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Bracketbird
| | Posted on Saturday, July 13, 2002 - 2:05 am: | 
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Would anyone happen to know the voltages on the plug for the seperate power supply that plugs into amp......thanxs |
2600
| | Posted on Thursday, July 18, 2002 - 4:27 pm: |
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Sure,
Pins 7 and 8 supply 120 Volts AC to the transformer primary.
Pin 1 is tied to pin 3, pin 2 is tied to 4. One pair on each side goes to the 12.6 V ac winding. They doubled up the pins to carry the high current feeding the tube heaters. The current required at 12.6 V ac is about 6.5 Amps. The tubes are wired as pairs in series, so each of three pairs of tubes split the 12.6 to get 6.3 V on each tube heater. The tubes draw 2 Amps each, times 3 PAIRS, adds up to 6 Amps, plus another half-Amp or so to run the meter light, relays, preamp and bias voltages.
Pins 5 and 6 carry the high voltage AC to the HV rectifiers. Here's where it gets tricky. The 300A was built with two different transformers. They both look alike, and have the same plug. The rectifier used inside the amplifier for the HV was configured TWO ways, and the transformer HV winding has to match it. The version that had the rectifiers arranged as a voltage doubler calls for 315 Volts AC at about 1.5 Amps. The transformer that matches the BRIDGE rectifier inside the amp box is 630 Volts AC at about 3/4 Amp (750 mA).
If you find an original transformer with the matching plug and cable, it's a 50-50 coin toss as to whether it's the right one or the wrong one. The safest way to tell if it's the right one or not is to trace the rectifier wiring on the power supply PC board underneath, and determine whether it is wired as a 'full-wave bridge' or as a 'full-wave voltage doubler'. Hooking pins 7 and 8 of the transformer to a PROTECTED, preferably isolated AC supply and metering pins 5 and 6 will tell you whether it is the 300-volt or the 600-volt HV winding.
There are two possible WRONG combinations of transformer and amplifier. If you have the 300-volt transformer and an amp wired for the 600-volt version, you'll have an amplifier that is stuck on 'low' side all the time. The tubes would last forever, but you'd be disappointed with the power output. If you plug the 600-volt version of the transformer into an amp with the DOUBLER circuit (needs 300-volt version) you'll get a large POOF either the moment you turn it on, (later version with NO relay underneath) or the moment you first key it. (earlier version had a relay underneath that keyed the HV).
Likewise, taking a close look at the two large filter capacitors on the power supply PC board underneath is ALWAYS a good idea. If they are original, they are just too old to trust. If they show any visible signs of failure (swelling, brown powder on the positive end, a "zit" visible on the rubber insulator) they should BOTH be replaced ALONG WITH THE BLEEDER RESISTORS. If they go kaboom, other parts can be damaged.
73,
2600 |
Jyd
| | Posted on Thursday, July 18, 2002 - 8:28 pm: |
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impressed, thats good. |
Bracketbird
| | Posted on Wednesday, July 24, 2002 - 9:34 pm: |
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thanxs for the info 2600.....i havent checked it yet but it looks like brand new. let me throw this at ya...i was given this amp and heres the problem. driver tubes glow whether on high power or low power. only one set of the other pair burn and tubes do check at about 70%. replaced both capacitors , preamp works great but as soon as you key it bam the fuse blows . any ideas for me? thanxs for any help |
2600
| | Posted on Thursday, July 25, 2002 - 11:55 pm: |
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Well, my first prediction is that this one has an open-frame power relay on the UNDERSIDE of the chassis. The later versions did not have this relay, and the high voltage was fed to the tubes all the time through the OPERATE side of the standby switch. The additional large relay UNDER the chassis was used to turn the HV off until you key it, but ONLY in the earliest version.
The heaters in ALL 6 of the tubes should be on ALL THE TIME. The high/low switch re-routes the drive AROUND the driver tubes for low side, but the heaters are ALWAYS supposed to be on, high or low side.
The pair of tubes that stay dark may have a bad solder connection under a socket. It's pretty common for the solder on the tube sockets to develop 'fatigue' cracks around the hole in the circuit board where they are mounted. The heaters are run from pins 1 and 12, the pins on each side of the 'gap' in the pin circle. ANY cracked or suspicious solder on a tube socket pin should be resoldered to restore a reliable connection.
The first test to try for the slammed fuse is to unhook the cap clips on all 6 tubes, AFTER discharging them to ground FIRST, of course. If it still blows the fuse when you key it this way, suspect a power supply problem like blown HV rectifier diodes (under the center one of the two large filters), OR A MISMATCHED AMP AND TRANSFORMER. The filter capacitors should BOTH have the positive end connected to the FRONT end of the circuit board. If someone installed a filter reversed, and you put yours in the same way, that's usually instant death for that filter, or more likely both. Yeah, I've done it, but not for a long time. That's how I know.
