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Fisher 500c Tubes to Improve Sound

davstev

davstev

Well-Known Member
Hi Fisher people,

I recently acquired a really nice Fisher 500C. It's the first tube receiver I've owned. It's been largely recapped, and with new selenium rectifier, etc. Basically, it's been upgraded and tuned up.

But I have to say, the sound I find still kind of blah- not that distinctive, a bit flabby. It just doesn't have what I am looking for, but I hope that some tube rolling will improve things.

The tubes in there now, I am not sure what they are. A lot of the markings have rubbed off and I am no expert in identification. But I think they are quite average in quality and they seem fairly modern and new, as the pins have no tarnish or anything. A couple of them are marked "the Fisher" 12AX7's, but I am not sure if they are very good or not.

Can anyone in the forum give me an opinion on what tubes I can/should put in, and where, in order to improve the sound?

I've heard that V14, V15, V16, and V17 are important 12ax7's. I won't be using the phono stage, rather, an outboard phono and running a line in to AUX.

Thanks for your opinions and experiences!
 
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On all of the 12ax7's look in the base (inside the pins) for a DIAMOND/square. The Diamond is a trademark of Telefunken. Most FISHER Small Signal Tubes are Teles. If the output tubes are original they will be Marked "The FISHER" on the Bakelite base, and or on the glass. They were made by Westinghouse. Good Tubes as long as they are not worn out. Same with the Tele's. As the tubes wear out, you'll notice it takes less power to get distortion. You need to test all the tubes to make sure they at least meet or exceed minimum emissions and gm. Do NOTE that HICKOK tube testers are notorious for reading 12ax7's low. There should be more than a few AK'ers in the Montreal area who would have a Tube tester.

Don't cut the internal phono preamp short. With good matched tubes in it, they are quite good. Dave G. did a testing protocol on and 400 or 800C (they all use the same circuit), and it did very well. He did some minor part changes I believe which are quite easy. Look for Phono changes to 400 or something like that (or just search for threads by dcgillespie that pertain to the 400-500c-800c) Note the 800-C is a 500C with an AM band added to the tuner.

I'm not going to give you specific tube recommendations as my ears are not good enough to tell small nuances.
But I will say that of the domestic tubes (12ax7's) Sylvania are what FISHER used near the end of production of the 400-500C-800C. These replaced Tele's. RCA's and some GE's are good but they are getting hard to find because everyone wants the RCA's (black plate). I've been hearing good things about the Tung-Sol ReIssue 12ax7's and the Sovtek 12ax7LPS. Also the Mullard 12ax7 re-issue. If you're not too picky, the EH12ax7's, and the rest fo the Russian tubes are quite good. Chinese 12ax7's are junk. Basically it boils down to be a matter of taste based on your total gear package , room layout, how good your ears are.
 
The 12AX7's that are marked "the Fisher" were probably made by Telefunken or Mullard if the lettering is faint or wiping off. They are great tubes if still good, and I've also found them to be quiet when used in the phono stages. The original tubes Fisher put in their units are quite good.
 
The 500C Owner’s Manual shows the tube layout. V16 and V17 are for phono and tape head, which won't come into play if you use the AUX input.

Here’s what I found to sound the best as the result of my tube rolling last year:

V14, V15 12AX7: Tung-Sol new production (Russia). I removed Fisher branded tubes from GB.

V12, V13 12AX7 (phase splitter & driver): Genalex Gold Lion 12AX7 / ECC83 / B759 gold pin (Russia). (Note that the non-gold-pin Gold Lion 12AX7 is a completely different tube - made in China, short plate – and doesn’t sound as good, IMO.) I removed Fisher branded tubes from W. Germany.​

Here's my findings re new 12AX7s in general: best new production 12ax7?

I think that its worthwhile to buy from a distributor who tests new tubes, and can deliver balanced triodes, and matched pairs.

I believe that the output tubes affect the sound quality less than the input tubes - assuming that the 7591s are good and the amp is adjusted properly. When Craig / NOS Valves restored my 500C he installed a matched quad of JJ 7591 output tubes, and made the necessary adjustments (e.g., bias).
 
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Here's the thread about sorting out the phono stage. Its not that far off to begin with though.

http://www.audiokarma.org/forums/index.php?threads/the-fisher-phono-preamp-and-riaa.600690/

Tired output tubes make things sound flabby. Could be that yours are tired. If there is no way to check or adjust the bias, they may also be incorrectly set up. A replacement rectifier will usually output more voltage than the original, which can be the wrong voltage to get the tubes operating properly.
 
Hey, just briefly, thanks all for your replies. Fisher buffs are good people.

