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 on: August 15, 2018, 08:13:11 PM 
Started by WBear2GCR - Last post by WBear2GCR
Ok, I'm working on this KWS-1.
Got it making some signal through the low level stages.
It's making signal @ the VFO frequency.

The way it is supposed to work is the VFO +/- 250Khz = Dial Frequency.
The "unwanted" lower frequency is rejected by a tunable "trap".

I'm not getting much if any mixing action.

The attached pdf file shows the circuit and description.

They call the tunable section that sits between pins 1 and 6 is referred to as a feedback
filter. Since pins 1 and 6 SHOULD be out of phase with each other, whatever is output on
pin one and then tuned to the lower ( -250kHz) frequency will cancel if it is also on pin 1.
Good enough idea.

I'm seeing ONLY the VFO frequency at the output, as far as I can see, so far.

No sign of the 250kHz component.

What puzzles me the most is that the text refers to the ratio of the VFO to the 250kHz signal
as a bout 1.5v to 0.1v respectively. I'm failing to understand how one mixes two signals
of such disparate amplitude and gets a usable sum and difference signal??

I find those two voltages, approximately... seem reasonable.

Maybe this works just fine, and I have some bad components in or around the mixer/filter.
Have yet to find that. It's also not the easiest place to work in. (nice design work there
Collins! Yeah... right.)

Anyone got insight/ideas??


 on: August 15, 2018, 07:25:13 PM 
Started by VE3ELQ - Last post by vk3alk
Thats a nice waveform after the transformer.... Smiley



 on: August 15, 2018, 07:11:19 PM 
Started by VE3ELQ - Last post by VE3ELQ
The 6 FET deck has been re-installed in the TX and is working FB.

The small deck has now been retrofitted with four 1200V 10A SiC FETs and is performing very nicely, no explosions. Smiley
With the same transformer ratio it produced exactly the same power as the GaNs did, as it should, but ran just slightly warmer.
A 1/2 turn was removed from each secondary to unload the deck a little which tamed it down to 310W from 350 with a corresponding reduction in drain current since its now only good for 20A vice 40. It modulates well to about 1.5KW PEP.

Pete thanks for the comments, not a big fan of transorbs, these FETs are good to 1200V so lots of voltage headroom, should be OK.

As requested a scope trace attached with it dialed up to 400W carrier showing the transformer output (yellow) and across the load after low pass filtering (blue). Harmonics, especially the 3rd, are within regs even before the L tuner which adds another 2 poles of filtering. Its a keeper so will build yet another TX for it as small as I can. 

73s  Nigel

 on: August 15, 2018, 06:57:52 PM 
Started by Knightt150 - Last post by w4bfs
I don't have a rx scizmatic so I am assuming a 455 kHz if .... epay has Murata 6 pole filters (cf455e) afaic remember around a buck apeace in quantities of 5 or so .... I swept one of these a few years ago and they were as advertised .... loading info is out there and is around 1.5k source/load impedance .... wouldn't hurt to try

 on: August 15, 2018, 06:37:52 PM 
Started by W1JS - Last post by w1vtp
Too young - 66.


Way too young

 on: August 15, 2018, 04:32:57 PM 
Started by Knightt150 - Last post by Knightt150
Hello: I am in need of a AM filter for my yaesu FR 101 receiver I think. I think the AM filter in the receiver is cracked, I can hear stations 20kc away on both sides of the dialed in frequency. The AM filter in the receiver is 6kc , not 40 kc wide. The receiver did get drop about 6 months ago, if the filter is not cracked then what is the problem? My ssb filter is working great so it would seem the receiver is working great.

John W9BFO

 on: August 15, 2018, 03:21:17 PM 
Started by Detroit47 - Last post by Detroit47
Crystal cover for Valiant II. Pm or Email me. I have a lot of Johnson knobs will trade.

John N8QPC

 on: August 15, 2018, 02:46:52 PM 
Started by W8ACR - Last post by KA3EKH
All that broadcast stuff ran at 0 Db balanced so you need a microphone pre amp anyway. Get yourself an old production console and a couple cart machines and you’re on the way to building a late seventies AM Broadcast station!

 on: August 15, 2018, 11:55:23 AM 
Started by W8ACR - Last post by W1DAN

I'd run the CRL set. Don't have to crank tool hard to get decent audio.

If you are not interested in the CRL set, I would be.


 on: August 15, 2018, 11:24:27 AM 
Started by W8ACR - Last post by W8ACR
OK, thanks for the replies. This helps. I plan to use an RE-27 mic. Is there a more modern single box of any sort that would suffice for decent audio?

Thanks again,

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