The AM Forum

I always liked Sylvania......


http://k9axn.com/attachments/THE_6146B_STORY_9U2.pdf

K9AXN lifted a lot of information from Glenn Zook's article, but neither of them ever really understood power tetrode physics and Neutralization circuits.

Phil

I’m still waiting for someone to give me proof that RCA ever retracted their statement that the 6146B could replace the 6146 and 6146A. I’ve used B’s as replacements for dozens of them and still haven’t found a radio they wouldn’t work in. This includes equipment Zook specifically called out.

Darrell

I did the same and the set performed as well. IIRC a Tempo 2020. Used plain 6146s because I had n no money but had some tubes. Decades ago but why would that matter? My only test equip. was a LPF, dummy load, wattmeter and scope. No spectrum analyzers etc. Just lucky? Maybe.

I was involved with Kenwood hybrid radios and 6146B's didn't work well either. The radios used S2001's.....I keep seeing Youtube vids and folks using 6146B's as subs. Maybe Chinese tubes don't play well.
The only tubes that worked well and were cheap from China were 833's
Fred

S2001 tubes are "identical" to 6146B's; the later version, S2001A was also "identical" to the 6146B.
I've been running a pair of 6146B's in my Kenwood TS-830S transceiver and Kenwood T-599D transmitter for many years with zero problems.

The problem issue(s) of substituting 6146B's for 6146 and 6146A tubes has been highly exaggerated over the years.

   ;D Hey! I read it on the Internet so it must be true  ;D
And some just like to blow smoke

I ran Marconi 6293's in my Knight T-150, and do not see any performance differences between them and 6146's, 6146A's, 6146B's, or 6146W's. Neutralization has never been a problem with any of them. Looking at the interelectrode capacitance and transconductance specs they are all the same among this family.

The information I could gather on the 6293 was it was essentially a specially processed version of the 6146.

It had slightly larger gauge molybdenum wires for stability and heat conduction, ceramic (higher voltage dielectric) wire guides/insulators instead of mica, and a zirconium coated and carbonized plate of nickel for long-term gettering. Carbonizing the plate allowed for better IR radiation.

During construction, it had a greater vacuum "draw down" than did its cousins, and a slightly thicker glass envelope.

In the case of the KWM-2, the initial neutralization circuit was not designed with enough capacitance variation to accommodate even the exact same tube types. If you take a sample of 6146A's and measure the inter-element tube capacitance, you will find a slight variation in those inter-element tube capacitances' from lot to lot. If your neutralization circuit does not have enough variation at the beginning, then yes, you may well have problems.

I.e., The Collins neutralizing circuit was bad from the very beginning and was unable to handle many 6146 and A's to be fully neutralized on 10M. It was close enough to work on the lower frequency bands. The later version neutralization circuit was what should have been there at the beginning. Collins did NOT have the greatest engineering brilliance in several areas, some of it caused by the egomaniac at the top. The 30L1 was another example of a firecracker waiting to explode even after a steady run of changes during its production life.

As an example, review the schematics for the military manual (TM11-5820-529-15). There are two sets of schematics in this book with two distinctly different neutralizing circuits. It appears that the earlier KWM-2's have a 1.8-8.7pF variable cap while the later version has an 8-50pF cap. The changes chronicled in part 7 of the on-line KWM-2 manual show Collins had design changes and problems throughout the respective equipment histories.

Neither have I had neut. problems running any 6146X's in HeathKit's such as DX-35, DX-40, DX-60, Apache TX-1, or EF Johnson equipment such as the Viking I, II, II-CDC, or the Valiant.

Quoting from Glenn Zook's paper he posted on every forum for years....

"The whole problem stemmed from the fact that the "B" series of tubes is not the same as the "plain" and "A" series.  The parasitic oscillations were caused by the different bias requirements and by the "fixed" neutralization of the driver and/or amplifier tube in the Motrac.  There was no practical way to change the circuitry to handle the "B" series tubes.  Also, making such a change would void the "type acceptance" of the units. "

Right here he contradicts himself regarding these tubes.
These Motorola Motrac radios did not have an adjustable neutralization ckt because they were 'type accepted" to operate on VHF/UHF with a specific tube(s).
Of course those tubes burned up because RCA changed the tube design!
This was not Zooks fault.

He kept up the notion for years that the Collins ceramic trimmer neut ckt in the KWM-2 and 32S-x series of radios would instantly burn up if a certain 6146 version was used etc etc and spooked half of the Amateur population for years.

I know for sure that there are plenty of Amateurs that have/had these transmitters and tried to tune them and when they could not tune them....just kept on tuning and tuning....when in fact the unit did not have an antenna attached or on the wrong antenna....any combination of operational mistakes.
We have all done this at one time or another but....the difference is....you notice a problem and STOP!!
How about lightening or high static voltage build up on the antenna??
This can certainly damage that ceramic neut trimmer.
Collins changed the neut cap to open frame later in the production run but I doubt this tube issue Zook promoted for so long was the cause.

I have neutralized some 70 or so KWM and 32S units with all versions of 6146 and some Chinese tubes too with the ceramic trimmer and never had a problem and always achieved a definite bell shaped null.

I call BS on this whole 'thing' that has been around for decades confusing most new guys...and some of the old guys too!!

Off rant!!

My 6146 story - I built a Heathkit HW-101 in 1971.  I assume at this point that the original finals were 6146A's. In 1973 a friend gave me some new 6146B's and so I swapped them in. I did get some arcing later in the neutralization mica compression trimmer. I didn't suspect this was fault of the tubes (me - 22 years old at the time); I presumed that the compression trimmer's voltage rating may be marginal for the application.  I changed the neutralization cap to a small air variable and never had any trouble after that, nor suspected any.

Interesting. I purchased an HW-100 when they first came out. Heathkit supplied RCA 6146B’s with it. They slipped a card into the manual stating that RCA was having trouble supplying 6146A’s so they had substituted B’s. The card went on to say the B’s were equivalent to the A’s. I installed the B’s and never had a bit of trouble with them.

Just to clarify, Glen and I were friends who had parallel career paths.

He and I both started out at Motorola Service Centers and wound up at the same company (RC) in different locations.

He and I had about a 3 month discussion on another site regarding his article.  :D

I was sad to see him go SK as he was a good microwave engineer.

Phil

Above all he was a nice man.  I worked with Glen many times when he had the Dallas Recondition Depot.  He never forgot his customers and would go the extra step to please them.