Der Loudenboomer!
|
Ok,
I am going to probably show my ignorance of choke input power supplies but here goes!! I am rebuilding my HT45 power supply.? My HT45 is Hallicrafters branded but probably like many, has the Radio Industries PS-2A power supply. I am guessing that Hallicrafters probably had a LOT of them laying around and used them until the supply was exhausted and then started putting their own name on them.? No matter, there doesn't appear to be any electrical difference. Testing mine, I have noticed that if I use only the existing 210K ohm total bleeder resistors (series 100k + 100k + 10K), I hear what is best described as a faint "clicking" sound in the choke!? And the voltage is upwards of 3750V.? (too high in my book) Although I don't see any discussion of it in the manual, the schematic shows the 4-16H (swinging) choke with what I would call an "arc-gap" (maybe internal) for protecting the choke (I guess) . With no load (but with the 210K resistors) on the power supply the voltage is a little more than 3700V.? If I add some load (an additional 50K like an idling 3-400) drawing a total of 87 ma, The voltage drops to about 3460v and the clicking stops! And before someone tells me how a choke input power supply works (needs a minimum load etc)? I did read the handbook discussion on choke input power supplies! My question (and I'm hoping Walt jumps in here) concerns the jumper on the back of the HT45.? This terminal allows "shorting" across a 150 OHM resistor in the 3-400 cathode circuit that is there to increase bias and reduce cathode current during STBY. The manual talks about using a T/R relay controlled by PTT from the exciter with additional contacts for this purpose.? This is also done with the HT33 I have and many other amplifiers. (Note 5.) I am just wondering what to expect with the reduction?? I have experimented with the power supply a little and have discovered that with the current swinging choke I have, the existing 210K ohms aren't enough, an additional 100K isn't enough, and I had to put another 100K in parallel to get the choke to stop "ticking" 210K + 100K + 100K? all in parallel (about 40K) produced enough current to stop the ticking and clicking and put the output at 3460V with 122VAC on the primary. Anyone have experience with one of these? -- 73/Rick WA6III __________________________________ No critters were injured transmitting with Hallicrafters transmitters except the ones that wandered into the final amp cage Bug-Motel!! Bugs check-in, but they don't check-out! |
|
Howdy,
toggle quoted message
Show quoted text
Thanks for the reply Well, since the voltage across the choke is dependent on the current through the choke, it shouldn't make any difference. Position of the choke in the circuit, positive or negative doesn't really affect the voltage "across" the choke.? It only changes the actual voltage on the windings referenced to the grounded iron core Putting it in the negative lead would only take the high voltage off the windings (which is certainly desirable).... but I don't think the "snapping" is due to "winding-to-core" arcing.? If it was, it would likely be continuous.? I.E., it would short, stay shorted and pop the fuse.? This is more a "clicking", snapping", ticking that I think is due to internal arcing across windings (or the arc "gap" depicted in the schematic) and that voltage is directly related to the (pulsating) current in the windings. Either way, my original question is more related to the the idling current when the amplifier is in the STBY mode.? (I know what it should be in the transmit mode.....It should be around 120ma, and that's more than enough current for the choke) And in fact, I went back to the manual and read a little closer and actually found what I was looking for! I guess I should just RTFM? before asking questions!!? But at 40ma, I'm thinking it's not going to be enough unless I add an additional bleeder. I found that using only the power supply bleeder resistor of 210k Ohm (with only an 18ma draw) , the voltage was high at around 3750+ volts.? (and there was "ticking")? When I added an additional 100K in parallel,? I still had around 3750+ volts ,? total resistance around 68K,? resulting in a total 55ma draw (still ticking!!) When I added an another 100K in parallel, I saw a significant voltage drop.? Voltage was 3460v, no ticking, with a combined resistance of about 40K. Total current draw due to the total 40K (210K + 100K + 100K parallel) was around 86ma. I know choke input power supplies have a lower limit of current that must be present to prevent the voltage from "soaring" (ARRL handbook term!) The part that I am concerned about is that since the tube will draw 40ma (according to the instruction above) when the T/R "jumper" is removed, that's only going to be a total of about 18ma + 40ma? =? 58ma. If you note above that I still had "ticking at 55ma, I am having a hard time believing that 3 additional ma will be the "break-point" of where the choke starts to "choke" Maybe it will.?? This is where my lack of experience with high voltage (swinging) choke input supplies is somewhat lacking.? I would REALLY like to hear from someone else that actually has or has played with one of these power supplies hooked up to an HT45? so I can compare notes! On Sun, Oct 23, 2022 at 02:16 AM, D. Platt wrote: <!doctype html> K3HVG? -- 73/Rick WA6III __________________________________ No critters were injured transmitting with Hallicrafters transmitters except the ones that wandered into the final amp cage Bug-Motel!! Bugs check-in, but they don't check-out! |
|
Hi Jim,
Thanks for the info!? It appears that I was replying when you were and then, I left the computer sitting without pushing the "SEND" button!? So you can see my what I discovered experimenting? below! I absolutely did (first) power it up using only the existing bleeder !? I of course discovered exactly what you're talking about!?? The NE51 was not installed at the time.? Everything is disconnected? and standing alone.? I am using 2 SEMTECH 5000v diodes in place of the old 866A's and the filament transformer is also gone. Again, I am still concerned that the 40ma of additional current draw due to the tube will not result in enough current to make the choke work but I will try it.? If I have to add a little more bleeder, I can easily add another 100K.? The NE51 I have is in fact an NE51H I do have a good tube (actually I have 3!!)?? I tried all of them in my L-4B and they all do at least as good as the 3-500's I have in it now.? (same roughly 1300w out)? As an aside, the Eimac 3-500's I have fit perfectly (slightly shorter than the plate choke)? in the HT45 so I am tempted to use one of them and just use the 3-400's in the L-4B but that's another thread to discuss!! Anyway, I am going to do exactly what you're suggesting.? I am going to try it with the HT45.? If the voltage is "ok", I'll leave it alone.? If the voltage is still high, and an additional 100K doesn't work,? (maybe the choke is NOT actually the original choke, or it's defective) ? I may just see if I can get another swinging choke.? If I cannot find one, I am going to use the extra Drake L-4PS I have.? (it's less than ONE HALF the size of the PS-2V!!) The downside of using the L-4PS is the 2700 no-load voltage.? I think the 3-400 (or 3-500)? will work pretty good with 3200-3400v? 73/Rick WA6III __________________________________ No critters were injured transmitting with Hallicrafters transmitters except the ones that wandered into the final amp cage Bug-Motel!! Bugs check-in, but they don't check-out! |
Rick W7IMM