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Author Topic: GU43b vs. GS35b vs. GS31b?  (Read 9179 times)
NZ5N
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« on: April 11, 2010, 06:20:52 PM »

Hello,

I am still looking for an HF plus 50 mhz amp for my summer QTH in Slovakia.  There's a highly regarded Hungarian ham who makes various amps of this type:
* 2xGI7b tubes, 800w out
* GU43b tube, 1.2kw out
* GS31b tube, 1.5kw out
* GS35b tube, 1.5kw out
For further details about these amps, see http://web.axelero.hu/amplitec/hf50_eng.html

Any thoughts on the pluses and minuses of each of these tubes?

The 1.5kw amps are $400 more than the 1.2kw model, and the 800w model is $400 less than the 1.2kw model.

Thanks for any info and 73,
Bill
NZ5N
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VK1OD
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« Reply #1 on: April 12, 2010, 01:27:14 PM »


Any thoughts on the pluses and minuses of each of these tubes?


Bill,

Designs that claim to develop very high power from each of these tubes abound on the 'net.

Have you looked at the datasheets for the tubes, and reviewed the operating point for claimed output power.

The common thing is that the load line is way off the published anode characteristics for the tubes. To some extent, the fact that hams have found an application for the tubes way beyond that envisaged by the tube manufacturer sound something of a warning.

One wonders if the tubes were over endowed with anode dissipation, and then designs by rule of thumb raise expectations of extraordinary output power for their rated voltage and current.

Another 'feature' is that the transfer characteristics are decidedly non linear. I have seen the GS35B described as a 8877 equivalent, but if you compare the transfer characteristic they are chalk and cheese. (The only similarity is that they both specify 1500W anode dissipation under certain conditions). This doesn't necessarily translate to excessive harmonic output or IMD... but I do not recall ever seeing such measurements or specifications even for a manufactured linear PA using these tubes.

I know that some of these tubes are very popular for VHF and UHF amps, but I make the observation that people seem to tolerate quite dirty amps on these bands compared to HF.

Owen
« Last Edit: April 13, 2010, 03:48:52 PM by Owen Duffy » Logged
KC8VWM
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« Reply #2 on: April 12, 2010, 11:44:39 PM »

Keep in mind the Russian tubes are originally designed to be used for pulse radar equipment.

In other words, "pulse" and not "continuous" transmission operation.

Haven't used one myself but I have read about some designers that have experienced output to start out good at the beginning of a transmission then output appears to sag a hundred watts or so after a period of extended TX'ing.

Apparently, the output is restored back to full output power again after a period of unkeying and listening. But it is reported the condition resumes again during another period of continous transmission sort of thing.

Also be sure you get some verification in terms of the tube actually functioning up to par. Many of these are "pulls" and as such, they may not actually be tested in terms of any measured or actual functional operation.
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NZ5N
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« Reply #3 on: April 13, 2010, 03:07:45 PM »

Interesting comments, thanks.  This is the first time I've heard any serious criticism of these tubes.  Hams I know with these amps have given them great reviews.

73, Bill
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SV1BDO
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« Reply #4 on: April 13, 2010, 04:49:06 PM »

Bill,
Russian tubes have their pros & cons. Not all of them are for pulse radar applications, enough of them were designed primary for RF transmitting devices. As far as I know, none of the tubes you mentioned are designed for radars (like GI-7B). GS-35B is a triode similar with 3CX1500, but it is not a direct replacement. Most Eastern tubes are compared with similar Eimac tubes, mainly in the anode dissipation data only. Even thought they are rugged and cheap, their major negative point is that most of them are NOS and are not manufactured any more, as their production stopped around 1987-1990.

A very popular (and cheap) amplifier manufacturer in Europe is Vlad UY5ZZ, who has 3 HF+6m models, with GU-74b (750W), GU-43b (1200W) and a higher 1600W model. His prices are much cheaper than HA8UG & HA1YA. (ie Vlad's ZZ-750 model with single GU-74b costs aprox 750 Euros, delivered within Europe, while HA8UG model with 2xGI-7b costs 1600 Euros plus 140 Eur shipping.)

