Purchased 800C to restore: currently working perfectly

I've participated in a number of double blind tests over the years regarding this vary sort of thing, where caps, tubes, wire, you name it was subjected to this kind of testing. It was a non-scientific (I'm sure some element of strict protocol was violated), scientific (a strong effort was made to make it an honest a double blind scenario) study a couple of decades ago conducted among friends and fellow enthusiasts. Probably close to a dozen tests in all. In a nut shell, virtually all the claims made for improved sound from certain caps, tubes, and wires etc. basically went down in flames, with never a majority of contestants that could accurately state when a change was made, and to which component of those being tested over 50% of the time. The power of expectation bias is huge when you are intimately involved with making the changes (therefore knowing when it was made) and making the audible determinations that result from those changes -- this on top of dealing with subjective judgements being hard enough to begin with. The problem is, those in the camp that feel that different caps do sound different believe what they believe (they're entitled to), with no amount of scientific testing results being able to prove otherwise in their minds. It always falls back on the test procedure somehow being defective, and you don't hear what they hear. Fair enough, so the best you can do is respect each other's position, and agree to disagree.

Because it is such a passionate subject, I don't really chose to engage such discussions much anymore, other than to report what the tests I was involved in revealed, to the virtual agreement of all involved. For me, quality parts will get you there 99.9% of the time. But there are cases where components do make a measurable/audible change, such as sometimes when oversized caps that are many times the physical size of the original device are shoehorned into a place that was never intended to have such a large component installed, and then interacts with adjacent circuits in a way that the original components never did. But I realize -- and respect -- that not everyone agrees with this point of view. It is discussion that is a product of the new age of vacuum tube audio (it used to be we only argued about whether triodes or pentodes sounded better!), and likely won't get solved anytime soon. If it ever does, it will just be replaced with some new controversy! What would audio be without it? :)

Dave
 
Not A/B blind tests but there was a precis on different types of caps and how they fared on a scope with regard to even and off harmonics, slew rate, and a bunch of other parameters. The results were so close that it was pretty much impossible to tell apart except on the scope.

I agree with you on the nice vs. crappy looking rigs. If I hadn't driven and ridden in ambulances and black and whites (in the front seat!!) my hearing wouldn't be so crappy and I might (I said MIGHT!) be able to hear some differences, MAYBE. But like everything else, you have to train yourself to hear nuances, and such, and at my age and condition, it ain't gonna help any.

I'll try anything once. If I like it I will probably give it a go again. Which is why I don't go for the Russian caps any more. Too expensive, too large in most cases, and I have to dirty them up with heatshrink. The DME's or yellow axials do the same thing, sound similar to me, and cost a hell of a lot less than K40Y or K42Y's. Now if the amp was a $5K amp, I'd put in more expensive caps to maintain it's 'boutique' feel. But sub $1K receivers and amps get the least expensive, documented reliability caps. And I'm perfectly happy with the sound.
 
My hearing is diminished too (music teacher) and I honestly can't hear a difference even changing small signal tubes in my numerous amps. As for caps, I put what I have on hand at the moment. Shame, I can't even hear how ceramic caps in my Eico HF-81 ( original couplers) are supposed to sound bad...
 
I doubt that a properly installed resistor of that value, coupled with what I assume to be a .1uf cap, would cause the distortion you're hearing. Check your solder joints.





Everyone approaches restoration differently depending on methodology based on experience. If you know your cans were producing sound without distortion, then I'd leave them alone for now until I correct the noise issue. I think you mentioned that the receiver was "working perfectly" before you changed anything. That suggests that the cans are fine for now. If I were sitting where you are, I'd be scratching my head as to why there is now distortion. That said, the can caps are always one of the first things I change. Correctly operating/up to spec power allows for a confident voltage check down stream.





You could. Many believe that you should install a mix of caps so as to not develop a sonic signature skewed toward the sound of a single make cap. Of course, that is one of those "can of worms" debates so really, it is up to you. I go to the "mix em up" church. Bear in mind that you have to allow newly installed caps to settle or "form" before you can expect them to operate properly. Assuming the installed components are properly valued and you're not getting fireworks, I'd let it run for at least 15 minutes. Hearing distortion from just installed caps is not unusual.



