SV: [AMPS] AL-80 / SB-1000 circuit improvements

measures 2@vc.net
Tue, 29 Feb 2000 10:15:40 -0700


>sm5ki wrote:
>> 
>> Rich you now said:
>> 
>> "4.  disregard the users' manual's ok of more than 500mA of anode current.
>>  No 3-500Z/8008 manufacturer has Ever rated this tube at more than 400mA."
>
>We've had this discussion numerous times in the past.  I have an SB1000.  The
>manual describes a tuning procedure that allows 500 ma current for a short
>period only, so that the tank circuit will be optimally loaded under PEAK
>conditions in SSB service.  

The constant-current curves for the 3-500Z/8008 show that the highest 
peak current for linear operation is approx. 1.2a-peak.  This corresponds 
to an indicated current of 400mA. 

> The manual is quite clear that you MUST reduce drive
>to a level that will give NO MORE THAN 400 MA for CW use.  

This discussion is about SSB use.  . 

>It also suggests that
>the 'modulation crest' in SSB service shouldn't exceed 400 ma, although it 
>isn't clear how you determine that.  

... you read the meter during modulation.  In SSB service, with normal 
human speech, the meter should indicate roughly double the ZSAC  (only 
for thoriated tungsten filament tubes).  .  In other words, roughly 
150mA.  

> The manual does NOT recommend operation at 500 ma.
>
>I asked the designer of the amp (who Rich declines to name, but is W8JI) 
>and he confirmed that this was his intent.

A few years back, Charles Thomas Rauch, Jun. stated that he had an 
official Eimac letter allowing 500mA for SSB use.  He said that he would 
post this letter.  Mr. Rauch has not yet posted this letter.  At this 
point, it's starting to look kinda like the letter was a shenanigan.  

My guess is that Mr. Rauch was trying to offer a true kilowatt amplifier 
with one 3-500Z.  Unfortunately, due to emission limitation, bring this 
off with less than 4000v is simply not possible unless one runs 500mA at 
3200v in.  With the SB-1000's existing bandswitch contact spacing, going 
with a 4kV supply would have been risky.  Also, with the added 
amplification provided by a 4kV supply, something better than the stock 
parasitic suppressors would have been needed to avoid parasitic 
oscillation.  //  It is my opinion that Mr. Rauch will never admit that 
the RF resistance of Nichrome, increases with frequency.  
>
cheers, Vic

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