[AMRadio] single 833

k9muf at comcast.net k9muf at comcast.net
Mon Feb 9 17:19:17 EST 2009

I built a transmitter with a single 833A modulated by a pair of 810s. I chose that combination of tubes because of their looks and also because they do not require any forced air cooling.
I put windows in front of the tubes so one can see the tubes glow.What a beautiful sight.

I used my own design based on ideas from many of the old handbooks, mostly the Editors and Engineers. Most of the information was not specific to an 833A but to triodes in general. The circuit was varied to fit the parts I had on hand and to the specifications of the 833A.

I used a modulation transformer and reactor from a 1kw broadcast transmitter. 
I am using a pair of 6L6s to drive the 810s. For the interstage transformer I rewound the secondary of an output transformer from an old broadcast receiver that used a pair of 6L6s in the output stage.

I am using a common plate power supply for both the RF and modulator tubes that puts out about 2200 volts.

The RF carrier power is about 300 watts when driven with about 35 watts.

Now here is the problem I am having with it. 
I am getting acoustical talkback when it is modulated and I can't find out where it is coming from. I have temporarily substituted a different mod transformer and bypassed the mod reactor, but I am still getting it. 
So that is where I am at now. I don't want to put it on the air until I get that problem resolved.

Don    K9MUF

----- Original Message -----

From: Mike Sawyer 

To: Discussion of AM Radio in the Amateur Service 

Sent: Mon, 9 Feb 2009 21:13:24 +0000 (UTC)

Subject: Re: [AMRadio] single 833

I always wanted a rig that uses the 833. It such a neat and different tube. 

I have a good supply of 810's so I figured a pair will modulate one nicely. 

I like the BTA-500/1MX's. As a matter of fact, I was supposed to be wheeling 

and dealing on a -500MX with Eric, WB4VVI (SK) before he went SK. Oh well. I 

like the prospects of the 810's and the single 833. It won't weigh near as 

much as one of those boxes. I have some nice black krinkle panels so a 

krinkle motif is in the cards.




----- Original Message ----- 

From: "John Lyles" 


Sent: Monday, February 09, 2009 9:39 AM

Subject: [AMRadio] single 833

There's a fellow near me that built a single 833 modulated by a single 833, 

one of a class A bias-changing heising design. I gave him a big reactor for 

it. I can get details if anyone wants.




on the road from Oklahoma City this morning


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