An interesting modulator circuit

[KM1H]

Its in the Feb 62 QST starting on Pg 34 using cathode folowers to drive low mu connected sweep tubes. Stated total distortion is 2% or less which beats or equals some pricey antique triodes. That is for the basic version. A deluxe version with agc compressor and clipper is included.

Other than changing a few component values for wider fidelity I didnt see any glaring problems or parts availability in a quick read. A later FB gave corrections for the 6GJ5 pinouts. It could also be used as a driver for some big triodes.

Carl
KM1H

[k4kyv]

The only problem is that to-day, with the long ago demise of tube type TV's, sweep tubes can be as expensive and hard to find as the older vintage triodes.

A good example is with the Yaesu FT-101 series.  Because at the time the sweep tubes were far cheaper, they used a pair of 6JS6's in the final instead of 6146's.  But over the years, the price of the sweep tubes gradually crept up, until now they cost several times more than a good n.i.b. 6146.  There have been numerous articles on how to convert to the latter.

In the  early 80's, the Japanese sweep tubes became scarce, and some rigs wouldn't properly neutralise with U.S. made tubes, which were still widely available at the time.  This was a topic of much discussion in the Fox-Tango newsletter.

[WBear2GCR]

Scan & Post? Fair use copyright law rules say it's ok.

               _-_-bear

[N4LTA]

ESRC has both the sweep tubes listed in the article at $6 (6GW6) and $8 each(6CJ5).

Pretty cheap audio power tubes.

[Steve - WB3HUZ]

You'd be wrong. ARRL sez differently.

But, if you are a member, you can get it online. It's a very interesting article. But it does use interstage transformer, so some improvements could be made.

Scan & Post? Fair use copyright law rules say it's ok.

               _-_-bear

[N4LTA]

Anyone got a spare 55-60 watt modulation transformer? I have a few 30 watt'ers, but no 60. I'd like to try this circuit.

Pat
N4LTA

[WBear2GCR]

You'd be wrong. ARRL sez differently.

But, if you are a member, you can get it online. It's a very interesting article. But it does use interstage transformer, so some improvements could be made.

Scan & Post? Fair use copyright law rules say it's ok.

               _-_-bear

I am not an attorney - but I think that the federal rules say otherwise... excerpts are "fair use" - and "fair use" is permitted in a non-commercial setting, like this one. The ARRL says lots of things, fwiw.   

[Steve - WB3HUZ]

It's their copyrighted material. I've had previous interactions with them regarding posting articles on the AM Window Web Site. They denied my requests. I would not advise any one to post their stuff without asking them first, fair use or not. Why put this site at risk?

[KC4VWU]

Carl,
         Strangely enough, I was digging through some stuff today and discovered some long forgotton issues of QST. While I was leafing through them I found somthing very similar. If you have it, reference the July "62 issue and the article by Lew McCoy. Should be the identical circuit that he chose for modulating the transmitter in his prior article of the June '62 issue. It also uses a pair of 6GJ5's in the PA. He does warn to recheck the 6GJ5 pinouts of the original article as they were wrong.

Now I'd like to find a multimatch 60 watter! Might be a nice universal mudulator for the low to mid power stuff. Plate modulated DX-60!

Phil

[KM1H]

The only problem is that to-day, with the long ago demise of tube type TV's, sweep tubes can be as expensive and hard to find as the older vintage triodes.

There are many inexpensive sweep tubes still available. There are octal varieties for the 40-60W range and high voltage filament types for the 100W level that arent in demand in ham gear, CB amps and a few hi fi products where demand has driven prices thru the roof. Their benefit is the very high perveance design with much reserve emission. There are also a few Russian versions that are good for 300W+ for a pair. BTW, the 6JB6 (and 12JB6 can be used) is a plug in replacement for the 6GJ5 in case anyone has a stash left over from Drake, National, and a few others.

Ive been reading old CQ's at the kitchen table (on 1955 now) and QST on the throne . If I come across other articles of interest I'll mention them here.

Phil, I figure 2 more days to get to the July issue

Carl

[Jim, W5JO]

Speaking of modulator circuits take a look at this one by WA0ZHH.  It uses 4-6336s to cathode modulate an SB 200.  What a deal!

http://www.kc3ol.dynip.com/forums/showthread.php?t=476&highlight=WA0ZHH

[KX5JT]

Speaking of modulator circuits take a look at this one by WA0ZHH.  It uses 4-6336s to cathode modulate an SB 200.  What a deal!

http://www.kc3ol.dynip.com/forums/showthread.php?t=476&highlight=WA0ZHH

Hey Jim,

Nice to work you this afternoon with K5SEE and others on 3.885.  Great sounding signals all around.  I was looking at this cathode modulator with you during our QSO.  Looks like the audiophools have driven the price up on the 6336's to more than 50 bucks apiece!  Sure would like to know if anyone ever tried this ciruit!

[W7TFO]

6080's or 6AS7's ought to work FB as well. Cheap, too.

Dennis

[Jim, W5JO]

Good to talk with you too, John.  I don't know why that circuit interesed me so much, but it is a way to put an SB 200-201 to work.  Too bad the tubes are so expensive but Dennis has a point about a way around the problem.  I wish someone with a 200 would try this so I could hear.  I bet it sounds good.