I've acquired a high power 50 watts plus tube type hifi output
transformer. I'd like to try modulating a pair of 6146's with a hifi
amp. The circuits I see use a modulating inductor in series with the B+
to the final to keep single ended dc off the transformer secondary.

Here's the rub. Where do you find a 30-50 henry inductor for 800+ volts?
I was thinking of checking out the secondary of a tv transformer? (Not
many left used to be common whatever happened to those tv's).

Anyone have any ideas on winding one? Seems to me taking an old
transformer apart and scramble winding as much wire as one can afford
might do the trick?

Ideas?


Thanks,


Tony,

WA6LZH

Where did you get the 30-50 henry inductor figure?

www.telstar-electronics.com

I assume you are talking AM modulation and that you really want plate
modulation.

Otherwise you are discovering why screen modulation was so popular
with 6146 finals!

de W8CCW John

On Thu, 18 May 2006 19:56:21 -0700, Tony Angerame
wrote:

I've acquired a high power 50 watts plus tube type hifi output
transformer. I'd like to try modulating a pair of 6146's with a hifi
amp. The circuits I see use a modulating inductor in series with the B+
to the final to keep single ended dc off the transformer secondary.

Here's the rub. Where do you find a 30-50 henry inductor for 800+ volts?
I was thinking of checking out the secondary of a tv transformer? (Not
many left used to be common whatever happened to those tv's).

Anyone have any ideas on winding one? Seems to me taking an old
transformer apart and scramble winding as much wire as one can afford
might do the trick?

Ideas?


Thanks,


Tony,

WA6LZH
John Ferrell W8CCW

Yes... I think he should seriously consider low-level modulation
instead of high-level modulation.

www.telstar-electronics.com

On 19 May 2006 10:32:56 -0700, "Telstar Electronics"
wrote:

Yes... I think he should seriously consider low-level modulation
instead of high-level modulation.

www.telstar-electronics.com

Looking at your web site I see you seem to manufacture CB amplifiers?
I also see you fail to post the 3rd and 5th order intermodulation
performance info. They must be pretty bad.
Also no low pass filter to attenuate the harmonics. -30 db second and
third harmonics are unacceptable. And those are at below power spec
on the amplifier.

How do you measure peak envelope power?
Where do you come up with PEP at 3 times carrier power?
What makes you think that PEP is going to be any greater than the CW
power output capability of the amplifier?

73
Gary K4FMX

"John Ferrell" wrote in message
...
I assume you are talking AM modulation and that you really want plate
modulation.

Otherwise you are discovering why screen modulation was so popular
with 6146 finals!

de W8CCW John


I suspect he is talking Heising modulation, which normally is used
with a single-ended Class A modulator whose plate is directly tied
to the PA plate (the choke is used to provide a high impedance to
the filter chokes. But, what I wonder, a 50 watt tube audio amp is
very substantial, and is probably running Class B P-P. I don't see
how Heising modulation would work in that application.

Pete

Tony

What you need to do is to find a universal modulation transformer and
replace the audio output transformer used on the audio amplifier. That is
the most practical solution to your quest.

Pete

"Tony Angerame" wrote in message
...
I've acquired a high power 50 watts plus tube type hifi output
transformer. I'd like to try modulating a pair of 6146's with a hifi
amp. The circuits I see use a modulating inductor in series with the B+
to the final to keep single ended dc off the transformer secondary.

Here's the rub. Where do you find a 30-50 henry inductor for 800+ volts?
I was thinking of checking out the secondary of a tv transformer? (Not
many left used to be common whatever happened to those tv's).

Anyone have any ideas on winding one? Seems to me taking an old
transformer apart and scramble winding as much wire as one can afford
might do the trick?

Ideas?


A blast from the past: Oftentimes the voltage rating of chokes was more
a limitation of breakdown from conductor/windings to the core or case rather
than interwinding breakdown. So........... a quick method of cheating on the
rating was to mount the choke on standoff insulators or at least insulating
the choke from any metal in the chassis or frame of the RF or modulator
deck. Only thing then is to be sure to treat that choke core or case as if
it might be at high voltage potential......yikes!
Although Choke modulation (or Heising as one respondent mentioned) is
"high level" modulation if applied to the RF final plate/s, it takes a lot
of tinkering to achieve 100% modulation (balanced, above and below zero).
Almost always a compromise in Amateur gear, and some broadcast gear came
close, but at great expense.
Many will throw rocks at me for this, but "low level" modulation is a
huge waste of RF power, and in the good (?) old days, was just another
weakly modulated hetrodyne the howling AM section of the bands. OH, OUCH,
OWEE, HEY!
Old Chief Lynn W7LTQ

Enjoyed reading your post Lynn...

www.telstar-electronics.com

Low level modulation is a huge waste of RF power?? Hey, _AM_ is a huge
waste of RF power, and of spectrum to boot! Except with unusual
modulating waveforms, 2/3 of the power is in a useless carrier. Now,
compared with plate modulation of the PA, low level AM modulation
followed by a linear amp may be somewhat less efficient (though a waste
of DC power, not RF power), but remember, the modulator, presumably
being a linear audio amplifier, isn't all that efficient either. In
addition, there ARE ways to generate AM with low level modulation and
efficient RF amplification--they have been used in AM broadcast
transmitters.

For the cost of a good high-level modulator, how many kilowatt-hours
can you buy?

Cheers,
Tom