400 heater question (I think) and other Q's

Finally measured those tubes. I hope I did it right. There was a CD player connected to aux and playing for audible checks, but during the testing the unit was switched to phono which had nothing connected. No audio, no hum, no crackle. Neg of the DMM was connected to chasis, Pos to the pin in question.

v14

pin 1 351 V
pin 2 -22.3 V
pin 3 32.5 mV
pin 4 0 V or 3.3 V AC
pin 5 0 V or 3.4 V AC
pin 6 -22.2 V
pin 7 350 V
pin 8 0 V or 365 mV AC
pin 9 377 V

v15

1 350 V
2 -22.1 V
3 67.6 mV
4 3.3 V AC
5 3.4 V AC
6 -22.1 V
7 350 V
8 1.3 V AC
9 377 V

V16

1 351 V
2 -22.3 V
3 90.2 mV
4 3.3 V AC
5 3.3 V AC
6 -22.4 V
7 351 V
8 1.7 V AC
9 378 V

V17 (didn't really glow today as viewed through the socket like it normally would)

1 351 V
2 -22.3 V
3 as high as 34 mV but sometimes sagging to 0
never seen it do this before. Don't know if it was the socket
or what. Did I make a cold solder joint or a short putting in the
10 ohm?
4 3.25 V AC
5 3.37 V AC
6 -22.4 V
7 351 V
8 312 mV AC
9 378 V

You can see the accuracy error in my DMM from the slightly different voltages on direct connected pins, but it should be good enough to sound any alarms.

After the tests with the unit right side up again I took each tube's temp from above straight down so the tube crown filled the view port of the IR gun and got v14 172.7 F, v15 182.6 F, v16 172.7 F, v17 150.8 F.


I did notice while under there that there is a factory looking resistor connected between 2 pins on v17 that doesn't exist on the other three tubes. Pictures available if needed.

The Bach organ and violin stuff I'm playing sounds pretty good at volume similar to being in the front of the original performance. I haven't really tested much for very low or very high volume.

Extra credit question: Anyone familiar with the Decca 1961/1993 Arthur Grumiaux 2 CD set of Bach Complete Sonatas and Partitas for Solo Violin, and if so does anyone know what is that terrible background rumble throughout the recording? Was that venue built directly below the Autobahn or something? It sounds like a diesel ship 10 miles away. I suppose it must be the HVAC, perhaps resonating off a tympany left exposed instead of being covered.
 
The voltages on pins 7 and 9 of the output tubes looks low, but the AC line voltage to the unit appears to be good, because the heater voltages look good. The low B+ voltages then is somewhat puzzling -- particularly since the output tubes aren't drawing any significant current.

Your voltages on pin 3 are low because the voltages on pins 2 and/or 6 are too negative. This voltage needs to be reduced (closer to zero) until the voltage on pin 3 reads about 300 - 340 mv. As is, the power amplifiers are producing significant distortion, due to the extremely low quiescent (no signal) current flowing through the tubes.

Dave
 
Thanks, Dave. I have not replaced power supply capacitors or done stuff to the power supply other than the stuff from the FisherDoc kit. Someone a long time ago mentioned in this thread a possible problem with a voltage doubler section.

There is something about bias supply voltage in the kit as item 7 in the Updates document linked below. It sounds to me kinda like this step has something to do with what you are refering to. What audio test can I do without special tools beyond the Mark 1 earhole to check out this distortion you mention as in normal use I'm not hearing anything weird. Would these tests be better done with the Fisher 66bs or the Koss TD/80 over ear phones?

Service Manual for S/N 30000 and up. This manual has been removed since close examination showed it to be the 40000 and up manual with a wrong cover page.

Update Guide
http://mynet.whitehat-inc.com/fisher400/Fisher 400 Updates/Fisher 400 Updates.zip

(manual emailed to fisherconsoles)
(so far I can't figure out how to deal with akdatabase.)

Thanks again everyone.
 
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I'm not familiar with what's included in the FisherDoc kit, so I don't know what components have been replaced. Typically however, the voltages on pin 9 are usually at least 400 volts, and with today's higher line voltages, 420 volts is hardly uncommon. Since these voltages are derived directly off of the voltage doubler, it does bring the health of those components into question. Still however, this is really not your biggest concern; the low quiescent current draw is. Resolving any voltage doubler issues will help with this issue, but I doubt it will fully address it.

As a first step, it would be good to get your tubes tested -- this to eliminate them as any cause for low current draw.

