Kl 203p HIGH swr

Hi guys,

What I said wasn't specifically knocking any one manufacturer or country of origin.

The circuits are all the same regardless of manufacturer, compare a RM, Zetagi or Chinese knock off KL circuit and they are all basically the same - wide band RF linear amplifiers.
(Although the 'linear' aspect can be argued )

The circuit is as old as time, originally using a push/pull valve pair, then transistors, epitaxial RF devices and ultimately MOSFETs. The latter being readily available and cheap as chips hence their use. It's as technology progresses and the next wave of cheap devices become available that we start seeing problems, such as MOSFET devices that can switch at higher frequencies.

The 'Ham' linears are usually much more expensive because they have low pass or even band pass circuits to prevent spurious harmonics being emitted. The CB ones don't add such extra circuitry to keep prices low. (Technically a good basis assuming the CB has decent output filtering - but they usually don't.)

These type of amps used to be advertised as CB linears with a typical 26-28MHz range, they now get advertised as 26-30MHz to capture the 10m Ham market. (They're still the same things!) A lot of Hams used to change the MOSFETs out on them to make up cheap 6m amps and indeed nowadays they can be used 'off the shelf' for such frequencies.



Hence my original point, if you are amplifying any harmonics, (especially the secondary at 54-56MHz), it will show a poor SWR when running. The SWR meter won't differentiate what frequency is coming back, just how much.



But I agree Martin, places such as RM and Zetagi etc. have reputations to keep and I personally don't know their supply or manufacturing chain. I just know the circuitry is the same....


Anyway, all of this was trying to help out the original OP with a problem - it'll probably turn out his second hand amp is a duff one. But if you have a nice new shiny rig, new linears and have got a SWR problem....then this knowledge just might help

Just sling in a cheap TVI filter.


All the best,
Victor

TBH my preference is a  old valve amp but nobody seems make them now well not that I know of ,perhaps some specialist radio manufacturers may do custom ones ,I use to have one once OK it use take about 5/10mins to warm up and you had to tune it (plate and load) but I never had any problem with it apart from as time went on I found it a bit harder to find the valves for it ,then someone offered me a nice price to take it off my hands ,don't know the make of it as it was a homemade one i think had no name on it, because I brought it second hand anyway myself.

I miss my old Bremi BRL500's Martin
(Used to have some BRL300's too!)

Nothing like that Pi-Network tuning output!

There used to loads of the old PL509/519 handmade jobs around but I haven't seen a set in years.

If anyone reading this doesn't know, the PL509 was a line output or 'sweep' thermionic valve that used to be common in TV sets right up till the early 1980's. Cheap as chips and could be pushed into service as RF linears. Quite often you could dig them out of discarded TV sets so getting them for free!!

Bit harder to stick in the car mobile though Martin!

Flip me, happy days. There are new valve amps available nowadays but be prepared to break the old credit card!

I will admit Victor I didn't know that about old TV valves was the same or could be used to build amps ,my electronics skills in that dept is nill, we used to have in my area a proper old school large electrical shop who sold everything and the old boy who owned it knew everything too so that's where most of us went to and got things like valves and other radio stuff TBH anything to do with electronics,there was always a load of knowledge of electrical stuff to be learnt in that shop from the old boy and his staff plus other customers, not all radio I will say because it wasn't a radio shop as such  but as time went on and electrical stuff became disposable products he business slowly dried up and when he passed away the shop just shut down, shame none of his staff took it over but as I siad most electrical goods was coming from Hong Kong/China made cheap sold cheap so chuck it when broken so no one bothered I suppose, but that was a brilliant shop.
RIP Frank Mozer 
Owner of Frank Mozers Electronics
Edmonton North London

We could have a whole new thread on that Martin!

I remember Frank Mozer's and Crescent Radio. There were more electronic shops in London and surplus outlets than you could shake a stick at. Edgware Rd was full of them, I think Smith's (?) was the big one. I used to do a run for spares, D P Hobbs in Luton, Surplatronics also, if they didn't have the part then onto Watford and often finally landed up in London. I remember a surplus warehouse outlet at Waltham Cross too, can't remember their name but loved the old 'Pie & Mash' shop round the corner! Warmed me up for the motorbike journey back home.

