INTERMITTENT DROP-DOWN ON RECEIVE SONAR FS 2340

nomadradio said:

Yeah!

Brings to mind the old phrase "More issues than National Geographic".

'Bout fell over the first time I heard that one.

I'll see if the picture showing where to put the jumper wire in place of the R50 preamp relay goes. Had it, but haven't seen it in a while. Never made a list of which pics fell into the data drain over the years.

73

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I truly hope it's as easy as that. I'll be home late Sunday. If not I'll add the pics on Monday. My fingers are crossed. I really enjoy this 300a and have for many years. I'd hate to have to retire it but I have no illustrious. If not for you it would've been packed up and in the closet already. Thanks Nomad. 73

Thanks.

M0GVZ said:

Last time I had a similar fault where the RX dropped until I keyed the mic it turned out to be a faulty connection in a PL259 socket at the antenna end of my coax run.

Before deciding it is the amp bypass it but keep the patch leads you're using with the amp still in play by using a female to female adapter to link patch leads on the amp input and output together.

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It's definitely the amplifiers preamp.
No issues with Tha Madison and Phantom setup on the Same antenna. The recive/transmitt are fine..
I switched the preamp in the on and off position and what happened now is that the preamp not only works but needs to be left in the on position.
The preamp in the off position drops the recive down to almost nothing and keying then un keying the mic no longer helps. The recive basically get shut down with the preamp in the off position. It must be left in the on position which is strange to say the least. This preamp like most on these old 11 meter tube amps preamplifier option stoped working about two months after it was delivered brand new from the factory. Thanks for the advice. It could've very well been the situation but in this case it's 100% the 300a's preamp causing the issue. Thanks again. 73

tecnicoloco said:

Hi Sonar:

I wish I can help you but I am not qualified to work on anybody else equipment and I know you can find a reliable technician that can help you in the US also I live south of the border in the Baja

Regards
Andy

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No problem Andy. I do have an excellent tech but it never hurts to have another. Have an excellent weekend. 73

nomadradio said:

One way to check for a problem in the standby side of an amplifier's relays is to put a SWR meter between the radio and the amplifier's radio socket. With the amplifier UNPLUGGED, hook the amplifier's antenna socket to a dummy load.

Key the mike on AM and set up the SWR meter, and see what the SWR is feeding into the amplifier turned off.

Now tap the relays, one by one and see if the SWR reading jumps up.

A tiny upwards flicker is probably okay if you tap the relay hard enough. But if a relay is dropping out, you'll probably get a bigger rise out of it, revealing bad contact points.

73

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It's definitely the 300a's preamp causing the issue of the receive dropping out.
These are photos of the amplifier in question.
I hope that with this particular preamplifier configuration there's a way to either bypass it completely or possibly fix it.
Like most I don't use the preamp nor do I have a use for it.
I hope these photos help you decide whether it can be fixed, bypassed or (and I hope not) if it's time for the amplifier retirement home. Thanks again for all your help nomad. 73

Paul-W5lz said:

I think I'd find the relay that pre-amp works through and clean/replace it.

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The oddest things happen and they always seem to only happen to me.
I of course am waiting on nomad to weigh in, but with the preamp in the on position is working as if it never stopped.
I would of course prefer to have the amp functioning 100%.
On The other hand it's working as it was when purchased 35+ years ago.
I never use amplifier preamps even on the amplifiers i own where they actually still work.
I've left the sonar and 300a on for 5 hours now and periodically held a few local qso's and even heard a station from Missouri. So I called to him and had a short qso with Haystak.
With a preamplifier that hasn't worked in who knows how many years in the on position my receive hasn't and isn't dropping out as it did while it was in the off position. I don't even want to turn it off. It might begin dropping my recive ever 20 seconds or so then I'll have to quickly key and un key the microphone in order to get it to come back up. I don't have to do that any longer.
I guess for now I will just leave it in the pre amplification position and although it tends to bring up the noise level it doesn't affect the stations that I receive in any adverse way.
As I mentioned I would like to fix it so that I can leave it in the off position without it D amplifying my received signals
But until nomad weighs in and lets me know if there is a way to either fix or better yet bypass the pre amplification stage in this Palomar 300a all together, I'm just going to use it the way it is.
It's working fine. Stranger things have happened but this is definitely in the top 5. At least for me. 73

nomadradio said:

Somebody has already beefed up the original R50 relay that serves to key the tubes. That black relay on the perfboard is a lot more robust than the original. The red wires lead to where the other R50 relay was originally found on the pc board.

I'm sure I have a pic here somewhere that shows where to insert a wire jumper after the preamp relay is removed.

I'll have a look for it.

Aha! Found it!

73

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I had this 300a restored about 2 year's ago. I'd like to say everything that could've been done to have it working 100% (probably better than new) except the preamp.
I used it yesterday and left the amplifier and 2340 on for about 8 hours
The preamplifier was in the on position the whole time.
The 300 a's preamplifier is working 100%.
Problem is I can't turn it off.
When it's turned off the receive drops out and unlike last week no keying and un keying will bring the recive back. I appreciate the photo but my lack of knowledge is making it impossible for me to figure out what I need to do in order to bypass the preamp. If it's not too much trouble could you explain or possibly add a couple of circles around that photo where the Jumper needs to be installed? From you reply I'm assuming I'll have to remove the preamps relay then add the jumper. Correct? 73 PS One good thing to come out of this was that since the cover was off the 2340 as I tapped on the recive tubes in order to eliminate weather the receivers dropping out because of a bad too or relay. I made sure everything including the relay was set properly in place, I decided to go and replace the mixing Crystal with a new one I had laying around. I occasionally had to use the Delta tune as some stations would sound off frequency. It's been some time since I could leave the Delta tune in the 12 o'clock position. The old Crystal must've been out of spec as the new one has all my received stations sounding excellent while the Delta tune is in the 12:00 position. Good deal!

nomadradio said:

Somebody has already beefed up the original R50 relay that serves to key the tubes. That black relay on the perfboard is a lot more robust than the original. The red wires lead to where the other R50 relay was originally found on the pc board.