Much more likely however, is the combination of the (somewhat) lower than normal screen grid voltage (at pins 1&7), coupled with much higher than normal negative grid bias voltage (pin 2&6) supplied to the tubes. In the original design, the grid bias voltage is specified at -17 volts, while the screen grid voltage is specified at 365 volts. You have lower screen voltage and greater bias voltage -- a combination that acts to shut the tubes down, which is exactly what you have noted with their cool operating temps.

I strongly suspect that some of the FisherDoc components you replaced caused the bias voltage to be significantly increased, leading to the problem you've encountered -- or they've been installed incorrectly, leading to the same result.

I couldn't open your update guide to access the bias information you mention, and while it would be helpful, a good pic of the area would be the best resource for us to help. In any event, getting the quiescent current draw properly set will automatically take care of the distortion I mentioned earlier.

Dave
 
chaz;

On v17 check and reflow your solder joints to and from the resistor on pin 3.

Resistor between 2 pins on V17??? If it's RED RED BROWN Silver It's a 220ohm heater circuit balancing resistor to GROUND.(R36,or R37) There should be another one on either V15 or V14 on the opposite heater pin. (one on pin 4 the other on pin 5). If it's not that post a picture of it please.

Also, the ONLY AC Voltages on the tubes are on the heaters (pins 4 and 5). Everything else is DC. Don't worry about pin 8. It's not used on the 7868 and shouldn't have anything connected to it, except as a tie point. But it's not used by the tube.

Dave; On the 48001 series and up units I've done, I've noticed that the voltages on pins 1/7 and pin 9 are usually about 20V lower than the schematic says with wall voltage of 120-125v. My current unit has a pin 9 voltage of 380-385 with a screen voltage of 345-350. And that's with completely rebuilt P.S.'s.
 
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Thanks Larry. We should start documenting this stuff. My own 400 is a 48001+ unit (you might remember it generated all the data about the different OPT specs used in the later versions), and it routinely produces a B+ of (typically) 435 vdc from a 121-122 volt line. I wonder if Fisher didn't change the specs on the power transformer as well at some later date. It's entirely possible.......

Dave
 
The one I have now is 48291U. I'm waiting on a quad of EH's to be delivered, so I'll recheck all the voltages once i get them in and bal/bias'ed.
 
Let's see if I can keep all this straight...

First, to post the work done in answer to dcgillespie:

Couldn't download? Couldn't open? Didn't have the time? I checked again and I'm not having any problem with those links from multiple places in the world. Anyone else try them?

Items addressed in the FisherDoc kit:

Replaced components:

main chasis
C32 .1uf 250V
C41 10uf 50V
C42 100uf 50V
C63 .01uf 630V
C64 ditto
C69 .022uf 250V
C70 ditto
C81 .047uf 400V
C82 ditto
C93 .047uf 630V
C94 ditto
C95 .047uf 400V
C96 ditto
R28 41.2K
R34 5.6K
CR2 100V 3A
CR3 ditto
CR1 600V 3A

MPX

C210 1uf 350V
C214 .0047uf 400V
C216 .001uf 630V
C217 ditto
C221 .047uf 250V
C222 ditto
R222 16K
R223 ditto

Steps in the guide

1. R222,R223 move de-emphasis to 74.8us.
2. L101, L102, L103 check for 65 ohms on 101 and 10 ohms on the others.
3. C216, C217 prevent channel imbalance through leaks
4. R28 mono de-emphasis
5. Cathode resistors on outputs
6. Replace bridge rectifier
7. R34 bias supply shunt from 2.2K to 5.6K in order to move bias supply into -20 to -24 range to cool off output tubes. It claims this will have no effect on output power. (Certainly assuming a good doubler.)
8. Change all other listed components for leak prevention


There is the answer to part of the question. The kit moved those voltages on purpose. I think I would like to look into adding the individual bias trimmers at some point, but I'll have to hang out here and read a lot before I'm ready to do that.

What is a normal operating temp for 7868s in this application?

Also, after turning the unit right side up that cold tube came in line with the others, so solder and socket examination on the table now.

To reiterate, I'm not experiencing an audible problem. I admit I haven't tried very low volume to see how it sounds, but conversation level up through vibrate couch (3.5 to 4 on the volume knob) sound clear and tight. Enough sensitivity to hear the foibles of recordings like HVAC and audience or the director humming along. Solid bass, clear highs. I should say that I am still recalibrating my Mk 1 earholes after years of 384kbit mp3, but I don't hear anything alarming. I just didn't get cathode currents that made sense compared to reference docs.

