SA-300 welcome

Hi,
I've traded with JohnVF. He now has my Spendor BC1s and I now have his Fisher SA-300.
He'd had it worked on and most every cap under the hood had been updated, but the power supply caps were undone. I've included a photo that shows the workmanship, which is good.
Sonically, I used it for a few 10 hour days to get a feel for it and to let it relax in. My experience with tube gear that hasn't been used for a while or a lot is that it takes time to show its true colors. I don't know if it's the heat, or the charges in the caps, or what, but some change occurs.
I was surprised to find that Sprague 715P output caps were pretty good. Not the best, but good.
After initial break-in, I cleaned all the tube sockets, put a Mullard 5AR4 in place of one of the two that was a Brimar, replaced the two 12AU7s with NOS 12BH7s I bought from byoungman1, and started rolling in 12AX7s. I also replaced the one non-XF-4 Mullard EL-34 with an XF-4.
Well right now I'm running Sylvania black plate 12AX7s, which brightened it up a bit. The amp has also sped up on the bass, which was sounding kinda vintage-like, if you know what I mean.
I used it this way for a month, then last night I put it on the bench and replaced the four output coupling caps and a few resistors. Now it has Jensen PIO silver leadout caps purchased used from analog addict. They fit. The space is tight. They're .22uf caps, which tend to be big, and long ones won't work. I also replaced the 1000 ohm resistors to each EL-34 with Kiwame carbon comps.

The difference is pretty dramatic. The amp has a lot more authority. Bass is much more extended and liquid and the highs are also much more extended and smooth.

This one's going to require some cleaning up and it'll get the attention it needs, just not right now. One of the two can caps gets fairly warm and will have to go, but it's not intolerable. I know that the power supply upgrade will add transient response, speed and power.

I also knocked a couple of dents out of the cage and it'll need a rattle-can upgrade.

Has anyone got a service manual? I have a schematic, but I have no procedures to set AC and DC balance. Are there rule-of-thumb guides for how this should be done?
Can someone help? I'm sure there should be a certain value of output load resistor used and a sequence of switching the bias controls as well as target voltages for certain places.

If I have to I'll buy a manual on ebay, but there's none I've found in the AK digital docs forum or in the Yahoo Fishergroup archives, or through some google searching.
Thanks in advance.

Another shot.

Don -- if you can post the schematic, I'll be happy to help with any bias procedures. Congrats on getting a great unit!!

Dave

I'm really happy that this went to you and it's getting the care that it needed (as well as allowing me a pair of the BC-1s I've wanted...the nicest BC-1s around...). I'd be curious to hear it now after the few things that you've done. I think I told you this but it was restored to be closer to 'vintage'/original sound than something more modern. I have always regretted that direction, even though its the direction I gave when the choice was thrown out there by the tech I went to. I always knew that there was much more potential in this amp. Best of luck as you continue to dig into it.

Well done, Don :thmbsp:

Keep me in mind when you want to trade some Fisher gear

That's a sweet amp. Nice coupling caps.

Attached is a schematic. When all is said and done, I'll archive everything I have in the digital docs forum.

My Fisher President VIII Console uses the SA-300-B amplifier.

I don't see any difference between the SA-300 and the B version.

The service manual for the VIII has the information for the R200 tuner, 400CX2 Preamp, and the SA-300-B. You might want to use it in conjunction with the Sams schematic posted by audiodon.

You can download the service manual for free at:

http://www.fisherconsoles.com/service manuals/FISHER PRESIDENT VIII 8000 SM.pdf

Good luck with it.

Thanks Jonboy.
The good stuff I was looking for is in there.
I don't know of circuit differences or what the SA-300B offered over the 300 other than the center channel tap, but the testing is likely to be similar.

Don -- As I'm sure you've surmised, this design runs the output tubes near the limits of their dissipation, with nearly 26 watts at the plate (which is over the Design Center rating of 25 watts), and nearly another 3 watts at the screen. This is based on data from the Fisher service manual, and so could easily go higher with today's higher line voltages.

Based on total cathode current, as long as your tubes are reasonably matched, keeping the total dissipation level (both plate and screen) at 26 watts per tube, will still deliver very good tube life, and very good performance as well.

I know you will enjoy this one!

