Heathkit SB-1000 problem

The first thing to check is to see if HV is present on the plate of the final. If not, there's something blown open, likely in the HV rectifier circuit. Check rectifiers and capacitors on the HV rectifier and HV filter boards. Also, make sure there's continuity from the HV rectifier to the plate of the final. An open circuit there means an open resistor or inductor between the plate and HV rectifier/filter.

Cheers,

Did you ever get this figured out? I have exactly the same amp with the exact same problem.

Thanks,

Ed

Since that's a fairly old posting you may not get a direct response.

Looking at the thread in the archives: it was suggested that this symptom probably means that there's a fried component, between the HV filter board, and the tube anode. According to the schematic I see, the red wire from the filter board goes to a small bypass cap to ground and into a choke (RFC3). From the output of the choke, it goes to the anode/plate of the tube via what shows on the schematic as a resistor (100 ohm 2 watt?) in parallel with a choke or coil of some sort. At a guess, this may be a "coil wound on resistor" parasitic suppressor. There's also a connection at this point to the HV blocking caps and then out to the output-match circuit.

If the choke (RFC3) or this coil/resistor combination is burned or damaged, it would prevent the tube from receiving any high voltage. This wouldn't be apparent from the meter reading (since the meter pickoff is on the HV filter board) but you'd see no plate current being drawn. Careful inspection of this current path should show you where the continuity ceases to exist ...

... IF YOU DO THE INSPECTION WITH PROPER CARE AND PRECAUTIONS. This is a DANGEROUS high-voltage part of the circuit, and contact with it while it still holds charge can leave you dead, dead, dead in very short order.

For what it's worth, I understand that Ameritron offers a professional repair service for this amplifier (it's a "licensed copy" kit version of the Ameritron AL80A, designed by W8JI).

See

And since he wants help, he should have just posted instead of replying to an old message. Not that replying to old messages is ever good.

And it's not like an RF power amplifier is a complicated thing. I've seen people build them that would be fearful of building something that does more. An amplifier has a tube or two, and a power supply, and because it is a power amplifier, everything is big and easy to work on. One could just check the components one by one if they had no skill in troubleshooting.

Michael

FWIW there appears to be a schematic at :

I got it and unzipped it and it looks clean. A PDF result form Google comes wuith a warning from google about "harm your computer" so I didn't get that.

If there is plate voltage then there is, that part works. If something went poof it is probably in the cathode circuit, if anything is. If not then in the grid circuit. If so, that tube is probably shorted of has alot of leakage of some type.

In fact without drive it probably should be redplating.

Probably the plate choke. Replace it with the MFJ 10-15197, pie wound, plate choke. Some of the original plate chokes used by Heathkit have resonances out side the bands for which it was originally designed. I used one of the MFJ chokes in my Dentron Clipperton L an made it stable in all bands, including the WARC bands. K5ZYZ

LOOK AT THE DATE

Oh slap my ass! :)

At least it was a good read, it brought back memories!

Jamie

yeah...I am presently scanning my old negatives and just came across a photo of me in my shack back in 1971