D&A Phantom 500 resurrection & Re-Tube Need Help hit a Big BumP

[nomadradio]

If you really want to make the Final Load control last a while, add a safety choke across it.

Every Phantom I see with crunchy Load control plates is lacking this choke.

Doesn't have to be on the top side of the deck to work. Not much room up there for this.

But stringing it from where the output coax center conductor meets the antenna relay to the grounding solder on the antenna socket is easy to reach.

Leaving this part out of the Phantom can cause the Load control to have BOTH the RF voltage and a portion of the DC power-supply voltage across the plates.

The safety choke serves to reduce that DC part of the voltage across the plates of the Load control to zero, so that only the RF voltage appears across the tiny air gap.

It gets the name "safety" choke because it will also serve to dead-short the B+ DC power to ground if the output-blocking capacitor were to short. Prevents 950 Volts DC from feeding out to the antenna when you key the mike.

Hence the term "safety".

73

 

[giboni]

Thank you Nomad for this information.

I always wondered what the purpose of the choke connected across the "load variable

in my Ken-rich Eagle 500 & 525 ? I just get a similar part as in the Eagle ?

Inductance wise/current rating ?

15-20 years ago . Worked on a 515. Showed my friend. Why the Eagles ate 20LF6's.

I connected 7 VOM's . One on each tube. He then paid me to install a rectifier/filament

transformer ! https://www.alliedelec.com/triad-magnetics-vps20-6500/70575337/

.6 amps x 7 = 4.2 amps. That resistor mod is for the Golden Screwdrivers.

Shoosh My Pride Dx300 has been out of action for about a decade. Bet its the HV board

Best PuppetMaster.

 

[giboni]

Ahh so hard to find anything on the Allied electronics Web site. they have a 4.5 amp.

transformer 20v. Perfect. 6.5 Amp might have a voltage higher than 24v with these

tubes. The 24LQ6 Phantom 500

required replacement of the DC blocking cap on the final tank circuit.

They would open after awhile. When tested out of circuit. Tested good at -20 of rated

value. Never experienced a blocking dc blocking cap short on a sweep tube amp.40

years. The brand new ceramic 20KV discs ought to last 50 years plus.

I will need that space occupied by the 2x red door knob DC blocking caps eventually.

In the 12 tube phantom. Pi-L Tank . The inexpensive 20KV .4700 will replace them.

Without a return path. I do not fathom what happens if a DC blocking cap shorts.

Maybe. The ones I replaced were Shorted !!!!!!!!!!!!!!