GG Amplifiers Bias Cut Off
In older commercial grounded grid amplifiers, it is common to see a cahngeover relay used to switch between a zener diode or similar bias regulator and a bias cut off resistor.
My question is, why did they do it like that?
To me, it is bad engineering, in that during the change of state between transmit and receive, there is a short period where there is neither cut off nor idle current bias applied. OK, it is a very short period but it happens.
In my view, it is surely better to have the bias cut off resistor permanently in series with the bias regulator and simply have the relay contact short the resistor when the amplifier is keyed. That way, that small period of open circuit bias can never occur. Why couldn't the designers of these old amps see the simplicity and sense of doing this?
73, Alek VK6APK.
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Re: TL-922 tube filament voltage.
Before retiring and while still active in the field, precision
D.M.M.¡¯s were important, not in themselves, per se, but as
a reference point in any possible report ensuing from having
to have employed a meter at all.
?
Being able to say ¡± ¡°a Fluke 89-4¡± multimeter confirmed the
proper voltage,¡±¡± would immediately be acceptable as an
observation deemed correct.
?
So there in and there out different Fluke meters were supplied
to people doing these reports, and they were deemed calibrated
when received, but no Proof of Performance quality checks were
ever specified to even see if those were correct¡
?
As the years wore by the collection of those ubiquitous yellow
rubber handhelds accumulated. I remember the last time I
sent in the ¡¯89 to the factory, only to be told:
- We don¡¯t have any more parts to fit the meter, and,
- We can¡¯t do any minor repairs, and,
- We can¡¯t do any more calibrations.
?
Well, the battery holders were turning to cheese and in order to
get the meter to come up it was necessary to jury-rig a connection
between the AA cell compartment and the meter, proper.
?
Then, the AA battery holder hardware turned to cheese on the ¡®289,
and Lo! and Behold!? ¡° Fugeddaboudit.¡± There are no parts to fix it.
?
There are other meters, newer models, and they seem to be working,
and when setting up a bench to observe a ¡°standard,¡± the readings
are all over the place. Fluke. Thousands of dollars to buy and then,
when the rubber needs to meet the road, they can no longer be trusted.
?
A case-in-point:? Recently an experiment regarding the various measurements
of signals and amplitudes came up. Both the ¡¯89 and the ¡®289 can be
configured for dBm, and even the reference load values adjusted for
a wide range of activity, like 50 or 300 or 600 ohms.
?
Even with a new set of AA cells, and a proper warmup, using the meters
to show what the new bench supply says is ¡°something¡± in the 50 ohm
dBm Land, the readings are different. Not too, too different, but still not
right on the money as Fluke would have been relied upon to produce.
?
So yes, there are a new set of DMM¡¯s coming out that are Orders of
Magnitude cheaper than new Flukes, and best, is that many of them
come with certificates of calibration right in the box.
?
Forums like the eev blog compare quality and consistency to test
gear day after day. They are the first to raise a ruckus when something
is squirrely.
?
Hal Mandel
W4HBM
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Re: G3SEK Tetrode Boards documentation
GM3SEK? Here is a link that turned up.
No longer sold it seems, and a quick search for gerbers turned up nothing for me.?
The schematic is in the manual so one could do a board run if so inclined.?
Bob H N9NRW
?
http://www.ifwtech.co.uk/g3sek/
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http://www.ifwtech.co.uk/g3sek/
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Re: G3SEK Tetrode Boards documentation
Attached to this email are the manuals for the G3SEK tetrode and triode boards as well as the tetrode board design documentation. Maybe the moderators can add these to the group files section.
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G3SEK Tetrode Boards documentation
Mike,
Try this:
73 Bill N4LG
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At 11:17 AM 12/28/2024, Mike Peace via groups.io wrote: Hi,?
Would anyone have the G3SEK schematic and PCB drawings for download?
The link seems to be broken for me:
<>
Cheers,
Mike Peace
VK6ADA
On Sat, Dec 28, 2024 at 9:52?€?AM Mike WB2FKO via <>groups.io <mph=<mailto:[email protected]>[email protected]> wrote:
The tetrode boards aren?€?t particularly complicated if you only implement the screen current trip. On my tetrode amplifier, I eliminated the control grid current trip and ALC circuitry. Their primary purpose is providing regulated screen voltage with most of the larger components placed off the boards. The schematic diagrams are still available on G3SEK?€?s website so spinning up an equivalent set of PCBs ¡ª perhaps just one PCB is all that?€?s needed ??€¡± should not be difficult.
Mike WB2FKO
On Dec 27, 2024, at 9:03?€?PM, Billy Pickering via <>groups.io <pickeringw=<mailto:[email protected]>[email protected]> wrote:
???
