[Amps] Requesting opinions on a Drake L-4b's tubes

[gudguyham at aol.com]

Henry amplifies ran a pair of 3-500 tubes up to 2000 watts output.  You simply can’t over drive a pair of 3-500’s with a Drake L4 amplifier unless you drive it with 125watts or more.  That doesn’t mean you can’t ruin the tubes!!!!  Improper loading will cause tube damage but it won’t be from over driving with 100 watts or less.  Like Henry amps did to get 2000 watts pep output without over driving.  They could obtain this by using 4000 volts on the plate.  WHAT DOES KILL 3-500 TUBES IS OVER DISSIPATION.   You can easily over dissipate the tubes with improper loading and mode selection at increased time intervals.  Also remember that by merely operating lower output does not mean you are doing any good deeds for the tubes versus higher output.  It’s possible to run the amp at a lower power and dissipate more heat than at higher power by running the amp at a lower efficiency range.  Many people are way to anal about grid current on 3-500 tubes!!!  The grids are very hearty on these tubes and running high power SSB will not hurt the grids even when loaded to a maximum of 200ma each.  Be concerned about running AM with its inefficient carrier.  I can go on but I think you get the point.

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On Friday, December 23, 2022, 7:42 PM, Jim W7RY <jimw7ry at gmail.com> wrote:

Better yet...

How much drive are you putting into it?

What radio are you using?

Jim W7RY


On 12/23/2022 6:36 PM, Curt Nixon wrote:
> Seems odd that you say overdrive giving 100ma of grid but 400w with 225ma
> grid..
> This is perhaps a tuning issue with mis adjusted loading.  Are you using
> relative output and grid current to tune or trying to dip the plate
> current.  What is the plate hv doing in those two conditions?
>
> On Fri, Dec 23, 2022, 6:31 PM A Lawrence Fibich <lfibich at sbcglobal.net>
> wrote:
>
>>  Please accept apologies - I misspoke on being push pull - surely finals
>> are in parallel - I was more focused on trying to explain simply and
>> 'fingers did their thing' again, sorry for misspeaking. LarryW6EF
>>      On Friday, December 23, 2022 at 12:48:28 PM PST, A Lawrence Fibich <
>> lfibich at sbcglobal.net> wrote:
>>
>>  I just acquired this Drake L-4b as the third owner and no nothing about
>> its history. It puts out 400 watts with recommended Plate and grid currents
>> (.56 amps, and 225Ma respectively). If overdriven (.8 amps; 100ma) it will
>> do 600 watts. At 'idle/resting' should be 0's but shows .1 plate amps & 75
>> ma grid current- which I think shows a tube problem.
>> Now my request for an opinion, what do you suggest:
>> 1. I got 2 unopened tube boxes from Drake - thinking to simply replace/use
>> them and see what happens.
>> 2. Surprise - 1 is the 3-500G- (Graphite plate) - the other turns out to
>> be a 3-500Z (old style) . 3. The unit has 2 (original/old) - 3-500Z's in it
>> and really no way to test them4.  So? what to do?5. Live with it, and leave
>> the 2 in the unit and live with 400 watts and? or- maybe overdrive them and
>> go for 600 watts? ? how long do you think they would last?6. Use the 'new'
>> 3-500Z with one of the 'old' 3-500Z's?7. Use the 'new' 3-500G (graphite)
>> with the 'new' 3-500Z?8. Use the 'new' 3-500Z with one of the
>> 'original/old' 3-500Z?
>> Of course, the finals in the Amp are push pull configuration -2k PEP & 1K
>> CW input watts.
>> Thanks for ALL your suggestions/recommendations.  73Larry F.W6EF
>>
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-- 
Thanks and 73, Jim W7RY
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