Demon ssb delay.

[klj2497]

My demon 250, unkeys too soon on ssb with the ssb delay on. I replaced all but one of the blue can capacitors. It should be here by friday. Im wondering where is the ssb delay capacitor, and what should i change the value to. so i can increase the delay. Thanks.

 

[klj2497]

I Also noticed some of the adjustments do not seem to be working very well. I sprayed the tube and relay sockets and used emery cloth on both of the relays contacts and inside the nobs. the top relay is pitted really bad i was able to clean it with emery cloth. I noticed the middle tune nob does not peak and drop. i turn it all the way to the right and it increases until it runs out of adjustment. It transmits about 220-280 watts am . On ssb it transmits about 250 watts and if it drops to about 200 watts it unkeys with the ssb delay switch on. it is worse with the ssb switch off so the switch must be doing something.

 

[nomadradio]

I'm pretty sure it will overheat the tubes, "cherry" the plates and break down with some kind of loud noise.

The tubes in this amplifier have zero grid bias. The grids are all directly grounded. This causes the current each tube draws with no drive to be excessive.

The AM carrier from the radio is all that controls the tube current in this amplifier.

The odd behavior you see may be the tubes overheating. Old electrolytic caps cause trouble. And the tubes may not be perfect.

I do not have any pictures of the process to add grid bias to the tubes in this amplifier. The schematic we have is the same one posted at CB Tricks. The pin numbers on the tube sockets and the value of each component are totally missing.

Adding bias to tame this box is probably not a good "first" project.

73

 

[klj2497]

Now no output. i turned it on and let it warm up switched the standby off and back on then i keyed up and the demon has no power out. the relay works, the ssb delay works the pre amp receive works, but now its dead i do not know where to start. im really frustrated.

 

[klj2497]

The top relay is shot . Im looking for another one.

 

[klj2497]

i fiddled with the relay and got it working again. the ssb still clicks off and on at about 200watts so ill have to keep the modulation up. i have 1 more of the can capacitor to replace. i wonder if this ssb delay is normal for the demon 250

 

[Shadetree Mechanic]

Operating in side band mode is going to kill the amp especially if the load knob won't peak. It needs to have 2 or 3 watts dead key going into it to properly bias the tubes as Nomad said, this is the only thing that keeps the tubes from overdriving without modulation. The side band mode is extremely hard on the tubes but tubes were cheap when this was made. The load control needs more capacitance to bring it into adjustment for some reason. Maybe the wrong tubes or a bad tube?

 

[klj2497]

i think i may have been miss read. the middle tune knob is the one that runs out of adjustment the load knob is peaking okay. there are 3 knobs on the front and three adjustments in side one is next to a tube and two are next to the coax hookups. The front knobs are left to right, load, tune and drive . the front the load knob peaks and seems to work the middle tune knob runs out of adjustment and the load knob doesnt do much but i think it works. i am going to be sure to put 2 1/2 watts into it i am putting about 4 into it now.Thanks Robert

 

[klj2497]

i found a relay that is the same as the Demon one but its for ac current. if i buy this for about $14.00 and transplant the relay contacts would that work to repair the worn out contacts

 

[Dmans]

klj2497,
If it were me, which it's not, but if it were, I would ditch the relay. The metal is not meant to be "sanded". It won't last.
If contacts are dirty, I would normally drag a dollar bill soaked in DeoxIT across them to clean them. Sanding will only drastically shorten the life of the contacts.

There is a plethora of relays available on the market. Identify the coil voltage needed and order one. Yes, current capacity is important. I don't know enough to calculate RF current needed for the relay but I have used a 4PDT relay in the past to replace a 2PDT relay and simply doubled up the contacts to "double" the current capacity of the 4 Pole relay. It may not mount exactly the same as the original but if there is enough room in the chassis (physically) you can find a way to mount a new relay.

To extend the SSB dropout time of the relay, follow the AM/SSB switch wiring to an electrolytic capacitor. (It should "add" the electrolytic to the circuit when in the SSB mode.) Increase the uF of the capacitor to extend the "dropout" time and decrease the uF to shorten the "dropout" time.

Good Luck!

73's
David

 

[klj2497]

Thank You Dman I ll ditch the relay its been sanded and so much is worn off there is nothing left of the little round contacts.

 

[nomadradio]

A relay that's rated to use with 12 Volts AC has a much lower coil resistance then the one rated for 12 Volts DC.

This will cause it to draw a lot more current through the keying transistor and blow it out.

Same rule applies to a linear that has a small tube to key the relay. The original will typically be marked "110 Volts DC". The resistance of the coil is usually between 9000 and 11000 ohms.

A relay coil rated for "120 Volts AC" has a DC resistance of around 2000 ohms. That will cause it to draw way too much current through the keying tube and cause it to fail prematurely.

If it even keys up at all.

I suspect your AC-coil relay will be a disappointment.

73

 

[klj2497]

I found a replacement for the demon 250 relay part number ka4473 On ebay. it cost $23.53 . it is used but it has a 2 year warranty.

 

[w9cll]

Why not key the relay with an external switch like a foot switch, I did this with the 2k VHF amp I had years ago. No delay issues, press when you start talking and release when done... problem solved.

 

[klj2497]

I am very intrigued by this external relay. but i have the replacment relay i ordered, and it is working great. Unfortunately the ssb is still clicking too soon at about 200watts. it swings about 250 on ssb. to increase capacitance, i found a 1000uf 16v cap. and a 2200uf 16v cap. im wondering if one of these would be the right amount of increase. to replace the 470uf 16v that is in line with the ssb switch to increase the ssb delay. Im also wondering what else i need to replace. Thanks.