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Author Topic: Dentron Clipperton V 2m amp?  (Read 6292 times)
G0HVQ
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« on: August 20, 2007, 07:34:06 AM »

Wonder if anyone can shed any light on the Dentron Clipperton V 144MHz amp? Have searched the 'net but not found much.

Got one here at the moment, it's been in storage for years and I've got it out to test, seems to work OK and produce 200W for about 10W in, but given the size of the thing I'd have thought (hoped) it would put out a bit more. Anyone have a spec for it?

Tnx and 73
Darrell G0HVQ
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WB2WIK
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« Reply #1 on: August 20, 2007, 08:32:28 AM »

I've put a few of these back together over the years.  It wasn't a good design from the factory.

The 4X150/4CX250 is capable of nearly 500W RF output power under the right conditions, but this amp doesn't do it.

A lot of Clipperton-V amps as shipped were pretty unstable and if they applied enough screen voltage to make the amplifier really work properly, they could oscillate.

[The power gain of the 4X150/4CX250 tube is normally about 20 dB (amplification factor of about 100) with an efficient grid circuit, plate circuit and proper operating bias (Class AB1).  If it had a really efficient grid circuit, 10W drive would blow the grid (and likely the screen) to smithereens.  My PP dual 4CX250 two meter amps run "full power" (~1 kW PEP output) with maybe 7W drive, for two tubes.]

If it seems stable and doesn't require re-tuning as it warms up, and produces 200W output reliably, I'd leave it alone.

WB2WIK/6
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G0HVQ
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« Reply #2 on: August 22, 2007, 09:13:25 AM »

Many thanks for the info.

I've done some further testing and yes, it does seem to kick out bang on 200W reliably. Have got a rather high SWR between the radio and amp, though. I have the option of buying it but think I'll pass, given that I've got 100W out of my radio already, and lookout for something a bit more.

73
Darrell
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N8FVJ
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« Reply #3 on: January 27, 2019, 11:58:14 AM »

A better inexpensive 2 meter amp in this power range for 2 meters is the Gonset 903. The Gonset has a strip line tank and produces 375 watts out with 5 watts input.
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W9FIB
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« Reply #4 on: January 27, 2019, 06:44:46 PM »

I ended up with a V in my collection. Opened the cover to discover it has been hacked up. Probably someone trying to make it work better at some point.

I also found the schematic I found online didn't match up well to what was there. I read in an old review a few years ago that Dentron was making production changes as they came off the line. Based on what I saw, I think that info may be accurate. It sits on the shelf gathering dust for the day I may get around to rebuilding it. Basically a home brew in the Dentron box. I don't see a full restoration being feasible due to the problems it was born with.

With the new semiconductors and designs available, I don't see much future in rebuilding it with tubes. But hoping to keep the front looking vintage, so it might turn out pretty nice. And 50V high power supplies are cheap compared to building up an HV power supply. And not as lethal. And I have not found the specs on the HV transformer to see if it is beefy enough for different or more tubes, which would also drive me to a SS solution.

Maybe the Gonset design might be feasible. But I would have to research it first. Just as some other home brew designs I have found.

Any way you look at it, this was not Dentron at its finest.
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73, Stan
Wisdom is knowledge you gain after you know it all.
K4PF
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« Reply #5 on: January 27, 2019, 09:42:00 PM »

Hi,

I bought a 2m Clipperton V, new, in late 1982 or early 1983. It was sold as a "project" unit, in that the 4CX250B was not included.  Differences from the schematic show desperate cost-cutting. There was no thermal time-delay relay for plate voltage delay. Instead, a scrap piece of punchboard had a NE555 timer to serve that function.
The final plate choke wasn't an Ohmite Z-144 but was instead a hand-wound choke on an insulating ceramic post, using enameled wire, with no coating to keep it mechanically stable.  The link-coupled plate coil looks really flimsy  - a "hammy ham-bone" job.
The screen supply was unregulated, unlike the zener-regulated supply shown on the schematic.
In short, the Dentron company went bankrupt, and they "finished" as best they could what they had on hand with no additional funds to get them out the door. The price was right, though - I remember it cost about $200. The transformer looks husky, and it +did+ work. I saw 50 Watts out with my 2.5W output FM handie-talkie as the exciter..
The circuit is interesting - The 4CX250B has normal DC voltages as for an class AB1 amplifier, except the rf input is supplied between the cathode and ground.
The control grid is grounded for RF, not DC. No neutralization required. There's an RF-controlled changeover relay, similar to contemporary CB amplifier practice.

73,
Ed Knobloch
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N8FVJ
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« Reply #6 on: January 28, 2019, 06:27:24 AM »

Gonset 903 has regulated screen circuit. Performs very well and extracts full power from the 4CX250B unlike the Dentron.. It is also hard to find (rare).
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W1BR
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« Reply #7 on: January 28, 2019, 08:40:23 AM »

A 4CX250 should not need neutralization in grounded cathode on any frequency.... but the screen bypass capacitor design is very critical on VHF and UHF; Eimac produced a socket with an internal mica screen bypass cap that was part the of screen contact finger assembly.

