The Fisher X-100B Testing Help Needed

K7JHG

Member
I just got this X-100B and it is in very nice condition and sounds great. All of the function switches and controls seem to do what they are intended for. I believe it has all original parts and tubes - they all say Fisher on them. I replaced the bias capacitor (the big orange one on the bottom) but there is no room for replacing the one single and two multi stage filter capacitors under the chassis. The cans are not large enough to re-stuff - at least not with the caps I have. Do I need to purchase custom made cans for replacement??? That is the direction I am going. The 7868 output tube pins 3 and 9 voltages are good (40 and 432, respectively). I'm relatively new to restoration... what other testing and/or components replacements should I be looking for. Suggestions welcome. Thanks...
 

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Sharp looking unit!!

Along with what you have already suggested, you will also want to at least replace the coupling caps connecting the phase inverter tubes to the output tubes. That, along with the cathode bypass cap you have already replaced will ensure the safety of your output tubes.

There are many here with an X-100B that can offer plenty of wisdom as to how to best go about replacing the power supply caps.

Good luck with it!

Dave
 
Thanks and funny that is my first response since I've been trying to find out what and where the coupling capacitors are. I've come across that recommendation on other internet searches. Can anyone call them out by their I.D. per the X-100B service manual and I can look for them on the schematic? I'm kind of new at this so the more guidance the better. What are the phase inverter tubes - one or more of the 12AX7s I assume? NEVER MIND I see them now as the V6 and V5 12AX7s for channels A and B. Thanks...
 
Looking at the schematic I'm going to GUESS that the coupling capacitors are the four 0.047uf/400v caps between these tubes and the 7868s???
 
BINGO! Give the Newbie a Cupie Doll! Bump the voltage on the coupling caps to 600. Too many to choose from but a good baseline cap is a Sprague "Orange Drop (715 or 716 series.) The only difference I know of between the two is steel(715) vs. copper(716) leads. 716 Not worth the difference in price just to go with copper. I've not heard any difference in sound. A lot of guys put in the K40Y or K42Y Russian PIO (Paper in Oil) caps. BIG!!!! Definately better sounding. BUT! They are BIG!! And they need insulating as the container is bare metal. If you want to hear the difference, put the O.D.'s in, listen for a while, the put in the Russian caps.

As for the Main Filter Caps. www.Hayseed Hamfest.com. CUSTOM Made, and better price than trying to figure out JJ's or whatever at AES. Also TOM Bumps the voltages higher a little, and runs the capacitance up slightly but still within parameters. Good Prices, Well made, and very nice to deal with. The only down side if you want it finished now is the 2-3 week lead time for manufacturing. But you get Can caps that FIT physically, are set up as original, and WORK!

NO AFFILIATION. VERY SATISFIED Customer.

Larry
 
I've been in touch with Tom "Hayseed" and will probably go that route. Don't know what are JJs or AES? I will bump the voltage on the coupling caps up to 600 and compare cost between steel and copper leads but probably not mess with the PIO. I'll try and keep up. Thanks again.
 
JJ is a manufacturer of electrolytic caps, vacuum tubes and probably other stuff I don't know about. AES is Antique Electronics Supply, tubesandmore.com
They sell all kinds of electronics parts for tube gear as does Radiodaze and a host of others.
 
K -- "AES" stands for Antique Electronic Supply out of Tempe AZ. They are very good to deal with. You can find them at www.tubesandmore.com

JJ is a manufacturer of electrolytic caps. Their product is good, and they have a good reputation. AES sells many of their cap offerings.

Dave
 
I appreciate the explanations as I will no doubt find need for these resources in time. Thanks to all.
 
Progress

I have replaced almost all of the caps and the bias electrolytic (save the two on the loudness contour circuit pending taking the face plate off). I have new filter caps/cans ordered from the Hayseed guy. All seems to work well. Still a small amount of hum at startup - seems to come and go within the first 5 or so seconds at startup. Is this likely to go away with new filter caps? My Pin 3 bias voltages range from 39.2(117V with Variac) and 42 (120V line voltage). All four are the same at any reading. One thing I noticed on this amp is that someone - maybe the factory? - has sealed the bias adjustment control with some type of sealant. It could be easily removed but I think I'll leave well enough alone since my bias voltages seems within spec??? Here is a pic of my work. Constructive criticism appreciated.
 

