Heathkit GR-681 TV schematic?

Hello,
I have a curbside find...chassis of a Heathkit GR-681 TV. Pretty well
stripped, but this on had the transformers, and lots of caps, resistors and
other small goodies. Also had the HV supply (this is surplus as far as I'm
concerned, read on).

My interest is in figuring out if I've got stuff that could be used to make
a homebrew guitar amp (low output is fine), but I don't have any info on the
transformers. I'm seeking possibly a schematic and even better info about
what's what on the transformers. I've got five pieces of iron that I'm
trying to figure out. Any help would be appreciated. Thanks.

Power transformer
94-143 (hard to read)
394-7242 (Foster, 42nd wk, 1972)
lots of wires (10 in all)

Filament transformer
54-275
549-7249 (Midwest Coil & Transformer, 49th wk 1972)

Vertical output transformer (any possible audio use?)
51-158
549-7304 (Midwest, 4th wk 1973)
six wires on the secondary

Audio Transformer
51-157
60-7301 (Mfg? 1st wk 1973)
H2A2B
Terminals #1 , #2 on once side
Terminals in this order on the other side #3 #5 #4

Choke
45-52
60-7240 (mfg? 40th wk 1972)
H2C1
What rating?

 

One man's junk is another man's gold!

 

Only if I can figure out what I've got!

 

update: p/n is probably 54-243; Herm from Foster emailed me today, so maybe
I'll get lucky :~} Still looking for help on the rest.

 

Can't you just use a voltmeter to identify the voltages on the power
and filament transformers? The colors should indicate center taps.

 

Mike,
I've got a bit electronics experience, but feel out of my depth here. I've
been dabbling in this for about 2 years, so there are many things others
take for granted that I'm clueless about. These trannys are all pulled from
the chassis, so there are no hints except for the PT and the VOT which both
had the yellow wire soldered to the chassis. I'm not clear what the yellow
to chassis tells me. You say the colors should indicate center taps. Which
(typical) colors? What are the indicators?

Also, I think you are assuming that I've got AC running on the primary. I'm
not sure which wires are the primary, so I don't know how to hook them up.
If I did, I could bolt the trannys to a board and start figuring it out.
For example, how do I identify the primary on the PT when all the wires come
out of one hole? Should I remove the cover and look inside? What are the
chances that I'll get the cover back on OK? How do I figure out the rating
of the choke? How do I figure out the secondary taps on the audio OT? I
think you get the drift. I need some pointers or even some reading about
this. Willing to help?

Thanks.
Phil

 

Power and filament transformers almost always run from the AC
line, so let's assume you can use your standard AC voltage. On
a typical power transformer, the black leads are primary -- sometimes
you'll find a centertap, often black with a colored stripe, so you can
use the transformer for 117 or 234 volts. Though it's less common in
consumer electronics, there may even be taps for high and low line
voltages (ie: 110 v. and 130 v. primary taps).

Filament is almost always green, and a centertap is usually green with
a yellow stripe.

Everything else should be secondaries -- look for matching color pairs,
with a striped wire of the same color being a probable centertap.

 

Mike,
Thanks for the lesson. I just needed someone to tell me that what I thought
was right. Fortunately for me, someone at Foster Transformer emailed me
with the PT specs and colors, so I don't have to fish for them. I'll bolt
the filament xfrmr to a board and power it up. It will be simple to measure
it. I'm not sure what to do about the Audio OT and the Vertical OT, but
maybe if I get the filament xfrmr running, I can use it as a low voltage
source on the secondaries to see what comes out on the primary. From there
I might be able to figure the ratio and therefore the ohms. Then there's
the choke. Essentially the same as a big resistor?

BTW, the filament is Yellow + Yellow/Green and the primary is either
Black+Black/Red or Black+Black/White!

Phil

 

Just see what the windings are connected to. If the output transformer has
wires which go to the speaker, note which ones they are. Often, there is a
singel primary winding, and a tapped secondary (ie com-4ohm-8ohm) For a
guitar amp, its not too crucial, just note which side is connected to the B+
and which goes to the speaker. Measure the speaker resistance as well, and
note what output tube it uses. Also note what rectifier tube the set uses
(5U4 by any chance?)

Vertical output transformer may be useful, dunno.

Power tranny will definitely be useful. Also try and save any metal can caps
that don't look swollen or have a burst base, they will probably be ok when
reformed. Also any ceramic sockets or tagstrips are worth saving.

Some darn good guitar amps can be made with those bits, thats for sure.

 

This is a nice thought. Unfortunately the opportunity wasn't present. This
chassis was pretty well stripped and nothing connected when I got it. The
OT is puny and it's clear which is the primary (two terminals) and secondary
(3 terminals), but it would be real helpful to know what the combinations
are.

I'll be harvesting caps, resistors, terminal strips, and wire. No sockets
present. The power tranny is borderline for a 2 tube amp with a bridge
retco.

Thanks anyway.