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

[Steven Katz]

I didn't understand the original post, either.

800mA Ip is not overdriven if the Ig is below 300mA.   800mA is the rated Ip for two 3-500Zs, and they're rated for that under CCS (broadcast) conditions; they can surely handle 1A Ip intermittently, like SSB voice peaks.

But you can't tune up at reduced drive, then just increase drive without re-tuning.  The LOAD control has a pretty big effect on grid current and if the amp is lightly loaded, grid current may be excessive and efficiency poor.



-----Original Message-----
From: Amps <amps-bounces at contesting.com> On Behalf Of Curt Nixon
Sent: Friday, December 23, 2022 6:37 PM
To: A Lawrence Fibich <lfibich at sbcglobal.net>
Cc: amps at contesting.com
Subject: Re: [Amps] Requesting opinions on a Drake L-4b's tubes

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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