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eHam Forums => Amplifiers => Topic started by: N9XTF on February 25, 2013, 09:27:50 AM



Title: 1970's RCA 811A tube specs vs new outsourced tubes
Post by: N9XTF on February 25, 2013, 09:27:50 AM
I've had an Al-811 amplifier new in the box, sitting on the shelf for 8+ years.  I purchased it from an outfit that had gone out of business; I acquired it at a very reasonable price but never put it into service then ham radio went by the wayside for some years.  I recently got back on the air and decided to give the new amp a try. 

The amp was purchased without tubes and a quick look in my closet revealed some NOS RCA 811A and some NOS Amperex 811A tubes.  I decided to install a set of 3 RCA's, put the amp inline and tuned it up on 10M according to the original amplifier documentation.  To my surprise, for the exception of a flaky iP-HV switch, it loaded up quite easily and produced 600watts +- without any cracks, bangs, arcs etc.  After tune-up, I reduced the drive to achieve 500 watts +- and operated SSB for 3 or 4 hours. 

I recently came across a revised tuning procedure written by W8JI that more clearly states the max grid and plate current values.  Was the supplement written to accommodate the new outsourced tubes or just to clarify the original tune-up procedures. 

The 811A tubes that I have, albeit I cannot decipher the date codes, are early 70's anyway.  Should I have found a collector and sold them and used new outsourced tubes or just pound away on the good old RCA's?

Regards,

Doug Coffman


Title: RE: 1970's RCA 811A tube specs vs new outsourced tubes
Post by: KD0REQ on February 25, 2013, 10:03:41 AM
new production is nowhere near the tubes you have in those RCAs.  run 'em and be glad.


Title: RE: 1970's RCA 811A tube specs vs new outsourced tubes
Post by: KE3WD on February 25, 2013, 10:04:10 AM
Use your good old stock US built tubes and know that you are ahead of the game.  

Those things might just outlast you if you treat them well, avoid loooong tuneups, etc.


73


Title: RE: 1970's RCA 811A tube specs vs new outsourced tubes
Post by: K2DC on February 25, 2013, 11:00:55 AM
I suspect that the spec's for the newer off-shore tubes are identical to those for the older RCA's and Amperex's.  Whether or not they actually perform that way is an entirely different story.

73,

Don, K2DC


Title: RE: 1970's RCA 811A tube specs vs new outsourced tubes
Post by: G3RZP on February 25, 2013, 03:53:02 PM
KE3WD and K2DC have hit the nails firmly on the head. Think yourself lucky you have those RCA tubes!