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Author Topic: Reactor's sparking when carrier goes off  (Read 52168 times)
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AMLOVER
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« Reply #50 on: February 25, 2011, 11:20:04 AM »



Jim,
I also think the right way to make that ac capacitor by connecting some dc caps together is B or C but I saw your reply to this thread  http://amfone.net/Amforum/index.php?topic=22341.msg161638#msg161638 that confused me because it seems like D which is a series dc capacitor connection.

W2PFY,
It seems like solution A hasn't that much popularity in the net, I couldn't find anything like that googling around but I'll give it a try connected the output to a speaker and listen to.

Gito,
I specially have 2 problems on the modulation-hv side of the transmitter. The first that was the EMF and the huge spiking on the reactor was solved by shorting reactor's ends by a resistor=Rdc, driving the stored energy in the reactor back to the HV capacitance bank. Keep in mind that I keep Hv on the tube all the time and I use fixed bias (-50v to -200v as much I wish) but with a parallel leaking resistor like in the sheme below.
In this configuration I can't really idle the tube with the screen voltage off in any fixed bias level from -50vdc to -200vdc. Screen voltage shuting down is a very important safety cure even I have added a very fast and reliable security sircuit in any case. I wish to keep screen off during receiving periods. You are very right though about the heising capacitor decharging energy but as long I keep HV always on, this capacitor is charged when I step start the HV begining of the evening and stay so till I turn off the amplifier on the end of the night and the HV supply is dicharged slowly through the bleeding resistors.
The second and very main problem is that sometimes, can't really say what from is depending, some trancient is coming through the modulation transformer back to the 4 ohms bridged mode output of the solid state af amp and mosfets are blown up.
That happened twice unreasonably after 40-50 on-off periods with lot of transmission in full power mode.
Now I'll try ato involve between the output of the AF amp and the primary of the modulation transformer some kind of ac capacitor to block any trancient or dc upseting direction Af solid state amp.
I know that you guys have not that sensitivity matters because of the push pull tubes af amps but in my case with solid state involving in a HV heising sircuit special care must be taken on.
Gito, what is your opinion about the ac capacitor?
Thanks

Stefano


* bias supply.JPG (37.56 KB, 1210x639 - viewed 1105 times.)
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Gito
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« Reply #51 on: February 25, 2011, 09:14:11 PM »

Hi

You are right when You wrote since You  have the B+ always on then the Coupling won't discharge.

But sometimes we forget The  voltage in B+ loaded and without load,
reading Your reply ,the B+ is slowly discharging till the next morning,
than The B+ power supply has no or enough R Bleeder ,and if You used Capacitor input Power supply,Than what happen
When You Unkey the transmitter,The B+ soars up to maybe1.2% or 1.4%.(not loaded)

When it happened A current flow from B+(1200VDC) to Coupling C (1000VDC },. via the Reactor. So a back EMF is build around this reactor.

It just a theory.

When You used a resistor to short the Reactor ,That doesn't mean that the back EMF is gone,
You only reduced to a voltage to a low level that makes this voltage "low enough" that it cannot make a spark to jump in the reactor,but actually it's high enough , but  not the enough to make the spark jump.

But the voltage is still there and coupled to secondary winding to the Amplifier.
Maybe when You short the reactor omitting  The R (bypassing the resistor and reactor},than it won't happened.

The Idea of making the Amplifier in conduction state  (by varying it's min bias/varying Cathode resistor) ,is making a  path where this energy (EMF) can flow through the Tube
As the AC cap .it is believed that it's a "form" of low pass filter .limitiung the frequency response of the audio,so it deppents on the" Frequency "of the "spark"?

Gito
 

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Gito
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« Reply #52 on: February 26, 2011, 02:35:01 AM »

HI

As We know the reactor that causes the spark,why don't we used a relay to bypass this reactor ,when We unkey first the relay A and B closes ,than a part of a second  later followed by the closing/stopping of the driver.

Since at that time the reactor and the Mod trafo is shorted/bypass,I believed there is no spark to worry.
Maybe We can used a vacuum/high voltage relay to bypass the reactor.

 Sorry for my English.


