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Reviews For: Dressler D200S

Category: Amplifiers: RF Power - 6M/VHF/UHF+

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Review Summary For : Dressler D200S
Reviews: 5MSRP: dressler 200s
Description:
Compact (akin to desk top PC) 4CX350A 144MHz amplifier.
Product is in production
More Info: http://
# last 180 days Avg. Rating last 180 days Total reviews Avg. overall rating
0054.8
GM0ULK Rating: 2020-01-05
Repair and review. Time Owned: 0 to 3 months.
I recently acquired a D200s as a spares or repair for a very resonable price via the auction site everyone loves.

On receiving the amplifier, I checked it over and found the following faults.

Fault 1 - The mains input tracks under the board, adjacent to the input socket, had shorted and had burned away. This was repaired using insulated wire and finished using an insulating lacquer as the tracks that conduct mains potential current are quite close together.

Fault 2 - A number of tracks had become debonded from the board and were repaired using lacquer and wire reinforcements. This is an age thing, especially if amp had been stored in a damp environment.

Fault 3 - HT fuse blown. Not able to find a replcement here so a 800 milliamp HT fuse for a microwave oven was pressed into service with minor modifications to the original fuse holder.

Fault 4 - On power up, using a auto transformer, the capacitors were checked before going to full voltage. But the PTT would not function. Fault traced to the inverter IC on the logic board.

Once the above rectification was carried out, a tested 4CX350a tube was fitted and the amplifier powered up. The amplifier produced a good level of power, about 400 watts at about 8 watts input, (with amp attenuator in) without any signs of stress so I concluded that the amplifier is working as it should - so far.
I have yet to go for maximum power testing but the amplifier appears to work well an meet expectations. The only issue remaining to inspire full confidence would be to get a service manual to check that a number of internal potentiometers have been adjusted correctly - there are a number of test points to establish this. However, there are no service manuals at all the usual internet sites, so a bit in the dark here.

In conclusion, for review purposes. The amplifier seems very well made, apart from the mains input spacing allowances on the main board. Those who have these amps in use should review this as the tracks are quite close. For an amplifier that houses a 4CX type tube with all the power considerations (Anode/screen/grid, 12vdc/15vdc and heater) it is very compact. The cooler blower (squirral cage) is not too loud but nonetheless, operation in close proximity to these amps can be tiring with white fan noise on constantly.
The tube is protected from overload by devices (comparators) on the logic board and providing the tube is tuned and loaded correctly, there seems to good and reliable output from this amp.
These amps are becoming more of a rarity today and keeping a well serviced amp is essential when you consider the voltages inside. This amp has currently got the original HV caps and will undergo a complete replacement when I have time, but considering this amp is about 40 years old, it is in remarkable condition.
So.... Would I buy one of these amps again? Yes - definately, but - that is me and I can understand these devices. Although everything is accessable, physical component replacement is not difficult, the downside would be to find the right sized transformers to fit in it's very compact case should you need these. Also, there being no service data anywhere to set multiple pre-set potentiometers to their correct settings could be an issue. As a final modification, I will raise the 4 x feet to allow more space for the induction of cooling air through the base. Other than that, it's old, but a winner! Finally, I will still be getting a solid state 144Mhz amp at some point as this is the way to go, 4CX350a tubes are no longer plentiful and becoming more expensive so the logistics of owning and operating an old amp can have these pitfalls.
G8DZC Rating: 2010-10-30
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: 2008-12-04
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: 2007-05-29
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: 2004-05-10
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.