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Author Topic: Replacing Tubes with Russian Tubes  (Read 3880 times)
K0WA
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« on: May 04, 2005, 07:05:05 AM »

I have seen a lot of articles on replacing tubes in older amplifiers with Russian made tubes as the GS35B and the GI7b.  My curiosity has been peaked a little here since years ago I put together a pair of 3-500Zs.  It seems, some of these tubes can be dropped in, change the filaments and bias a little, and you are good to go.  I know there are a lot of articles about doing this on the net, but there doesn't seem to be a lot of articles about the exact changes one has to do.  For instance, I have a nice AL80A.  Runs a nice 3-500Z (Eimac and the tube is OK), but how would you drop in one of these Russian tubes.  Would you use a GS35 or a GI7B?  Looking at the specs, it seems the power supply inthe old AL80A would not have enough current to get anymore power out of the unit.  If one was going to replace the tube, would it be logical to gain a little more power when it was done?  It seems the there would be issue with the Pi circuit, the input circuit and enough plate current to make these tubes sing.  I would love to read others comments.
Lee - K0WA
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K0BG
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« Reply #1 on: May 04, 2005, 12:54:24 PM »

The single single item most overlooked by folks attempting to upgrade their amplifiers is the power supply. As you pointed out, just because you changed out 811s with 572Bs, doesn't mean you're going to get any more power out. In some cases, you'll get less.

There are other considerations besides the power supply. Plate reactance, grid bias, and cooling to name a few.

I'm not saying it isn't possible, it is just that there are so many different configurations, writing an article to cover even a few is rather difficult. It's sort of like replacing an old flathead Ford with a modern cammer. Seems simple until you get into the middle of it.

Alan, KØBG
www.k0bg.com
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WB2WIK
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« Reply #2 on: May 04, 2005, 01:48:11 PM »

First of all, I have to wonder if you're kidding...

The 3-500Z is a glass tube requiring low pressure cooling.  It's good to 110 MHz, is "instant on," inexpensive, and perfect for the job it does in the AL80B.

The GS35 and GI7B you reference are ceramic-metal tubes requiring forced air cooling (high pressure) and coaxial sockets that aren't even vaguely similar to the 3-500Z socket.  It's not only not a "drop in" replacement, it isn't any kind of replacement.  These tubes also have tons of gain up throughout the UHF spectrum and keeping them stable requires precautions not found in the AL80B, since that's an HF amp.

Using a different tube to substitute for the 3-500Z in an AL80B is plain silly, when it already uses the best possible tube for the job.

To run more power with the AL80B is a totally different matter, however.  The AL80B pushes a 3-500Z about as hard as it can be pushed, although higher plate voltage (like 4000V instead of 3000V) could result in more output, along with more gain, i.e., lower drive requirement.  However, the "benefit" isn't much use, since the AL80B already runs just about 1 kW PEP and that's quite a lot for this tube.  It's a well designed amp.

My suggestion as the solution to running more power with the AL80B would be to lift the AL80B off the bench, slide in an AL82 in its place, and connect up to that!  :-)

WB2WIK/6
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K0WA
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« Reply #3 on: May 04, 2005, 03:04:42 PM »

WEll, I was wondering about this for an AL80A, not the B model.  The A model is quite straight forward.  I do realize that there would have to be some pretty good changes made to the unit...not that I am going to...I was wondering what the design criteria would be.  The issue I see is if the power supply could provide the current...then there is the issue with bias, and forced air cooling, which is not really an issue if you look at other projects doing the same things to say a MLA 2500 amp. Again, it comes down to if the power supply would take the current need to reallyput these tubes to full output.  Then you would really have to rejigger the PI net because of the difference in plate impedance.  I just thought it would be an interesting project.  There is not reason to do this.  Might find a MLA2500 and do it to that unit, but I was just curious as to the technical issues surrounding such a project.
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WA9SVD
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« Reply #4 on: May 04, 2005, 11:40:11 PM »

"...would it be logical to gain a little more power when it was done?"
=============================

  The question is, "How much is a 'little bit more power?'"  A few watts? Even a few dozen watts?  It's hard to believe (even assuming a direct substition is possible; otherwise complete re-design is necessary) that with a given power supply, there would be a worthwhile or even noticable increase.  At the linear amp power level (assuming 500 Watts or higher Output) an increase of even 100 watts (20%) would not make much difference in a received signal; all it will probably accomplish is pushing the equipment (tubes, power supply, etc.) harder than necessary, with the end result only to make the electric company happier.
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WB2WIK
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« Reply #5 on: May 06, 2005, 10:58:17 AM »

RE: Replacing Tubes with Russian Tubes  Reply  
by K0WA on May 4, 2005  Mail this to a friend!  
WEll, I was wondering about this for an AL80A, not the B model. The A model is quite straight forward.