I'm sure I have a pic here somewhere that shows where to insert a wire jumper after the preamp relay is removed.

I'll have a look for it.

Aha! Found it!

73

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Nomad. I didn't want you to or anyone who replied with information on how to possibly get the preamp issue straightened out wasted their time.
I looks like if I'm going to get it fixed I'll have to send it out.
For now it's working fine.
With the preamp in the on position that is.
I'm guessing switching the preamp on and off toggle enough times had something to do with the preamp which hasn't worked in years to begin working again. As long as I leave it in the on position the receive is fine. Of course the signals that are coming in are amplified constantly. if I switch the toggle for the preamplifier off the receive drops down and won't come up to it's normal function no matter what. I am tempted to give that preamplifier toggle a shot of deoxit but I don't want to press my luck.
I'm kind of getting used to having the preamplifier on.
Those preamplifiers always bothered me and I never use them. As everybody knows they not only preamplifier the signal but I want to know he's along with it.
I guess having no choice has kind of got me used to it.
I'm assuming this isn't going to last and the toggle being on will eventually begin to either drop the signal down as it did when this toggle for the preamplifier was off, but for now I'm just going to use it the way it is. I have come to the realization that when it comes to any type of soldering or the jumping of wires from one point to another no matter how simple, is just beyond my capabilities physically. From now on when I ask about an issue I will do so with the thought that it will have to be sent out for repair. I will still ask letting me know beforehand what will be needed beforehand as far as what my tech will be doing. Thanks for everything. I appreciate the time You took to help me try to rectify this issue. 73

nomadradio said:

Somebody has already beefed up the original R50 relay that serves to key the tubes. That black relay on the perfboard is a lot more robust than the original. The red wires lead to where the other R50 relay was originally found on the pc board.

I'm sure I have a pic here somewhere that shows where to insert a wire jumper after the preamp relay is removed.

I'll have a look for it.

Aha! Found it!

73

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Nomad. My 300a's preamp has began acting up like never before. It's making it impossible to enjoy using the Sonar.
I appreciate the photo that shows the red wire that needs to bypass the preamp. I have to cut down on radio and amp repair. It's the damn shipping cost that's killing me. I decided to finally send the phantom out to address the low output on high. I'm adding the two pictures I originally posted of my amps relays. Can you please point out exactly which relay needs to be removed and exactly where I need to put the Jumper? I have to try myself to bypass the preamp myself. Or give it to a knowledge local who with your direction will have no problem completing the bypass. He doesn't have much knowledge about amps but does have a very good understanding of circuts, relays, and will with your directions be able to complete the preamp bypass. Thanks for your help. PS I've tried to save and add the photo of the board and red wire but for some reason I couldn't.

nomadradio said:

The preamp relay that gets removed is the white "R50" relay alongside the plug-in relay.

Once it's removed, the hole pattern in the circuit board will look just like the photo above. The two holes in the circuit board nearest the plug-in relay get the jumper wire across them as seen above.

I'm incredibly close to just building a pc board that accepts a normal, easy-to-find DIP type relay and drops into the circuit board where the white R50 relay used to go.

Hard part at the moment is finding what they call a "nail-head" pin. This is what goes into my adapter board, to mate with the holes in the amplifier's pc board. Cheapest ones I found at Mouser are over a buck each. Putting eight of them into an adapter board is more than the entire cost of the rest of the thing. Gotta find a chinese source, looks like.

73

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Nomadd. I appreciate you taking the time to help me correct this issue. This is something I would not attempt myself. The preamp issue made it totally impossible to enjoy the sonar. Until I decide on whether I'm going to ask this local who is knowledgeable enough to do the bypass, what I did was I switched the 300a over to the Madison. I only use the Madison on SSB. I thought the preamp wouldn't affect the SSB receive as it did with the AM only Sonar.
I was right. Although 300a takes out my received audio signal on the Madison's in AM (as it did with the sonar) it doesn't do the same in SSB mode on the Madison. For now I'm just going to let it ride that way. On the other hand I don't like using equipment that isn't working 100%. But I am assuming and I hope I am correct that this issue will not cause any further damage to the amplifier or future issues with the Madison. I hope I am correct. I should get around to contacting the local whom I know can absolutely do this bypass after reading your replies and instructions. In the meantime the 300a is working very nicely along with the Madison on SSB. Output is 400 watts on my autek wm1 with about 10 watts, and no one notices the difference between the Phantom, or 350Z. Both of which I used in the past with the Madison for SSB use. Once again Nomad I appreciate all the time you've spent replying to my questions on more than just this post. You answered many questions along with many other members when I was having issues with the Phantom. I won't let anyone else touch the Phantom except out friend in Pennsylvania. So that's where the Phantom will be going soon. Once again I cannot thank you enough. Have a great week my friend. 73