I am in need of a 60 watt mod xfmr. I want to use P-P 807's to modulate a
command transmitter about 120 watts input to the 1625s.

Just missed a new Triad unit on eBay due to dumb bidding. Stancore ,
Thordarson etc all fine.

Please state condition and price.

I have and ART-13 Mod xfmr but have no idea the pri and sec impedances.
Maybe it would work. Any ideas?

Ken NAØY

On Mon, 12 Apr 2004 10:57:25 -0500, "Ken Fattmann"
wrote:

I am in need of a 60 watt mod xfmr. I want to use P-P 807's to modulate a
command transmitter about 120 watts input to the 1625s.

Just missed a new Triad unit on eBay due to dumb bidding. Stancore ,
Thordarson etc all fine.

Please state condition and price.

I have and ART-13 Mod xfmr but have no idea the pri and sec impedances.
Maybe it would work. Any ideas?

Ken NAØY


It will work fine.

73
Gary K4FMX

"Ken Fattmann" wrote in message ...
I am in need of a 60 watt mod xfmr. I want to use P-P 807's to modulate a
command transmitter about 120 watts input to the 1625s.

Just missed a new Triad unit on eBay due to dumb bidding. Stancore ,
Thordarson etc all fine.

Please state condition and price.

I have and ART-13 Mod xfmr but have no idea the pri and sec impedances.
Maybe it would work. Any ideas?

Ken NAØY

The original ARC 5 mod transformer is perfect for this. seems that
they are hard to find..another idea is look for an old AM marine ship
to shore radiotelephone..there are lots of them somewhere,they are
obsolete. most common transmitter used pair 807s final and pair 807s
modulators..if you find one it will cost a whopping $20 or less.lots
of other good parts also..original marine freq. 2 to 3 mhz.AM at 150
watts input.. good luck 73 Harold W4PQW

Gary Schafer wrote in message . ..

It will work fine.

Hmmm...PP 807's @ same load Z as PP 811A triodes...interesting...

On 15 Apr 2004 08:45:07 -0700, wrote:

Gary Schafer wrote in message . ..

It will work fine.

Hmmm...PP 807's @ same load Z as PP 811A triodes...interesting...


It doesn't matter what the actual impedance of the modulator or the
final is. It is the ratio that matters.

The ART 13 transformer has a primary rated at 15000 ohms and the
secondary at 7300 ohms. That is a ratio of about 2:1.

The Johnson viking 2 (pair of 1625s modulating a pair of 6146s) used a
transformer with a ratio of around 2.4:1 or so if I remember right.
That was a little high as the modulators would go into clipping before
100% modulation could be achieved on that rig. A little lower ratio
mod transformer would have allowed a little more modulation.

So the ART 13 transformer is just about ideal for that kind of setup.

73
Gary K4FMX

Gary Schafer wrote:

Hmmm...PP 807's @ same load Z as PP 811A triodes...interesting...



It doesn't matter what the actual impedance of the modulator or the
final is. It is the ratio that matters.

The ART 13 transformer has a primary rated at 15000 ohms and the
secondary at 7300 ohms. That is a ratio of about 2:1.

The Johnson viking 2 (pair of 1625s modulating a pair of 6146s) used a
transformer with a ratio of around 2.4:1 or so if I remember right.
That was a little high as the modulators would go into clipping before
100% modulation could be achieved on that rig. A little lower ratio
mod transformer would have allowed a little more modulation.

So the ART 13 transformer is just about ideal for that kind of setup.

73
Gary K4FMX

One small thing, don't go too ape s*** crazy with substitutions.
You must understand that for a given wattage transformer core, higher
impedance windings will have more turns than lower impedance windings.

It wouldn't be ok to sub a 2:1 transformer that was meant for 10K
for a 2:1 that was meant for 1K. Not at the design power for the
transformer.

