The AM Forum

Which is the best choice?
A matched set of 6146's or 6146'A for the low power drive section in the Invader 2000?
Definitely not the B's as I have read in the past somewhere....

Regards,
Len N2LEN

Len,

My Invader 200 I picked up restored and working last year came with the B version tubes and works fine.  I haven't finished the power supply yet for my 2000 but it came with all of the tubes and it also had the B version installed.

Most rigs will work fine with the B (and/or W version).  My Ranger, 2 Valiant 1's, and 1 Valiant 2 have a variety of variants (including some 6293 types) in use.  I don't mix types in the triple 6146 Valiant final but it really is only a small number of rigs that have any issues with neutralization with the B type.  The Invader 200 and 2000 are not a problem. 

So, you don't need to find the B version since the Invader didn't use it originally but if that is all you have on hand use them without concern. 

dont forget that the 6146B was really designed to run AB1 or 2 linear service for SSB, so it should be quite happy in this application. But, if you plan to use it mostly with the finals on, it really doesnt need the extra push from the Bs.

Some of the Collins S line era (includes KWM-2) had an issue with neutralizing with the B variant.  There is information on needed changes and I believe that later production Collins gear has the wider range neutralizing circuit.  I have not heard of problems with using the B (or W) version in other gear and I have a lot of 6146 based transmitters.

I know that there were some bad batches of 6146W tubes sold that would internally flash over with only 700 volts on the plate.  I got a group of these (Sylvania manufacture with the same date code) from Fair and the first two I tried flashed over.  This was in the mid 1990's and I found out others had experienced the same thing.  Fair replaced the whole group (I bought 20) with tubes with a later date code and those were fine.  I imagine a lot of the defective ones are out there and that has probably led to some of the internet reports of W tubes not working in place of plain or A variety tubes.  The only thing those particular W tubes would properly replace is a photographic flash bulb.  Sorry but it has been so long that I can't remember what the date code was on the bad batch.

the swiss cheese that masquerades as my brain is telling me that the problems occurred on the higher bands, 15 and 10... and that for the most part they are all stable on 75 and 160, at least that is what I recall from "back in the day"... Ymmv.

                      _-_-bear