I'll address the other responses when I'm not breaking from work...
 
chaz; I've been trying both all day. NO JOY! Both on IE and Firefox. Connection timed out. PM sent with my email address. Upload to me thru www.hightail.com IF they are UNDER 50MB each. Free subscription lets you upload one at a time.

I'll forward to Dave. Also I have a copy of the UNDER 29999 version of FISHERDOC's UPDATE Guide. I'll compare them and see if anything new is added.

It does sound like a connection problem on the one tube. But go ahead and swap that tube around just to make sure.
 
Agreed. I have Firefox and cannot open the links. Interesting that the kit doesn't address the power supply electrolytic caps that I can see.......

Dave
 
Dangit! One of my ISPs seems to have started filtering port 80. Should be fixed as soon as the changes make their way through the DNS.

Meantime I will respond in email from the PM. Thanks for the help getting this out there, and of course with the 400.
 
OK, I did the reflow.

The resistor between two pins is the 220. On v15 it goes from pin 4 to ground. On v17 there is a wire from pin 4 to pin 4 on v15. But on v17 the resistor connects pin 3 and 5.

At the bottom of the following link are pics from a couple days ago of the bottom of the 7868 sockets: http://mynet.whitehat-inc.com/fisher400/

By AC what I mean is that the DMM would show overload on all ranges unless I put the AC mode on, then it would show a small voltage. I'm not too worried about that since it was 4,5 and 8 that I got that result and 8 is the special NC pin.

Ugh, if pin 4 and 5 are heater on this tube then if I have a heater connected at all to v17 it is bridged through a resistor into my cathode!? Looks like an original. My schematic doesn't show the heater circuit.

My S/N is 64685W.
 
The tube with the 220 ohm resistor between pins 3 and 5 should have this resistor disconnected from pin 3, and then have its free end connected to the chassis. As shown, that configuration will cause a notable hum to appear in the channel that that tube serves.

Dave
 
Dave; I downloaded the files. Apparently the 30001 and up manual is an exact replica of the 48001 and up manual, down to the AX transformers and the extra If Transformer and tube. But this can't be right. I have still the pictures of my 1st 400 (32932S) that was clearly an EARLY model with the "A" transformers and 3 if transformers. Someone @ FISHER Screwed up or someone put the 30001 cover page on a late model manual. It's clearly not right for the series.

30001 manual # N1020-103AXA
48001 manual # N1020-103CX

The schematic # in the right hand lower corner is the same for both versions.


The Upgrade manual from FISHERDOC didn't change much between the up to 29999 version and 30000 and up version. He did change his tune on the Coils in the MPX unit, recommending an ohms check, instead of ripping them out. Otherwise it's pretty straightforward and the same. But he still maintains that the bias dual cap and the filter caps do not need to be changed out except if they puke or overheat. Reforming them is recommended method.


I sent via email to you, the 2 files plus the early version of Fisherdoc's "upgrade" kit document.
 
Chaz -- Thanks so much for making this information available! It helps all of us, help all of us........

Larry -- Of course, you're dead on the money as usual. This is deja vu all over again with the 800C manual fiasco. It's almost as if two completely separate divisions of the company were both issuing service manuals, with the left hand not knowing what the right hand was doing -- either that, or a completely new group came in to take over the old group's work, with the seam between the change over between the two groups leaving something to be desired.

This whole service manual "issue" with Fisher is quite a mystery. I get the occasional undocumented change. Heck, for how many times that ever happened with Fisher gear, H.H. Scott won the super bowl every single year for that metal. And I know that the Fisher operation must have been absolutely massive. Just think of all the tuners, receivers, integrated amplifiers, basic power amplifiers, preamps, console equipment, and even kits that were all being produced at the same time. Aligning supply and demand of raw materials and product production, let alone meeting product production needs for all the various models must have been a staggering effort that would have been thrilling to see. And that's exactly the point. For how well all this magic was performed -- and particularly throughout the 60s -- with minimal outward glitches that we as a group have found, the simple process (by comparison) of just keeping the service manuals straight seems to have flummoxed them. At least the 400, 800C, and X-202B service manuals all suffer from this same apparent inability to keep the records straight. I think there were others, too. And it's strange, because compared to other manufacturers, Fisher otherwise really tried to do a good job with this side of their business. It's just that against all of what the Fisher operation must have encompassed, to have such a glaring error as simple serial number correlation among various models for their service manuals is frankly stunning.