Hopefully :thumbsup:
 
OK, I got stalled on changing the can caps. Any one have any good ideas on the wattage needed to overcome the chassis heat sink? I can barely get the solder melted with 2 -140 watt Weller pistol type solder guns. It goes cold before I can get the solder sucker on with one still going.
I have some larger solder irons, but I left them at my mom's house when I was soldering some new solar connections for her trailer. I've tried my MetCal, but it has the tiny tip on the one I have. Help? I have another Weller 100 watt. Maybe 3 then have someone else use the solder sucker?
Or use the copper wick? It didn't go well initially. Help please, I know many have done this.
Ken
 
I use a thermostatically controlled 250 watt iron for such work. Always does a great job, but even then, another 50 watts would be nice.......

Dave
 
Way back when I quit trying @ 150w. Since I was halfway through the removal of the can, I resorted to filing down the solder with a dremel to free up the tab. NOT recommended. Later, after pondering the situation I decided to cut all future cans at the flange. Been a stuffer ever since.

I recently came into possession of my father-in-law's iron. He was an electrician and used it in his work. It's such a beast all I have to do is plug it in, show it to the can, and the solder melts itself in fear! Probably weighs about 2 lbs. Use the highest wattage iron you can get your hands on and be done with it.
 
Thanks Everyone! Looks like I'm searching for a large iron or wait till I get back to my mom's place and see if my 200 watt will do it.
I have a large sheet metal iron you heat an 8lb copper tip with a torch. ( for doing gutters and other sheet metal jobs). I think the tip is too large to get in to the areas without possible damage to other components, but might check it cold and see. I can set the temp with my laser temp meter.
 
I use my 1500W heat gun up close to the chassis as I can get it, for about 5 minutes while my Weller station is warming up. Preheating the chassis and can helps the iron cut thru the solder pile on the tabs. Keep the heat gun or hair dryer (provided the wife ok's it!!!) on while soldering & De-Soldering the can's. I'm using a 60 watt Sears iron on the Weller station with the biggest tip (it looks like a shovel) I can get for it while doing can's. Then switch back to the 50W weller iron with the small tip for the regular stuff.
 
I used a Weller soldering iron that they market for stained glass use. If I recall correctly, it is an 80 watt 900 degree iron and has a real hefty tip on it. With a little patience it worked fine. Seems like it was about $35 or so.
 
I'm back from Work travel and had some time to do some changes to see if I could figure out why I had developed some distortion when I changed the 330K grid resistors with 220k resistors. It appears it may be coincidence, but I checked my solder joints and all looked good, so I went on to replacing my large can caps that I just received from Hayseed Hamfest. ( Oh, yeah. I ordered a 200Watt soldering iron off ebay,( $23.95) works great for melting that solder to suck it and wick it out to remove the cans. It is large so you have to be careful) After the first can I replaced, I brought it up with the variac and the DBT. Looked good so removed the DBT and brought it to 100 V with the Variac and Music. No distortion??
So who knows if it was the Can or ?? So I have the second can in but found a couple of resistors about 15% out of spec. I will be ordering them, as I can't find any at Fry's or Radio shack as they are going out of business and never have them anyway. Hopefully I can find some at another store. I might put them in to test the can and remove them when they show up. I really want to get the last can in tonight.
OK all caps are replaced and It sounds good. Played it for around 20 minutes no problems, low heat.
Now I have to test all the voltages and see where I'm at and move to the BBAM or IBAM- Leaning to BBAM now.

