[Amps] Choices for valve linear project 1st timer!

[Simon Steed]

 Hi,

No problem Mark, in fact most of the replies I got were direct rather than
through the list. Thanks to everyone that's responded so far with tips etc,
I'm even more confused what to do now :)

I'll get the article I mentioned scanned in this weekend and put it on my
site for people to look at if they so wish.

In the meantime, I'll start reading more into it and trying to whittle down
1/ which valve to use & 2/ finding a suitable design to follow

Wish me luck!

Si

-----Original Message-----
From: amps-bounces at contesting.com [mailto:amps-bounces at contesting.com] On
Behalf Of Mark Hill
Sent: 01 February 2005 09:20
To: Amps Reflector
Subject: Re: [Amps] Choices for valve linear project 1st timer!

Simon,

Apologies, I sent my reply (below) direct to you and not via the reflector.
It just might be of interest to someone else.

Ian 'SEK has given the correct reference for the Russian valve site I was
trying to remember.  Modesty however prevents Ian from telling you that he
also makes a well engineered bias/control board suitable for most any RF
power triode, GS-31 included.  More details, including the manual for the
'Triode Board' that contains lots you should know when embarking on a first
amp. project, may be found at:

http://www.ifwtech.co.uk/g3sek/boards/triode/triode-1.htm

I have looked at the other references for a design that you quote in your
original post.  I personally would not advocate using transformers out of
old microwave ovens unless novelty is a prime design goal.  Peter Rodmell at
Linear Amp UK would I'm sure be pleased to sell you some 'off the shelf' 
parts to help get you off the ground quickly.  Take a look under components
at:

http://www.lauk.karoo.net/

Whatever you do, do it safely and get good quality (and cross-checked)
advice - there's plenty available from the contributors to this reflector.

Regards.

Mark.

---------------------------------------------------
Simon,

My advice would be to go for a 'KISS' design with a single Russian GS-31 (or
GS-35) valve in grounded grid.  The valves are cheap; there's no expensive
base to buy; the heater requirements are easily satisfied; the list of
plusses goes on and I'm struggling to think of any negatives!

For a first PA (any PA!) multiple valves are a hassle, metalwork can be a
hassle and tetrodes are definitely a hassle, as for them, you would need to
build screen and bias supplies, plus an amount of protection in case of
'accidents'.  In my opinion, the era of the 4CX250 is well and truly over.
There are far better, cheaper alternatives now (such as the Russian 4CX800
if you must use a tetrode) and for an HF linear, using a valve with loads of
gain at VHF can turn into a struggle.

Type 'QRO via Russia' or similar into Google and you will find a website
full of ideas.

I well remember the 'JST 4CX250 design.  Still have the article I think.  I
remember thinking at the time that the design, whilst somewhat innovative,
was not one that I personally would be happy to commend to a public
audience.

Regards.

Mark.

----------------------------------------
At 20:28 31/01/2005, you wrote:
>Hi all,
>
>I'm a UK ham who is limited to 400W & would like to build my own 
>linear, one as I've always wanted to play with valves and two because I 
>want to learn more from the experience.
>
>Now googlising has brought up many designs + I also have a few old 
>magazine articles for similar. A couple that have caught my eye are:
>
>1/One published in the UK mag Ham Radio Today & was designed by G4JST. 
>It uses three 4CX250B's with a HT of 1.3kv to produce 400W which is 
>apparently very linear output. I know the HT is low compared to what it 
>should be so I'm prepared to uprate it accordingly if this is feasible. 
>I can scan the article in if any of the more experiences users would 
>like to see it's design? There are some holes in the article though so 
>it may not be 100% suitable for my 1st project - I quite like it though 
>:)
>
>2/ Anyways the 2nd I've seen is on
>http://www.mbc.co.uk/RADARS/G3RIK/g3rik.htm#linear & uses the Gi-7B valve.
>Again not  great deal of constructional info but I've mailed the author 
>so hopefully he can assist should I need it. The circuit diagram for 
>this beast is 
>http://www.mbc.co.uk/RADARS/Pictures/HF_Linear/HFLinear1.jpg - again I 
>need more info, it only shows one valve on the diagram but two are used 
>in the project - being dumb I'm not sure if I'm totally missing something
here??
>
>OK so I've managed to find a couple of potentially suitable circuits. 
>Are there any others I could use? For background I'm using a Kenwood 
>TS690S with 10-100W available to drive the linear. I'd like something 
>like 600-800W output which when I use at the legal 400W limit *should* 
>produce very clean output power with low spurious harmonics etc. I also 
>don't want to spend an absolute fortune on the project and also need 
>projects where the components are available or easily made!
>
>Any suggestions greatfully appreciated!
>
>Regards
>
>Si
>G0IQC
>
>
>_______________________________________________
>Amps mailing list
>Amps at contesting.com
>http://lists.contesting.com/mailman/listinfo/amps

********************************************************
Mark Hill - G4FPH
E-mail: g4fph at mjha.co.uk
New web site: www.qsl.net/g4fph
Old pages mirrored on: www.g4fph.freeserve.co.uk

Dipoles resonant on 1940/3700/7080 kHz
2 ele delta loop beam resonant on 14180 kHz

Remember: A Texas Gallon is actually less than a UK one!
********************************************************


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