Transformer replacement
 

I have an HF amp that uses a single 811A in grounded grid. The power
transformer smoked. The transformer was from an old TV set I think it
was rated at 540VAC on the sec and I ran it into a voltage doubler for
about 1300 VDC . Any info on something I could use as a replacement
would be appreciated.

Jimmie

Transformer replacement
 

JIMMIE wrote:
I have an HF amp that uses a single 811A in grounded grid. The power
transformer smoked. The transformer was from an old TV set I think it
was rated at 540VAC on the sec and I ran it into a voltage doubler for
about 1300 VDC . Any info on something I could use as a replacement
would be appreciated.

Jimmie

There's an ample supply of used xfmrs at PTOP oldradioparts.com

I recently got one for my homebrew xmtr. You might have to buy some
other stuff to reach the $20 minimum order. I have never failed to find
other things that I 'need'.

-Bill

Transformer replacement
 

On Apr 18, 9:22 pm, JIMMIE wrote:
I have an HF amp that uses a single 811A in grounded grid. The power
transformer smoked. The transformer was from an old TV set I think it
was rated at 540VAC on the sec and I ran it into a voltage doubler for
about 1300 VDC . Any info on something I could use as a replacement
would be appreciated.

Jimmie

Andy comments:

You might investigate using a high voltage transformer from an old
microwave oven...... If the secondary voltage turns out to be too
great,
their construction makes it fairly easy to remove some turns...

I haven't tried this, .... just something to consider..

Andy W4OAH

Transformer replacement
 

AndyS wrote:
On Apr 18, 9:22 pm, JIMMIE wrote:
I have an HF amp that uses a single 811A in grounded grid. The power
transformer smoked. The transformer was from an old TV set I think it
was rated at 540VAC on the sec and I ran it into a voltage doubler for
about 1300 VDC . Any info on something I could use as a replacement
would be appreciated.

Jimmie

Andy comments:

You might investigate using a high voltage transformer from an old
microwave oven...... If the secondary voltage turns out to be too
great,
their construction makes it fairly easy to remove some turns...

I haven't tried this, .... just something to consider..

Andy W4OAH


Hmmm....come to think of it - they tend to go to 1000V AC secondaries -
but there is plenty of stray magnetic circuit usually provided which
might need knocking out of the core...

Brian W

Transformer replacement
 

On Apr 18, 10:22 pm, JIMMIE wrote:
I have an HF amp that uses a single 811A in grounded grid. The power
transformer smoked. The transformer was from an old TV set I think it
was rated at 540VAC on the sec and I ran it into a voltage doubler for
about 1300 VDC . Any info on something I could use as a replacement
would be appreciated.

Jimmie
HEY OM:
My choice is a MOT, with zero crossing phase controlled primary with
lots of snubbers and filters. Put the MOT in a box with a fan. A zero
crossing traic opto coupler regulated by a TL431 with an inverter pass
transistor. Power the TL431 seperately and make sure your voltage
divider resistors can handle the voltage, I use 1 meg 1/4 watt. they
can handle about 200 volts a piece. An MOT can put out up to 2400 VDC
no load depending on the type. You going to need a 25amp traic at
600prv or more. You can figure the TL431 to regulate that puppy at
1300VDC easy. And the zero crossing traic opto coupler gives you
tonnes of isolation. Been there done that.

73 OM
n8zu

Transformer replacement
 

JIMMIE wrote:
I have an HF amp that uses a single 811A in grounded grid. The power
transformer smoked. The transformer was from an old TV set I think it
was rated at 540VAC on the sec and I ran it into a voltage doubler for
about 1300 VDC . Any info on something I could use as a replacement
would be appreciated.

Jimmie
http://www.antekinc.com/details.php?p=92
I was thinking of using this transformer for the same purpose.
I assume this is the single 811A amplifier in the 1967 ARRL handbook?
If you use this transformer you can put the secondary windings in series
and use a bridge rectifier instead of the voltage doubler. You will get
slightly higher voltage this way (the tube won't mind). I think this
transformer might be able to handle TWO 811A's in parallel if you want
to beef up the amp.

