I acquired a GT550 along with its matching power supply about 10 years
ago from someone's garage. I've had the thing packed up for about the
same amount of time. I have the manual and tons of schematics along
with several hand drawn schematics from the previous owner(s) with
various notes and dates. I pulled it out over field day and turned it
on to listen to it next to the Alinco HF rig that hasn't been out in
at least 9 years to see if it still could hear. Surprisingly both
rigs worked and my oldest son, now 10 seems somewhat interested in the
hobby. Maybe he just likes all the dials and lights. :-) So, I'm
thinking I want to dig into this vintage radio and try to get it back
up to snuff as an electronics project for my oldest and I. Does
anyone have any hints and possibly and specific vendors that they've
had good luck with in the aid of restoring a vintage radio? Thanks in
advance and 73 de KE4RGH.

Hi. I remember the GT550; we had one at our high school ham club around
1975. It's nice that your son is showing some interest in the hobby.
Hopefully he'll be bitten by the bug.

Regarding your question, I think the answer depends on whether you're
looking for vendors to provide repair services, or to provide parts.
There are lots of parts vendors around. Digi-Key and Mouser are perhaps
the two biggest general-purpose electronic part suppliers who still deal
with small orders. They carry lots of resistors, capacitors,
semiconductors, and other general purpose items.

If you need parts that are specific to the GT550, you can post a message
here or at other ham-oriented sites like eHam or QRZ.com. Likewise if
you want to post technical questions as you try to repair the GT550 on
your own.

If you're looking for someone to ship the radio off to for repair, I've
heard of a few guys that offer repair service but I don't have any links
to offer you. Maybe someone else can assist.

73 & GL,
Joe K9LY



In article
,
William Stearns wrote:

I acquired a GT550 along with its matching power supply about 10 years
ago from someone's garage. I've had the thing packed up for about the
same amount of time. I have the manual and tons of schematics along
with several hand drawn schematics from the previous owner(s) with
various notes and dates. I pulled it out over field day and turned it
on to listen to it next to the Alinco HF rig that hasn't been out in
at least 9 years to see if it still could hear. Surprisingly both
rigs worked and my oldest son, now 10 seems somewhat interested in the
hobby. Maybe he just likes all the dials and lights. :-) So, I'm
thinking I want to dig into this vintage radio and try to get it back
up to snuff as an electronics project for my oldest and I. Does
anyone have any hints and possibly and specific vendors that they've
had good luck with in the aid of restoring a vintage radio? Thanks in
advance and 73 de KE4RGH.

"William Stearns" wrote in message
...
I acquired a GT550 along with its matching power supply about 10 years
ago from someone's garage. I've had the thing packed up for about the
same amount of time. I have the manual and tons of schematics along
with several hand drawn schematics from the previous owner(s) with
various notes and dates. I pulled it out over field day and turned it
on to listen to it next to the Alinco HF rig that hasn't been out in
at least 9 years to see if it still could hear. Surprisingly both
rigs worked and my oldest son, now 10 seems somewhat interested in the
hobby. Maybe he just likes all the dials and lights. :-) So, I'm
thinking I want to dig into this vintage radio and try to get it back
up to snuff as an electronics project for my oldest and I. Does
anyone have any hints and possibly and specific vendors that they've
had good luck with in the aid of restoring a vintage radio? Thanks in
advance and 73 de KE4RGH.

You will want to replace all the electrolytics in the rear apron mounted
audio board.
If you can find the xtal calibrator, it is a nice addition.
One of the flaws in this rig (and the SBE SB-34, and likely many other BA
xcvrs) is they have one adjustment that is to equalize the VFO for RX and
TX. This can only be done on one freq- above and below, there will be an
increasing delta between the two- w/o an RIT, this is problematical.
The 2 planetary drives in series always seem to develop backlash over time-
keep them lubricated and reduce friction along the drive train as much as
possible.
Wonderful looking rigs though.

Dale W4OP

You will want to replace all the electrolytics in the rear apron mounted
audio board.
If you can find the xtal calibrator, it is a nice addition.
One of the flaws in this rig (and the SBE SB-34, and likely many other BA
xcvrs) is they have one adjustment that is to equalize the VFO for RX and
TX. This can only be done on one freq- above and below, there will be an
increasing delta between the two- w/o an RIT, this is problematical.
The 2 planetary drives in series always seem to develop backlash over
time- keep them lubricated and reduce friction along the drive train as
much as possible.
Wonderful looking rigs though.

