Fisher 400 Output Transformers - Testing Continuity

[TravAndAlex]

Hi. Just picked up a Fisher 400 in pretty rough shape and I'm trying to get a feel for what needs to be done. One of the first things I'd like to test is continuity on the output transformer windings. Can someone tell me what wire color pairs need to be tested?

They appear to be twisted:

Blue / blue-white
Black / green
Black
Red
Yellow

I'm really hoping I shouldn't have continuity on the blue / blue-white pair as I do not on either transformer. I fear otherwise, however. I do get continuity on black / green (to speaker outlets) and Yellow and Black.

Thanks!

 

[TravAndAlex]

Found this in another thread which I believe means the primaries on both output transformers is bad (pin 9 to pin 9 are the blue / blue-white wire pair have and have no continuity nor resistance):


Ziradog, Dec 19, 2016gadget73
usually I read those plate to plate for the primary side. If 7591 tubes, measure from pin 3 to pin 3 on the tube socket, you're probably looking for 150ish ohms. If its 7868, check pin 9 to pin 9. The secondary side almost never has a problem on an output, but measure from the C terminal to 16 ohm. You're looking for 2 ohms or so. Real testing you'd have to feed some voltage in and do some measurements but most of the time if the wire isn't broken inside the transformer is fine.



What are my best bet (ie reasonable price) for replacement or repair for output transformers?

 

[bhamham]

The two red wires from each transformer should be tied together. Check resistance from this point to each pin 9 of each 7868. You should get something around 140 ohms.

 

[TravAndAlex]

Tried that. Nothing. Oh-oh.

 

[bhamham]

Just so I understand, you put one lead of your DVM on the junction with the two red wires and the other lead of your DVM on pin 9 of each 7868? Was there any resistance or just open for each pin 9 reading?

 

[TravAndAlex]

Just so I understand, you put one lead of your DVM on the junction with the two red wires and the other lead of your DVM on pin 9 of each 7868? Was there any resistance or just open for each pin 9 reading?

Yup. Exactly. Open for each pin 9 reading on the 4 sockets.

 

[bhamham]

Wow, haven't seen where both went bad. Must have been some catastrophic meltdown. Sorry.

 

[TravAndAlex]

Yeah. Yay me. The power transformer seems ok, so I foolishly assumed the output transformers may be as well. Anything I should look for that might cause both output transformers to go? Or perhaps just negligence as they are pretty rusty?

I was stupid and got excited and ordered a refresh kit already, so I'm further committed than perhaps I should be with 2 bad transformers.

 

[larryderouin]

Thanks to Dave G for the following;

The (nearly) standard Fisher color code (particularly in the stereo years) is:

Black = Secondary Common
Brown = 4 Ohm
Green = 8 Ohm
Yellow = 16 Ohm

Blue w/Tracer = Plate Lead (in phase polarity with 16 Ohm tap)
Red = B+
Blue = Plate Lead

Dave

Also see post # 26 by Dave G. in this current thread on the X-100-3. It details how problems crop up in output transformers. http://audiokarma.org/forums/index....tput-transformer-recommendation.722537/page-2

Pull the tubes and front plate and stick it UPSIDE DOWN in the oven on an expendable baking sheet. Bake at the lowest temperature for 6-8 hours. This heats up the transformers and with it upside down any accumulated moisture will steam off and vent thru the holes in the end bells. To prevent a potted transformer from dumping the tar like potting the transformers are put upside down to hold in the potting. After baking, let it cool down overnight. Make sure you have the vent fan ON to remove any undesirable odors. Toss the baking sheet or mark it for use in shop only!

Then ohm them out again. Make sure you have fresh batteries in your meter.

 

[TravAndAlex]

Thanks! That is very useful.

I'll give it a shot in a few days when my significant other is at work. Can't hurt I suppose! Although from reading the post, it appears to me that if I'm reading open, the damage is done and the baking can't repair the winding. Could be wrong in how I'm interpreting that.

 

[TravAndAlex]

In case this is useful for someone else down the road, I'll document here the responses I receive for repair or replacement:

http://www.Transcendar.com : Doesn't appear there is any way to contact them currently. This looked like an easy solution. Anyone know what they cost?

Al Pugliese - FisherDoc@aol.com : Response within hours. Also has never seen 2 go bad in this way at the same time. No replacements in stock and recommends Ebay.

Gary Brown - xfrmrs528@gmail.com : We can do a complete rewind for $190.00/each plus shipping. I am just north of Bangor, Maine.

Brian Sowter - support@sowter.co.uk : We could make replacements using our custom service. See: http://www.sowter.co.uk/custom-output-transformers.php Please check the dimensions carefully and let us know which size would fit if you would like to proceed.

Aryln Arendsen - aryln@heyboertransformers.net : There is not much we can do to repair them, I have the specs to wind new ones. Cost for this would be $120.00 ea plus Shipping and takes approx 3 weeks.

 

[bhamham]

2 on ebay right now - pricey though. They come up for sale pretty frequently.

 

[TravAndAlex]

Do I need to be concerned about Early vs Late model changes between transformers? Of course, none of the Ebay listings list such things.


Early Fisher 400
Fisher Part Number T 1020-116
For Receivers with Serial Numbers Lower than 48000
6.4K Push-Pull to 4, 8, & 16 ohms 25 Watts
Frequency Response: 10 Hz to 100 kHz +/- 1 dB @ 1 Watt
Primary DC Resistance: 225 ohms
Primary Inductance: 90 H @ 120 Hz
Part Number TT-429-OT
Weighs 3.8 lbs. (1.7 kg)




Late Fisher 400
Fisher Part Number T 1020-116
For Receivers with Serial Numbers Greater than 48000
10K Push-Pull to 4, 8, & 16 ohms 25 Watts
Frequency Response: 10 Hz to 100 kHz +/- 1 dB @ 1 Watt
Primary DC Resistance: 270 ohms
Primary Inductance: 120 H @ 120 Hz
Part Number: TT-430-OT
Weighs 3.8 lbs. (1.7 kg)

 

[gadget73]

You can use either, but you'll need to make sure you do any circuit tweaks needed to make it behave. Somewhere Dave Gillespie has a workup about the late 400, and how to make it actually work properly with the late style transformers. if yours is an early one and you don't want to have to fool with anything, put what came out back into it.

 

[kward]

The late model Fisher 400 output transformers that I have seen have a suffix on the part number of "1AX" or "2AX". Thus, T-1020-116-1AX, whereas the early model output transormers do not have this suffix. At least that is my experience in the several that I have seen.