Help with identification of Fisher Amplifiers

[madwing]

@dcgillespie will tell you NOT to move any of the wires inside the chassis. keep them running with all weird bends and oddness. apparently they were tweaked to sound their best with the wires done the way they came from the factory (lowering interference, or something, but with the search engine down i can't say).

 

[Sam Cogley]

Those are fairly modified 80AZs. The 100 had a four-position terminal strip. It would be pretty easy to put the brass "Fisher" panels back on the front faceplates. I may have one around here from a dead 80AZ that I got when I was restoring my 70-A and 70AZ (which I turned into a 70-A-2).

If you're going to keep using those pretty ST-bottle 5V4s, add pre-rectifier diodes per dcgillespie's recommendation. There is a reason why there aren't many ST-bottle 5V4s out there - they're notoriously unstable. They were replaced quickly by the 5V4GA, which fixed the problems with the early tube. As long as you have a couple of diodes in there to make sure they behave, they're fine. Fisher switched to the 5V4GA when the 70-A-2 was introduced, at the latest - some later 70As might have shipped with them. I'm not sure why 80AZs have a tendency to turn up with 5V4s instead of 5V4GAs.

Definitely put the tube shields back on the 12AT7s, or get some if you don't have them. They're just the bog-standard plated steel clip-on shields that everyone used in those days.

 

[Sam Cogley]

Thank you. 40+ years in. I know that I don't know anything.

The frustrating/disappointing part is I do not have to tools or skills capability to set the phase inverter. I'm out here on an island searching and watching videos and I'm simply from a different generation.

Thank you, again.

Look up one of my threads or posts about the 70A. You should be able to find simplified directions for setting the phase inverter provided by dcgillespie.

 

[Sam Cogley]

I've been trying to suss out what those switches are doing. Am I seeing correctly that the purple wire is connected to pin 8 of one of the EL37s? The orange wire is connected to the output ground terminal. If that was connected back to the 12AT7, it would be there to provide two-stage modifiable feedback without the pot giving a greater range of adjustment.

Edit: looking at the photos, it appears that the purple wire from the switch is attached to the ground terminal of the one EL37 socket. It's hard to tell from the photos. If it is, that's only providing an extra ground path for the output connection.

 

[qogApS*2%HhV]

Looking forward to

I've been trying to suss out what those switches are doing. Am I seeing correctly that the purple wire is connected to pin 8 of one of the EL37s? The orange wire is connected to the output ground terminal. If that was connected back to the 12AT7, it would be there to provide two-stage modifiable feedback without the pot giving a greater range of adjustment.

Edit: looking at the photos, it appears that the purple wire from the switch is attached to the ground terminal of the one EL37 socket. It's hard to tell from the photos. If it is, that's only providing an extra ground path for the output connection.

Thank you for the help. They sound wonderful but I'm still struggling with how to set them up correctly and why/who/how they were modified. If there are in photos you are looking for please let me. I'm flying blind. toggle switches are some sort of "loudness contour" switch. The sound like magic but I'm concerned I'm hurting them without the right equipment/guidance. THANK YOU AGAIN!!

 

[qogApS*2%HhV]

Look up one of my threads or posts about the 70A. You should be able to find simplified directions for setting the phase inverter provided by dcgillespie.

The search function appears to be down. Any links or further guidance to the instructions would be most appreciated.

 

[Sam Cogley]

Looking forward to

Thank you for the help. They sound wonderful but I'm still struggling with how to set them up correctly and why/who/how they were modified. If there are in photos you are looking for please let me. I'm flying blind. toggle switches are some sort of "loudness contour" switch. The sound like magic but I'm concerned I'm hurting them without the right equipment/guidance. THANK YOU AGAIN!!

If you could take a photo that more clearly shows where the purple wire leading off of that toggle switch on the front panel is connected, I may be able to get an idea of what the modification was intended to do. Right now, where it appears to be connected makes no sense at all, so I'm sure that I'm seeing it wrong.

The search function appears to be down. Any links or further guidance to the instructions would be most appreciated.

Just use Google with the search string "site:audiokarma.org" (without quotation marks) at the end. Much better than the built-in search function. Anyway, I happened to know the right keywords to grab that thread quickly, so here it is. You want post #37: http://audiokarma.org/forums/index.php?threads/fisher-70a-questions.489818/page-2

While the Fisher 70A/70-A-2/70-AZ/70-AZ-3 were ultralinear rather than the more Fisher-standard circuits used in the 80AZ and 100, the phase inverter instructions should be the same. My 70As behave very well after following the first option in Dave's instructions, so I haven't felt the need to do anything more ambitious.

 

[Sam Cogley]

Another thread you may find helpful: https://audiokarma.org/forums/index.php?threads/70a-monoblock-followed-me-home.963359/