Fisher SA-100 sn10529A recap

[ronton3]

Okay thanks, I will let that one go. I just ordered these for the .022 replacement.
Sprague Axial Film Capacitor .047uF 200v 118P47352S2 Audio Vitamin Q New 0.047uF, they are supposed to be very good, if they are not the right thing I will find a place in another application.

 

[heyraz]

118P series is very nice. Difilm series, I think. Very clear.

 

[heyraz]

Heat is the enemy of capacitors so I try to keep capacitors away from heat.
This was my amp before. Notice the damage to the red capacitor on the left


It never stood a chance, it was surrounded by wire wound resistors



I moved the capacitor to the other side of the terminal strip keeping both capacitors (replaced electrolytic and added 0.01uf bypass) away from "the electric grill"

 

[vendo81]

I finished the soldering and deoxiting last night, brought it up over a couple of hours on a variac, placed it on the testing cart with wood blocks to keep the heat down(I have heard so much about it) hooked it up to Marantz Imperial 6's, a Fisher 100T tuner preamp, and an OPPO 83.
This morning I turned it on and waited for the hum to begin--complete wonderful silence--I then began playing Sitting Still Within, a meditation tape(now a digital file) I have heard a 1000 times. It was wonderful. I then noticed that 7189(V2) had a moderately red plate. My first inclination was to turn it off, but I waited, and a few minutes later the red had diminished, not long after that it had disappeared(was that a new cap breaking in?). I believe I will change the orange drops at C10,11,18 and 19 for russian oils, they are 047/400. I have the owners manual telling about the bias adjustment etc and will get in to that soon. I no longer listen to the radio, can I just pull all the radio tubes from the 100T, or is there a better way to deactivate the tuner section, in a way it could be easily restored? Thanks for the good
advice, it was very helpful.

Three hours later and I can hold my hand on all the very warm transformers.

There is a .047/400v cap going to pin 1 of the 7247s, the russian oils I want to install have an arrow on the side, should the arrow point to pin 1? Thanks ron

View attachment 1129092 View attachment 1129093

Very nice SA100! The SA100 is a perfect match with the 100T preamp. You will be making great music for a long time

 

[ronton3]

Very nice SA100! The SA100 is a perfect match with the 100T preamp. You will be making great music for a long time

I am very pleased with the way these two made for each others, match up with the Marantz Imperial 6's, all times greats working together in beautiful harmony.

I am hoping that the way I have the bias diode and cap located will be okay, the 50/50 Sprague atom is much smaller than its predecessor.

 

[heyraz]

You replaced the original red cap with an Atom, it should work fine.
Did you check the 4.7K resistor's value? Those carbon comp resistors drift with age and why I replaced mine with carbon film.

More importantly, I think you should firm up the ground connection tab to the chassis. That was one of the first things Dave G realized and it was a really good call. He discovered an inherent design flaw.
There are two different metals contacting each other and not sealed from the atmosphere in solder. A galvanic reaction in the presence of oxygen is inevitable between the two dissimilar metals which will result in a resistance developing between the two.

This might be part of your bias problem. Any of those unprotected tab to chassis interfaces are subject to failure.

Fortunately, it's easy to measure and easy to correct.

You can measure any resistance either directly from tab to chassis or look for a voltage drop across the tab to ground interface. If there is no resistance, there should be no voltage drop at all.

To fix and eliminate the problem you can polish the copper chassis and tab and seal it over with solder. The solder will provide the path to chassis ground. I believe Dave G took it a step further and dimpled the tab to chassis with a punch before sealing it in solder.

See how I polished and globed the solder on:

 

[ronton3]

I did check both resistors and they are right on the money. I will do the grounding. Thanks for the advice and picture to explain it.

 

[ronton3]

Last night for the first time I listened to records on the 100-T/SA-100 combo, with a Sota Saphire, Alfhason 100s, and Sumiko high output moving coil cartridge. I thought the sound of Norah Jones was wonderful with immediate presence, lifting from a silent background, I did have a grounding wire hooked to the 100-T. I am still waiting for the caps for the phono section. When I first recapped it years ago I used orange drops, I changed the output caps to russian oils. Would there be any benefit to changing any of the caps in the tone control circuit, I keep them flat.
I had found 2 Mullard 7247s, I have also found a quad of the brown stained Mullard 6BQ5s(from an Eico HF81), but I am concerned that the voltages may be a little high. I have the bias set at .6, but when I tried to do the dc balance I get a string of 0s, on the fluke meter, perhaps I am doing something wrong. I left the 20w8ohm resistors tied to the speaker hookups, and put the leads on 16 ohms and ground, with the meter on vdc, should I have been checking for vac? I have both the photofact and fisher manual schematics they do not read the same. Bias voltage on the photofact after the diode says -23v on the Fisher print it says -24.5, I have -25.3. Should I be concerned? On the Can Cap on A to ground I have 412 v, B 306, C 315, D 310, are these within tolerance? Thanks for any advice. ron

