Palomar 200X issue

[Rok55]

Hello again all. I realize I may be posting in the wrong section as I am a CBer but I don't see a section for CB amps and the Palomar is a Base amp. I'm looking for comments and advice on a Palomar 200X that I acquired a few years back but am just attempting to putting in line. I'm very new to CBs and trying to learn as I go. I've searched for similar threads and not really come up with any answers. I have a copy of the User manual and schematics downloaded from cbtricks and have setup/tuned the amp per those instructions.

My (base) setup is a Uniden 980SSB with a Maco V58 at approximately 20' to feedline connection. SWR without the Palomar is 1.2 - 1.3 across the band. With the Palomar inline (3' jumper) and turned off SWR jumps to 3.9 and higher, turned on jumps to over 8.1.

What should I be looking for to correct this or do I just need to find a reputable repair tech to go through the amp.

Thanks in advance for your help.

Rocky

 

[BlowinSmoke]

With the Palomar in line and off the SWR you see is from an impedance "bump" you are probably getting from the open frame relay inside the amp. Then when you turn it on an you see a very high SWR, that could be from a whole bunch of things. You have ti make sure all the tubes are good and are working. There is an adjustment for tweaking the driver tube unti the final that might need adjustment. Have you tried loading it up with a full carrier?

 

[Tallman]

Post the link to your schematics and maybe I can help you. A lot of those amps have a trimmer on the input to match the transceiver to the amp.

 

[jon666]

check your jumper to the amp.

 

[Sonar]

Go with the most likely and easiest thing. And that's listen to Jon666. Before moving on to anything else and that includes opening up the amplifier and sticking your fingers in there. CHANGE ALL THE JUMPERS. You might be pleasantly surprised. I had the same issue with one of my amplifiers (all of which are sweep tube CB amps) and that's exactly what was causing the high swr issue. Good luck. 73

 

[tecnicoloco]

Be careful opening the covers on a tube amplifier if you do not have experience

That amp from the 70's needs an overhaulin staring with the power supply capacitors, diodes,resistors out of tolerance,maybe a new relay or clean the current one and the list goes on and on

My 2 Pesos

 

[Rok55]

Thanks for the comeback folks ..... heres the latest.

With the Palomar in line and off the SWR you see is from an impedance "bump" you are probably getting from the open frame relay inside the amp. Then when you turn it on an you see a very high SWR, that could be from a whole bunch of things. You have to make sure all the tubes are good and are working. There is an adjustment for tweaking the driver tube until the final that might need adjustment. Have you tried loading it up with a full carrier?

I'm pretty dumb about some of this .......... by full carrier do mean carrier with modulation? If so . not yet.

Post the link to your schematics and maybe I can help you. A lot of those amps have a trimmer on the input to match the transceiver to the amp.

http://www.cbtricks.com/Amp/palomar/200x/graphics/palomar_200x_base.pdf

check your jumper to the amp.

Bench tested the 3' RG8U jumper and found no issues with continuity or resistance.

Go with the most likely and easiest thing. And that's listen to Jon666. Before moving on to anything else and that includes opening up the amplifier and sticking your fingers in there. CHANGE ALL THE JUMPERS. You might be pleasantly surprised. I had the same issue with one of my amplifiers (all of which are sweep tube CB amps) and that's exactly what was causing the high swr issue. Good luck. 73

Decided to try an 18' section of RG58A/U I have and found a substantial improvement. The 18' was wrapped in a 8" coil if that matters???

Amp off = 2.95
Amp on in Standby = 2.95
Amp on / Rec Amp off / Low Power Transmit = 1.0
Amp on / Rec Amp on / Low Transmit Power = 1.0
Amp on / Rec Amp on / High Transmit Power = 1.0

Went back to the RG8 and had better results than previous but still around 3.0 with amp off or with amp on in standby. In transmit mode both low and high were 1.0

Went back to RG58 and got baffled ......... now all readings are 1.0

Be careful opening the covers on a tube amplifier if you do not have experience

That amp from the 70's needs an overhaulin staring with the power supply capacitors, diodes,resistors out of tolerance,maybe a new relay or clean the current one and the list goes on and on

My 2 Pesos

Was planning on opening up for a general cleaning but haven't done so yet ... Lord knows what the inside of this old girl is like. I don't have experience with tube amps but have done some minor repairs to other electrical equipment (mostly light / sound mixing boards and speakers), am fairly handy with most things and not afraid to give it a try if needed.

What should be my next step

 

[Tallman]

Be very cautious around the capacitors. If the unit has been unplugged for a time they will still have voltage present.
I was working on a microwave and had discharged those caps and reached inside to get a screw I had dropped and I still got ZAPPED! Some how there was a residual charge that built up. I double checked the power cord and it was laying on the bench. I short the caps out now when I work on a microwave and leave the shorting clips in place.
I don't repair microwave ovens, I salvage parts from them for future projects.

 

[Tallman]

I looked at the schematic and did not see any input matching trimmer capacitor in the input circuits. Coiling the cable will have an effect on SWR. I would suggest replacing the capacitors and the relays.

 

[Rok55]

I looked at the schematic and did not see any input matching trimmer capacitor in the input circuits. Coiling the cable will have an effect on SWR. I would suggest replacing the capacitors and the relays.

I suppose 1st step will be to fab up some new short jumpers. Then open her up for a look see. If SWR stays low do I still need to change the caps and relays?

 

[Tallman]

I suppose 1st step will be to fab up some new short jumpers. Then open her up for a look see. If SWR stays low do I still need to change the caps and relays?

My favorite saying is "If it ain't broke don't fix it." Maybe just clean the contactors in the relay. Inspect them and if they are pitted and burned a little sand paper and elbow grease will fix you right up.

 

[nomadradio]

The high SWR on standby is caused by the long, unshielded wires that carry your barefoot power down to the main relay, up to the preamp relay, through it, back down to the main relay and from there to the antenna socket.

In the 200X this adds up to 8 or 9 inches total unshielded wire or the equivalent from the radio socket to the antenna socket.

Strip 8 inches from a coax jumper, put it in line and check the SWR. You'll find that it's higher now.

Back in the bad old days we would use small coax to make those four links, to/from the preamp relay, to/from the rear panel. Doesn't totally bring down the standby SWR, but got it down to 1.5 or so.

The long, unshielded signal path through the preamp relay can be eliminated with a very-short jumper wire on the main relay. This will help. Odds are that the preamp is not too useful unless your local noise level is incredibly low. This will bring down the standby-side SWR.

The input-side SWR while you're keyed is another proposition. I favor eliminating the driver tube and driving the two final tubes directly from the radio. But since you have such a low SWR with the amplifier keyed maybe this is a "If it ain't broke don't fix it" moment.

Keeping in mind the rule of the shade-tree mechanic. "If it ain't broke keep fixing it 'til it is broke".

73

 

[Rok55]

Thx for the replies ............ just found out I have to make an emergency trip out of state so I'll get back on this when I return. Thx again ..........