Ha! Definitely off topic now mate!

Sorry mate and others  to go off topic but I just wanted to share that memory,  Crescent Radio is still there but it's just a very very small shop now in a side street it use to be on the corner of the same street but sold out to move to smaller premises,bit of a coincidence you knew Mozers.

No worries Martin, off topic can be enjoyable

We've probably been stood right next to each other and never even known mate
Such is the strange world we live in.

@21ASN93 Where are you measuring the SWR, exactly? Do you have any power output from the amp into the aerial (or dummy load)? Is there any output to the aerial with the amp connected but switched off?

Victor wrote:

We could have a whole new thread on that Martin!

I remember Frank Mozer's and Crescent Radio. There were more electronic shops in London and surplus outlets than you could shake a stick at. Edgware Rd was full of them, I think Smith's (?) was the big one. I used to do a run for spares, D P Hobbs in Luton, Surplatronics also, if they didn't have the part then onto Watford and often finally landed up in London. I remember a surplus warehouse outlet at Waltham Cross too, can't remember their name but loved the old 'Pie & Mash' shop round the corner! Warmed me up for the motorbike journey back home.

Ha! Definitely off topic now mate!

I remember the first (and only "proper") Maplins at Hammersmith before they tried to be a retail consumer electronics chain!

There was Crescent Radio, Watford Electronics, and some other mob who advertised in the radio and electronics mags of the day that I got all my cheap components form in mixed bags...can't remember the name, but as a schoolkid, money was tight!

Can't remember the one at Waltham Cross though....what year are we talking?  I might have found someone older than me!

Re the amps...a lot of the Ameritron amps are valve, and are significantly cheaper than the newer solid state ones for a given power output.  If any of the US vendors do them in the Black Fridays sales though, I'm treating myself to the solid state ALS-500M, as it's a "no tune" amp and with our power limit being only 400w PEP and me running a 12v/solar station, it's ideal.

Hi Jeff,
(We're totally off topic now, I'm a terrible admin )

Yeah Maplin, I still remember the spaceship on their '79 catalogue! Mixed bags of components - the old 'Bargain Bags'?
Waltham Cross was a guys warehouse, think his main shop was on the Edgeware road, used to do me the odd deal
1980's Jeff.

Luuuuv Ameritrons! Would build a valve linear in a heartbeat....apparently Foundation doesn't allow me to

Right, slapped wrists all round. We'll haver to start our own "Trips Down Memory Lane" posting.

Victor wrote:

Hi Jeff,
(We're totally off topic now, I'm a terrible admin )

Right, slapped wrists all round. We'll haver to start our own "Trips Down Memory Lane" posting.

A proper admin would split the topic and spawn the new one for us old buggers. 

Just a thought, did you re-calibrate the SWR meter after putting the amp in-line?

73's Gary.

GaryWilson wrote:

Just a thought, did you re-calibrate the SWR meter after putting the amp in-line?

73's Gary.

I did explain that to him Gary and didn't really get a answer from the OP unless there was a misunderstanding in translation as the OP is Swedish and admit his English wasn't that good .lol

NUBSTER wrote:

TBH my preference is a  old valve amp but nobody seems make them now well not that I know of 

There are plenty of manufacturers. 

OM Power do a whole range including a 4kW one...
Acom do several.
The Ameritron AL80 is still available to buy new along with several others they do

And that's just from one retailer.

https://www.hamradio.co.uk/accessories-linear-amplifiers-all-linear-amplifiers-pc-843.php

Cheers Coner I will have a look at that link.

NUBSTER wrote:

GaryWilson wrote:

Just a thought, did you re-calibrate the SWR meter after putting the amp in-line?

73's Gary.

I did explain that to him Gary and didn't really get a answer from the OP unless there was a misunderstanding in translation as the OP is Swedish and admit his English wasn't that good .lol

Sorry Martin, it's the only thing I could think of that would be an obvious oversight, I missed that detail in your reply.

Stay safe buddy. 

73's Gary.

No worries Gary mate I've explained  Victor has done the same so it's down to him to sort it now.