>Subject: Re: [AMPS] Heathkit SB-1000
>Sent: 3/27/1997 11:29 AM
>Received: 3/27/1997 11:49 AM
>From: Tom Rauch (W8JI), W8JItom@worldnet.att.net
>To: amps@contesting.com
> John Watson, jwatson@mail.cde.com
>
>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.
To see some photos of bandswitches that were almost certainly........,::
http://www.vcnet.com/measures
>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.
According to the photographs of toasted AL80 bandswitches, the 160 m
padder contacts on AL-80 bandswitches appear to evaporate no less readily
than other bandswitch contacts. OTOH, the TL-922 bandswitch is more
prone to arc than the bandswitch in the SB-1000/AL-80 This is also the
case for late-production SB-221s which have the wider-spaced tune cap.
...snip...
>I designed the AL80A first, and then sold the kit-only rights to Heath.
>So the Heath is a "licensed copy" of the AL80A.
Did Mr. Rauch design the AL-80?.
>Someone else said:
(the un-'expert')
>> 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.
......brown is colorful?......
>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.
However, no name is provided. I wonder if this is the elusive Mr "XXX'"
with the bogus 'Eimac' e-mail address?
>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.
To see if Mr. Rauch's statement washes, refer to Eimac Curve #4364 for
the 3-500Z. If you do not have a copy, see Figure 17 at the
aforementioned Web site. The items of principal interest are the
plate(anode) current=1.4a and 1.2a peak current curves. For linear
amplifier service, to convert peak anode/plate amperes to average
amperes,, divide by 3. Thus the 1.4 a curve is equivalent to about
466mA, and the 1.2a curve equivalent to about 400mA. The 1.4a curve
stops abruptly at 500v while the 1.2a curve continues down to 250v. Why?
If the 1.4 a curve were to continue below 500v, the curve would hook and
shoot off the graph into Saturationville . On page 2 of the Technical
Data, the maximum rating is said to be 400mA. The idea that more than
400mA is good engineering practice, is contraindicated by Eimac's own
constant current curves.
>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.
This statement seems not to wash. How smoothly Mr. Rauch glides from the
real issue--distortion--to service life and warranty issues. IMO, the
term 'transfer function' is somewhat technoblatherous.
>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 ....snip...
During the vhf suppressor debate, Mr. Rauch accused me of faking
photographs of arced bandswitches. ....... Rush to judgement. Fake
photos. .I think I've finally......--Bzzzzzzzzzzzzzzzzzzzzt. cough,
cough. I'm outta here. I need some fresh air.
R. L. Measures,ag6k, [805]386-3734
--
FAQ on WWW: http://www.contesting.com/ampfaq.html
Submissions: amps@contesting.com
Administrative requests: amps-REQUEST@contesting.com
Problems: owner-amps@contesting.com
Sponsored by: Akorn Access, Inc. & N4VJ / K4AAA
|