On Fri, 20 Jan 2012, coffelt2 wrote:


"it9xxs" wrote in message
...

Hi, I'm looking for a low-power modulation transformer. I'd like to
build a QRP (5W?) tube AM transmitter for the 10m band. Thanks, 73s,
IT9XXS


Are there any old tube type CB radios around?

I suppose size might matter, but sometimes old tube type
power transformers can come up with a "close enough"
impedance ratio.

I barely see solid state CB sets around, so I suspect the
tube ones have long disappeared.

Besides, he's not in North America, and CB was mostly a North American
thing.

Another old time solution was to find a tube type speaker
output transformer, with the secondary on an outside winding
which could be stripped away, making room to add a new
secondary. (keep a log of turns removed on the old
secondary, so a good estimate of new turns required)
(to get impedances fairly close.. precision not required)

Or find a 400Hz transformer, nobody wanted them so at one time they were
not only available but cheap. Various articles said they worked fine,
since voice didn't have to go down to 60Hz.

Michael VE2BVW

On Jan 21, 9:56*am, Michael Black wrote:
On Fri, 20 Jan 2012, coffelt2 wrote:

"it9xxs" wrote in message
...

Hi, I'm looking for a low-power modulation transformer. I'd like to
build a QRP (5W?) tube AM transmitter for the 10m band. Thanks, 73s,
IT9XXS

Are there any old tube type CB radios around?

I suppose size might matter, but sometimes old tube type
power transformers can come up with a "close enough"
impedance ratio.

I barely see solid state CB *sets around, so I suspect the
tube ones have long disappeared.

Besides, he's not in North America, and CB was mostly a North American
thing.

Another old time solution was to find a tube type speaker
output transformer, with the secondary on an outside winding
which could be stripped away, making room to add a new
secondary. (keep a log of turns removed on the old
secondary, so a good estimate of new turns required)
(to get impedances fairly close.. precision not required)

Or find a 400Hz transformer, nobody wanted them so at one time they were
not only available but cheap. *Various articles said they worked fine,
since voice didn't have to go down to 60Hz.

* * Michael *VE2BVW

Get a single ended triode type of audio output transformer and drive
it from a hi-fi amp.