Well, I was lucky enough to pick up a Henry Tempo 2006 that did not have any tubes. Yes, 3CX400A7 tubes are expensive so we were looking into modifying it to run 2 or 3 4CX250B tubes instead. I know we need to have screen power for these tubes, and was wondering if anyone was currently making the GM3SEK tetrode control boards. I guess we could come up with something from scratch, but those boards are really nice.
?
I guess if it really come down to it, we could modify to run the single 3CX800A7 we have, but not sure if the tube is any good as it was pulled from a commercial unit.
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Hi,? Would anyone have the G3SEK schematic and PCB drawings for download?
The link seems to be broken for me:
Cheers, Mike Peace VK6ADA
The tetrode boards aren¡¯t particularly complicated if you only implement the screen current trip. On my tetrode amplifier, I eliminated the control grid current trip and ALC circuitry. Their primary purpose is providing regulated screen voltage with most of the larger components placed off the boards. The schematic diagrams are still available on G3SEK¡¯s website so spinning up an equivalent set of PCBs ¡ª perhaps just one PCB is all that¡¯s needed ¡ª should not be difficult.
Mike WB2FKO On Dec 27, 2024, at 9:03?PM, Billy Pickering via <pickeringw=[email protected]> wrote:
? Well, I was lucky enough to pick up a Henry Tempo 2006 that did not have any tubes. Yes, 3CX400A7 tubes are expensive so we were looking into modifying it to run 2 or 3 4CX250B tubes instead. I know we need to have screen power for these tubes, and was wondering if anyone was currently making the GM3SEK tetrode control boards. I guess we could come up with something from scratch, but those boards are really nice.
?
I guess if it really come down to it, we could modify to run the single 3CX800A7 we have, but not sure if the tube is any good as it was pulled from a commercial unit.
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I have ran into a couple of those online. Wanted to put one in my Thunderbolt,
as it uses the gas filled tubes to regulate the screen, but I was gonna try a string of Zeners
soldered into an old tube socket as an experiment.
Then I learned if you over drive the input of the amp with too much RF,
you will get screen current and the result is IMD splatter.
The new fancy amps seem to be able to detect this, and they disable the tube
somehow - probably by putting the tube into cutoff via the control grid I guess.
--
Steve Hearns [ KA2PTE ]
Technotronic Dimensions, VT [USA]
WWW.TECHNOTRONIC-DIMENSIONS.COM
E-Mail: Steve@...
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----- Original Message ----- From: "Mike WB2FKO" <mph@...> To: < [email protected]> Sent: Friday, December 27, 2024 10:19 PM Subject: Re: [ham-amplifiers] Amp modification The tetrode boards aren?€?t particularly complicated if you only implement the screen current trip. On my tetrode amplifier, I eliminated the control grid current trip and ALC circuitry. Their primary purpose is providing regulated screen voltage with most of the larger components placed off the boards. The schematic diagrams are still available on G3SEK?€?s website so spinning up an equivalent set of PCBs ?€¡± perhaps just one PCB is all that?€?s needed ?€¡± should not be difficult. Mike WB2FKO On Dec 27, 2024, at 9:03?€?PM, Billy Pickering via groups.io <pickeringw@...> wrote: ??? Well, I was lucky enough to pick up a Henry Tempo 2006 that did not have any tubes. Yes, 3CX400A7 tubes are expensive so we were looking into modifying it to run 2 or 3 4CX250B tubes instead. I know we need to have screen power for these tubes, and was wondering if anyone was currently making the GM3SEK tetrode control boards. I guess we could come up with something from scratch, but those boards are really nice. I guess if it really come down to it, we could modify to run the single 3CX800A7 we have, but not sure if the tube is any good as it was pulled from a commercial unit.
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The tetrode boards aren¡¯t particularly complicated if you only implement the screen current trip. On my tetrode amplifier, I eliminated the control grid current trip and ALC circuitry. Their primary purpose is providing regulated screen voltage with most of the larger components placed off the boards. The schematic diagrams are still available on G3SEK¡¯s website so spinning up an equivalent set of PCBs ¡ª perhaps just one PCB is all that¡¯s needed ¡ª should not be difficult.
Mike WB2FKO
toggle quoted message
Show quoted text
On Dec 27, 2024, at 9:03?PM, Billy Pickering via groups.io <pickeringw@...> wrote:
? Well, I was lucky enough to pick up a Henry Tempo 2006 that did not have any tubes. Yes, 3CX400A7 tubes are expensive so we were looking into modifying it to run 2 or 3 4CX250B tubes instead. I know we need to have screen power for these tubes, and was wondering if anyone was currently making the GM3SEK tetrode control boards. I guess we could come up with something from scratch, but those boards are really nice.
