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April 13, 2021, 06:25:39 AM *
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 on: Today at 12:34:33 AM 
Started by WD8BIL - Last post by K4RT

Hope you're feeling better.

Brad K4RT

 on: Today at 12:29:45 AM 
Started by ua3ral - Last post by K4RT
Thanks for posting that link. I saw that the first time it aired, I think on NBC. SCTV was tops.

 on: Yesterday at 11:38:50 PM 
Started by vk3alk - Last post by vk3alk
I think it looks good mainly because the PCB has been sprayed with lacquer...  Smiley

Have uploaded a circuit diagram....
The design is typical H Bridge using very few components really.....
To be honest its all about what FETs you use....and not many work well  Sad .... most are a complete disaster and are sure people have given up using H Bridge because of this...

But the IPP530N15 do work extremely well and you can expect efficiencies well into the 90s ...
Their main drawback is the maximum voltage of 150 volts.... but have pushed modulation peaks well above without any problems at all...  Smiley

I am not an engineer so just experiment a bit....
On 160/80 I use current limiting resistors between the IXDD and those inductors but on 40M found they caused issues so removed them.
Also on 160M and not so much on 80M the waveforms at the gates of the FETs are squarewave "ish" .... but on 40M there are no harmonics left just the fundamental so its like sinewave drive...

Have found too using H Bridge can duplicate modules making them perfect for use with Combiners etc:

Thats about it really....


 on: Yesterday at 10:36:54 PM 
Started by KK4RF - Last post by Noddyswl
Re KA's inquiry...you can switch the B- line or disconnect the B+ to the IF's for example. The set was built with
connections to just that purpose (terminals 6 and 2 on the Jones socket at rear of set) and you have to join
hem for operating the Rx... or open for Tx. If the Jones plug has been removed, follow the circuitry and reinstate
the wiring for the stand-by.

 on: Yesterday at 10:23:25 PM 
Started by ua3ral - Last post by Sam KS2AM
60 years.

Coincidentally this is also the 40th anniversary of the first broadcast of "What fits into Russia"  https://www.youtube.com/watch?v=BXqKkYYALMU

 on: Yesterday at 10:14:50 PM 
Started by KK4RF - Last post by Noddyswl
The B- is confusing. Yes. What seems to be missing in all the comments is that the Choke was not put into the
Audio transformer to use up left-over wire. The bias system was commonplace and a development from using
grid battery in the 1930's when the set was designed and worked well.  The BC 348 power supply was filtered
using a choke in the B-line and provided bias to the audio tube at the same time. I admit that the power supply
situation is poorly explained....The explainers and presenters of BC348 mains supply design do not see the
confusion or don't understand what's going on. I didn't even after reading numerous articles. Then it clicked..

Yes you can substitute a resistor but why?...because you don't understand that all your B- should go through the
choke? and don't understand that the designers actually knew what they were doing unlike the ruinous mod's
from USA in the 40's-70's. Henry from Boulevarde likes to filter to the B- line and also the chassis...I don't know why
that is but he knows the sets well...Just look at you power supply as B+ and B=, the B- being to the audio choke
rather than the chassis. You can earth the chassis but dont simultaneously earth the B- line. If you don't run the B- to
the choke but instead to chassis you will have distortion and overheating of the audio tube.

If you bypass the choke and use a bias resistor you lose some good filterin. Use the choke and keep B+ less than
220volts filtered dc. If usng diodes organise some delay in switching-on B+ until heaters have warmed...say 30 seconds.
The simplet way is to switch the B+ after say 30 seconds from turning on the set. I used a switch pot for the volume control
so as to feed the p/s. I  neatly placed an RF gain control to right of the tuning dial but you could swap the lighting
rheostat for a 20k w/w switch pot to separate the AF and RF controls (thus the change also to 300k or thereabouts switch
pot for audio ) .

I'm notmuch in favour for using the AVC-OFF-MVC contacts for switching B+(or B-). I'd rather not put that switch at risk as it
was ok more or less carrying 4A (plus start-up) at 28 volts in its design. You could use the BC348 switch to operate a 6 or 24
volt relay of course but again they are not rated (usually) for dc though sure as eggs are eggs someone will have dozens of
suitable relays or small timers or some solid state delay which will take the dc B+  voltage. You could of course switch the
B- line..noting rong with that.

Rather than switch 220v dc on a 240v ac rated switch I'd look at using a relay with HV rated contacts OR....just use a tube in the
power supply. Then heating up will pretty well take care of itself.

 on: Yesterday at 09:35:34 PM 
Started by KD2AZI - Last post by Noddyswl
Hi....80 watts input is enough to get you around the world....QRP's do it on under 10watts.  US Amateurs have for
decades been a tremendous nuisance not only taking over entire frequencies for contests, netting, but in a power -mania..
like the Atomic bomb...just blast your way into the ether. Thing is its mostly humbug in this way...increasing power and
increase in performance are not linear. Yes you can increae power...or there may be some fault in the set...but 80W
would be fine. You don't get through to someone you hear....could be skip...could be you are marginally off frequency.

My opinion is get used to the set....remember these sets used training antennas and did not have dipoles or really long wires.

njoy using it whilst reading up what you can but a plea, "do try to not get obsessed with power" ...work with what you have
and what's simple for you to change...could  be antenna....ART 13  needed its antenna tuner.

 on: Yesterday at 09:20:06 PM 
Started by WD8BIL - Last post by Steve - K4HX
Good luck with the recovery Buddly.

 on: Yesterday at 07:51:39 PM 
Started by ua3ral - Last post by AG5UM
The April ARRL QST Mag. shows the Yuri Gagarin International DX contest (CW) was the 10th and 11th of April 2021.
gc.qst.ru/en/section/32  website.
I guess I just missed it, sounds fun, Hope to make the next one.
I'm going to need to buy a Russian keyboard for the computer at some point, Thank goodness for these translator programs.
._ _.   ._.   ..   ..._   .   _             

 on: Yesterday at 06:36:23 PM 
Started by K8LEN - Last post by K8LEN
Anyone on  3885 am around PAOLI, SALEM INDIANA.
Just got back on after a few or more years off. Running 25 watts to a end fed.
POB/K8LEN Smiley

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