[Amps] 8877 Time Delay Query

[Will Matney]

I imagine that Alpha figured if you bought one of their amps, you'd already know to let a tube warm up? That kind of reminds me of an instruction manual that came with a VCR I had bought. The very first page showed Superman reading the manual and scratching his head. Anyhow, I always let any of them warm up at least 3-5 minutes. A lot of people complain about warm up time but to be honest, it don't take that long if you remember to fire up the amp as soon as your in the shack, and not wait until you need it. Trading off a little warm up time for life expectancy means a lot. And I'll still about bet a tube will outlast solid state 2:1 in rough conditions.

Best,

Will

*********** REPLY SEPARATOR  ***********

On 7/28/05 at 1:42 PM Phil Clements wrote:

>Another to add to the list; Alpha never bothered to delay HV on any of
>their
>8877 amps.
>
>(((73)))
>Phil, K5PC
>
>
>-----Original Message-----
>From: amps-bounces at contesting.com [mailto:amps-bounces at contesting.com] On
>Behalf Of w2cqm at juno.com
>Sent: Thursday, July 28, 2005 7:15 AM
>To: Amps at contesting.com
>Subject: [Amps] 8877 Time Delay Query
>
>Can anyone help with specific knowledge about the 3 minute time delay and
>the application of HV on the Eimac 3CX1500A7/8877? The 8877 tube data
>sheet only specifies a 3 minute filament warmup. However it does not
>mention whether HV can be applied when the tube is turned on (no
>excitation of course) and filament voltage applied.  Ameritron (AL1500) 
>holds off application of  HV for the full delay period.  Dentron did not
>in their 8877 amp with no apparent problems! I hasten to mention that I'm
>not too confident about the general level of Dentron circuitry and that
>testimonial.   The 3CX800A7, smaller version of the 8877,  date sheet
>specifically admonishes the ham not to apply either  RF excitation or
>high voltage "...for a minimum of three minutes (of filament warmup)...to
>allow for proper conditioning of the cathode surface". At this point, I'm
>not certain if the 8877 is materially different from the smaller, yet
>similar tube. If the application of HV makes no difference with the 8877
>during the warmup period, it saves a lot of  control circuitry and a
>separate filament transformer;  especially when both windings are from 
>the same xmfr. Consequently, the delay can be incorporated in the antenna
>relay circuit only. In the 8877 amps I've built, I've always delayed the
>application of HV just to make certain there'd be no damage.   Any
>comments  based on first hand engineering data would be appreciated. Ron
>W2CQM/3
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