Bird Slugs - How to Repair Them?

[K1JJ]

I have an intermitent 250W Bird HF slug. I tried cleaning the whoole surface with alcohol, but it still does not work most of the time. It does not seem sensitive to vibration - just works when it wants to. All of the other slugs work FB, so the Bird wattmeter is OK.

Is there a way to take them apart to repair, or does anyone have suggestions for the above symptoms?  I doubt sending it back to Bird would cost any less than buying a new/used one.

T

[Jim, W5JO]

If you send it to Bird, get ready to drop a C note.  You might look for Calibration Labs elsewhere and do better.  The only thing I know for sure is that the cover on the front of the slug comes off.

Are you sure it is the slug rather than the coax connecting the meter to the inline system?  Check all connections.

[WA1GFZ]

Tom,
I bought anew 5KW slug with the same problem but lost the paperwork on it.
I contacted Bird and told them it was about a year old but I lost the paper work.
I told them their stuff was so good I never considered it to be a problem.
They took it back and gave me a new slug when they confirmed the same problem. I bought it from Richardson at a flea market if I remember. fc

[K1JJ]

Interesting Frank -

As Jim suggested, I took the front top off and there were screws inside to take it apart.  I could see a variable pot and a resistor inside, and maybe a hidden diode. All checked out OK as referenced against my other slugs on the VOM.

So, still dead. I'll call Bird and see what they have to say. They may be like EV and the RE-20, where it has a lifetime gaurantee.

BTW, I'm thinking about building up a new PDM tube rig. I only have 5500 VDC to work with, so was thinking of maybe using quad 813's in the final, but can't decide upon a SINGLE switching tube that will work at low voltage, like 2500V, etc. Maybe a single 4-1000A wud work with screen voltage at that plate voltage, or do you have some suggestions for a tube line up for 5500vdc?  [8-10kv is what ya really need for series PDM, in case anyone's wondering]

T 

[WA1GFZ]

Tom,
I've collected the parts to build a 813 PDM rig with T195 PTO as VFO.
Some day I mmay actually build it. I was going to do about 3 KV.
I was thinking of 4-6DQ5s as the switch.
I think Steve's first PDM rig was an 813. I thought it sounded better than the
bigger one. he used a 4-400 as a switch if I remember.
Contact Steve I think he has been down that road.

[K1JJ]

813's are tempting.

The problems with the tetrode final is floating the screen and grid supplies.

I'm wondering if a string of zenors in the cathode wud do for the protective bias?  I've always had bad luck with them shorting out and maybe that wud not be such a good idea.   

After a lot of thought, it almost seems that an airless TRIODE wud be the best RF final. No screen supply and no blower noise. Thus, a pair of 833A's would be a good choice there. That's when a zenor string wud be great, meaning NO floating supplies at all. [Hmmm... actually if it was ALL grid leak bias tied back to the filament, that wud work too, with precautions - then no supplies at all except the HV!]   

T

[WA1GFZ]

Tom,
you could put exrta windings on the floating fil transformer or have a floating transformer to do G1 and G2 voltages. Zeners would require some sort of bias voltage but could serve as a regulators.