So this is a MetalBone and Hayseed Cap upgrade and a few resistor mods.
Is this something I should look at doing like this prior to adding the BBAM? Remember I am learning tubes. Not the same as Transistors. Hopefully I'm not crossing some fix with another.
Another hour of my real job and I may bring the 800C in and listen with the Klipsch Heresy's I'm using some INfinity Bookshelf speakers incase I did something wrong and didn't want to toast the Klipsch.
Screen%2BShot%2B2017-02-22%2Bat%2B09.47.58.png
 
Ski -- Adding Screen Stability resistors is something you definitely want to do now that you have replaced the power supply caps with modern units. The lower ESR values of today's caps can cause instability problems with the output tubes such that if triggered, can be very harmful to the tubes (cause arcing) and even damage the output transformers as well. It is a solution that I first proposed regarding these problems in my AudioXpress article on the subject some 12 years ago now, and all but eliminates any concern for this type of damage. Today, it has become virtually standard practice to implement whenever the power supply caps are replaced with modern devices. The drawing is only partially complete however, as ALL connections that were originally connected to pins 4&8 (except for the jumpers connecting these pins together) should be removed and attached to pin #1. Then the 100 Ohm resistors are added between pins 1&4 at each output tube socket. The point is that there are more connections to move to pin #1 than are shown on the drawing someone has provided you.

The installation of Screen Stability Resistors addresses a completely different set of issues from that addressed by the installation of the BBAM. Therefore, for the best operation of your Fisher, both of these modifications should be installed together, without concern that one is acting in place of the other.

Dave
 
Ski -- Adding Screen Stability resistors is something you definitely want to do now that you have replaced the power supply caps with modern units. The lower ESR values of today's caps can cause instability problems with the output tubes such that if triggered, can be very harmful to the tubes (cause arcing) and even damage the output transformers as well. It is a solution that I first proposed regarding these problems in my AudioXpress article on the subject some 12 years ago now, and all but eliminates any concern for this type of damage. Today, it has become virtually standard practice to implement whenever the power supply caps are replaced with modern devices. The drawing is only partially complete however, as ALL connections that were originally connected to pins 4&8 (except for the jumpers connecting these pins together) should be removed and attached to pin #1. Then the 100 Ohm resistors are added between pins 1&4 at each output tube socket. The point is that there are more connections to move to pin #1 than are shown on the drawing someone has provided you.

The installation of Screen Stability Resistors addresses a completely different set of issues from that addressed by the installation of the BBAM. Therefore, for the best operation of your Fisher, both of these modifications should be installed together, without concern that one is acting in place of the other.

Dave
 
Thank you very much Dave.
Is there an thread on this anywhere? I think I should be able to follow everything you have discussed above, but I always like to check 2X's then do the work since I'm a newbie. Again thanks and I'll stop listening until I get this update in place. Then I'll start with all the voltage testing to see where I am really after all the updates and then start any adjustments and then the BBAM.
I'm getting close. I can't wait to move it in and start listening.
Then I'll go back to do the same on my Futura VI with the 59A and 59T. Caps only as it is a Hybrid. ( I believe I have some updates on adjusting the transistor balance there also- but that is after the 800C is done)
Again thanks for the responses.
Going back to work now.
Ken
 
Try the drawing on page 2 of the common parts for FISHERs STICKY THREAD for the screen resistors.
 
Try the drawing on page 2 of the common parts for FISHERs STICKY THREAD for the screen resistors.
Hi Dave,
Here is what I've done, but before I do the DBT and Variac turn on I wanted to verify my work. Blow is the drawing of what I did and then some pictures of it. One more question: Solid core or stranded wire? I used stranded for the daisy chain of pin 1's. ( 18 GA ) solid would have been easier.

The below is from Larry on that thread for the 7591 models which my 800C is.
I have the 80 ohm resistor on pin 5 to ground per the MetalBone kit also.

7591 ONLY IMPROVED SETUP
1.) disconnect the old buss wire from the tubes.
2.) run a new wire of sufficient length to daisy chain the tube sockets at pin 1.
3.) install a 100ohm resistor to each tube socket from pin 1 to pin 4. Pin 1 is not used and is not connected internally.
4.) connect flying end of the 7W resistor to one of the center tubes. PIN 1. It must be before the 100ohm resistors.
5.) Connect the new buss wire to each tube's pin 1 in turn. Solder all connections.
Larry

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