Dave

Well, I got a couple of hours on the bench and some clean-up time on this amp this weekend.
My touch-up paint wasn't perfect. I had to mix four colors and will need to redo but I have to get some gloss red and black to shift the color somewhat. It looks better than aluminum scratches look though.

On the bench:
1. I changed the mullard outputs to Amperex double-D getter EL-34 closely matched pairs.
2. I put in a pair of CL-90 thermisters on the power transformer primary leads.
3. The bias was quite cool at about 5 volts when I started. The spec calls for 7.8 average. I ran it up so that the hottest tube was 8.1VDC on pin 8 with the input voltage being 124VAC.
4. For the Hum and DC balance, I don't have a DVDM, so I did the best I could with my DMM.
5. I was happier with the results of the AC balance, which came out pretty close channel-to-channel.
6. Tube voltages: (Actuals at 124VAC)
Pins 3 of the EL-34s - expected 370-380VDC. Actual 376
Pins 4 of the EL-34s - expected 355-375VDC. Actual 364
Pins 1 and 6 of the 12AU7s (using 12BH7s) - expected 205-230VDC. Actual 216
Pins 1 and 6 of the 12AX7 - expected 100-125VDC. Actual 116
I used a variac and ran the amp up to 124VAC and adjusted the bias so the hottest tube was at 8.1.

That looks great, Don. One more nice tube piece up and running in "Fishertown, Massachusetts." Our town sounds good! (Don and I live a mile or so apart...)

Beauty! :thmbsp:

Hey Don, is that Turtle Wax? Is whatever you used safe on the lettering?

Thanks


Steve

I used Blue Coral because I own it. When it runs out, I'll use up my Mother's Carnauba Wax bottle. I'm still picking wax residue out of vent holes and hardware screw heads and the sides of tube sockets.
Any carnauba based wax without a cleaner will do. I suppose you could use a cleaner, but I cleaned it already.
I'd cleaned it beforehand with a thin strip of rag containing some mineral spirits.
The lettering was fine.

I'd touched up a bunch of spots with some touch up paint I'd brewed from four bottles of Testor's model paint before I polished. The polish helped match the gloss and blend the slightly differing colors, plus it protects the paint, both new and old.

I need more high-gloss deep red and some more high-gloss black in the touch-up paint. Slightly more crimson in the brown is the goal. I think I'll still be experimenting with that part of it.

It certainly looks better than the aluminum showing on the chassis or the brass showing on the logo.
It's the same stuff I used in the sticky about deep cleaning a tube amp at the top of this forum.

I'd gone to a few hardware stores and the local hobby shop to get the best brass colored paint for the cage also. I tried to imagine what I looked like before everything on the cage became pitted and this was the darkest, least brash and least greenish alternative.
I think it came out pretty well. A couple coats of spray paint, a couple hours in the sun, followed by a clear-coat of satin polyurethane finished it off.

Hey Don, what about sanding and getting the cage plated?


Steve

Whoa Steve,
You know, I haven't fully committed to this amp's capabilities yet and I'd need to do that before I'd decide to take it up multiple levels.
It's a Fisher, so I know most all resistors are still within tolerance, it sounds good and I like it a lot, but it's not love . . . yet. I still think I can take it further sonically.
I'm not a strip the chassis, replace the tube sockets, have painted at the autobody shop, redo the silk-screen and rebuild from scratch kind of guy . . . at least at this point in my learning curve.
Up to this point, when I really like a piece, I learn the sonics on one and search for another in excellent physical shape and then up the ante on the sonics on the one in good physical shape. Then that second one is my keeper.

Hey Don, I assumed it was a great sounding, keeper amplifier.
Its little bro pictured in my signature is gonna stay with me forever.

Good luck, and I hope you end up happy with it when all is done. Sure is pretty. :yes:


Steve

You're a busy guy, Don!

Nice work on that Fisher. I've always liked the way they look, and the SA100 I had sounded pretty great, too.

Thanks Nate. I've learned to let an amp's qualities reveal themselves through repeated heating and cooling of the components and repeated listening before reaching a final judgement.
At this point, I'm thinking this one rivals the best I've run into in the +35 watt tube amp department, but that's going to take some heavy lifting to ultimately determine. Let's say that it's the best EL-34 amp I've heard, but whether that's enough I'll reserve judgement on.
Pretty nice design and well laid out inside. The voltage amp tubes and the phase inverters use 6 volt AC filaments.