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Swap-ping Tubes from a Fisher 400C to a Fisher 500C

B

Beattles

New Member
I have a Fisher 500C that I have been using for about 8 months and it has performed well. I also had a Fisher 400C that I used for a short timebefore I got the 500C. I like the extra power of the 500C with my Large Advents. The 400C did not have the capacitors replaced, like the 500C (both had Silicon rectfiers), and occasionally the volume would drop on one channel. I got an Eico Tube tester and have tested the 12AX7s. On the 400c the 12 AX7s, all Fisher (made in USA), test at 880. On the 500c most of the 12AX7s are like the one pictured (a couple are Fisher, Baldwin, Sylvania made in (W)/Germany) and all test 960-980. Should I swap out the unbranded 500C tubes for Fisher tubes? Can anyone ID the tube pictured? And will I have any problem with the difference in results if I do swap some of the tubes?
 

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You can certainly swap them back and forth. Listen for differences in sound to determine which you like best. The stencil type printing on the pictured tube is indicative of GE.
 
Pinch plate Sylvania or GE. Could even be a JAN Sylvie or GE. I've got more than a few of that style from both.

If the 400 is/was a receiver, then it's a 400. Not a 400C. There is no 400-C in FIsher'sEDIT:RECEIVER:END EDIT lineup anywhere.

Anyway. You won't notice anything reference to gain, but you might hear a slight difference in tonal quality, depending on who actually made the tubes.

You know how to check for Telefunken's? Diamond or square shape in the circle on the base of the tube inside the pin diameter.
 
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12AX7 tubes don't work very hard. Made in Western Germany is often a Telefunken tube if it is original to the Fisher. For the most part, an amplifier does not usually need perfect testing tubes. Tubes that are used in preamplifiers usually just loaf along.

The best tube tester is a working piece of electronic equipment. One would be surprised how well weak tubes will still perform.
 
Swapping tubes

Thanks, should the GE be similar to the Fisher Made in USA tubes? Is there a problem having some tubes in the 960 range and other in the 880 range? Both are well in the good on the Eico.
 
Thanks for the info. Yes it is a 400 (w/ headphone jack), my 500 is a C. The German/W German Fisher tubes are Telefunkens, even the made in Gr Britain has a triangle on the base. I am changing out the tubes to check the sound, I was concerned that the tubes in the 400 all tested 880 and the ones in the 500C tested 960-980 and didn't know if that was a problem. Again thanks to all.
 
Depending on your general use, with all the 12AX7s in those Fisher amps, some times it's not a bad idea to pull a few of the more valuable Telefunkin tubes and just store them for a rainy day. I have a 500C currently as my daily-driver.....and have removed the 3 telefunkin 12AX7s that were in the FM Multiplex unit.....and subbed in some cheap Chinese 12AX7s....mostly because I listen to the FM radio very infrequently. However, I might add that the cheap tube perform admirably well in that functions. I hear virtually no difference in the FM quality if I put the Tele's back in there. Also, there are two 12AX7s in the phono stage that, if you're not using the 500C's phono pre-amp, you can also put some US tubes in there. For the record, do NOT run the amp without a full compliment of 12AX7s, as four of them are used in the bias scheme.....the filaments make up part of the bias circuit. And, in general, I don't believe in running any amp with 'empty' tube sockets if it's not designed to do so. But, swapping lessor quality tubes into positions where their performance is really not significant....that's not a bad idea as far as I'm concerned. Other's may disagree.....so I submit this as IMHO. WC
 
I had a note that told me which tubes were for each section but I can't locate it. It may have been a bookmark from the forum I lost when my HD crashed last summer.
 
The Fisher branded tubes are Telefunkens which many consider to be the finest 12AX7 ever made.

Every Fisher 12AX7 I've seen has the Telefunken diamond on the base. They may not bring quite the price of a Telefunken labeled 12AX7 but they are the same.
 
This weekend I may rotate my 400 back into my set up and swap in some modern production 12AX7’s just for kicks. I haven’t listened to my 400 since I rebuilt my Klipsch Forte’s this past May.
 
Destructor,
Try some long pinched plate Sylvanias in the phono stage. Those tubes have tons of gain and the Fisher phono stage loves tubes with tons of gain.

beattles,
That original tube pictured looks to be a long plate GE tube.
That's a pretty good sounding tube.

The positions that like evenly matched triodes (both sides of the tubes) are the phase inverter positions. There are two of them right in front of the output transformers.

When you were mentioning the 960 range as opposed to the 880 range, I wasn't sure if you were talking about one triode of the tube or both triodes. If mismatched between triodes, what is the known good minimum level?
With that many tubes to choose from, don't use any weak ones.
 
Generally, I've had good results with Sylvanias in pre-1958 Fisher gear, and Telefunken or Mullard in later stuff.
 
I did both tests listed on the Eico and the ranges were right on. The GE tubesin the 500C all test 960-980 and the Fisher tubes in the 400 test 880.
 
larryderouin said:
I changed the sentence. In the context it's in I thought it was self explanatory that it was receivers I was talking about.

Larry
Click to expand...

You're probably right, but at the same time there was potential to confuse those who are less familiar with Fisher gear. It would have made more sense to call the receiver something like "300" or "450" considering that the 400CX2 was produced at the same time.
 
Larry.......... I gotcha the first time.........

Also.........got a 'present' for ya. On my way back from Michigan tomorrow am. I'll try to drop it over to you first of the week.

Tom
 
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