500-T Time capsule

jdsalinger

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Thanks to RickDatsun for passing along a Fisher 500T in pristine condition. I say "time capsule" because this unit is in superb condition. Even all of the foam is there. Considering it is about 50 years old, it is in nearly show-room condition. I'll get some pics of the case when I button it up.
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I had one a couple of years ago. I remember it sounding warm & smooth with good detail. I really missed it.

Then, I was talking gear with Elusive at Twangfest last weekend and told him about my old 500T. 30 min later, he tells me, "hey, there is a 500-T for sale in the swap meet". What luck!
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This one was in much better condition than my old one. It came in a cabinet that was different but better than the cabinet from my first 500T. Not sure if this one is official Fisher, but it is of a higher quality with a lot of routed vents and a really solid build.

It has the typical weak channel, so I'm planning on doing a recap. Already did the de-oxit treatment. All bulbs burnt out. Very minor issues that can easily be dealt with and corrected.

There are actually fewer electrolytic caps on this than I remembered. Some are obvious, but I was wondering what the little gray plastic body ones are. Sure are a LOT of them, so I'm hoping they are film and not electrolytic.
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I am going to use some Vishay Sprague Atoms in the signal path for the Driver board. It's all Mouser had for 200/35. Any problems with those?
 

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The gray one's are lytics. Mallory Brand. Probably 4.7uf 35V.

It does look kind of sparse without an AM board on it. Otherwise it looks like my 550-T.

Larry
 
Thanks Larry. I guess I assumed that all electrolytics had crimped aluminum bodies. Good thing I ordered replacement lytics for them then.

I'm not sure what I did but the channel imbalance is corrected. Maybe it was the deoxit treatment. I also replaced the 500/35 filter caps, but those shouldn't have any effect on the channel balance. :scratch2:

Mouser order is on it's way. I am recapping the tone control board with 1uF Elna Simic II's. For the preamp and pre-driver boards, I chose Nichicon Muse 4.7 uF non-polar lytics to replace the 1uF ROE gray eletrolytics. No special reason other than just to mix it up a little and I don't think there are any NP Elna Silmics. Does that sound OK? I think it was Larry's suggestion to use NP in the signal path on the preamp and pre-driver boards.

For the 2500 uF filter cap, I bumped it up a little and went with a 3300 uF Nichicon KW. For the 1200 uF coupling caps, I am using 2200 Nichicon FG. Mouser didn't have KZ or any good audio grade 1200 uF caps. FG should be a decent cap for the 500T. I used FG on my Marantz 2230 and they sounded good to me.

I'm going to give a shot to using the original filter capacitor cans. If it doesn't work out, I'll just use some 3M VHB double back tape to hold them down.
 
That wasn't me. I would however suggest stacked films for any lytic's with a value less than 2.2uf providing there is room. Panasonic ECQ's work well for this. The FG and FW, or KZ's aren't going to improve anything in the 500-T, including your wallet. Power supply use UPW and signal path use UKL's. Even Nichicon's worst caps have betterspec's than the best caps from 1967. The UPW's and UKL's have been proven to be consistantly good in the PIONEER's and are recommended highly by Mark the Fixer. All I use for lytics.
 
That wasn't me. I would however suggest stacked films for any lytic's with a value less than 2.2uf providing there is room. Panasonic ECQ's work well for this. The FG and FW, or KZ's aren't going to improve anything in the 500-T, including your wallet. Power supply use UPW and signal path use UKL's. Even Nichicon's worst caps have betterspec's than the best caps from 1967. The UPW's and UKL's have been proven to be consistantly good in the PIONEER's and are recommended highly by Mark the Fixer. All I use for lytics.

You're right, it was Fred Soop who suggested the NPs. Sorry for the misquote.

About the audio grade Nichicons...I hear what you're saying about not improving....but now you have me worried. Would it hurt anything to use the audio grade for filter caps? I guess I thought that even though they aren't used in the signal path...they had some other quality that was more suitable for audio applications? I'm asking whether using those would be a poor choice for a PS. I don't want to make another Mouser order unless my choices just wont' do.

By the way, I've seen several references to a "power supply board". Where is this board? As far as I can tell, all PS caps and the rectifier are point to point. Filter caps are held in by clamps.