Dale W4OP


In addition:

Replace any waxed/paper caps (typically used in coupling of stages, cathode
bypass, etc). And check all the carbon composition resistors for tolerance.
They tend to drift higher. If you replace any resistors use a non inductive
resistor (carbon compositions) in circuits above....say...18mhz or less.
Mica and ceramic caps should be OK. They age well over time.

See these pages of my experiences for some possible tips from different
gear.
http://www.ppinyot.com/H/hammarlund.htm transmitter.
http://www.ppinyot.com/N/national/national.htm Rcvr
http://www.ppinyot.com/H/sx_71.htm Rcvr.

Good Luck,

Paul P

William Stearns wrote:

up to snuff as an electronics project for my oldest and I. Does
anyone have any hints and possibly and specific vendors that they've
had good luck with in the aid of restoring a vintage radio? Thanks in
advance and 73 de KE4RGH.

Hi,
I've never worked on a GT550 but I've done three of the Galaxy V models
which I think are somewhat similar in many respects. The main gotcha
that I encountered was a bad output bandswitch on 2 of the 3. Its a
rather under-rated looking rotary switch and not impossible to find a
replacement for.
Don't know if the GT550 uses the same switch but I thought I'd mention it.

I love the silky tuning and the way the dial is backlit on the Galaxy V
models! I had the hots for the 550 when I started hamming.

Oh, on the dual vernier drives if they are goofed up...I've heard of
guys prying them open for cleaning. I've never had to, though.
Sometimes just an extra little crimping tighter helps a worn one. At
any rate, you can find them easily enough if you need to replace them.

Good luck with it!

-Bill

"Paul P" REMOVE paul @ REMOVE ppinyot . REMOVEcom wrote in message
...

And check all the carbon composition resistors for tolerance.
They tend to drift higher. If you replace any resistors use a non
inductive resistor (carbon compositions) in circuits
above....say...18mhz or less.


Ordinary film resistors, either carbon film or metal film, will work
fine. The inductance is not significant unless the value is below 100
ohms. Above this value,
shunt capacitance dominates the impedance. A ten ohm resistor starts
becoming inductive around 20 MHz and a 1 ohm resistor starts becoming
inductive over 1 MHz. If your email works, I'll send you some graphs.

73, Barry WA4VZQ

"Dr. Barry L. Ornitz" wrote in message
...
"Paul P" REMOVE paul @ REMOVE ppinyot . REMOVEcom wrote in message
...

And check all the carbon composition resistors for tolerance.
They tend to drift higher. If you replace any resistors use a non
inductive resistor (carbon compositions) in circuits above....say...18mhz
or less.


Ordinary film resistors, either carbon film or metal film, will work fine.
The inductance is not significant unless the value is below 100 ohms.
Above this value,
shunt capacitance dominates the impedance. A ten ohm resistor starts
becoming inductive around 20 MHz and a 1 ohm resistor starts becoming
inductive over 1 MHz. If your email works, I'll send you some graphs.

73, Barry WA4VZQ


Barry,

Graphs would be good. Graphs would be much appreciated.

I have been on many manufacture's web sites looking for their published
tests. I even emailed Ohmite about their OX line and received a polite
reply about their test tech using their impedance bridge and what he/she
found. But they could (would?) not supply and published data. So I must
take it on their word.
http://www.ohmite.com/cgi-bin/showpa...t=ox_oy_series

I have brought this discussion to other newsgroups to receive comments and
opinions devoid of hard data. Not that I am complaining. I cant seem to
easily put my finger on any myself.

I realize that even carbon comps have inductive qualities at certain
frequencies and at certain lead lengths. Exactly what they are? I do not
have that data either.

I prefer facts to guesses. And guessing and a few bad experiences is all I
have to go on at this time. So I am left with establishing some criteria
for my self that I am sure can be a bit of over compensation.

It is well accepted that wire wound resistors are inductive. It seems to me
that a spiral carbon conductor around a ceramic core would set up an
impedance starting at some frequency. So when replacing resistors in the
front end of a Hallicrafters or Hammarlund that is above 18 MHz (18 MHz
selected because no carbon film resistor has given me any grief in a finicky
Transoceanic) I am not going to take the chance (again) until I see some
welcome hard data or spend the time required doing A/B comparisons and
testing.

And I would like to post your graphs, with permission and due credit, on my
web site for all to benefit.

Thank you in advance for the extra digging,

email: paul at ppinyot dot com.

Paul P.
www.ppinyot.com