Design help: Modulator schematic
 

Reference "Design Help" thread in rar+p

Thanks for any advice you may have.
--
Say no to institutionalized interference.
Just say NO to HD/IBOC!

Design help: Modulator schematic
 

"Brenda Ann" wrote in message
...

Reference "Design Help" thread in rar+p

Thanks for any advice you may have.

Just noticed I forgot to draw in the caps across the diodes in the
schematic. There is a .047/630V cap across each diode.

Design help: Modulator schematic
 

As others in the other group have mentioned, you're pushing your luck with
600V diodes. They have over 700V on them (or they would have if things were
working right). Replace them with 1000V diodes. This also means you need
to replace those capacitors with 1000V capacitors, preferably AC rated.

As someone else said, you have a major problem with the power supply. The
output voltage should be much higher.

--
Jim Mueller

To get my real email address, replace wrongname with eportiz. Then replace
nospam with sacbeemail.

"Brenda Ann" wrote in message
...

"Brenda Ann" wrote in message
...

Reference "Design Help" thread in rar+p

Thanks for any advice you may have.

Just noticed I forgot to draw in the caps across the diodes in the
schematic. There is a .047/630V cap across each diode.

Design help: Modulator schematic
 

"Jim Mueller" wrote in message
...
As others in the other group have mentioned, you're pushing your luck with
600V diodes. They have over 700V on them (or they would have if things
were working right). Replace them with 1000V diodes. This also means you
need to replace those capacitors with 1000V capacitors, preferably AC
rated.

As someone else said, you have a major problem with the power supply. The
output voltage should be much higher.

--

I think I have kenned out what that problem IS. It's not a 250-0-250.. it's
a 125-0-125 on the secondary.. which would output pretty much what I'm
getting.

Design help: Modulator schematic
 

"Brenda Ann" wrote in message
...

"Jim Mueller" wrote in message
...
As others in the other group have mentioned, you're pushing your luck
with 600V diodes. They have over 700V on them (or they would have if
things were working right). Replace them with 1000V diodes. This also
means you need to replace those capacitors with 1000V capacitors,
preferably AC rated.

As someone else said, you have a major problem with the power supply.
The output voltage should be much higher.

--

I think I have kenned out what that problem IS. It's not a 250-0-250..
it's a 125-0-125 on the secondary.. which would output pretty much what
I'm getting.


This is my transformer. From Mouser

http://www.hammondmfg.com/pdf/5c0030.pdf #261G6
261G6 45250V C.T.@ 130 ma 6.3V @ 2A 1 4.00 2.50 2.63 3.56 2.0

Design help: Modulator schematic
 

"Brenda Ann" wrote in message
...

"Brenda Ann" wrote in message
...

"Jim Mueller" wrote in message
...
As others in the other group have mentioned, you're pushing your luck
with 600V diodes. They have over 700V on them (or they would have if
things were working right). Replace them with 1000V diodes. This also
means you need to replace those capacitors with 1000V capacitors,
preferably AC rated.

As someone else said, you have a major problem with the power supply.
The output voltage should be much higher.

--

I think I have kenned out what that problem IS. It's not a 250-0-250..
it's a 125-0-125 on the secondary.. which would output pretty much what
I'm getting.


change it to a bridge rectifier across the whole 250V winding, and
everything should work fine!


This is my transformer. From Mouser

http://www.hammondmfg.com/pdf/5c0030.pdf #261G6
261G6 45250V C.T.@ 130 ma 6.3V @ 2A 1 4.00 2.50 2.63 3.56 2.0

Design help: Modulator schematic
 

"maxhifi" wrote in message
news:U5fsi.22399$_d2.19727@pd7urf3no...
change it to a bridge rectifier across the whole 250V winding, and
everything should work fine!


*repeatedly kicks self in arse for not thinking of that in the first
place.... * It did clear up almost every issue I was having. Next thing I
think I'll do is add negative feedback.

Design help: Modulator schematic
 

"Brenda Ann" wrote

As others in the other group have mentioned, you're pushing your luck
with 600V diodes. They have over 700V on them (or they would have if
things were working right). Replace them with 1000V diodes. This also
means you need to replace those capacitors with 1000V capacitors,
preferably AC rated.

As someone else said, you have a major problem with the power supply.
The output voltage should be much higher.

--

I think I have kenned out what that problem IS. It's not a 250-0-250..
it's a 125-0-125 on the secondary.. which would output pretty much what
I'm getting.


This is my transformer. From Mouser

http://www.hammondmfg.com/pdf/5c0030.pdf #261G6
261G6 45250V C.T.@ 130 ma 6.3V @ 2A 1 4.00 2.50 2.63 3.56 2.0



What is the modulation transformer you're using?

If it's a mains transformer it could be going into saturation. Proper
modulation transformers are designed to accomodate a d.c. bias through the
windings which normally requires an airgap in the core. In an ungapped core
the dc bias will drive the core somewhere up the BH curve and the effects
will be exactly as you describe - clipping on one of the peaks

Design help: Modulator schematic
 

Brenda Ann,

There are several ways to go here. First, the specs for the
modulation transformer- impedance, watts, and if it is for push-pull or
single-ended. From that, we can get the right tubes, maybe a pair of 6V6 or
6AQ5. Those tubes are happy with 185 volts. If your modulation transformer
can use the 6L6, you can easily change the power supply circuit to a "Full
Wave Voltage Doubler" and I can e-mail the RCA circuit. Is this circuit
designed so the current for the 6L6 and the current for the transmitter tube
are on separate windings that cancel each other out? The transmitter may be
a bigger headache than the modulator, and this power transformer may limit
the choices, as it is small.
Don

As someone else said, you have a major problem with the power supply.
The output voltage should be much higher.

I think I have kenned out what that problem IS. It's not a 250-0-250..
it's a 125-0-125 on the secondary.. which would output pretty much what
I'm getting.

This is my transformer. From Mouser

http://www.hammondmfg.com/pdf/5c0030.pdf #261G6
261G6 45250V C.T.@ 130 ma 6.3V @ 2A 1 4.00 2.50 2.63 3.56 2.0

What is the modulation transformer you're using?

If it's a mains transformer it could be going into saturation. Proper
modulation transformers are designed to accomodate a d.c. bias through the
windings which normally requires an airgap in the core. In an ungapped
core the dc bias will drive the core somewhere up the BH curve and the
effects will be exactly as you describe - clipping on one of the peaks

Design help: Modulator schematic
 

What is the modulation transformer you're using?

If it's a mains transformer it could be going into saturation. Proper
modulation transformers are designed to accomodate a d.c. bias through the
windings which normally requires an airgap in the core. In an ungapped
core the dc bias will drive the core somewhere up the BH curve and the
effects will be exactly as you describe - clipping on one of the peaks

I don't have exact specs on it. It's a Stancor, an actual modulation
transformer with isolated secondary so that the RF final could be run off a
different B+ supply if desired. I bought the transformer from a ham who had
pulled it from an AM rig that used sweep tube outputs, and he had assured me
that the match to a 6L6 would be good on both primary and secondary. Perhaps
I can get a mH reading on it with my LCR meter, and someone can do the math
for me.. I haven't used that math in many many years, and it's left me, I'm
afraid.