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Reviews Categories | Amplifiers: RF Power - 6M/VHF/UHF+ | Dressler D200S Help


Reviews Summary for Dressler D200S
Dressler D200S Reviews: 4 Average rating: 4.8/5 MSRP: $dressler 200s
Description: Compact (akin to desk top PC) 4CX350A 144MHz amplifier.
Product is in production.
More info: http://
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G8DZC Rating: 4/5 Oct 30, 2010 06:45 Send this review to a friend
Worth the money they go for  Time owned: 6 to 12 months
Before I say too much, some of you might ask why I rated this with a four, rather than five. So here is why. I should also say that mine is the D200 rather than the S. But they are both the same apart from what I would call minor changes.

(1) Not that keen on the use of 1 amp diodes for the EHT supply. Too close for comfort IMO
(2) No dust filter on the air intake, which happens to be on the base plate of the amplifier.
(3) The use of a hard to get EHT fuse (85mm long) that is very expensive, if you can find them.
(4) PA Valve airflow marginal for long chats on FM.

It cost me a fair amount to get this amplifier and I can say that it was worth it. The construction of the amplifier was what I would expect from a professional piece of kit, and it is very easy to work on this unit. Apart from things like the transformers, you will find that spares are easy to find, and the manufacturers have used things that are available from most electronic suppliers.

Work that I carried out before putting it into service was as follows: Replace EHT diodes to 3 Amp devices, modify EHT fuse holder to take a standard (40mm) microwave oven EHT fuse. Raise some wirewound resistors from the PCB to reduce charring to the board. Add glitch resistor to anode feed. Fix VOX delay time and use that control to vary the grid bias so that I can go from class AB to class B for FM. Of course I did a little more work than what I have said. The above ones are the important ones IMO.

I do have some reservations as to the ratings of the coaxial relays. The output one is being run on and above its limits. But that may be countered by the fact that it isn't being hot switched. The sophisticated relay timing circuitry takes care of that.

As for operating. The amplifier seems to be optimised for operation at around 144 Mhz rather than above 145 Mhz. I haven't been able to find out why that should be. Using this amplifier on FM running at around 150/200 watts is no problem. For SSB it runs happily at 300+ watts.

For those people wanting that bit extra from the D200. There is nothing stopping you changing the valve to a 4CX350A and altering the screen supply with some additional components, and component changes in the control grid supply, to make this amp run at D200s levels.
 
VK2UL Rating: 5/5 Dec 4, 2008 01:52 Send this review to a friend
Great German Product  Time owned: more than 12 months
I got my Dressler way back in 1992. The serial number is 8632248.

The amp was given me as being dead. The original owner was the University of Queensland and had been purchased for Plasma research. I understand that it had been sent back to the dealer a number of times who could not fault ir so seems likly there was a finger problem involved like how was the excitation obtained for the plasma project?

I got it home dusted it off took the covers off and blew out a few dead insects. I read the manual before hooking it upto my Kenwood TR-9130 and applied power.

I let it soak for a week before I applied RF then on low power went through the tune up process. It worked first time I then applied the full 25 watts and was able to get full power in all modes.

I run our legal limit 400watts PEP here and it just loafs along. It still has the original 4CX350A with the date code 7821.

In the box was a spare tube with the National Electronics Brand name.

I understand these amps sold here in Australia for close on $3000.00. I would recommend to any one that if they saw one for sale its well worth grabbing.

Alan VK7AM
 
W4MAC Rating: 5/5 May 29, 2007 21:44 Send this review to a friend
Well, It's all that.  Time owned: more than 12 months
I bought this amp about a year 1 1/2 ago, without knowing anything at all, exept what the previous poster here had said. It was on consighnment at a local repair shop, and knowbody knew anything about it. It didn't have a power cord, so they made one up for me to see it work. They fan barely moved and the meters didn't light up. I took the top off and stared in amazment at the craftsmanship of the board, the cooling system for the tube, and the fact that the transformer was stamped "220 Mains Only". I had just watched the shop owner hook it to 110! I offered half what they wanted, he made a phone call, and took I it home. Randy, at "The RF Shop" put some caps in the power supply for me, and I've never looked back. I work it at about 500 watts on SSB, and it has never been opened again. Nice and compact, well lit meters, and dependable as the day is long. Great Amp!
 
G8MDG Rating: 5/5 May 10, 2004 06:21 Send this review to a friend
300W CW 144MHz Amplifier  Time owned: more than 12 months
It is a smallish professionally designed black box with a discreetly air cooled Eimac 4CX350A running at about 1600VDC at standby 80mA (class AB1 SSB ) and 300mA transmit. The manual claims 1 kilowatt PEP SSB (on "HI" mode) - but then recommends just using 750 W PEP (on "ATT" mode) for keeping the output signal as clean and narrow as an 80 W transistorized amplifier.

I've used the Dressler for years and many QSO's with only once when the 0.8 A 3KV EHT fuse went 'bang' for no apparent reason. I also shipped the amplifier back to Dressler Hochfrequenztecnik gmbh in Stolberg for them to change the chain of 100uF 550V electrolytics when I suspected the cap's of leaking. Perfect service!

The amp features very flexible switching, from "RF-VOX" or "PTT" contact or "Us" (e.g. ICOM) +5 to +15VDC positive switching line. The amp also produces (on RX) +15VDC for powering a mast head pre-amp e.g. Dressler VV200GAAS.

It also can operate with up to 400W out (biased at 0mA class 'B') for FM, but I can't see a need for 400 Watts to access the local repeater - though of course I have tried that occasionally just to check it works!

summing up :
This Dressler Amplifier is a trouble-free, compact, powerful - with robust 4CX350A valve (tube) provided it is not overdriven with more than the recommended 10 to 12 watts of grid drive. But it's nice to know that for short time e.g. MS or EME you can drive it to the full kilowatt PEP for the full (splatter!) experience.
 


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