Gito

 


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AMLOVER
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« Reply #53 on: February 28, 2011, 11:30:57 AM »


Gito,

my English are even worse  Smiley
I attach a plan of the existing reactor sircuit plus what I am thinking to add between af solid state amp and moulation transformer.
If you or anybody else have something to notice, you are welcome.
Thanks

Stefano


* Gito.JPG (60.16 KB, 1210x639 - viewed 1105 times.)
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w3jn
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« Reply #54 on: February 28, 2011, 01:30:33 PM »

Guys, I don't want to hear any apologies for your English.  Both of you have better English than half the native English speakers -- and MUCH better than my Greek or Italian  Grin

Stefano - if you know the guy who was running on 1620 KHz this past weekend, you might let him know his second harmonic on 3240 was much stronger than his fundamental.
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AMLOVER
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« Reply #55 on: February 28, 2011, 04:06:20 PM »

Johny,

I don't know him because there are many around this frequency. They don't belong to our team, they are "locals", they use vertical fishing rods 8-15m long 4 wires for top hat and lot of radials on their roof in order to almost broadcast for the city of Athens. I am 99% working 1670-1700 and only communication radios. The "rule" is 1600-1630 local level broadcasting by using the broaden receiving properties of the old analog receivers, 1630-1650 local chats with 50-200w, 1650-1670 medium power comms 250-1000w, 1670-1680 high power national comms 1000-3000w, 1690 the big guns 3000-10000w, 1700-1710 the Crete island power net and 1710-1730 empty for music tests, then a little 100khz jump and legal again.  Cool Of course all are welcome to every frequency but it is difficult to survive next to those huge sidebands if less than 6db of them...  Undecided
Some are 24h broadcasting at 909, 1204 and almost in all channels every 9khz in the MW band.
The majority have bought the trs from few low level educated in electronics constructers and of course they don't use any Pi network, the letter Q is totally unknown to them. The most of them have connected the wire antenna straight on the anode blocking doorknob cap with max Q=0.001, 50 ohm and swr are allien terminologies...
See that plastic yellow can with the modulator swimming in extra virgin Greek olive oil...  Grin
 
Stefano



* parizianos larisa.jpg (217.33 KB, 900x675 - viewed 1353 times.)
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Gito
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« Reply #56 on: February 28, 2011, 10:12:21 PM »

Hi

You are right ,we don't need to bypass/short the modulator trafo.
I do that because as  we read there are so many theory ,how this spark happen,but is this theory true /which one is ?

So to make sure, if there's still a transient ,that happen,because   switching off /on the transmitter that goes in the B+ power supply,or the soaring B+ ,since even the Reactor is shorted,the B+ is still connected to C  coup (surge current from B+---C coup--secTr mod---ground).  ,


So it;s only an extra protection ,to make sure ,there's  not a "spike" induced to the Amplifier trough the Modulator trafo.

Gito

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w3jn
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« Reply #57 on: February 28, 2011, 10:49:40 PM »

Wow, I had no idea the hobby broadcasting community in Greece was so vibrant.   That's a really cool transmitter - 4 4-400s modulated by a pair of 150Ts?
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« Reply #58 on: March 01, 2011, 12:22:26 AM »

Jim,
I also think the right way to make that ac capacitor by connecting some dc caps together is B or C but I saw your reply to this thread  http://amfone.net/Amforum/index.php?topic=22341.msg161638#msg161638 that confused me because it seems like D which is a series dc capacitor connection.


Stefano, Maybe I did not say this well:

" If your voice has much asymmetry, running that Crown into a near DC short circuit will cause a DC current to flow into the transformer primary (4,8, or 16 ohm taps). This will use up some of the Crown power supply ampere budget. Crown in their manuals for the big amps recommend a series capacitor between the AMP and the load (if under 2-3 ohms DC). One possibility is dual 10,000mfd caps back to back with the + ends together to make a poor mans AC capacitor placed in series with the load. Remember that large loudspeakers usually have a DC resistance that is just under the AC impedance rating, so no series Cap is needed there. When you drive say the 4 ohm tap of a transformer, the DC resistance of that primary might be just a few tenths of an ohm.."

  The capacitor value depends on the lowest audio frequency used. I just stated "dual 10,000mfd caps back to back with the + ends together" which was intended to be a series connection, not parallel.

  Also your schematic shows two sets of capacitors. This is not necessary, just using one pair will accomplish the same thing with less reactive low frequency roll off.

Jim
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« Reply #59 on: March 01, 2011, 11:11:18 AM »

Id say 3-500 graphites or 5868's if triodes but could also be European 4-400 equivalents as I dont see any QRO driver stage. There is also what appears to be a screen supply on the upper left shelf.

This reminds me a bit of Rich Measures 75M 4CX10000A plywood box amp Grin

The other glass look like 250TH/TL's.