This was not really an issue during the 50s at Fisher, but of course, the operation at time must have been rather simple compared to what was to come. It must have been an unbelievable effort for Fisher to handle with the double whammy of Stereo as a new product feature, and FM MPX Stereo sweeping the nation both at the same time. Everything had to be redesigned and retooled. Not to mention the effort required to then turn on a dime again to facilitate the production of SS equipment a few years later........ Again, against ALL of that, and for how incredibly well Fisher managed that onslaught, the so obvious issues with simply keeping the service manuals straight kind of makes you just shake your head! But I digress..........

As for the change in thinking regarding the MPX coils, thank heavens FD saw the light! Removing those coils produces a serious loss of performance, and can even damage speakers under the right conditions........

Replacing the power supply caps has to be judged for the scenario at hand. For individual owners doing their own work who are comfortable with the work required and regularly monitor their equipment, then the recommendation makes perfect sense. But for those who are not so inclined that simply want the unit to be dependable again for another 50+ years with minimum fuss, then the recommendation only adds to the notion that vacuum tube equipment is problem prone -- a very unfair accusation in my experience.

Chaz -- Sorry for the deviation in your thread, but it all does fit -- kinda sorta.......

Dave
 
I would recommend notifying Jonboy55 about the manual and ask him to NOT issue it in the database @ FISHERCONSOLES. I can do that if doublechaz doesn't mind.

You're right Dave, this is DEJA VU ALL OVER AGAIN. I feel like Bill Murray in Groundhog day.

This isn't bad compared to SANSUI. They were the worst @ undocumented changes and manuals that didn't match the units. For instance, the 2000A and 2000X receivers were brought out in 1968 and 1971. I've found "X" model boards in "A" models, and "A" model boards in "X" models and some boards that aren't even documented. Trying to sort one of those out is almost a Hitchcock movie in itself. And the 1000A (last of the tube receivers), has at least 7 different manuals from a production run from 1964 to 1972. You figure out which one by the Voltage selector(4 different), bias pots(3 different setups), and a couple other parameters. What a mess!!! My feeling is the longer a unit is in production the less the line communicates with the drafting/engineering dept.
 
As for the change in thinking regarding the MPX coils, thank heavens FD saw the light! Removing those coils produces a serious loss of performance, and can even damage speakers under the right conditions........

Dave


Dave sorry for ask and deviates a little bit the thread but I would like to have a clarification about the coils where in the new document from FD are not disconnected; is maybe because they act as a attenuator in the output stage on the MPX and the LC circuit limits the output waveform at the plates that feeds the preamp stage in the 400? I don´t wanna be a devil´s lawyer but after made this mods in the MPX as result I´ve had considerable results in the reception but I noticed that the volume is higher in the FM mode and no broken speakers until now .

Regards

Luis
 
Yes, I certainly condone blocking that manual at the consoles site re: the confusion. I think I should also edit my post above and remove the manual from further circulation. Agreed?

As to my unit, I haven't had the cover off again since we last talked so working from memory I was thinking that without the fisher doc mods, that pin3,5 resistor was effectively going to ground through pin 3, and now is held away from ground by the added R. Right? That would explain why there is some hum that wasn't there in the old days.

I'll get under the hood again before I run the unit.
 
Yes go ahead and pull it. I sent Jon an email asking to pull it.

And yes on the resistor from pin 5 (or pin 4) to pin 3. Run it directly to the tube socket grounding ring, from pin 4 or 5. There are 2 of them one on 1st pair and one on the 2nd pair.
 
I've corrected the resistor. Since it originally went from pin 5 to pin 3 to ground, I have run it from pin 5 to ground rather than from 4 to ground. I suspect that 4 and 5 are nearly a dead short inside the tube at the heater, but this way made more sense to me, and I don't actually know much about the inside of tubes.

Now that I am starting to take all this more seriously I notice that v17 seems to not be heating, that there is hum in that channel that wasn't there 10 years ago, and that that channel lacks life in the reproduction until that tube finally heats up. After a minute or two the other three were at 105F and v17 was only 80f. It does seem to eventually heat up, or it did last time I shot them. Probably it is bad for tubes to operate them without being heated?

On this tube stuff I don't have a lot of confidence yet. Am I right in thinking that, lacking a tube tester, my next step is to swap v17 with one of the others and see if the heating problem follows the socket or the tube? I don't know how hard it is to completely blow up one of these units and would rather not make a big mistake.


While I was in there I finally corrected the headphone channels.
 
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