Sometimes the plate blocking cap on the old ones would short. There is one disc capacitor feeding from the top of the driver plate choke to the 'driver tune' control in the rear, and one from the top of the final plate choke to the front panel tune capacitor. When these fail, they nearly always have some visible sign of damage.
If, on the other hand the fuse blows ONLY with the tube-cap clips connected, the tubes look more likely as the culprit. If other pins on the tube sockets are poorly soldered besides the heater pins, this can make a good tube act psychotic and do nasty things, or even hurt itself eventually.
You DO have a load attached to this thing before you key it don't you? Every radio owner's manual stresses the risk of keying a barefoot radio with no load. The bigger an amplifier is, the more of a big deal this becomes. A dummy load, or your base antenna coax has to be connected before you key it. Honest.
73 |
Bracketbird
| | Posted on Sunday, August 04, 2002 - 1:59 am: |
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Mr 2600....i would like to thank you for the help as i finally got time to fool with it again. had to resolder a few pins on 2 tube bases and all tubes glow. I also replaced 2 diodes under capacitor and bam...im up and running. works fine thanxs to your info....Jesse |
2600
| | Posted on Sunday, August 04, 2002 - 11:12 pm: |
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Congratulations. This amplifier is one that folks always miss after they have sold it. Or so dozens of them have told me. The one operating detail worth mentioning is the "High Side" driver Plate Tune knob in the back. This control does not have an end stop like the ones on the front. The front-panel Tune and Load will not turn beyond just one-half turn end-to-end. The one in back spins 360 degrees either way with NO end stop. This one can fool you into thinking it has a peak when it really doesn't. If you plan to use High side, watch the wattmeter for a peak while turning the rear Driver Plate Tune knob ONE FULL TURN all the way around. There should ALWAYS be TWO PEAKS on the wattmeter in that ONE full turn. If you see ONLY ONE peak, that means the control has reached the end of its travel WITHOUT EVER REALLY REACHING A TRUE PEAK. Peeking under the cover at the spot on that knob where you read the ONE "PEAK" shows the plates are either fully meshed as far TOGETHER as they will go OR all the way APART as far as they will go. This happens when the control just doesn't turn far enough. The risk of running it that way is of overheating the driver tubes, and the plate choke that feeds High Voltage to the tube caps. If, on the other hand you DO see TWO separate peaks, you're home free. The plates will overlap each other the same PERCENT at two positions in one whole turn, so if your peak occurs INSIDE the end limits of the knob, there will always be TWO of them inside one full turn. Doesn't matter if they are really close together or 180 degrees opposite from each other. Just so you have TWO of them.
Enjoy, and resist the urge to just TRY driving it with even a small amplifier. It was built to be loud as the devil with JUST a barefoot radio. The meanest base stations in 1975 or 1980 would barely swing 20 watts. 35 or 40 is more common now, so be nice to it. Base stations just didn't GET that big 25 years ago.
73 |
Bracketbird
| | Posted on Monday, August 05, 2002 - 2:18 am: |
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i havent tried it on high side yet except breifly to see if it worked....it did. ive got a pretty good radio it is a 2970 . its a nice unit that has been expertly massaged..Ive got that radio, all Rg8u coax, d104, pdc 600s, to a astroplane bout 40ft. to the mount it did a great job before but now i might get to really talk on those nights you need it. Thanks |
2600
| | Posted on Wednesday, August 07, 2002 - 11:38 pm: |
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You're welcome.
73 |
2600
| | Posted on Friday, August 09, 2002 - 12:15 am: |
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Oh, man, I just noticed you said "2970" there. It's a LOT bigger than the barefoot radio that a 300A is meant to match. If you have a standby switch on the radio to turn off the internal amplifier, the radio 'barefoot' will match it fine. Running a 2970 stock, or with the internal linear turned ON, will probably hurt the keying circuit in the 300A if you key through it TURNED COMPLETELY OFF. It's really meant for a barefoot radio. And barefoot radios were a lot smaller 25 years ago on average than they are now. Seriously, I predict harm will come to this amp with a 2970 at full bore driving it. If low side holds up, hey cool! High side will just hurt itself. Quickly.
Hope I didn't mention this too late.
73 |
Bracketbird
| | Posted on Friday, August 09, 2002 - 9:51 pm: |
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im only running 0n the low side of amp...my radio is set at about 10 watts swinging to about 50... is that to much on low side?If so i will change radios or put a switch in it to turn the built in power off.By the way whats the 2 adjustments under the driver tubes?. I havent touched them , i was just curious. |
Rci2990
| | Posted on Saturday, August 10, 2002 - 10:56 am: |
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I run my 300A on the -low side- driven with my AR ranger 3500 100 water and get a 150 watt carrier and swing "quite a bit more" out of it. I run it on -high- with my HR 2600 driving it with about 25 to 30 watts pep and get a 250 watt carrier and swing "quite a bit more"!!!! Great amp as far as i am concerned!!!