With all the loonies rioting in Athens it must make for interesting radio broadcasts  Roll Eyes

Carl
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« Reply #60 on: March 01, 2011, 11:22:02 AM »

Johny,

I don't know him because there are many around this frequency. They don't belong to our team, they are "locals", they use vertical fishing rods 8-15m long 4 wires for top hat and lot of radials on their roof in order to almost broadcast for the city of Athens. I am 99% working 1670-1700 and only communication radios. The "rule" is 1600-1630 local level broadcasting by using the broaden receiving properties of the old analog receivers, 1630-1650 local chats with 50-200w, 1650-1670 medium power comms 250-1000w, 1670-1680 high power national comms 1000-3000w, 1690 the big guns 3000-10000w, 1700-1710 the Crete island power net and 1710-1730 empty for music tests, then a little 100khz jump and legal again.  Cool Of course all are welcome to every frequency but it is difficult to survive next to those huge sidebands if less than 6db of them...  Undecided
Some are 24h broadcasting at 909, 1204 and almost in all channels every 9khz in the MW band.
The majority have bought the trs from few low level educated in electronics constructers and of course they don't use any Pi network, the letter Q is totally unknown to them. The most of them have connected the wire antenna straight on the anode blocking doorknob cap with max Q=0.001, 50 ohm and swr are allien terminologies...
See that plastic yellow can with the modulator swimming in extra virgin Greek olive oil...  Grin
 
Stefano


Stefano, that's one of the most interesting posts I've seen this year! The picture tells it all.  It sounds like the wild west USA in the 1800's.. Grin I'll bet you guys are having a lot of fun.  It wud be cool to tune in with a remote web global tuner and listen in to you guys some time.

T
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« Reply #61 on: March 01, 2011, 12:14:02 PM »

Take a listen, T, these guys really play some great music.  The engineering ranges from iffy (FMing, overmodulation, and distorted audio) to indistinguishable from professional.

The breakin QSOs are not much different from a good breakin session on 75 meters.  Wish I could understand the language!

I believe there's a globaltuners or similar node in Greece.

While yer there, take a listen to the Athens AM station on 666 KHz.  That station epitomizes what AM radio can/should be in the States.  Huge variety of music, outstanding audio, and nice wide freq response.  In the WJ's 16 KHz position it sounds fantastic.
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« Reply #62 on: March 01, 2011, 12:32:30 PM »

Gito,
Its true that after shorting the reactor and having grounded one leg of the mod transf secondary all are very safe looking from modulator primary side. I am thinking that if trancient was the reason why the disaster happens only after 40-50 times on-offs?Huh?Trancient should be there all the time but acts like a phantom after 40-50 on-offs?Huh?
I start thinking that the problem is RFI that comes after some different amp tuning and loading. So I now see that Jim WD5JKO was very right to say that a big ferrite making a common mode choke with some inductance and 4 by passing caps (1-10nf), 2 in each side of the choke would act as an RF trap and keep the Af solid state amp undisturbed.
So I'll try when I have the time to make the Rf trap in conjuction with the dc trap, ac varistors+ac caps.
Jim,
I have understood you right but I have 16 caps of 800uf/450v each so I need to put every 8 of them in parallel to create 2 cap banks of 6400uf and then to connect those 2 banks back to back + with + together.
Or I'll look for some 10000-20000uf ones and make it with just 2 of them. Oh, it's good that I'll  need to place the poor man's ac cap only to one side. It's more convinient.
Johny,
The guy is in middle of Greece, in the city of Larisa and I think that he uses 8xQB4-1100s, there are 2 rows of 4 tubes and modulates his plywood box with 2xTH250, I think.
The driver seems like 1x6146b.
Tom,
As far you like the photo I'll post few more with USA on 1700 and 1900... Grin
Have a look and much fun. Believe me some of them takes very seriously and they can almost die if their "beauties" get some sickness and can't sing any more. Sure we have lot of fun specially when we listen to all that .....proudness coming out of their crystalic microphones.... Grin


Stefano


* 1700.jpg (323.23 KB, 850x638 - viewed 1322 times.)

* 1700-2.jpg (270.97 KB, 800x600 - viewed 1445 times.)

* 1900.jpg (136.01 KB, 500x668 - viewed 1540 times.)
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K1JJ
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« Reply #63 on: March 01, 2011, 02:26:04 PM »

Quote
Have a look and much fun. Believe me some of them takes very seriously and they can almost die if their "beauties" get some sickness and can't sing any more. Sure we have lot of fun specially when we listen to all that .....proudness coming out of their crystalic microphones....

That's pretty funny, Stefano. Yes, we get depressed when our precious creations crap out, for sure... Grin

From the pictures, I can see you prefer to build "broadcast style layout" in Greece...  Easy to service.   Back in the 1970's my homebrew stuff looked a lot like those rigs. We used the parts and cabinets that were available.

