HV power supply

[n2ffl]

I received a Drake L7 amp earlier in the year. Unfortunately the power supply was missing so I have been looking around for a complete supply or at least a suitable transformer for building one. Well I finally found a rather robust HV supply that will fit the bill quite nicely. It was originally built to power a pair of 3-1000s, is well built, compact and quite heavy (I'm guessing around 100 lbs.). It should be able to power a pair of 3-500Zs during old buzzard AM transmissions without breaking a sweat.

[n2ffl]

Another pic with the front panel removed...

[n2ffl]

I was interested in finding out the specs on the transformer but no luck so far. I'm told the supply produces 3,200 to 3,700 VDC out. The name on the transformer is H.E. Johnson & Assoc. Inc, Clearwater, FL. Haven't been able to find anything on the company yet.

[WQ9E]

The power supply should have no problem but don't cook your 3-500Z tubes in the L-7.  Drake switched from the nice forced air/chimney system of the L4/L4B to a SB-220 style fan for the L-7.  I sometimes run my TR7A, R7, L7 setup on 160 AM for a local net but it gets very hot in a hurry with the automatic fan staying in high speed mode.  If you are going for old buzzard mode you are going to have a really hot amplifier running at Drake's maximum rated 500 watts carrier input.  

Your power supply voltage is also considerably higher than what the Drake supply furnished, the original L-4 used 3-400Z tubes (generally specified for 3,000 volts on the anode) and all of the L series amps continued to use the same supply even though they switched to 3-500Z tubes with the L4B.  The Drake supply is rated for 2,600 volts no load dropping to 2,400 volts full load on the high tap (SSB position) and 1900 dropping to 1750 in the CW position.  At 2,600 volts the 3-500Z  pair is supposed to draw around 260 mils.  If you also use your L-7 for SSB/CW then the idling power dissipation is going to be significantly higher so expect plenty of heat in those modes also.

The L-7 is a very nice looking unit and the fan is quiet but the cooling system isn't the best.   It is somewhat ironic that the 4 line transmitters and transceivers ran controlled carrier AM so they were very easy on their matching 4 line amps but the TR7 transceivers run full carrier AM with the lighter duty L7 amp.  

[n2ffl]

Yeah I don't think I will be running it at 500 watts, 250 - 300 will do me just fine. I want those tubes and the amp to last a loooooooong time!. I have to pull it apart and may upgrade the cooling if it can be done without too much drilling and blasting. Right now I'm just checking out the supply to make sure it's in good working order. Then I have to interface it to the amp so it's going to be a little while before it's all up and running.

[N8ETQ]

Yo'

  Hit the primary with 6.3 VAC from a filament xfmr and measure the secondary voltage.. You can calculate the  turns ratio and go from there.. Yet another great use for a Variac. If the thing is 220
hit it with a 12.6 CT filament job.

GL and Make sure you have your shoes on!

/Dan

I was interested in finding out the specs on the transformer but no luck so far. I'm told the supply produces 3,200 to 3,700 VDC out. The name on the transformer is H.E. Johnson & Assoc. Inc, Clearwater, FL. Haven't been able to find anything on the company yet.