The AM Forum

I would appreciate some advice. I have an old Warrior with a bad 3B28.

Would it be best to replace the two tubes with W2AW 6kv solid state replacements at $5 each or

buy two new 3B28's at $25 or so each or should I try to get away with just replacing the one bad tube?

The bad 3B28 doesn't glow and my HV is around 900v instead of 1600.  I know the SS would increase HV so I would also add some resistance in series.

Some one mentioned the original wiring not being HV wire. What is preferred? Teflon? And is it readily available?

Thanks for the help.

Mark   KC4KFC

Hi Mark,

I also have a Heathkit Warrior amplifier. Mine came with the original 866As. I replaced them with the plug-in type solidstate rectifiers that were sold to the broadcast market as aftermarket replacements for the 866As, etc.

The difference in voltage drop between the 866As, the 3B28s, or the solidstate replacements is essentially zero or negligible.

This being the case, go ahead and solidstate that Warrior plate supply with no fears!

73,

Bruce

If you can find just one good 3B28 it would be OK to replace the bad one.  Of course you cannot predict when the other one will go bad, but you might just as well get all the usage out of the one that is still good, that you can.

The only situation where you need to add series resistance is when the solid state diode is replacing a high-vacuum tube type rectifier.  MV and xenon gas rectifiers have no more than about 16 volts drop regardless of the current you are pulling through them.

If you replace them go higher than the 6KV ones for an additional margin, not much more in cost.

Thanks for the good advice. I think I'll order those 14kv diodes from W2AW which are $10 each instead of $5 for the 6kv. I wonder if he sells heat sinks for them, too.

This thing is very heavy. I think the 3B28 could have been physically jarred in moving it around. I'm looking forward to getting it going.
73'
Mark   

Good move, I think it would have been possible have a higher surge PIV than 6Kv.   They come in a single plastic block, you can bolt them to the chassis, you could use heat sink compound under them.    They come with stainless steel spade terminals.    You have to solder wires to a spade connector then connect them, you can't solder directly to the terminals on the diode block.   Changed my 866/3B28 years ago to the same ones, never a problem.   I kept the tube sockets in place in case in the future someone wanted to do an authentic restoration.   W2AW was easy to deal with, if he is still the actual owner.   I sent a check, he called me on the phone to see if I was really me and then mailed them right away.

 

By the way, I was incorrect. Its not W2AW but K2AW. His ad is in the back of QST.

I spoke to him this morning; very nice guy. He said he was 94 years old and apologized for being a little hard of hearing. He sounded much younger. He doesn't do credit cards or paypal; just wants me to send him a check when I get them.

Don't they still make those? 

My BC1-T come from the broadcast station with a pair of direct replacements for the 8008, and I had a pair for the 866A's in my junk box.  I wired up a replacement for the 5R4 bias rectifier on a separate terminal strip, which freed up the octal socket so I could employ it for the 6AS7 protective bias stage, using a novel circuit taken from the 1947 (west coast) Radio Handbook.  The protective bias circuit allows me to use the transmitter for CW.

Probably the only AM broadcast transmitter in the country that has been modified for cw capability.

I got stacks of those sticks. How many ya want!! 10KV, just like the 866A and 3B28. Mine are full height, same as the tube.

Thanks for the kind offer, Patrick. I ordered the K2AW modules and will bolt them in when I get them and see how they work.

BTW I am painting the case of the Warrior today. Tractor Supply has great old tractor colors and I think I will go with  Ford Creme color. They have nothing close to the Heath Green. John Deere Green is a little too green.
The case looks cool stripped as its copper clad steel but I think it needs the protection of the paint.

I've never seen 811's lit up before. They glow bright white. I hope this is normal. All four look the same anyway.

73
Mark

be SURE to check fil voltage ... older equipment set up for 110/220V and will tend to overvolt when run on 120/240V ...thoriated tungsten fil generally run a straw color not bright white...73...John

Straw color is a good description and much more accurate to the color of my 811's. I will check the fil voltages though, thanks, John!

I was wrong about the color. I used Cub Cadet Beige. Looks pretty good.....

Ordered the K2AW modules on Monday and they arrived Thursday. I don't know why, but these days I am surprised when I get fast results and good service. And from K2AW who told me he was 94.