[Heathkit] Grounding the grids of 3-500Z tubes

[Carl]

Of those mentioned one is not an engineer and another hasnt made it above 
3rd rate companies.

As an engineer Ive had ideas rejected during the design review process but I 
havent felt the need to create a web site pushing alternative theories out 
of spite.

I prefer to put my faith in the real pros as well as my own education and 
experience.

One of the most unstable 3-500Z amps is the AL-82. When it decides to let 
loose it takes many components with it. Would you call that a good design?

Its strange that those who blindly follow the direct ground theory have yet 
to show spectrum analyzer proof of the claimed benefit. I dont consider 
another 100W a benefit.

Carl
KM1H







----- Original Message ----- 
From: "John King" <k5pgw at yahoo.com>
To: <heathkit at mailman.qth.net>
Sent: Saturday, August 22, 2009 4:27 PM
Subject: [Heathkit] Grounding the grids of 3-500Z tubes


> While I am not an engineer, I take advice from Engineers very well.
>
> Several years ago, I had a 3-500Z in ONE of my SB 220 amps short and take 
> out grid caps and chokes. I had NO original components to use, so I sought 
> advice from W8JI AND Rich Measures without telling either that I was 
> picking the brains of either. They were very friendly and helpful.
>
> W8JI told me that he was working for Heath, as an Engineer, when the SB 
> 220 was designed and disagreed with Heath's decision to use the caps and 
> chokes on the grids of the SB220. He told me that Heath told him that they 
> were using the caps and chokes on the grids BECAUSE BILL ORR W6SAI 
> recommended that practice to limit IMD. W8JI told me he didn't agree with 
> that practice at the time and did not when I talked to him. He recommended 
> that the grid pins be grounded through a low value resistor  from each pin 
> to ground. So each tube pin ended up with a 3 ohm 1/2 watt resistor to 
> ground. One OR BOTH of the two Engineers told me that if there was some 
> type of momentary arc in the tube that it would open the small resistor 
> like a fuse and protect other components. As you may know, W8JI has been 
> the design engineer for Ameritron and other companies and none of those 
> amps I have seen have anything except wither direct grounding the grids or 
> grounding through a
> low value, low wattage resistor.
>
> Collins 30L1 seems to have started the cap/choke design with Heath, Omega, 
> Henry (2K series, which I own one of)and Kenwood TL 2000 following the 
> design. Yes, I know the 30L1 uses 811As but grounded grid design was just 
> copied. My Amp Supply 3-500 amp was designed with directly grounded grids 
> at the socket also. My GSB 201 MK III has directly grounded grids on the 
> four 572B tubes. My experience has been very good with the amps using 
> directly grounded grids, however I like the suggestion of using the small 
> value resistors to protect against momentary shorts.
>
> The foregoing is not my CLAIM to being an expert and isn't attempting to 
> evaluate the engineers who have so kindly assisted me with information. 
> The information supplied to me by BOTH was good and WORKED!!
>
> Several years of use supports the SB220 grid grounding scheme with 
> success. 73, John, K5PGW
>
>
>
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