Transformer replacement
 

On Apr 18, 10:22*pm, JIMMIE wrote:
I have an HF amp that uses a single 811A in grounded grid. The power
transformer smoked. The transformer was from an old TV set I think it
was rated at 540VAC on the sec and I ran it into a voltage doubler for
about 1300 VDC *. Any info on something I could use as a replacement
would be appreciated.

Jimmie

I found a transformer that would work out in the barn but it is
freaking huge, I would never get it in the box.

Jimmie

Transformer replacement
 

On Apr 19, 7:10*pm, Kenneth Scharf wrote:
JIMMIE wrote:
I have an HF amp that uses a single 811A in grounded grid. The power
transformer smoked. The transformer was from an old TV set I think it
was rated at 540VAC on the sec and I ran it into a voltage doubler for
about 1300 VDC *. Any info on something I could use as a replacement
would be appreciated.

Jimmie

http://www.antekinc.com/details.php?p=92
I was thinking of using this transformer for the same purpose.
I assume this is the single 811A amplifier in the 1967 ARRL handbook?
If you use this transformer you can put the secondary windings in series
and use a bridge rectifier instead of the voltage doubler. *You will get
* slightly higher voltage this way (the tube won't mind). *I think this
transformer might be able to handle TWO 811A's in parallel if you want
to beef up the amp.

Yes that is the one, more or less, Back when I was in high school I
built it as a CB amplifier in my junior year 69-70, Im so ashamed. I
do have another power supply I might could use with it. Its built in a
rack mount chassis and would not be my first choice. Ive found 200W
PEP to be more than adequate but I may consider that option. I wanted
to complete the amplifier by adding the rest of the ham bands.\\

Jimmie

Transformer replacement
 

On Apr 18, 10:22*pm, JIMMIE wrote:
I have an HF amp that uses a single 811A in grounded grid. The power
transformer smoked. The transformer was from an old TV set I think it
was rated at 540VAC on the sec and I ran it into a voltage doubler for
about 1300 VDC *. Any info on something I could use as a replacement
would be appreciated.

Jimmie

Ive got a couple of Variacs less the mechanical bits. I was
considering the possibility of winding a secondary on these.

Jimmie

Transformer replacement
 

On Apr 19, 12:30*pm, AndyS wrote:
On Apr 18, 9:22 pm, JIMMIE wrote:

I have an HF amp that uses a single 811A in grounded grid. The power
transformer smoked. The transformer was from an old TV set I think it
was rated at 540VAC on the sec and I ran it into a voltage doubler for
about 1300 VDC *. Any info on something I could use as a replacement
would be appreciated.

Jimmie

Andy comments:

* You might investigate using a high voltage transformer from an old
microwave oven...... *If the secondary voltage turns out to be too
great,
their construction makes it fairly easy to remove some turns...

* *I haven't tried this, .... just something to consider..

* * * * * * * * * * Andy W4OAH

Was also going to suggest an ex-microwave oven transf. Have a number
of scrapped microwave transformers.
Here (Canada) I've checked the ratio between the 115 volt input
winding and the secondary and it's close to 1:20.
In a 230 volt country I guess it would be around 1:10???
The secondary is therefore around 2200 volts RMS. That's toot high;
but if that was half wave rectified through a single diode with a
choke input filtering circuit etc. and capacitors with sufficient
voltage rating you might end up with a suitable 1300 volts or so?
Alternatively various methods of reducing the input voltage from 115
or 230 volts could be experimented with. Voltage bucking (opposing),
removing turns from the secondary or maybe even some sort of voltage
dropping circuit in the input winding?
Of course the 811A needs heater voltage from somewhere as well!
Just thinking out loud!

Transformer replacement
 

On Apr 18, 10:22*pm, JIMMIE wrote:
I have an HF amp that uses a single 811A in grounded grid. The power
transformer smoked. The transformer was from an old TV set I think it
was rated at 540VAC on the sec and I ran it into a voltage doubler for
about 1300 VDC *. Any info on something I could use as a replacement
would be appreciated.

Jimmie

I never did get a chance to see if my idea would work, I found a
suitable replacement transformer and then gave up on the idea until
next time. It did seem that getting enough wire wound in the core
could be a problem. It may be possible but I don't think that the 1KW
transformer I had could be used at that power level. I guessing at
maybe 30 to 40% of the max .

Jimmie