500 watts from a single tube is a bit optimistic. Best I was able to achieve with a pair of 4CX300 tubes was around 600 watts on HF.  Screen voltage regulation and metering is very important for IMD and tube life.

regards

Pete
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N8FVJ
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« Reply #8 on: January 28, 2019, 04:19:30 PM »

Gonset 903 produces about 350 watts output. Large cabinet for power out, but does not need a 70 amp power supply like a SS amp that produces 350 watts out on 2 meters.
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W9FIB
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« Reply #9 on: January 28, 2019, 05:26:52 PM »

Gonset 903 produces about 350 watts output. Large cabinet for power out, but does not need a 70 amp power supply like a SS amp that produces 350 watts out on 2 meters.

True, but a large power supply like that can run a kW where it would take a much bigger HV supply then a 350W has to do the same thing. For the price of a big enough HV transformer, I could buy more than 1 LV DC supply. (At the time, I got 4 of them for $100.) So it becomes a matter of price per watt. Not to mention I already have the LV DC supplies to build SS. And it fits into the Dentron cabinet.

Actually, that pretty much rules out a tube rebuild now that I am putting some thought into it.
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73, Stan
Wisdom is knowledge you gain after you know it all.
N8FVJ
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« Reply #10 on: January 28, 2019, 08:51:06 PM »

You are stating 1KW input, not output as mentioned. TE systems 2 meter amps use 56 amps for 350 watts out with 772 watts input. Astron makes a 50 amp & 70 amp poser supplies, thus needs the 70 amp rated power supply. The 50 amp model is too small. A switcher power supply can be found for less money vs the Astron though.

All a vintage Gonset 903 needs is new power supply caps for about $30. No new HV transformer needed, no amp building required. Price per watt appears cheaper with the Gonset 903 than building a SS 350 watt amp with power supply.
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W9FIB
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« Reply #11 on: January 28, 2019, 10:56:30 PM »

You are stating 1KW input, not output as mentioned. TE systems 2 meter amps use 56 amps for 350 watts out with 772 watts input. Astron makes a 50 amp & 70 amp poser supplies, thus needs the 70 amp rated power supply. The 50 amp model is too small. A switcher power supply can be found for less money vs the Astron though.

All a vintage Gonset 903 needs is new power supply caps for about $30. No new HV transformer needed, no amp building required. Price per watt appears cheaper with the Gonset 903 than building a SS 350 watt amp with power supply.

Your data is based on 13.8VDC. I am not using 13.8VDC. I am using 50VDC devices which uses roughly 1/3 the current. Here is a link to a design I am considering. But who knows if something better is designed in the future. Could be better options down the road. I am at least a year away from even starting this project.

http://www.communication-concepts.com/content/2M_1KW_Amplifier/RDMRFE6VP61K25H_2M_Amateur_Application_Note.pdf

Also you keep going back to 350W. I am thinking about going for about 800 - 900W since I consider the V as being dead. I doubt that the power supply in the Gonset will handle 800W minimum output. Changing a few caps is not going to cut it. And I don't believe the original V power supply (which is what I have now) will either. So therefore a transformer/power supply upgrade would be needed to operate at the higher power I am looking at.

Also other parts of the Gonset or V probably would cook in a higher power setting. So they would also need replacing. And also adding in modern control and safety is needed either way to make a modern amp. So that cost would be similar.

Then compare the cost of a tube or more than 1 tube depending on which tube you choose to the SS device. Same as or less than new tube prices. Example: At DX Engineering, a 4CX800A is $349.99. The SSD from Communications Concepts is about $100.00 less. And that cost difference is just 1 part of the amp.

If I wanted 350W, then I would buy a high power brick and forget about it. But when your shooting for the moon, those extra dB come in handy. So rebuilding something at a lower power level does not make a whole lot of sense in my particular case. Besides...building things is fun! And if your not careful, you may even learn something.

Then again if I wanted to be lazy, I could order one of them Beko kW amplifiers. But what fun would that be?
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73, Stan
Wisdom is knowledge you gain after you know it all.
WB2WIK
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« Reply #12 on: January 29, 2019, 11:05:55 AM »

Gonset 903 has regulated screen circuit. Performs very well and extracts full power from the 4CX250B unlike the Dentron.. It is also hard to find (rare).

The 903s weren't rare at all in the mid-to-late 1960s and through the 1970s.  I've owned them and modified them for internal T-R (coaxial relay) keying and stuff, so they're a bit more "universal" to use.

It's a good design but does not run the 4CX250 at "full power" because the plate voltage is too low (~1600Vdc).   To run the tube at full power requires 2kV key-down, otherwise screen current will be too high when fully driven.

But it was a pretty solid amp with a good stripline plate tank circuit.   They sold a lot of them!   (And the 913A for 6m, also.)
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