[AMPS] Heathkit SB-1000

[Tom Rauch (W8JI)]

John Watson wrote:
> 
> I have a SB-1000 that I recently bought. It has all of the paperwork,
> etc. I have used it a total of 2 to 3 hours maximum.
> I have read here that the 3-500Z's are supposed to be no longer made by
> Eimac, and are being made by Svetlana.

Eimac sold the glass tube designs to Triton, a former ITT tube
manufacturing plant in Pennsylvania. Triton is already producing 3-500Z
tubes.

> Is there any "updates" or mods to this amp? 

Contrary to rumors started by one person, VHF parasitics almost
certainly do not damage
bandswitches. The reason the SB1000 switch has many times the failure
rate of the AL-80A (a similar PA) is Heath left out a anti-corona washer
on the 160 tune capacitor padder terminal, and they did not spec the
transformer as tightly for voltage sag.

You can't do much about the transformer, but I recommend carefully
checking the lead dress around the switch and adding the anti-corona
washer.

Be sure there are no sharp points or close spaced wires in the area of
the switch, both of which aggrivate voltage breakdown problems. 
   
>I know that the ameritron
> AL-80A is supposed to be a "clone" of this amp.

I designed the AL80A first, and then sold the kit-only rights to Heath.
So the Heath is a "licensed copy" of the AL80A. 

Someone else said:
 
> Forget about the 500mA+ blather in the SB-1000 or AL-80 owner's manual.
> Eimac says that for linear operation, 400mA is the absolute maximum
> rating.  500mA is bovine feces.

That is colorful language, but is completely untrue. 

The manual's recommended rating of the 3-500Z plate current was accepted
and approved by Eimac's tube engineering department as an IVS rating. 

Cathode saturation current of a 3-500Z begins at approximately six
amperes, and at 500 mA of meter indicated anode current, PEAK cathode
current (which includes grid current)is only about 2 amperes. There is a
3 to one safety margin.

400 mA is the CCS cathode rating, in ICAS (amateur) service the life
difference would be undetectable. IMD performance is also virtually
unchanged, since the cathode is far from saturation. Linearity is more a
result of the transfer function than 100 mA of extra current, since the
tube is FAR from saturation.

Heathkit and Ameritrion have full Eimac factory warranty when the tube
is operated at the manual's ratings, with Eimac's approvial. Sometimes
people who are outside the loop rush to judgement with good intentions,
but they don't always know what is really going on.

It is always best to contact the manufacturer. 

73 Tom


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