I have a Passion PAK-A11 power amplifier that one of the out put
transformers has failed. The amp is a push pull design using paired KT88
tubes in the out put stage. The transformer is ultralinear with 6500 ohms
input impedance and has 45 audio watts. I am unable to find a Passion
transformer at an affordable price, so I want to replace both output
transformers with Hammond 1650 series. Hammond has two that might work:

1.) # 1650H, 40 audio watts, 6600 ohms input impedance ultralinear
(recommended two tubes 6L6GC or EL34)

2.) # 1650P, 60 audio watts, 6600 ohms input impedance ultralinear
(recommended two tubes 6L6GC, EL34 or KT88)

My question is can I get by with the lower watt transformer as it will fit
in the available space better or go with the 60 watt design? Any other
suggestions? Thanks for your help

Mike

Kettneraspis wrote:

I have a Passion PAK-A11 power amplifier that one of the out put
transformers has failed. The amp is a push pull design using paired KT88
tubes in the out put stage. The transformer is ultralinear with 6500 ohms
input impedance and has 45 audio watts. I am unable to find a Passion
transformer at an affordable price, so I want to replace both output
transformers with Hammond 1650 series. Hammond has two that might work:

1.) # 1650H, 40 audio watts, 6600 ohms input impedance ultralinear
(recommended two tubes 6L6GC or EL34)

2.) # 1650P, 60 audio watts, 6600 ohms input impedance ultralinear
(recommended two tubes 6L6GC, EL34 or KT88)

My question is can I get by with the lower watt transformer as it will fit
in the available space better or go with the 60 watt design? Any other
suggestions? Thanks for your help

I'd buy the bigger ones because its good practice to choose as much iron as
possible.
Warn the moths in your purse of a change of address....
The 1650P are 8 lbs, and 3.5Kg, while the H are 6.5 lbs, or a puny 2.9Kg,
and my idea of a decent OPT for a pair of KT88 starts with OPT weight at
4.5Kg, which is barely enough.
Hammond themsleve do not recommend the use of KT88 wuth the 1650H.
See
http://www.hammondmfg.com/1608.htm

If you find the larger 1650P has to be too close to hot tubes, say less than
5mm, then perhaps you are forced to use the smaller ones, But even if
clerances are tight, the OPT will take all night to heatup inside even though
the outside is close to the tubes, so it still is doable to have the OPT close
to tubes.

Just watch out for instablity when you substitute the old OPTs, unless you
know about stablity and FB
you may find the amp will oscillate unless just the right compensation values
of R&C are used around the circuit
to suit the OPT.

With such values correctly chosen, the amp should not be able to be provoked
into
any HF or LF oscillations without a load at all and should not oscillate with
0.22 uF
across the output terminals with no other load.

If you don't know how to set up the new OPT to get **unconditional**
stability,
then take it to someone who knows all about it, or be prepared to learn a lot,
or put up with some smoke....

Goodnight and goodluck,

Patrick Turner.





Mike

Thanks Patrick. I will try the larger OPT's.
Mike


"Patrick Turner" wrote in message
...


Kettneraspis wrote:

I have a Passion PAK-A11 power amplifier that one of the out put
transformers has failed. The amp is a push pull design using paired KT88
tubes in the out put stage. The transformer is ultralinear with 6500 ohms
input impedance and has 45 audio watts. I am unable to find a Passion
transformer at an affordable price, so I want to replace both output
transformers with Hammond 1650 series. Hammond has two that might work:

1.) # 1650H, 40 audio watts, 6600 ohms input impedance ultralinear
(recommended two tubes 6L6GC or EL34)

2.) # 1650P, 60 audio watts, 6600 ohms input impedance ultralinear
(recommended two tubes 6L6GC, EL34 or KT88)

My question is can I get by with the lower watt transformer as it will
fit
in the available space better or go with the 60 watt design? Any other
suggestions? Thanks for your help

I'd buy the bigger ones because its good practice to choose as much iron
as
possible.
Warn the moths in your purse of a change of address....
The 1650P are 8 lbs, and 3.5Kg, while the H are 6.5 lbs, or a puny 2.9Kg,
and my idea of a decent OPT for a pair of KT88 starts with OPT weight at
4.5Kg, which is barely enough.
Hammond themsleve do not recommend the use of KT88 wuth the 1650H.
See
http://www.hammondmfg.com/1608.htm

If you find the larger 1650P has to be too close to hot tubes, say less
than
5mm, then perhaps you are forced to use the smaller ones, But even if
clerances are tight, the OPT will take all night to heatup inside even
though
the outside is close to the tubes, so it still is doable to have the OPT
close
to tubes.

Just watch out for instablity when you substitute the old OPTs, unless you
know about stablity and FB
you may find the amp will oscillate unless just the right compensation
values
of R&C are used around the circuit
to suit the OPT.

With such values correctly chosen, the amp should not be able to be
provoked
into
any HF or LF oscillations without a load at all and should not oscillate
with
0.22 uF
across the output terminals with no other load.

If you don't know how to set up the new OPT to get **unconditional**
stability,
then take it to someone who knows all about it, or be prepared to learn a
lot,
or put up with some smoke....

Goodnight and goodluck,

Patrick Turner.





Mike