Another question about using low leakage caps (KL) for the signal path. If low leakage are better than their audio line, then why doesn't Nichicon catagorize those as "audio grade"? That's why I avoided them. I assumed KL was a general purpose cap.
 
The Power supply is point to point on the 500-T. I think "POWER SUPPLY BOARD" is an unconcious typo as 99.9940% of Solid state units have a board for their power supllies. My 550-T and 700-T are the only Solid state units I have in the house that are point to point, everything else is boarded. Habit I guess.

The thing about "audio grade" is more of a marketing thing, along with "computer grade". AFAIC the only real difference is how much $$ Nichicon is getting in their grubby little pockets. As for "possibly hurting your unit using Audio Grade for filter caps".....No. The power supply tolerances aren't so tight as to cause any problems.
Go ahead an put the one's you have in.

As for the KL in the signal path. Like I said in post 5.....Nichicon's worst cap today is way better than 1967's cap. Any cap today would be considered low leakage compared to the '67's. There are other things involved with the construction of the cap that I don't understand. But empirically, I can tell you that the UKL to me is better in the signal path.

Larry

Larry
 
Check the supply voltage and make sure that the main filters have a high enough rating for todays higher line voltages. My 600-T runs ±39 volts and had 3000 µF 40 volt capacitors. Replacements were selected based largely on physical dimensions in order to fit in the same holes and clamps. I ended up with 10,000 µF 100 volt units.

Unrelated to Fisher, but my Harman Kardon Citation 21 (excellent circuit but not quite the same build quality) had many capacitors being operated too close to the voltage rating which was probably the root cause of the intermittent problems that seem to be gone after a complete recap.
 
Thanks for the advice Fred. The original, primary 2500uF 75V cap will be replaced by a 3300uF 100V.

I just realized that I may have goofed. The original output coupling caps are 65 W.V. replacements I ordered are 35VDC rated. I selected 35vdc because that coupling cap is right after a "center voltage" test point of +27.5V. I figured that is what the coupling cap will see. But now I'm wondering why Fisher chose a 65 W.V. rating? Is +27.5 center voltage like a bias voltage which will go up and down from that center point?

Last night, I removed the output coupling caps and pried the can apart. I did OK, but the edge is kind of ragged. I'm debating whether or not they will look nice enough when I roll the edge down after installing the new caps to make this worth the effort.

Also, I have 4 Panasonic stacked film 1uF caps. So, I will probably use those for the preamp and pre-driver signal path (2 each board). Would those be called "input coupling" caps?
 
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B+ to the output's is 55V. Because of the way the output section is set up(Full Complimentary?), the upper transistor see's 55V and the lower of the pair see's 27.5v(or 1/2 of the upper). But the cap can see the full B+ under certain conditions (at least as I understood the explanation). So you want the cap to have a working voltage (W.V.) higher than the B+. A 63v cap will work fine here. If you don't like the voltage variance, go up to an 80V or 100V cap.

You want the lower transistor to have 1/2 of the upper transistors B+. Hence the Center voltage adj.

re:1uf caps. On the 1278 Control board and 1478 predriver, yes. Make sure the voltage rating on the stacked film's are higher than the lytics. IIRC those are 1uf/70V caps. A 1uf/100V stacked film is fine. It'll get a bit tight, but you can use stacked films for all 1uf caps on both boards.
 
Thanks again for the advice, Larry.
I ordered some 63V rated output coupling caps and ultra fast diodes.
I'll sleep better now!

Here are pics of my can caps with the guts removed and ready for the 2200uF Nichicon KW's. Hopefully I can roll the ragged edge down nice and tight, so they look decent.
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Sprague caps (MPX decoder) intalled.
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B+ to the output's is 55V. Because of the way the output section is set up(Full Complimentary?), the upper transistor see's 55V and the lower of the pair see's 27.5v(or 1/2 of the upper). But the cap can see the full B+ under certain conditions (at least as I understood the explanation). So you want the cap to have a working voltage (W.V.) higher than the B+. A 63v cap will work fine here. If you don't like the voltage variance, go up to an 80V or 100V cap.
.....