Why does this matter? Subbing a much higher impedance transformer
for a low impedance transformer will result in greater losses due
to the higher resistance of the windings. Subbing a low impedance
transformer for a much higher impedance transformer will likely result
in core saturation and loss problems due to the higher fluxes the
core sees. There aren't enough turns on the core.

Try find a sub that is close to the design impedance of your desired
transformer.

-Chuck Harris

On Thu, 15 Apr 2004 14:21:46 -0400, Chuck Harris
wrote:

Gary Schafer wrote:

Hmmm...PP 807's @ same load Z as PP 811A triodes...interesting...



It doesn't matter what the actual impedance of the modulator or the
final is. It is the ratio that matters.

The ART 13 transformer has a primary rated at 15000 ohms and the
secondary at 7300 ohms. That is a ratio of about 2:1.

The Johnson viking 2 (pair of 1625s modulating a pair of 6146s) used a
transformer with a ratio of around 2.4:1 or so if I remember right.
That was a little high as the modulators would go into clipping before
100% modulation could be achieved on that rig. A little lower ratio
mod transformer would have allowed a little more modulation.

So the ART 13 transformer is just about ideal for that kind of setup.

73
Gary K4FMX

One small thing, don't go too ape s*** crazy with substitutions.
You must understand that for a given wattage transformer core, higher
impedance windings will have more turns than lower impedance windings.

It wouldn't be ok to sub a 2:1 transformer that was meant for 10K
for a 2:1 that was meant for 1K. Not at the design power for the
transformer.

Why does this matter? Subbing a much higher impedance transformer
for a low impedance transformer will result in greater losses due
to the higher resistance of the windings. Subbing a low impedance
transformer for a much higher impedance transformer will likely result
in core saturation and loss problems due to the higher fluxes the
core sees. There aren't enough turns on the core.

Try find a sub that is close to the design impedance of your desired
transformer.

-Chuck Harris
------------------------------------------------

While it is true that there is a limit as to how far you can "stretch"
the impedance of a mod transformer before getting into trouble, you
can go an amazingly long ways.

As an interesting example: The Stancor Poly-Pedance transformer that
has multiple taps to obtain various impedance ratios (15 to 120 watt
series) uses the same taps for 2000 ohms primary to 1150 ohms
secondary (1.74:1 ratio), as it does for 20000 ohms primary to 11500
ohms secondary. Also the same 1.74:1 ratio! That's a 10:1 range!

The link below has the ART 13 and other transformer info.

http://www.amwindow.org/tech/htm/modtran/modtran.htm

Select Miscellaneous to find the ART 13 transformer specs and
connections.

Other transformers (stancor etc.) are listed also.

73
Gary K4FMX

Gary Schafer wrote:


Try find a sub that is close to the design impedance of your desired
transformer.

-Chuck Harris

------------------------------------------------

While it is true that there is a limit as to how far you can "stretch"
the impedance of a mod transformer before getting into trouble, you
can go an amazingly long ways.

As an interesting example: The Stancor Poly-Pedance transformer that
has multiple taps to obtain various impedance ratios (15 to 120 watt
series) uses the same taps for 2000 ohms primary to 1150 ohms
secondary (1.74:1 ratio), as it does for 20000 ohms primary to 11500
ohms secondary. Also the same 1.74:1 ratio! That's a 10:1 range!

The link below has the ART 13 and other transformer info.

http://www.amwindow.org/tech/htm/modtran/modtran.htm

Select Miscellaneous to find the ART 13 transformer specs and
connections.

Other transformers (stancor etc.) are listed also.

73
Gary K4FMX

Hi Gary,

Yep, you can get away with alot if you start with a transformer
that is overdesigned. The Stancor Poly-Pedance transformer must
have an excessive amount of iron for the 20K range, and an adequate
amount for the 2K range.

Not always the case. One would tend to think that the ART-13's
tranny would be built to be on the light side, being as it was
made to fly in an airplane. But I don't remember them being all
that light.

-Chuck Harris