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Looks good so far. The bias pot probably has a little spot of glue to keep the shaft from moving from vibration etc. As long as your bias is in spec there's no need to remove the glue. Most of the hum you're hearing will likely go away once you replace the filter caps. I don't hear any hum from mine but you may have more sensitive hearing than I do. Some folks would replace the 2 silver diodes with new 1N4007s. As far as I know the old diodes are silicon but new ones are dirt cheap and readily available so replacement is an easy option.
 
The hum at start up may get better with new filter caps, but likely it won't. The most likely cause of power supply hum that is there only for a few seconds at start up is due the the output tubes not warming up at exactly the same rate. This could be because they are of different manufacture, or of unequal condition. It is hard enough to find tubes that are well matched once they are fully warmed, let alone also have them be matched during the warm up period.

When the output tubes do not pull a relatively matched amount of current, the residual power supply ripple at the point supplying the plates of the output tubes does not fully cancel in the OPT, causing the short period of hum during warm up. Once the output tubes all start drawing a similar amount of current, cancellation then takes place in the OPT, and the hum goes away.

Dave
 
Thanks all. I'll look into replacing the two silicone diodes. That makes sense about the output tubes warming up. These are original matched Fisher tubes and the voltages are pretty close. I hope/expect the minimal hum that I do here following warmup will be reduced following filter caps replacement. I really like this amp. I got an old TEAC reel to reel for free locally on Craigslist and all it needed was a new belt and general maintenance. I wish I had an owners manual (I have requested on another thread with no luck) for the X-100B so I new how to use the Tape Head, Tape Monitor, and Phono/Tape EQ controls. I just use the Tape Play input and Record Out and all seems to work fine with the reel to reel but I'd like to know more about those other controls.
 
If you have a tape DECK, (meaning a DIRECT line from the heads to the X-100B with no additional onboard amplification) that will work on TAPE HEAD. A TEAC A-4000(4010 without the amp underneath) can be setup this way. DO NOT USE A TAPE Unit that has an onboard amp/preamp with the tapehead jacks.

Tape/phono EQ back in the 50's / early 60's were all over the place due to no mandated industry standard, so FISHER included all of them. Put on a tape/LP and listen to them all. Use the one's that sound best to you, especially with LP's from about 54 and newer to about 63. By then the RIAA standard was mandatory and industry standard.

Tape monitor lets you listen to the tape as you are recording it. Any early FISHER OWNERS Manual from the early 60's can explain it better than I can. Go over ot www.fisherconsoles.com and look for an owners manual for one of the higher ended units. Even tho they might not be the same unit, the operation is the same.

Larry
 
Excellent info. As it turns out, the phono does sound better on the Tape Equilization selection. I understand the Tape Head inputs and did find an owners manual for a different model with good explanations of all of these controls. I found two faucet strainers with rubber stoppers that work perfectly for securing reels to the tape deck. They say China on them instead of TEAC but what the hey - they were cheap and are perfectly functional. About $4 a pop instead of $35 a pair on EPay. Would probably upset the TEAC purest. Thanks again...
 
Specifically to the Tape Monitor switch, for its intended purpose, it is only really useful with tape decks that have three heads; i.e. Erase, Record, and Play heads. A deck with this ability enables you to record from the selected source, yet while the Tape Monitor switch is in the Monitor position, let you actually hear what the Play head picks up a second later. Therefore, switching this switch back and forth during the recording session produces a slight delay in monitor mode, but allows for instant comparison of the applied signal (Input position), and the signal actually recorded on the tape (Monitor position). If your deck is not a three head deck, the monitor position may or may not work depending on whether your deck presents a signal at its output jacks during recording (most two head decks do not), but in any event if it does, it will only be a sampling of the signal available to record -- NOT the actual recorded signal on the tape itself as a true three head deck would supply.

Nowadays, the tape monitor switch is still (or also) very useful for using (say) and outboard equalizer in place of the tape deck. So connected, when the monitor switch is set to Input, you will then hear the direct signal, while in the Monitor position, you will hear the signal as modified by the equalizer.

I hope this helps!

Dave
 
It was suggested to me that after I replace the two N14007 diodes I replace some resistors to drop the current down to spec. This is beyond my understanding. Can anyone weigh in on this? Thanks.
 
No need. You're replacing the old silicon diodes with newer silicon ones to add an extra degree of reliability. 1N4007 are OK but UF4007 (UltraFast) or UF5408 seem to be more recommended.

Now if you were changing from selenium rectifiers... my understanding is that the efficiency due to the lower forward voltage drop of changing to silicon might require adjusting the current.
 
You are correct - I realized the person I got that info from was replacing a selenium rectifier. I will look into the UF4007 and UF5408 diodes. Thanks again.
 
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