Hello Joe:

I question whether there is a problem with the driver transformer. What are
the symptoms, other than the different value of resistance? Is this just a
general check of everything or is the audio section having a problem.

There are a number of possibilities. First, the factory could have
substituted a different transformer from that specified. This happend more
than infrequently, in order to keep the rigs flowing. They are not
critical. Secondly, the ohmmeter might be something other than a pure dc,
in which case the resistance might not be correct when inductance is
involved. Another possibility is that the factory put the wrong transformer
in the case and it got mismakred - but it was close enough that it passed
factory specifications.

A shorted driver transformer could cause excessive current draw by the
driver tube, or distorted audio.

If the winding ratio was different than the one specified, that would not
cause any problem for the modulator, other than possibly lower audio because
there was less drive to the modulators.

The 1958 thordarson catalog (which is about the time the T-90 was made)
shows a number of driver transformers. None of them have numbers close to
the number you cited.


73, Colin K7FM

In article . net,
"COLIN LAMB" wrote:

I question whether there is a problem with the driver transformer. What are
the symptoms, other than the different value of resistance? Is this just a
general check of everything or is the audio section having a problem.


Hello, Colin. This is just a general check before applying power to it
for the first time. I wanted to fix any obvious faults before applying
power. (Building the power supply will be the next part of the project!)

I've decided to leave it in for now and (carefully) watch what happens.

A shorted driver transformer could cause excessive current draw by the
driver tube, or distorted audio.


Will put a Simpson 260 across the cathode resistor to watch for
excessive current.

If the winding ratio was different than the one specified, that would not
cause any problem for the modulator, other than possibly lower audio because
there was less drive to the modulators.


Good to know that. I see that Antique Electronic Supply sells a Hammond
124D driver transformer that looks to be pretty close, in case the
original really needs to be replaced.

The 1958 thordarson catalog (which is about the time the T-90 was made)
shows a number of driver transformers. None of them have numbers close to
the number you cited.


Thanks for checking. That's exactly the right time frame. I'd bet it was
a custom part, and won't appear in any catalog.

I appreciate your comments, Colin.

73,
Joe K9LY

Sorry I'm late to this thread but just for interest I checked my T-90. I
don't think you have a problem at all. I get 183 and 202 ohms. It works
fine with excellent modulation. All original parts other than the caps I
replaced and a few out of spec resistors.

Chuck...K1KW



"Joe L." wrote in message
...
In article . net,
"COLIN LAMB" wrote:

I question whether there is a problem with the driver transformer. What
are
the symptoms, other than the different value of resistance? Is this
just a
general check of everything or is the audio section having a problem.


Hello, Colin. This is just a general check before applying power to it
for the first time. I wanted to fix any obvious faults before applying
power. (Building the power supply will be the next part of the project!)

I've decided to leave it in for now and (carefully) watch what happens.

A shorted driver transformer could cause excessive current draw by the
driver tube, or distorted audio.


Will put a Simpson 260 across the cathode resistor to watch for
excessive current.

If the winding ratio was different than the one specified, that would
not
cause any problem for the modulator, other than possibly lower audio
because
there was less drive to the modulators.


Good to know that. I see that Antique Electronic Supply sells a Hammond
124D driver transformer that looks to be pretty close, in case the
original really needs to be replaced.

The 1958 thordarson catalog (which is about the time the T-90 was made)
shows a number of driver transformers. None of them have numbers close
to
the number you cited.


Thanks for checking. That's exactly the right time frame. I'd bet it was
a custom part, and won't appear in any catalog.

I appreciate your comments, Colin.

73,
Joe K9LY

In article ,
"Chuck - K1KW" wrote:

Sorry I'm late to this thread but just for interest I checked my T-90. I
don't think you have a problem at all. I get 183 and 202 ohms. It works
fine with excellent modulation. All original parts other than the caps I
replaced and a few out of spec resistors.


Thanks for taking the time to check your T-90, Chuck. Interesting
result. I hope to report that all is well with mine once it's fired up.

73, Joe K9LY