*special note*
I DO NOT post wattage swing that i see on my meter because i dont want to have to get responses like "your amp will not do so and so on that meter" and BS like that. I just dont want to put up with that stuff ya know. |
Scrapiron63
| | Posted on Saturday, August 10, 2002 - 1:01 pm: |
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Bracketbird: For what's its worth, and maybe I've been lucky, but I've run high drive radios into the Palomar 300a amps for 20-25 years, and never had any problems. These included several hf ham radios, and the galaxy saturn turbo. Just be sure to keep the amp on low, that way the driver tubes are not working. I have a 300A now that I have run my Ranger AR3500 into, although the 100 watt Ranger, especially on SSB, will generally to the job by itself. Before this radio, I used an Icom 737 into the 300a, just for AM talking. The reason being, most HF rigs, or 100 watt radios will not have good audio at much over 20-30 watt keyup, however you can put that 20 watt key into the 300a, and it will sound great. I don't try to max the amp out, just use enough drive to get a couple hundred watts or so, just so I can make it across the county line, you know. scrapiron |
Bracketbird
| | Posted on Saturday, August 10, 2002 - 7:53 pm: |
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I appreciate the responses as this is my first 300a. im not that famaliar with it. ive had quite a few old small D&A tube amps and probably 4 90a. it didnt work when i got it and thanxs to 2600 i got it going again. seems to do a pretty good job so far.im just trying to learn as much as i can about it. it has a chrome top....is that original? ......73s |
Rci2990
| | Posted on Sunday, August 11, 2002 - 8:36 am: |
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Hmmm ive never had any problems with my 3500 on AM talking. Most guys just tell me its loud! But i had a Icom 735 that was simply AWFUL on AM. Very low muddy audio and hardley any swing! |
Scrapiron63
| | Posted on Sunday, August 11, 2002 - 12:13 pm: |
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2990, I didn't mean that the 3500 has any mod problems, they have excellent modulation.. What I meant to say is, all radios have a limit of keyup watts, at that limit they will start losing modulation in relation to keyup watts, like most of the dual final radios, if they are tuned right, you will get maybe 30 watts swing at 2-4 watts keyup. At 10 watts keyup, it may not swing anymore, and in fact might lose some modulation and swing, if checked on a rms meter. These are just reference numbers, as all meters are different. The "100 watt" radios are the same, they have a keyup limit of somewhere between 20-40 watts, where they will still show good forward and have good modulation. The ones i've tried don't sound good on a very small keyup either, too much forward. Most ham radios, and also the Ranger 3500 were just advertised as 30 watts AM. Some of the ham radios, like the Icom 737 that I ran, come with a power supply too small to handle very high AM watts, they will do fine on SSB. I ran mine on a larger power supply, and could run quite a bit more AM keyup and still kept good swing. |
Scrapiron63
| | Posted on Sunday, August 11, 2002 - 12:32 pm: |
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Bracketbird, Palamor made the 300A in several versions. The one I've had for several years has the chrome top, and the face is black with blue trim. I have another one that I got with some other equipment, doesn't have tubes, and it has a black vinyl finish top with a light blue face. I believe they made another one with black top and black face. All of them were nice looking amps, a little more dressed up than most of the older CB amplifiers. Like those older D&A amps you mentioned, they ain't pretty, but they were good'ins. |
2600
| | Posted on Tuesday, August 13, 2002 - 12:27 am: |
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Hey, Bracketbird,
It's hard to judge the TRUE modulated swing of your radio by just a meter reading. Any wattmeter that is set right should agree with another one on a DEAD KEY. This is how they are supposed to be calibrated, anyway. What they read for modulated swing is all over the map, unless you have some kind of lab-type PEP meter. Just the same, there's one unbreakable rule for driving the LOW side of a 300A. If you break the keying circuit, it was too much. If it still keys okay, you probably aren't overdoing it.
About those screws underneath. They are INPUT MATCHING adjustments. The one under the driver tubes is for HIGH SIDE ONLY, the one behind the high/low switch is LOW side only.
These are supposed to be set for lowest SWR reading FEEDING INTO THE AMP, KEYED. This requires a SWR meter patched BETWEEN the radio and the amplifier. If the radio has a decent built-in SWR meter, it will do. I don't much trust the built in SWR on the 2970.