?
I guess if it really come down to it, we could modify to run the single 3CX800A7 we have, but not sure if the tube is any good as it was pulled from a commercial unit.
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Can't beat the simplicity of a triode amplifier.
Sell your 4CX250's and purchase the 3CX400's ?
Main reason for looking into the 4CX250 is I have a ton of them, like 10-12 of them, sockets and chimneys as well.
?
My father-in-law who is also my elmer built an amp around the RF deck of a KWS-1 that had been destroyed in shipping which is why we have so many of those tubes. The Henry has the power supply in it and everything else, just not the tubes.
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Sell your 4CX250's and purchase the 3CX400's ?
Main reason for looking into the 4CX250 is I have a ton of them, like 10-12 of them, sockets and chimneys as well.
?
My father-in-law who is also my elmer built an amp around the RF deck of a KWS-1 that had been destroyed in shipping which is why we have so many of those tubes. The Henry has the power supply in it and everything else, just not the tubes.
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Main reason for looking into the 4CX250 is I have a ton of them, like 10-12 of them, sockets and chimneys as well.
?
My father-in-law who is also my elmer built an amp around the RF deck of a KWS-1 that had been destroyed in shipping which is why we have so many of those tubes. The Henry has the power supply in it and everything else, just not the tubes.
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I cut my teeth bringing an old Johnson Thunderbolt back from the grave.
(2) 4-400A tetrodes in parallel....learned a lot.
Key to that whole applicaiton is the neutralization....and the fact
if the gains of the tubes are so far off theres not really a perfect way to neutralize,
merely adjust the cap for "best effect" so there is no self osc, and max power out.
I believe ALL the RF transmitting tubes on the market are now made in Chyna,
and they always mass produce with sub-par materials from a "copied" sample
to cut their expenses as much as possible.
They seem to be also renumbering some tubes as "High performance",
merely giving the same tube a different part number with higher price
meanwhile theres no history of that part number tube or a datasheet.
--
Steve Hearns [ KA2PTE ]
Technotronic Dimensions, VT [USA]
WWW.TECHNOTRONIC-DIMENSIONS.COM
E-Mail: Steve@...
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----- Original Message ----- From: "Robin Midgett via groups.io" <RobinK4IDC@...> To: < [email protected]> Sent: Saturday, December 28, 2024 10:21 AM Subject: Re: [ham-amplifiers] Amp modification Hi Billy, I'm not an amplifier guru. I've studied & repaired a few. There's a notion in the RF amplifier camp that says "if your amplifier needs more than one tube, you need a different design." I agree with that line of thinking. If you're going to make the leap from triode to tetrode at the 400 watt /tube dissipation level, consider the 4CX400 or Russian GS-36b. They can be had for ~$100 each. Look into the mods online for the AM-6154 / AM-6155 FAA amplifiers as a starting point. Thanks, Robin Midgett K4IDC On Fri, Dec 27, 2024 at 8:03?PM Billy Pickering via groups.io <pickeringw= [email protected]> wrote: Well, I was lucky enough to pick up a Henry Tempo 2006 that did not have
any tubes. Yes, 3CX400A7 tubes are expensive so we were looking into
modifying it to run 2 or 3 4CX250B tubes instead. I know we need to have
screen power for these tubes, and was wondering if anyone was currently
making the GM3SEK tetrode control boards. I guess we could come up with
something from scratch, but those boards are really nice.
I guess if it really come down to it, we could modify to run the single
3CX800A7 we have, but not sure if the tube is any good as it was pulled
from a commercial unit.
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I would get the 3CX800 checked out and if good go with that. Socket is the same, filament voltage would need changed and maybe the bias. That should be it. Look at all the Alpha amps that have been changed from 400 to the 800 tubes. Must be a good reason.
Hi Billy, I'm not an amplifier guru. I've studied & repaired a few. There's a notion in the RF amplifier camp that says "if your amplifier needs more than one tube, you need a different design." I agree with that line of thinking.? If you're going to make the leap from triode to tetrode at the 400 watt /tube?dissipation?level, consider the 4CX400 or Russian GS-36b. They can be had for ~$100 each. Look into the mods online for the AM-6154 / AM-6155 FAA amplifiers as a starting point.
Thanks,
Robin Midgett K4IDC
On Fri, Dec 27, 2024 at 8:03?PM Billy Pickering via <pickeringw= [email protected]> wrote: Well, I was lucky enough to pick up a Henry Tempo 2006 that did not have any tubes. Yes, 3CX400A7 tubes are expensive so we were looking into modifying it to run 2 or 3 4CX250B tubes instead. I know we need to have screen power for these tubes, and was wondering if anyone was currently making the GM3SEK tetrode control boards. I guess we could come up with something from scratch, but those boards are really nice.
