Fisher 100 twins have arrived

Folks,
Courtesy of WhiteSE, I have had the good fortune to purchase these Fisher 100 monoblocs.
They operate, but each of them just slightly redplates one output tube. They each call for a pair of EL37s, but I purchased them with no output tubes, so I used the 6L6GCs I had on hand. I also replaced the provided 12AU7s with a pair of RCA clear tops I had. The rectifiers are 5V4s and the 12AT7s are RCA Command black plate 12AT7s.

I'm not quite sure what I'm going to do with them yet other than completely overhaul them. I won't get to it for a while yet.

I do have some questions for the experienced among you.
1. One of them has leaked some potting goo out of the power supply transformer. It's not enough to fill the bottom compartment, but it is probably a couple of ounces worth. Should I be worried about that?

2. I'm considering performing a complete strip and replace of components. I have a schematic. Does anybody have any other documentation about these (100- AZ) or the 80-AZ? I'd love to find out the marketing stuff, and I'd really like to have a parts list. I've already looked in the archives at the Yahoo Fisher Group.

3. Are there any components I should retain?

4. Does anyone know what the potentiometer on the tube board under the cage is for?

I took some pictures for your pleasure. The front panels look better than the pictures would lead you to believe.

More pictures.

Beautiful! Don't you dare redplate those RCA blackplates!

Thanks Jon, I won't.
Funny thing: Both amps slightly red plated one side of the same tube in the same position. Move the tubes around? Same glow in the tubes in the same positions.

That's one reason I was asking if anyone knows what the pot under the chassis does. It could be a bias pot but is unlabeled. And no, I didn't trace the wires to see what they do or look at the details of the schematic yet. I just wanted sound and tube glow for a half-hour or so.

Man those are really nice looking amps! Certainly worthy of a full overhaul .... though I can't blame you for firing them up - even for just 30 minutes of Tube bliss.

Those are beautiful, I'm sure you'll find a use for them once you've overhauled them.

The pot is either the bias level or for balance between the two output tubes.

audiodon said:

Folks,
Courtesy of WhiteSE, I have had the good fortune to purchase these Fisher 100 monoblocs.
They operate, but each of them just slightly redplates one output tube. They each call for a pair of EL37s, but I purchased them with no output tubes, so I used the 6L6GCs I had on hand. I also replaced the provided 12AU7s with a pair of RCA clear tops I had. The rectifiers are 5V4s and the 12AT7s are RCA Command black plate 12AT7s.

I'm not quite sure what I'm going to do with them yet other than completely overhaul them. I won't get to it for a while yet.

I do have some questions for the experienced among you.
1. One of them has leaked some potting goo out of the power supply transformer. It's not enough to fill the bottom compartment, but it is probably a couple of ounces worth. Should I be worried about that?

Click to expand...

At least somewhat. The PT is running too hot. My shorted 70A PT had leaked a fair bit of goo, but not that much.

2. I'm considering performing a complete strip and replace of components. I have a schematic. Does anybody have any other documentation about these (100- AZ) or the 80-AZ? I'd love to find out the marketing stuff, and I'd really like to have a parts list. I've already looked in the archives at the Yahoo Fisher Group.

Click to expand...

The 80-AZ Sams folder is online, I think I pulled it from Tom Bavis' page. The 100 schematic is also online, I think I got it from the same place. The 70A/70AZ, 80AZ and 100 all share the basic circuit, with slight differences in the transformers and parts selections.

4. Does anyone know what the potentiometer on the tube board under the cage is for?

Click to expand...

It's the phase inverter control. I have yet to find the instructions for setting it properly.

audiodon said:

Thanks Jon, I won't.
Funny thing: Both amps slightly red plated one side of the same tube in the same position. Move the tubes around? Same glow in the tubes in the same positions.

Click to expand...

Maybe just a dirty socket causing too much resistance? Could also be a failed passive component causing an imbalance. The part count is low enough in those that I'd just replace everything. 60+ year old carbon comp resistors are suspect, as are the caps. It's also possible that if the phase inverter balance is too far out of adjustment, one tube is working too hard.

I just wanted sound and tube glow for a half-hour or so.

Click to expand...

They should be very, very good. I have GE 6L6GCs in my 70A, and even just using an iPod to drive it, the sound is incredible.

Wow, those are gorgeous! Can't say I've ever seen Fisher 100 amps. Wish I had some experience with any Fisher power amps. 200s are on my ultimate wish list.

The pot is a semitry control Its in the driver section and contros the driver ballance if it off way to far to one side it could cause red plating , set it with a distortion analyzer or a signal generator and scope . Recap it before worring about the power transformer , the person that got the EL37's has an extra power transfomer from a Fisher 80AZ .