BTW, you might tell the owner of the 4CX-15,000 (pic #2) that it needs bigger air cooling as shown by the brown coloring on the top anode area. The seals may soon fail if not corrected.

All in all, those are creative looking rigs and you guys are certainly enthusiastic about radio.

T
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"Season's Greetings" looks okay to me...


« Reply #64 on: March 01, 2011, 03:07:55 PM »

Stefano et. al.

I am considering a new AM tranmmitter design concept that is inspired by various trends in supercomputing. I call it "massively parallel tetrode pooling".

The objective if to place a large number of readily available, low power tubes in parallel... so that the plate voltage is relatively low... and the plate current is relatively high ... therefore making the modulation resistance a perfect match to an 8 Ohm amplifier.

For example, consider 512 6CL6's in parallel, arranged in modules of 16 tubes each... running at 200 Volts B+ and drawing a total of 25 amperes (at carrier).

The input power, at carrier, would be 5kW. Assuming approximately k x75% efficiency, the output power at carrier would be k x 3.75 kW.... where k takes into account possible inefficiencies associated with combining the outputs of the 16 tube modules, tube mismatches,  etc.

If k = 0.1, then one would have a US legal limit transmitter that can be directly modulated by a 2500 watt, 8 Ohm audio amplifier.

Comments?

Stu
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« Reply #65 on: March 01, 2011, 06:04:59 PM »

Stu,

That's a good idea for very low Rdc, for low R input (grid driven closed to 50ohm) and Rload closed to 50ohm. Very safe arrangement with low high voltage, beautiful glassy shape, lot of heat and amazing ambience...
Many do it here with as many as 16 tubes but you can see the photo for 30x813...with 2500vdc and 6000ma (200ma each) this monster has Rdc=400ohm, Rload=200ohm and a modulator 1:7 for 6000w af solid state amp....15kva input and 11kw output power.....on that small low height antenna....poor neighbors... Embarrassed

Johny, this is the famous "Playboy radio" that broadcasts on 945khz every Sunday.....

Stefano


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Gito
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« Reply #66 on: March 01, 2011, 09:38:09 PM »

HI Stefano


When You short the reactor with an R ,than there's still a current flow in the Reactor,that makes a back EMF that causes a voltage to appear ,this voltage/energy is absorb By The Resistance,but there's sill a voltage at this reactor right,before it was absorb/dissipated in the R resistor,This voltage is coupled back to the the Amplifier via the C coupling and the Modulation transformer ,So the "reactor" is the source of that voltage that comes into the output terminal of Your Amplifier,if it's high enough ,it can destroy your Amplifier.
But when You short/bypass the reactor ,there's no current flow trough it.Than there's no voltage appear across it,so there's no voltage getting to the amplifier.

To make sure ,used an extra switch/relay across the Mod transformer.to short it.

As long there's An Inductance (Sec Mod Trafo)--Coupling C -- B+ and ground connected in serie ,a voltage change in the B+ can charge or discharge the coupling C ,that makes a current flow trough the inductance ---- making a voltage appear across  this inductance. and coupled to the primary winding of the Mod Trafo.

Maybe the voltage that's got into Your Amplifier is just small enough to destruct it,
But maybe  sometimes when Your line voltage gets higher than normal,making also the voltage that appear in/at Your output terminal (voltage from the React---C ---Sec Mod Trafo....ground Coupled to.....primary Mod.Trafo...output terminal.Ampli} of Your Amplifier high enough, that makes /destroy Your Amplifier.

You wrote after 40 or 50 times  ...... it happened ........

Stef I can asked You the same question ,if the RFI is there ,why it took so long till the Amplifier is destroyed.

And As I know when an RFI gets into an Amplifier ,that used to modulated ,it can oscilate ,because the audio that is rectified in the amplifier can  becomes a positive feed back ,or distorted if it becomes a negatif feed back .(the phases of the rectified audio)

 in my Expirience ,You can used the audio that is produced at the transmitter as a "simple judge " if there's RFI coming back in Your Amplifier,of course using an osciloscope is better.

 if there's big enough RFI that comes into Your Amplifier/transmitter ,that can Destroy Your Amplifier.Than I think Your Amplifier/Transmitter Can't produced a good audio.

Of course Stef I can be wrong

Gito

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« Reply #67 on: March 01, 2011, 11:38:10 PM »

Sorry to keep derailing your thread with comments, Stefano, but this is just fascinating.  It's seldom indeed we discover something new in the world of radio, and this whole subculture is largely unknown to us.