 

[dcgillespie]

The voltages are fine Ron. The voltage to be concerned with is the .6 volt bias setting when the output tubes are at a static DC balance. When using the Fisher approach to setting the DC balance, it is sometimes helpful to use headphones connected to the 16 Ω output, and adjust the DC balance controls for minimum hum. Then adjust the bias controls for the proper setting. The adjustments should be made with the level controls set full down.

Dave

 

[ronton3]

That is a relief, thanks for the DC balance alternative, I can say that this is one of, if not the quietest amps I have heard.

 

[ronton3]

The SA-100 is plugged into the T-100. I want to hear the Mullard 6BQ5s, but to ensure they would not be burned up I decided to try some 6BQ5s that were mismatched pulls first. When I turned the 100-T on the SA-100 lit up, one 6BQ5 did not, and when I tried to listen no sound. I then noticed that the 100-T was not lit up. The 6BQ5 had a cracked base, the 100-T has a blown fuse, but the SA-100 had continued to operate. I inspected the 100-T and see no obvious signs. I plugged my Iphone into the SA-100 after reinstalling the Russian 7189s, and it is fine. By the way as an aside, CDs I ripped to Itunes using Apple Lossless encoding, sound great and the Iphone volume can be too loud for comfortable listening. I am wondering if I should just put in another fuse for the 100-T, could the bad tube have caused the outage?

 

[dcgillespie]

The bad 6BQ5 would have nothing to do with the 100-T -- The only roll the 100-T plays in this scenario is that 1/2 of its AC power switch controls the power to the rear Auxiliary AC Receptacle that was powering the SA-100, that's it. The T-100's fuse is specified as 2A. Assuming the power supply caps in the T-100 have been replaced, I would install another fuse in it -- the worst it can do is blow again. But, if it does blow again, knowing when it blows is valuable information: a fuse that blows instantly indicates one set of potential problems, while one that blows 20 seconds or so after turn-on indicates others.

Dave

 

[ronton3]

Thanks for the advice, the new fuse did not blow. I do not believe it is related but when I first recapped about, I think 15 years or so ago, I installed a 10mfd Solen, in place of the 8MFD electrolytic, I think I read about this in Glass Audio, but it could have been somewhere else. I believe it is C4 8mfd 50V, It has been there for years, but I am wondering if I should replace it with an appropriate electrolytic, also what is the small white part with a reddish top across from it, should it be replaced. Thanks ron

 

[dcgillespie]

C66 is the 8 uF cap position that your Solen cap is installed in. It really should be replaced with a quality 10 uF 50 Volt electrolytic cap, as audio does not pass through this cap. The other component you are questioning is C49, a 900 pF 5% ceramic cap that works with the AM 10 kHz whistle filter.

Dave

 

[larryderouin]

Try to Whistle that high. 8 to 5 you can't make it.

 

[ronton3]

Thank you very much, I will replace the Solen, and leave C49 alone at least now I what it is. Thanks ron

When I was younger I was known for whistling, that time has gone by.

 

[ronton3]

I want to thank all the advisors and commenters, for helping complete the SA-100 recap: New power supply cap, new bias set-up(.6 volts on the adjustment-no hum), new oil caps, Mullard 7247s, Mullard "4 notch" 5AR4, Russian 7189s, with Mullard "brown stain" 6BQ5s, waiting in the wings. It is a wonderful sound.
I may still have a few question about the partnering 100-T, but if so, will start another thread. There is an X202 SN# 3308and a digit I can't make out, waiting in the wings, I have read Sony, Dave's and other threads, I know questions will arise. One final thing, I have been using a Weller 8200 soldering gun, and believe I need to graduate to a better arrangement for tight spaces, recommendations will be much appreciated, also what solder do others use. Thanks to all. ron

 

[moondogtn]

Very nice. I am hoping to tackle mine soon!
Soldering station/irons are personal preference but Hakko and Weller(I use currently) would be good choices. I’ll probably try the Hakko if/when this Weller dies as I hear good things.

Bill