is going on? Bad caps. --scott -- "C'est un Nagra. C'est suisse, et tres, tres precis." |
DX-40
If you check the screen voltage of the 6146 I expect you will see it pulsing
from 70 +/-10 volts to over 100 volts, possibly to 160 volts. Seventy volts is normal screen bias in the AM mode. With modulation it follows voice peaks to ~150 volts. The time constant of the 6DE7 to 6146 RC circuit is about 0.025 seconds. So, I would exclude the RC between the 6DE7 and the 6146 screen. I would check pin 6 of the 6DE7. It should be stable in the AM mode. The input circuit to the 6DE7 has a 0.1 second RC time constant. If the input is stable [pin 7] and the output is pulsing the replace the 6DE7. If the input [pin 7] is pulsing then check the RC from the 12AX7. /s/ DD PS: let us know what you find out. + + + Roger D Johnson wrote: While we are on the subject of DX-40s, I have one with a problem that's driving me nuts. In AM mode, just sitting at idle, the plate current pulses up about every second or so. The scope shows a pulse on the plate of the second 12AX7 audio stage. It's acting like some sort of relaxation oscillator. I've rebuilt the audio section to no avail. Anyone have an idea what the heck is going on? 73, Roger Remember the USS Liberty (AGTR-5) http://ussliberty.org/ |
DX-40
Scott Dorsey wrote:
In article , Roger D Johnson wrote: While we are on the subject of DX-40s, I have one with a problem that's driving me nuts. In AM mode, just sitting at idle, the plate current pulses up about every second or so. The scope shows a pulse on the plate of the second 12AX7 audio stage. It's acting like some sort of relaxation oscillator. I've rebuilt the audio section to no avail. Anyone have an idea what the heck is going on? Bad caps. --scott I assumed the caps had been replaced. But, replacing them is a GREAT idea for several reasons if you have not yet done so. There are four electrolytics. The two 40 uF in the high voltage supply. Mine warmed up immediately on power application and started to leak. They were replaced with aluminum electrolytics for about $9. There is a 20 uF 450 vdc cap on the audio, 12AX7, plate line with a one second time constant. Check that capacitor. The time constant matches your symptons. That makes it a good place to start. The final electrolytic is a 2 uF connected between the 6DE7 output and the 6146 screen. I replaced mine on principle ... I had no problems in this part of the circuit. |
DX-40
On Thu, 19 Apr 2007, Roger D Johnson wrote: Chuck Harris wrote: Roger D Johnson wrote: While we are on the subject of DX-40s, I have one with a problem that's driving me nuts. In AM mode, just sitting at idle, the plate current pulses up about every second or so. The scope shows a pulse on the plate of the second 12AX7 audio stage. It's acting like some sort of relaxation oscillator. I've rebuilt the audio section to no avail. Anyone have an idea what the heck is going on? Have you tried replacing the 12AX7? -Chuck Yes....several times! I don't have a spare 6DE7 however. You ought to get one. Tubes can sometimes have weird "heat-up-short" cycles and if everything else is _new_, look at what you have yet to not yet replaced. You might try "bridging" in -- with aligator clips--external electrolytics at those locations in the circuit where an on-board electrolytic might be going through some kind of "charge-up-discharge" cycle to cause the spike. One of the guys who answered this had a good idea about that. Did your rebuild the audio section with all new capacitors? Sometimes even new components can include a run of defects in a given lot. What else is the second plate of the 12ax7 connected to? Are the working voltages of the new capacitors you put in all higher than any voltage you expect on those circuits? Roger -- Remember the USS Liberty (AGTR-5) http://ussliberty.org/ |
Replacement electrolytics
"Dave" wrote in message
. .. I have just re-capped the power supply capacitors in a DX-40 with 40uf 450 VDC Aluminum Electrolytics from NTE Electronics in New Jersey. I have noticeable hum on the carrier. Measuring the ripple voltage with a 10 Megohm ac coupled meter shows 2.3+ volts [average/rms ... non-sinusoidal] on the 600 vdc line and 1.2 volts [average/rms ... non-sinusoidal] on the 300 vdc line. It appears the RS of the capacitors is way too high. What manufacturer or brand are others using with success? Does MOUSER carry suitable replacements? If so, what brand/style? Other sources? TIA DD, W1MCE FIRST, Mike Bryce, WB8VGE [The Heathkit Shop] http://www.theheathkitshop.com/ and Jeff Weinberg, W8CQ [Harbach Electronics] http://www.harbachelectronics.com/ have been offering replacement capacitors and boards for Heathkit products. An ideal solution for the inexperienced newcomer -- who does not wish to guess about replacements or repair parts. Here are the "Major" distributors for new electronic components. DigiKey http://www.digikey.com Mouser http://www.mouser.com/ Allied http://www.alliedelec.com Newark http://www.newark.com/ MCM Electronics (a favorite for radio-TV shops) http://www.mcmelectronics.com/ all have ample selections of Vishay/Sprague; CDE/Mallory and Panasonic models. Start with 2 of the major mfg. for specifications and selection. CDE - base in South Carolina (USA) http://www.cde.com/ CDE Selection Guide http://www.cde.com/catalogs/aesg.pdf CDE Application Guide http://www.cde.com/catalogs/AEappGUIDE.pdf and Panasonic (Japanese) - available from DigiKey **Panasonic has been slowly discontinuing some of their screw terminal models -- favoring the "snap in models" http://www.panasonic.com/industrial/...p_lcanelec.htm Panasonic Computer Grade http://dkc3.digikey.com/PDF/T071/1283.pdf Panasonic Snap-In http://dkc3.digikey.com/PDF/T071/1276-1282.pdf |
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