The GU81 may be a good choice.
It should be stable in grounded grid operation with all the grids grounded
unlike the 833. Check out the G1 to plate capacitance. It is very low which also
means that the cathode to plate capacitance is low in GG operation.
It looks like an 833 as well.
The question is if it will operate safely as a trioded conneted pentode.
Some tetrodes and pentodes do not but most glass envelope ones do.
Just about all the 4- series do except the 4-65.
73
Bill wa4lav
________________________________________
From: Máximo EA1DDO_HK1H [ea1ddo@hotmail.com]
Sent: Monday, February 27, 2012 5:37 AM
To: Fuqua, Bill L; amps@contesting.com
Subject: RE: [Amps] 4 x Glass Glowing tubes
Hi all, Bill,
Yes, Bill is right.
I am not looking for just watts. I don´t want a closed box with ceramic tubes
inside (I already own one).
What I would like to get is a beauty looking amp with good/high quality audio,
based on glass tubes.
Let me change the question.
What tubes do you recomend to me to build a 14 MHz monoband amp from these;
GU48/833A, GU81M or GU5B?
GU5b (triode) is powerfull, cheap and AB2 class quality, the only issue is the
blower/noise they need. http://tubedata.tubes.se/sheets/018/g/GU5B.pdf
GU81M, tetrode, are cheap, and I guess has quality as well, no blower (or small
one), but tetrode needs more power supplies
http://tubedata.tubes.se/sheets/018/g/GU81M.pdf
GU48/833A, (triode), are cheap, B class, unstable?
http://tubedata.tubes.se/sheets/018/g/GU48.pdf
It could be just monoband amp, for 14 MHz, may be I can add 7 MHz later on.
Thinking in 4 tubes to get blowing glass enough and power between 4 to 10 Kw).
Any other glass tube?
Any recomendation?
Thank you very much
73, Maximo
> From: wlfuqu00@uky.edu
> To: hsu4qro@gmail.com; ea1ddo@hotmail.com
> CC: amps@contesting.com
> Date: Mon, 27 Feb 2012 03:03:03 -0500
> Subject: RE: [Amps] 833A/GU-48 x4 Amp support
>
> I believe he wants 4 glowing plates. Larger the better.
> 4x 250th would work but a bit expensive compared to the Russan 833.
> I once ran 2x 250th in grounded grid driven by a pair of 6146Bs on 20 meters.
> So 4 should work.
>
> 73
> Bill wa4lav
>
> Subject: Re: [Amps] 833A/GU-48 x4 Amp support
>
> I don't think 833A is a good option.As it have long electrode and bad
> freqence response. I'm afraid it can not work in 20m in 4X
> parallel(self-oscillation).
> 3CX3000A7/F7 is better. But if you use ACOM2000A as driver, it will over
> drive easily.The drivering power is 400W (max) for 3CX3000A7/F7. or you can
> use low/ medium Mu triode
> in GG like 3CX3000A1/3CX2500A3..., they need more driving power. Just my
> thought.
> 73!Hsu
>
> -----原始邮件-----
> From: Máximo EA1DDO_HK1H
> Sent: Sunday, February 26, 2012 6:00 AM
> To: amps@contesting.com
> Subject: [Amps] 833A/GU-48 x4 Amp support
>
>
>
> Hi all,
>
> I am not an amps expert but I am thinking to build an amplifier using 4 x
> GU-48.
> I guess GU-48 is equivalent to 833A, not sur if all specs are same.
>
> This is trying to get an amp "looking beauty" and good audio quality, it is
> not looking for extremely high power. I already have an amplifier (Acom
> 2000A) i can use as driver.
> Something like this, but HF;
> http://www.luxurylaunches.com/entry_images/0511/17/Audio-Power-Labs-833TNT-tube-amplifier-1.jpg
>
> Gates BC-1g is an example too; http://w5ami.net/bc-1t/833.glow2.jpg
>
> It could be monoband amplifier for 20m, perhaps 40m too.
>
> I thought in GU5b and GU-81M before, but I guess GU-48 is better because
> needs no specific blower and is triode (easier to build).
>
> Please, Any of you have sperience with this kind of amplifier?
> Any squematic?
> Recomendations?
>
>
> Thank you very much
>
> 73, Maximo - EA1DDO
>
>
>
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