Yes, I think they are Mullards and Telefunkens but I will look into this closer.
 
One thing that I didn't mention about my (near mint) new 500C is that it was damaged in transit. :no:

The contour button was smashed and the rod on which it was mounted was bent.

I've looked on the auction site and nothing.

If anyone has one for sale or knows where I can get a standard 500C knob with brass face, let me know.

thanks,

David
 
davstev said:
One thing that I didn't mention about my (near mint) new 500C is that it was damaged in transit. :no:

The contour button was smashed and the rod on which it was mounted was bent.


David
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Sounds like you need a new knob, a new pot, and the bright.

The knob and bright come up quite often at auction. That pot is another matter. FWIW: I never, ever use that function. Me? I'd straighten out the spindle, wait for a knob to pop up at that place, and leave it at that.
 
I see guys parting out Fisher receivers frequently on eBay. I would try sending a message to anyone selling Fisher parts and asking if they have the loudness control. You might also try downloading the 800b/500b and 400 receive manuals and see if the part numbers are the same as for the 500c. Might speed up finding your control replacment on eBay.
 
800C is same as 500C. 800B- 500B - 400 is NOT the same (slide switches).

Part # needed is S990-129
 
How awesome are you guys? I am glad to have bought the Fisher just to meet such helpful folk.

I listened again tonight and I think my impressions have changed a bit. I mean, tonight I really had a chance to crank it, and it was really nice. Last night, with the kids in bed, I had to keep the volume low and listen mostly via the headphone jack. But tonight, a different story. Also, I had the speaker connected incorrectly last night! o_O I still got sound coming out last night despite the incorrect hookup but the vocals were really recessed, balance was off. For all of these reasons I incorrectly misjudged this fine receiver. It is sounding good. However, I am still going to experiment with tubes. That's part of the fun.

But the headphone output....maybe not super hot. I am using a pair of Grado HP-1000 drivers.

Maybe some tube rolling for the headphone section?
 
Glad you got the speaker connections sorted out. The 500C is a great sounding receiver. Have fun with the tube rolling.
 
I have been using a Kenwood 700c as my main power amp. I really like it but I'll have to do a comparison with the Fisher.
 
HEADPHONES are tapped off the speaker leads, before the speaker screw boards, with resistors inline to drop the power so the headphones can handle the power. 330ohm 1w dropping resistors at the headphone jack. One thing to check with headphones is balance. Turn balance all the way to right or left. If the sound follows to the same side, you're ok. If the sound tracks to the other side, no problem. Just reverse the resistors on the leads at the jack. How many ohms are the drivers on the Grado's. I find that a low impedance driver on my 400 and 800c tend to break up and distort faster and easier than a high impedance headphone. My son bought me a pair of Dr. Dre's for Xmas. What a friggin waste of materials on their part and $$ on his part. I played them for about an hours then sent them back. Brought out my old reliables. I have a pair of PRO-4A's I bought as high school freshman in 1969 (260ohm), a pair of Koss SP/3X cups (the frames broke up about 5 years ago) that I bought in 1974in the Navy, that I modded into a pair David Clark Military Ear Protector headset cups, and a New pair of Pro-4AA (260ohm). All 3 handle everything without problem.

So check the channel orientation and then clean the contacts in the jack with DeOxit and Q-tips. As it's an open design you can clean it after soldering, before closing it up. And check the value with a meter of the 1w 330ohm resistors. They are 10%, but I'd replace them if they are 5% or more high or low
 
larryderouin said:
...My son bought me a pair of Dr. Dre's for Xmas. What a friggin waste of materials on their part and $$ on his part. I played them for about an hours then sent them back. Brought out my old reliables. I have a pair of PRO-4A's I bought as high school freshman in 1969 (260ohm), a pair of Koss SP/3X cups (the frames broke up about 5 years ago) that I bought in 1974in the Navy.....
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Funny that you mention that. A few years back I bought both my kids a pair of phones: a Grado's and a Koss. This was just before the multi colored jobs hit the scene. I listened to both, and told myself I should buy myself a pair, or two. Well, then the big marketing push for the stylish phones made them ubiquitous. Needless to say, the next Xmas, moms bought both kids a pair of the fancy phones. I tried them. WTF!!! I had my kids do a shoot-out with the Dre's verses the PortaPro's, the Grado, and my Sennheiser HD 598. Didn't matter. They liked the Beats. But hey, this is America:

http://www.youredm.com/2015/06/29/a-pair-of-beats-headphones-costs-only-17-to-make/
 
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If your phones are a low impedance type, then simply use lower value dropping resistors to compensate for the lower impedance of the phones. Something around 100 Ohms at 1W may be more appropriate.

Dave
 
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