::So is the "B" model.  There's virtually no difference.


I do realize that there would have to be some pretty good changes made to the unit...not that I am going to...I was wondering what the design criteria would be. The issue I see is if the power supply could provide the current.

::No, it cannot.  It's a voltage doubler and maxed out at the 500mA it provides by design, in an ICAS (intermittent) service.


..then there is the issue with bias, and forced air cooling, which is not really an issue if you look at other projects doing the same things to say a MLA 2500 amp.

::Except the MLA2500 isn't force air cooled, either.  It's high-volume, low-pressure cooled using transverse cooled tubes no longer made by anybody.  The AL80A/B chassis doesn't lend itself to forced air cooling at all, without major sheet metal modifications because it isn't pressurized in any way.


Again, it comes down to if the power supply would take the current need to reallyput these tubes to full output. Then you would really have to rejigger the PI net because of the difference in plate impedance. I just thought it would be an interesting project. There is not reason to do this. Might find a MLA2500 and do it to that unit, but I was just curious as to the technical issues surrounding such a project.  

::I wouldn't use the AL80A as an experimental test bed because it's a perfectly fine amplifier just as it is.  I might use an MLA2500 as a prototype test bed because it's really old and the tubes it uses aren't available anymore, anyway -- so, once they're gone, you're probably out of business.  That would be a good rationale to try something totally different.  73 & good luck!

WB2WIK/6
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W9GB
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« Reply #6 on: May 06, 2005, 09:49:22 PM »

Lee -

Many of these conversions on the web are quite nice, BUT in almost every instance they are "last ditch" attempts to extend the life of the original amplifier that use TV sweep tubes (now expensive or unavaialble) or discontinued tubes (Eimac 8875) - by using "dirt cheap" (less than $40) surplus Russian military tubes.  Actually, these are really homebrew designs using the amplifier case and some parts as a starting point.

To "gut" a working 3-500Z amplfiier design (with readily available tubes and parts) for a surplus Russian tube conversion -- is very unusual.

Steve (WIK) is correct, unless the power supply is substantially upgraded for these conversions -- the true power output is not going to drastically improve (Power IN -> Power OUT, at maybe 50% efficiency).

w9gb
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W9GB
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« Reply #7 on: May 07, 2005, 04:56:18 PM »

Lee -

I actually did a "Google" search this afternoon to see if anyone had photos for a 3-500z to GS-35B conversion - and I did find one by Tom Adams WB8WJU using a Henry amplifier (Tom Adams does great "sheet metal bending").
http://groups.msn.com/tomstubes/henryampconversion.msnw

After looking closely at the photos, you can see that the original Henry "donor" amplifier was is pretty bad shape (rust on fan, dirty, cramped layout and power supply pushed to back).  This is a good example of what I mentioned earlier -- that many of these "conversions" are actually complete new builds using chassis and some key components from the donor amplifier.  This approach is also used in the tube audio amplifier hobby!  Notice that the power supply has to be external (like the old Drake L4B) in this new configuration.

Randy, NT8N and Tom, WB8WJU also did a TenTec Titan II conversion from the 4CX1600B tube (no longer made) to a pair of 4CX800A/GU74B tubes.
http://groups.msn.com/tomstubes/titaniiconversion.msnw

Lawson Summerrow, W4EMF Dentron GLA-1000 conversion to the GI-7B.  To resolve the high price of TV sweep tubes no longer in production with an inexpensive Russian microwave triode.
http://www.nd2x.net/w4emf-GLA.html

So, as you see many of these are either due to an amplifier in bad shape (used for parts) or where the tube is no longer available.

w9gb
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KC7NOA
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« Reply #8 on: March 17, 2010, 06:11:59 PM »

I have replaced 2@3-500z in a yokagawa P9306UL amp (HL-2K) with a GS-35b. pics sooner or later ...
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K0CWO
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« Reply #9 on: March 17, 2010, 11:42:09 PM »

A Chinese made 3-500 costs $175 and includes a warranty.  The GS35B about $100, and GI7B $40 (without warranty?).  I'm not saying that GS35B/GI7B equipped amplifiers are a bad idea, I know folks that love these tubes, but I cannot imagine I'll ever start hacking into my AL-80A and ruin its simplicity and reliability.
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K8OT
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« Reply #10 on: March 24, 2010, 10:14:54 AM »

Reading this over, I think Lee was just doing some what ifs.
To replace 3-500z's with russian ceramic tubes in a working amp of any kind would be dumb and would be like pissing into the wind.
ED
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