The LOW side screw behind the high/low switch can first be set for MAX MODULATED SWING on low side. Check the SWR on the meter in the INPUT side. If it is under 2 to 1, you are done. If it reads higher, key the radio (and amp) with the SWR meter set to 'reflected' or 'swr' or whatever it's marked. Rock the screw a little to each side of where it was set. In one direction the SWR reading will usually drop. Turn it that direction until you are below the 2-to-1 reading. This may take 10 % or 15% off the swing of the amplifier, but the radio will be happier driving a SWR under 2 to 1. That much drop in power is too small for anyone to see on an S-meter at the other end.
Using a smaller radio, the high side screw gets the same procedure.
If, by chance the LOW side input match screw HAD been set WAY off the peak, you will see a lot more power. When this happens, you will need to re-peak the LOAD/TUNE controls for max swing. If they aren't set that way, the input match setting will be wrong. If it was way, way off, you may have to go back and forth between the LOAD/TUNE and the input match a couple of times until both are peaked.
If it was already set right, or close to right, you won't see much power change.
73 |
Spiderleggs
| | Posted on Wednesday, September 11, 2002 - 9:00 pm: |
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2600, A friend of mine has one of the 300a's, and was looking at the schmatic, and says it seems as though you could set it up to be used as six finals, instead of two driving four. If possible can you explain how it can be done, email me if necessary and I will pass it along. Thanks, Allen |
2600
| | Posted on Thursday, September 12, 2002 - 12:01 am: |
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I don't recommend changing it to a "straight six". With the tubes laid out the way they are, making it stable, and making all six tubes 'balance' equally sounds like a nightmare. Little things like where you locate a part are a big influence on how an amplifier will behave or misbehave. This one probably won't behave well if it is set up like you suggest. I'm not saying that it CAN'T be done. Just that it doesn't look worth the trouble to try.
73 |
Spiderleggs
| | Posted on Thursday, September 12, 2002 - 2:19 pm: |
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Thanks 2600, I'll pass it along. |
Bracketbird
| | Posted on Wednesday, September 18, 2002 - 8:49 pm: |
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Thanxs for the answer on the adjustments underneath. with keyed up amp running swr meter between radio and amp is 1.4 and leaving amp with it keyed up is 1.6. i left well enough alone. it has worked flawlessly since you helped me fix her up. by the way i dont much trust the radios built in swr meter either. Thanks....Jesse |
Bracketbird
| | Posted on Wednesday, September 18, 2002 - 8:57 pm: |
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Just a note to say also that a freind is cleaning up his place(cb-antennae-tower-junk farm)and is giving me a small freestanding tower ...40footer i pretty sure and a set of m103 beams. he didnt have another rotor but whos complaining. I cant wait. let yall know how big a mudduck im gonna be. see ya....Jesse |
Dennis
| | Posted on Thursday, February 27, 2003 - 12:38 pm: |
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Hi Guys,
This thread is pretty old, but here is my dilemma. I need a powersupply for a 300A, or just the schematic and I will build one. I do have a power supply from a Swan 350 (I think it is the 117XC?) that may be modified (I hope)?
Any help is gratefully recieved.
email me at VE7DMY@aebc.com.
Regards,
Dennis |
2600
| | Posted on Thursday, February 27, 2003 - 6:05 pm: |
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The transformer in the Swan 350 power supply won't adapt. The 300A needs one high voltage winding large enough for six sweep tubes. The Swan power supply has one winding that runs the small tubes in the transceiver, and another one big enough for just the TWO sweep tubes (I think) that it used for the final power stage.
If you check farther back up the thread, you will find that there is not ONE correct transformer for the 300A. The amplifier was built in two basic versions. One used a voltage doubler. The transformer that matches that one provides 280 Volts (I looked it up) at 1.5 Amps.
The other version has a full-wave bridge rectifier for the high voltage, and needs 560 Volts at 750 mA. to match it. Until you have a look at how the H.V. rectifiers on the center circuit board underneath are arranged, it's just a 50-50 coin toss.
I don't have a schematic, as such, but it's pretty simple. The external box contains JUST a transformer and fuse holder. The transformer has only six wires. Two for the 120 Volt primary, two for the 12.6 Volt filament/relay power. The fuse in the holder goes in the hot side of this winding. The last two wires are for the High Voltage winding. The pin numbers for each of the three pairs of wires are farther back up this post. The standard Cinch-Jones part number for the 8-pin plug is P308CCT.
73 |
Crafter
| | Posted on Friday, February 28, 2003 - 12:08 am: |
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I got one what you got to trade ? |
Crafter
| | Posted on Saturday, March 01, 2003 - 10:00 pm: |
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Ok maybe you want to build one. |
Dennis
| | Posted on Thursday, March 06, 2003 - 12:06 pm: |
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Sorry Crafter, I am interrested - I was out of town with no computer. I have sent you an email regarding your PS.
/Dennis |
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