The upper transistor is connected to 55 V but only sees 55 minus 27.5, or 27.5 volts, same as the lower. This would be the DC operating point. Peak voltages will approach 55 volts in both transistors at full power. Theoretically, the capacitor would only need a DC working voltage of 27.5 V plus a safety margin, but I'd probably replace it with at least a 63 V unit. Todays capacitors are small enough and inexpensive enough. The higher rating would also help protect the speaker if a transistor failed. A 35 V capacitor with 55 V could do bad things.
 
Progress report. "Audio Control" board is done. All 1uF 50vdc Elna Silmic II's.
One board down, four to go.

Fisher made it VERY easy to access this board from both sides. Much easier than the Marantz 2230. Took a couple hours to do 10 caps, start to finish. Trying not to rush it though.

The correct output coupling caps should be delivered tomorrow.
 
The re-stuffing job turned out better than I had hoped (especially for a first time). Don't look spectacular, but not terrible either. For something that is under the hood, they'll do.

It's powered up and blasting FM radio now.

Sounds good. I don't notice a huge difference in the overall sound, or the bass performance, but I anticipate the sound will change over the next 100 hrs or so.
Don't think I messed up anything, going to 2200 uF coupling caps.

I'm just glad it is playing music after doing twelve caps without testing! :nono:

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I noticed this when I first acquired the unit, but just now asking the question...

The Aux mode (and to a lesser extent, phono and tape) makes a loud "click,click,click" or "blip,blip,blip" sound which is actually a series of very fast clicks that sound like one. To the ear, it sounds like approximately 3 clicks per second. No clicks on the FM mode.

I only hear it when an interconnect is plugged in and it seems to be coming only from the right channel. But in "tape head" mode, it is heard faintly in the LEFT channel. :scratch2:

It HAS to be a short or some component between the input jacks and the preamp, right?
But I'm really confused. The FM signal goes from the MPX decoder to the selector switch and into the same preamp terminal like all other components.

Gotta be something common to the input RCA jack panel.
 
Have you tried a shorting plug in the suspect RCA Jacks, and then activated them? Shorting plug is just a RCA plug with the center and outer shorted together.

As it's in all modes except for FM I'd suspect the 1398 board with the stereo separation switch on it. Note on the board says 3 versions. -1 has no switch, -2 has a 1K switch, -3 board has a 5K switch (POT!). IIRC the transistors are socketed so it should be fairly easy to swap left for right and see if the motorboating swaps channels.
 
OK, I tried shorting plugs and the motorboating was replaced by a buzz like a missing ground.

(so THAT's what motorboating sounds like? I always thought it would sound more like a motorboat)

WRT swapping transistors....if it was a transistor, wouldn't the motorboating be in FM mode too? The signal has to pass through the
preamp transistors in all modes, right?

I bought enough 2N2924 transistors to replace every one on the unit. Maybe I will do that as a preemptive measure.
Can't hurt, and I'd bet the semiconductor manufacturing methods are much better today than in the mid 60's.
 
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That sounds more like a missing ground. Check ALL GROUNDS from ALL Boards and on the boards before you do anything else. FISHER Riveted terminal strips, then used the riveted terminal as a ground. Some get loose and lose ground. A big enough soldering iron should take care of the terminal strips. I'd do this before replacing any of the 2924's.
 
This morning, I completed the power supply. Replaced and re-stuffed the 2500uF & 1000uF filter caps. If anyone is considering doing the same, I say "go for it". It gets easier the more you do it and to me, the finished look is very much acceptable.

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Replaced the rectifier diodes with 2A EGP20C ultra fast diodes. Glad that it's done.
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This made a big difference in bass response. I thought I remembered my previous 500T to have a nice fat bass response, but this one needed the bass tone turned to 3 o'clock or Loudness switched on. Seems smoother now.
Here are the original filter cap innards:
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Not sure what they are supposed to look like after 48 years, but they look a little dry to me.

I'm pulling in small town radio stations that are 75 miles away with only a wimpy ribbon antenna!
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After closer listening, I don't think I solved the channel balance problem yet. Left channel is slightly weaker. Plenty of caps to replace yet, so we'll see.

Also, I now have a very slight hum in the right channel. I didn't notice it last night when I tested the output coupling caps (before the power supply was done). The hum can only be heard when no sound it playing. Maybe I'll need to re-wet the negative joint on the right channel coupling cap.
 
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