Pull all the tubes , and connect it to an AC amp meter and a veriac ,and slowly bring up the unit with the black goo if there is no current reading your most likely OK . The large power resistor under the tranformer may have caused the goo problem .

Also check the cathode resistor on the output tubes to make sure it hasn't changed value . Recently found a ceramic cathode resistor that had shorted turns .

Mark

Got the docs, thanks Sam Cogley. They have a parts list. I think I'm going to do my first full rebuild . .. but not now.
Shelving these until I'm ready to deal with them.
Jaymanaa has no doc. Sending him a copy for his 80AZs.

audiodon said:

Got the docs, thanks Sam Cogley. They have a parts list. I think I'm going to do my first full rebuild . .. but not now.
Shelving these until I'm ready to deal with them.
Jaymanaa has no doc. Sending him a copy for his 80AZs.

Click to expand...

I'm glad that was where I found the docs, otherwise I was going to have to try to figure out where I got them! :lmao:

These are really pretty simple to work on. The 70A is by far the worst due to the chassis design. The long, narrow amps with the later interlocking chassis setup is much easier, you have a lot more room on the sides.

That's kinda why I picked these. I want to sharpen my ground-up rebuilding skills and these looked like good starting candidates.

They look great Don! Looking forward to the posts to follow after you complete your work! :thmbsp:

-Kory

If you read the Sam's folder for the Fisher 100, they tell you how to adjust the phase splitter. Unfortunately it does require a distortion analyzer, but this would be a good time to purchase a HP 334A (they're cheap, $30-40 if you watch and wait at that 'auction place').

I restored, or at least 80% restored a pair of these amps last year and have been using them daily since. Amazing amps, no noise, great dynamics and very, very nice sound on my custom Altec speakers. I found that over half of the resistors were right on spec and just left them alone. Also, if your preamp doesn't put out any DC, you might want to bypass the .22uF cap and level adjustment. Otherwise replace every capacitor, the screen resistors (R15,R17) and rewire with a grounded power cord.

If you need any help, let me know.

bigamps,
Hey, that's very thoughtful. I may ping you when I get to these.

I asked a body shop guy about painting the transformer pots and he suggested finding someone who does powder coating. Is that a valid suggestion for items that heat up like the potted transformers on these?

One of the reasons I'm such a big fisher fan is the component quality. Most restorations don't require you to lift a leg on every resistor in the circuit and test it because they're still very close. I love that reliability aspect.

Yes, both cords will have to go. They're cracked and copper is exposed.
Where would I find the Sams folder?

Plus, a distortion analyzer is on my list. Now that I have a part#, I'll be lurking.
Don

Don, The transformers don't get excessively hot when these amps are running properly and it's quite common to see the potting goo running out like example you have.

The multisectional resistor must get really hot when the caps start failing. You can see that the goo is coming out on the side of the amp where the first 100 ohm, 10 watt smoothing resistor is. That 100 ohm section sees lots of abuse since it is the first resistor in the power supply. One of my amps had that section of the resistor nearly melt down and it blew the contents of the cap all over. This was before I found it, I can only imagine the mess.

A good paint job would be sufficient and powder coat would be nice, but overkill.

I can't wait to watch this thread

and if I am lucky, since I am just down the street, hear them as they get rebuilt.

Love the Fisher logo, all that brass and maroon bake lite.

Well,
I bought that Wyred 4 Sound STP-SE preamp from Kimchee on Bartertown. There has been a lot of nice stuff that you used to see selling elsewhere selling on bartertown lately. I've benefitted from that a few times. Of course, now I'm pretty much done with the buying part of 2012.
I pulled these 100s out to test the preamp. I'm running them with some Russian 6n3CE tubes to replace the EL-37s, since I don't have any, and these require a bit more than a 6L6GC can deliver without redplating a touch. I'm running them off a variac at about 110 volts.
The combination is scary good. I may have to move these closer to the front of the restoration queue now that I have a decent preamp with a remote.

Those ought to sound quite nice as those were the amps used in the '59-'61 President consoles; although the 100's used in in that application omitted the Z-Matic feature and lacked cages.

I just compared a 1959 Sams 100-AZ schematic with a 1961 Fisher Corp. 100 schematic from the 1961 President V. Is it odd that the voltages would be significantly different on what was basically the same amp except for the Z-Matic circuit? Would that be a Fisher vs. Sams anomaly or was Fisher trying to correct a problem that existed on earlier 100's by lowering the voltage?

To be precise, it's only lower at the output stage (435V vs. 460V plate voltage on the EL37s), it's actually higher on the preceding stages. Perhaps significant is the secondary voltage at the power transformer which is lower in the later 100 amp (without the Z-matic circuit).