?
I guess if it really come down to it, we could modify to run the single 3CX800A7 we have, but not sure if the tube is any good as it was pulled from a commercial unit.
|
Hi Billy, I'm not an amplifier guru. I've studied & repaired a few. There's a notion in the RF amplifier camp that says "if your amplifier needs more than one tube, you need a different design." I agree with that line of thinking.? If you're going to make the leap from triode to tetrode at the 400 watt /tube?dissipation?level, consider the 4CX400 or Russian GS-36b. They can be had for ~$100 each. Look into the mods online for the AM-6154 / AM-6155 FAA amplifiers as a starting point.
Thanks,
Robin Midgett K4IDC
On Fri, Dec 27, 2024 at 8:03?PM Billy Pickering via <pickeringw= [email protected]> wrote: Well, I was lucky enough to pick up a Henry Tempo 2006 that did not have any tubes. Yes, 3CX400A7 tubes are expensive so we were looking into modifying it to run 2 or 3 4CX250B tubes instead. I know we need to have screen power for these tubes, and was wondering if anyone was currently making the GM3SEK tetrode control boards. I guess we could come up with something from scratch, but those boards are really nice.
?
I guess if it really come down to it, we could modify to run the single 3CX800A7 we have, but not sure if the tube is any good as it was pulled from a commercial unit.
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Re: TL-922 tube filament voltage.
You can buy many decent RMS multimeters like the Brymen BM857 that is a fully safety rated and protected meter that is much cheaper than the Fluke. There are others.? There is a Multimeter comparison Spreadsheet on the EEVBlog? forum.
?
Fluke is manufacturing many of its products in China and sometimes even buying a genuine Fluke product you never be sure if you getting crap from China, its a crap shoot buying Fluke products with the many fake "from same factory" products on the market. now.? In some tests that I have seen even their fuses are crap and not the proper? multimeter rated fuses that are made in Europe. Sad to see such a good brand name going "cheap made in china"
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Henry
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Well, I was lucky enough to pick up a Henry Tempo 2006 that did not have any tubes. Yes, 3CX400A7 tubes are expensive so we were looking into modifying it to run 2 or 3 4CX250B tubes instead. I know we need to have screen power for these tubes, and was wondering if anyone was currently making the GM3SEK tetrode control boards. I guess we could come up with something from scratch, but those boards are really nice.
?
I guess if it really come down to it, we could modify to run the single 3CX800A7 we have, but not sure if the tube is any good as it was pulled from a commercial unit.
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Re: Tube socket for 3CX1500A7 tube-socket broken
I located? a spare Johnson #247 socket (8877). Never been soldered on.? Make offer..
Dennis, w8nw
Sorry to be a pest guys!!
?
I've become the proud owner of a Dentron DTR-2000L amp with a broken tube socket and a missing cooling fan.
This came from an estate and I'm sure that the SK was not using this amp.?
?
I could use a suggestion on a fan, as I understand that the muffin fan was NOT a good choice for a fan.
The other question is if any one here has had experience with the Chinese sockets on E-Bay.? Here's the auction number.
184967626094.? $38.50 a great price, if the thing is any good.?
?
Any thoughts would be appreciated!
?
Thanks!!!
--
Kim Herron W8ZV
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Re: Tube socket for 3CX1500A7 tube-socket broken
On Wed, Dec 18, 2024 at 06:34 PM, Kim Herron wrote:
?
<I've become the proud owner of a Dentron DTR-2000L amp with a broken tube socket and a missing cooling fan.
<This came from an estate and I'm sure that the SK was not using this amp.?
?
<I could use a suggestion on a fan, as I understand that the muffin fan was NOT a good choice for a fan.
<The other question is if any one here has had experience with the Chinese sockets on E-Bay.? Here's the auction number.
<184967626094.? $38.50 a great price, if the thing is any good.?
?
<Any thoughts would be appreciated!
?
###? ?If I remember correctly, the 1st DTR-2000L's had this mickey mouse fan in there for cooling.? Local dealer had the 1st one in stock.? ? We all laughed when we saw the small fan...that killed sales asap.? Later units had a squirrel cage blower.? Also, I believe the fil V was on the high side on both versions.? That high fil V issue has to be addressed asap, or ur 8877 won't last.? There was no grid over current protection either..... which can save the (megabuck tube).? There was no glitch resistor in the B+....and no step start for the B+.? This is all stuff that can be sorted out... and has to be sorted out asap.? ? The HV filter caps? should probably be replaced...with 330 uf caps, or bigger.? Once that is all done, it should last.?
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HaL Mandel
Mike Peace
Technotronic Dimensions
Robin Midgett