Many, many, MANY thanks for sharing all of this!

I've seen a nice cage dipole on top of an apartment building in Kolonaki, I wonder if that's one of your compatriots?
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« Reply #68 on: March 02, 2011, 12:37:36 AM »

The CBers have nothing on these guys with the 30 813 tubes Grin Grin Grin I wonder how he cools that orange crate of 813 tubes? You could heat your house with that thing. 

Boy what fun it must be to be able to use what we call the broadcast band.  In this country, all radio frequencies are for sale by the US government except the ham bands so far.
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« Reply #69 on: March 02, 2011, 10:23:09 AM »

The CBers have nothing on these guys with the 30 813 tubes Grin Grin Grin I wonder how he cools that orange crate of 813 tubes? You could heat your house with that thing. 

Boy what fun it must be to be able to use what we call the broadcast band.  In this country, all radio frequencies are for sale by the US government except the ham bands so far.

Might I remind you of UPS and 220?


I've seen firsthand 4 X YC156 and up to 16 572Bs on "10 meters" before as well.  This is a huge kick, though.....  There are SO many more tube options at MF!


--Shane
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KC2ZFA
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« Reply #70 on: March 02, 2011, 11:00:19 AM »

I grew up in Greece and as a non-Greek citizen I couldn't get a ham license.
But I was into electronics and by age 14 I knew enough to become a "pirate"
(argh!). The pic is me at age 15 (1979) with my 6v6-6146 transmitter (no loading
cap, the antenna wire, about 200 feet long, went directly to the L-net coil and
loading was achieved by changing taps on it). I blew the horn to clear the
frequency  Grin In 1980 I modified the xmtr with an 807 buffer to drive an 811
at about 1kV. But in those days the authorities were still hunting pirates with
the DF wagons so I got in touch with Charlie Jackson, SV0AA, who examined
me for the by-mail Novice and in 1980 I was KA2KEV/SV0BU and the rest is
history.

Those were the days my friend !


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« Reply #71 on: March 03, 2011, 12:02:37 PM »

I wonder how long it will be before there are no more 813's remaining in Europe?

Im surprised there arent many multi tube GU-81M amps.

Carl
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« Reply #72 on: March 03, 2011, 01:03:12 PM »

The last time I was in UK, about 10 years ago, my brother-in-law told me that hardly anyone listened to AM any more, whether long wave, medium wave or short wave, and he couldn't comprehend why I had even the slightest interest in exploring those bands on his car radio while we were riding.  Now the UK is supposed to be phasing out analogue broadcasting, both AM and FM, and replacing it with some form of DAB. I wonder if in Greece and other European countries, so few people now listen to the AM broadcast bands that authorities don't really care who transmits there as long as they don't interfere with other services or become a general nuisance in the local area, kind of like what has happened here with CB and increasingly, ham radio.

I have heard it said that in the UK, more than one ham is running a converted broadcast transmitter on 160m at >1 KW, even though the power limit on that band is supposed to be 10 watts carrier output, and there has been no sign of a "crack down".

From my own past experience travelling around in Europe, I would suspect that authorities in UK, France, Germany, Netherlands, Switzerland and in a few other countries, radio laws would  be strictly enforced as a matter of principle, but in certain others authorities might tend to look the other way, especially if the appropriate palms were properly greased.

But, OTOH, with all the paranoia these days about terrorism and political movements trying to overthrow governments (which appear to be having some success in N. Africa and the mid-east), I would think that illegal broadcasting might be an item high on most governments' priority list.  Maybe they figure that the internet is a greater threat to public order than unlicensed broadcasters would be, so that's where they focus their attention. At least it is easier to control.
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Licensed since 1959 and not happy to be back on AM...    Never got off AM in the first place.

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« Reply #73 on: March 03, 2011, 01:24:33 PM »


Carl,
GU81M is very famous here because is cheap and ...pentode!!!
No neutralization at all. An easy going tube. The next photo is for answering your question...
Hundreds of 813s all around and tones of rusty irons.....

Don,
You are totaly right, authorities don't care because nobody listen anymore in Europe MW bands...The countries here are so small that with 3 repeaters of 1kw you can cover all audience in the FM band...
So we took advantage let say to try homebrewing in a free field...

Stefano


* 32xGU81M.jpg (141.39 KB, 850x638 - viewed 1251 times.)
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« Reply #74 on: March 03, 2011, 01:59:48 PM »

I was just listening to 1.650 over in Greece, Nice music in English and sounded very good. Any idea who that is and what the transmitter is? That was about 8:45 PM Greece time.
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