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Reviews For: Svetlana GU74B/4CX800A ceramic tetrode

Category: Electron Tubes

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Review Summary For : Svetlana GU74B/4CX800A ceramic tetrode
Reviews: 13MSRP: $100
Description:
Svetlana's $100 answer to Eimac's $500 3CX800A,
Product is in production
More Info: http://www.svetlana.com/docs/products/metal/4CX800A.html
# last 180 days Avg. Rating last 180 days Total reviews Avg. overall rating
00134.5
K9RLB Rating: 2021-03-19
GU74B - Good, and fine in QRO Amp, too Time Owned: 6 to 12 months.
Having seen a review of the GU74B - mentioned a QRO, The GU74B works well in the QRO. Measure the screen voltage starting @ -150v (Control Grid Voltage) and the screen voltage is fine. If you operate the amp as per manual, and don't over drive / abuse it, the GU74B will do quite well in the QRO.
W5RG Rating: 2020-11-10
LAST OF GOOD TUBE! Time Owned: more than 12 months.
Be careful where you buy these tubes..Array Solutions and DX Eing is the best place..and they will check them and back them for a year..I use a Alpha 8100 with these tubes and the 99 and 91b has these and be smart about loading these..run them at 1500 watts or less and they will last a long time..If you have a QRO YOU BETTER BUY SOME SPARES..That amp has way to much screen voltage..Just be smart..you will not gain much running them at 2400 or 2500 watts. I have a Alpha 89 also and I sure do not want to buy new tubes for it..GU74B's are still a good buy..stay away from e-bay..
I bought three new tubes from a seller on QTH from Russia..Paid extra to have them matched..Two were good and the other had a flash over.These are now VERY old tubes setting around and finding good ones is very hard..Plus you can not trust any seller..If you have a amp with these tubes as I do..you better off selling it and getting a triode tube amplifier.I do not see China making any of these tubes!!
KX2T Rating: 2020-11-09
Great RF tube Time Owned: more than 12 months.
I would like to add one thing to my review of these tubes, just look at any amp that has gone threw the ARRL lab on a review such as the Alpha 91B, 99 Acom 2000 or 1000 amp and take a real close look at the IMD specs plus spectrum display, They give the gain and power of the Eimac's way overpriced tubes at 1/3 cost plus even newer amp companies from EU are switching from China made tubes back to Russian tubes.
I have used these tubes since 1997 when I purchased the Alpha 91B amp that used a pair of them for a 1500W HF amp, back then I had the use of portable spectrum analyzers and never found those tube to be dirty as far as IMD, like any tube when you push them beyond there limits ANY tube gets dirty even the OMG Eimac tubes as well. Today I use just a single GU74B in an Acom 1000 amp, I have one tested back up and rotate them once a year, I run the amp at 800W on CW and between 900w to 1000w pep on SSB and it is clean as could be. To be honmest I have only seen the 4CX800A for sale on E bay and once on QTH.com but for the most part I have seen plenty of GU74B tubes for sale. I have only seen newer stock GU74B's for sale at around the $300 price range which seem to sport a larger anode than the pre 2000 year production samples but all I know is these tubes don't set you back a kilobuck like the 3CX800A7's do and there are plenty of NOS tubes in the marketplace at this time, more so than in the pulls MRI market cause many of the MRI machines have gone solid state. Some so called Amp experts just don't like these tubes cause of the country they were made so you have to take there comments with a grain of salt, its only a mater of time when we should see a Chinese made copy of these tubes also enter the market but like Chinese food goes you may have to wait for Best Quality tubes to arrive.
I would like to add one thing and this is not a plug for a USA seller but DX Engineering sells these tubes for around $350 each with a one year warranty, they are GU74B's not 4CX800's so you don't have to go threw E Bay and buy from some seller you might not trust, yes the ones on E Bay are cheaper but what you gonna do when you have a bad rube out of the box, penny wide and pound foolish applies here directly
KM1H Rating: 2018-06-14
The 800W is a fraud Time Owned: more than 12 months.
The GU-74B is a decent tube at its original Russian specs but the 4CX800A version is a complete fraud. It is a 600W dissipation tube and loses emission rapidly when run beyond specs.
I also have copies of the actual engineering tests from Svetlana in St Petersburg showing how poor the IMD really was.
K5DSQ Rating: 2017-12-02
Excellent Tube!! Time Owned: more than 12 months.
Excellent tubes that run in an excellent amp (Alpha ETO 91b)! Very hard to beat these workhorses, especially for the price.
M0HDX Rating: 2017-11-30
Robust..Reliable Time Owned: more than 12 months.
Four years since my last review the original Russian GU-74B in my amplifier is still producing full output and used most days.Very reliable and still reasonably cheap to buy compared to other tubes(3cx800)...I have 6 NOS spare GU-74B but at this rate i doubt i will need to use them.

Secret is do not try squeezing every last watt out of the tube and it should last a long time.
MM0IMC Rating: 2017-11-28
Wow! Time Owned: more than 12 months.
I bought this Soviet era NOS GU74B tetrode from Ukraine about two years ago, with a date code of August 1977 stamped on it. It was a spare for my new Alpin 100 mk3 at the time of purchase.

I had it in store and decided to test it against the GU74B that came with the amplifier (1983 date stamped on it). I conditioned it for about five hours with just the heater voltage applied.

It give me the same power out as the original GU74B did, stunning for a forty year old valve (tube)! Easily 1.3kW+ on HF and 1kW on 6m into a large oil can dummy load!
WB2VVV Rating: 2016-06-30
Great Tube! Time Owned: more than 12 months.
I bought a few of these tubes when they were first introduced and very attractively priced. I subsequently built up a mono band 6 meter amplifier using one of these tubes, and have been very satisfied with its performance. I am only using modest (quiet) airflow at the 500-600 Watt output level and the original tube is still working well. Gain is 13 dB and IMD is excellent!
N4RSS Rating: 2010-08-26
very good Time Owned: 0 to 3 months.
Just installed two NOS GU74b's into my QRO, dates codes 1984 and 1990 I believe, ordered from QRO Parts. The originals were fine after 9 years but I wanted spares.

Getting the pins to mate with the socket was tricky but that's my problem.

Power output of the new ones same as old, 45 watts in on 20m gives 1950 watts out.
K7ORK Rating: 2009-01-07
Nikmatvey for 91b replacement tubes Time Owned: 0 to 3 months.
Alpha informed me that the AC trip problem with my 91b (purchased 1997) was caused by the GU74B (4CX800A) tubes going bad. I panicked when they could not recommend a source for replacement tubes.

After searching eBay for replacements, I ordered two tubes from Nikmatvey in Russia for $400 plus $30 for shipping. The tubes were not tested nor matched. They arrived about four weeks later.

The tubes were installed in less than fifteen minutes. They work great…less drive power to get full output.

Now, I don’t have to consider replacing the 91b because of lack of tubes.

ron@vinecom.co.uk is a source offering matched and tested GU74B tubes, but at a higher cost.