You can find also a lot of used & new amplifiers in the major European hamfest in Friedrichshafen, Germany, 25-27 Jun.

73, Sotiris SV1BDO
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NZ5N
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« Reply #5 on: April 13, 2010, 05:03:53 PM »

Sotiris,

Thanks for answering my question on the eHam forum.  I have heard about the UY5ZZ amps, but where do you buy them?  I have seen his web page at http://www.qsl.net/uy5zz/PAs.htm , but it does not have any info about how to order.  Also, it only mentions amps for 1.8-28 MHz, nothing about an HF plus 50 mhz.

If these amps are ordered directly from Vlad in Ukraine, don't we also have to pay VAT and import tax because Ukraine is not in the EU?

73, Bill NZ5N
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SV1BDO
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« Reply #6 on: April 13, 2010, 05:25:49 PM »

Bill,
Vlads' amps are ordered directly to him. Current models DO have 6m coverage and seems his web page is not updated. There is no online ordering system, just emails. Don't worry, he is very reliable and he has very good reputation. It's better to contact him directly. He will answer all your questions. He told me that delivery time is within 30 days and he will be in Friedrichshafen this year also. I am thinking also for the ZZ-750 model, but as a 2nd hand from a friend, that he will upgrade to an Acom 1000. Look also at Acoms. All their models are top rated.
73, Sotiris
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NZ5N
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« Reply #7 on: April 13, 2010, 06:16:30 PM »

Thanks for the info, I have already dropped Vlad an email.  Do you by chance have a phone number or other contact info for him?  And you mentioned EUR 750 for the ZZ-750, do you happen to know approximate prices of the ZZ-1200 and ZZ-1600?  And do these prices include VAT and import duty?

I was at Friedrichshafen last year, hope to see you there this year.

73, Bill
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SV1BDO
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« Reply #8 on: April 14, 2010, 02:00:32 AM »

Hi Bill,

I have no more contact info except his email. I know that he has "delivery paths" in Greece and some other European countries as a lot of hams here have purchased amps directly from him, mostly the ZZ-750. I don't know prices for other models, but, if you learn them, let me know.

When I asked him for 100% duty cycle capability (operation in RTTY contests) he suggested me an additional ventilator for the transformer for only 30 Eur more, so you can ask for it also if it's useful for you. He also told me that he we will able to deliver in Friedrichshafen hamfest some orders that will be placed in time (within the one month period). His amplifiers do not have any protections, you have to add them later by your own. I asked him to add some protection circuits (step start for inrush protection) but seems that his English are not very well, as he did not understood what I was talking about.

In conclusion, his amps are very cheap, well solid built, simple construction. I have heard that the only weak point of the ZZ-750 model is the band switch, which is relatively small and you may face arcing problems. A fellow ham that had this problem has delivered free replacements, so his after sales support is also high.

Sotiris
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NZ5N
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« Reply #9 on: April 14, 2010, 05:34:20 AM »

Thanks.  The HA8UG amps do not appear to have protection circuitry either. The HA1YA amps do, but he does not make an HF plus 6m model.  ACOM of course does as well, but these amps are a lot more expensive (I was quoted 2400 EUR including VAT and shipping from Bulgaria to Slovakia for the ACOM 1000).

Vlad has not responded to my second email asking for more info and for suggestions on how to get one of his amps to SK.  He says he can only deliver to Germany and Poland.  Perhaps I will order one for delivery at Friedrichshafen, but my summer vacation will be half over by then.

73, Bill
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SV1BDO
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« Reply #10 on: April 14, 2010, 05:59:24 AM »

Bill, I suppose that Vlad is not very fluent with English language, and he maybe ask somebody (that is not familiar with tech terms) to translate for him any text that is difficult for him to translate. So, be a little patient when asking something more than the preset replies that he might have.
If you have already been in Slovakia, ask your ham friends there if there is any cheaper amp builder than "OM Power".
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NZ5N
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« Reply #11 on: April 14, 2010, 11:30:33 AM »

OM Power amps may be the best on the planet, but they are not cheap.  Their OM2500A autotune model compares favorably to the ACOM 2000a.  It delivers slightly more power than the ACOM and is comparably place.  All of the OM Power amps deliver 2k or more output.
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