Hi all,
for what it is worth - the QBL 5/3500 is a an updated version version of an old
Mullard
tube, the QY5-3000A. The two are practically identical and I have the original
Mullard
data book published in 1969 with all the curves etc. I have been speaking to
Rich about
this tube and it is readily available as secondhand broadcast pulls in this
country (ZS).
Cost typically $30 for a good tube. Don't know what the new price is but I
expect it is
over $100 at least.
John ZS5JF
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> From: Peter Sundberg <sm2cew@telia.com>
> To: Colin Lamb <k7fm@teleport.com>
> Cc: amps@contesting.com
> Subject: Re: [AMPS] Re: New G2DAF amplifier information
To: <amps@contesting.com>
> Date: Saturday, March 18, 2000 8:00 PM
>
>
> Gents,
>
> These are the parameters of the QBL 5/3500 used by me and others in a G2DAF
> circuit. The parameters are taken from the manufacturers book.
> HF Class B amplifier, single sideband (there are numbers for class B and C
> in the book)
>
> Vf 6.3 V
> If 32.5 A
> Direct heated thoriated thungsten
> Va 5 kV
> Vg2 800 V
> Vg1 -107 V
> Ia 1.3 A
> Ig2 75 mA
> Ig1 55 mA
> Wia 6.5 kW
> Wo 4.4 kW
> n 68%
>
> Max ratings at 110 MHz in class B are:
> Va 5 kV
> Ia 1.3 A
> Vg2 800 V
> Wg2 100 W
> Ig1 80 mA
>
> The xerox copies I have are not good enough for scanning and publishing as
> they are faded and the paper has turned yellow. Will try to copy them again
> and then scan them.
>
> The tube is mostly used in TV transmitters up to 250 MHz, class B,
> television service.
>
> Ciao,
> Peter/SM2CEW
>
> At 14:57 2000-03-17 -0800, you wrote:
> >
> >Rich said:
> >
> >"Any guesses at to what would happen if a 8660/4CX1500B were used in a DAF
> >circuit. - with say 20mA of grid current instead of 0.06mA of grid current?"
> >
> >Rich:
> >
> >I have heard no one - except you - suggest using an 8660 in a DAF circuit.
> >Your friend, Norm, used 4CX250 tubes in a mis-understood bastard adaptation
> >of the original G2DAF circuit, which hung an electrolytic capacitor on the
> >screen grid. It splattered badly. It was not a G2DAF circuit. Yet, you
> >use it as a basis to condemn any reasoning that is not consistent with the
> >world as you view it.
> >
> >Tubes do not have to be used as the tube manufacturer originally intended
> >them to be used, and amateurs by their very nature are experimenters. I
> >recently built an oscillator which used the screen as the plate. It works
> >fine. Tubes were not intended to be used that way. It is called a Dynatron
> >and was designed long before I was born (which is getting rare these days).
> >Building any circuit - "good" or "bad" - is fine, so long as the builder
> >makes sure he does not unreasonably splatter. Certain tube design
> >parameters must be met for the long term health of the tube. Beyond that,
> >the only other question is whether the output has undesireable
> >characteristics such as splatter, harmonics or parasitics. And, it is up to
> >the designer or builder to achieve those goals. It would be a boring world
> >if all the amplifiers looked exactly the same and used exactly the same
> >tube.
> >
> >The other day, I raised the question of increasing the screen voltage on a
> >grounded grid tetrode - from zero to something less than the "normal"
> >voltage. Your response was "DAF circuits produce feculance". The
> >"distortion" was in your response. I am sorry that Norm's splatter years
> >ago affected your outlook on life so much.
> >
> >73, Colin K7FM
> >
> >
> >--
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> >
>
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> Search: http://www.contesting.com/km9p/search.htm
--
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Problems: owner-amps@contesting.com
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