Discussion in 'Fisher' started by gtxtom, Feb 15, 2018.
That would definitely cause the problem. Don't turn it back on until it's fixed. Glad you caught it.
Joe. I wondered about that and asked Dave about originally. He said the same thing as you. I erased the gaffs on my copy, but forgot about it when I sent the copy to Fisherconsoles. I'll make sure Jonboy55 gets an updated copy and installs it. How's this grab you. Best I could do on Adobe Reader (free edition). Had to do 2 screen grabs at higher resolution as one page wouldn't show the connection from the B+ to C21 or C20.
So what is the updated schematic look like for the X-101-B? Remove C20 & C21?
No. Just make sure that the B+ line doesn't connect to C20 or C21 as shown in the schematic (see red lines). It's more of a schematic error than anything else. Mine doesn't have the connection.
Definitely a tell-tale sign. Replace the 100 ohmer. Same thing happened to me - I popped the 100 ohm resistor and got an unrealistic reading. One thing I learned... always by double parts so you have extras if either something goes wrong during installation or they go bad.
Larry is right. Those connections do not actually exist in the amplifier. The schematic just confuses the user and no such connection should exist in the unit. The red lines he drew are the bogus connections. Note that there are no round dot indicators of connections at the indicated points of connection by those "wires" of the schematic. Its another indication that the schematic has a problem there. Normally a true connection between components on a schematic have a dot that indicates a connection. Otherwise it is assumed that there is no connection where lines cross on the schematic.
Oh ok. Understood. Thanks for the heads up, Joe!
Thorne, I'm realizing that a little too late hahah
So when I deoxit these controls, which product am I using on which switch/knob?
DeOxit D5 and follow it up with either Faderlube or SHIELD. If you are short of funds, get the D-5, and go down to Home Depot and get some CRC 226 electronics lubricant.
So I replaced the 100 ohm resistor and checked everything again. Still have ~0.760 on V5. The odd thing to me is that when looking at the output tube sockets. V5 is the only output tube with this white wire (circled in green) connected to pin 5. The white wire goes to a junction where it goes to C18-C and also off to the 12AX7 heater circuit. Should this white wire be off to one end like on pin 5 of V4 so as to not affect one tube so heavily? I ran the amp for ~30 mins and no red plating. Audio sounded great. I'm wondering if it's getting current from the heater circuit and is throwing my reading off?
The white wire is your OLD link to the cathode bias circuit. You'll also find it on V9 and V10. It's normal and shouldn't have any effect on the reading you get at pin 5. Your 10 ohm resistor should be connected between the Pin 5 socket pin and the white wire. In your 1st photo it looks like the10 ohm is connected to a brown wire. Is that wire connected to the bias buss @ C-18. And also are the white wires on pin 5 connected to C-18 also. If so REMOVE ALL THE WHITE WIRES and leave the brown buss wire with the 10 ohms resistors to pin 5 intact. It looks like you have the original and the mod both connected and it's throwing the readings off. Verify this and post BEFORE DOING any cutting.
I was thinking you used 10 ohm resistors on the screens then realized they were 5 band resistors @ 100 ohms vs. 4 band like the 10 ohm on the bias.
Yes I have the correct resistors going to the correct spots. I never knew I was supposed to disconnect the white wire. The brown wire is the one I made up for the cathode bias resistor mod. So I should remove the white wire?
I don't have a white wire going to V9 or V10 (or V4 for that matter), only V5. So should I be removing the white wire?
No. I waswrong in my reading of the circuit earlier. You have a 6.3VAC lead from the transformer tap to the bias supply and the cathodes, plus -44V at the cathodes (Pin 5), which then is controlled by the 4 heaters, and the resistor network of the R89/R94/R95/R96/C-18-C. Putting it on the buss with the cathode resistors will drop the voltage to the resistors and tube heaters above. So leaving it as is correct. I realized something that needs to be answered by a pic. Your 1st pic with the Brown wire shows the resistor in a series configuration and the cathode wire connected to one side of the resistor and the buss wire. As the voltage goes down the line each succeeding tube has less and less voltage. Or the otherway around, as the voltage goes thru each succeeding resistor the voltage drops even more with the bias being lower than normal by (I'll let the einsteins of the group figure out the voltage drop as I'm getting a headache just trying to figure out how to even how or why). Anyway the bias tube heaters are starved even further and it takes longer to warm up. So lets see both ends of the brown wire terminus, and all the 10 ohm resistors in situ. They should be laid out like this with the cathode resistors in a parallel configuration to the buss. I added the white wire setup too.
Here's the setup. The white wire goes from pin 5 of V5 to pin 5 of V1
Leave it alone then.
So where do I go from here? I can't tell why one socket is so different. I swapped the tube from V5 with another tube, V10 and the one that got swapped into V5 still read about double the current as the other 3. I also tightened up the pin sockets on V5 as well to no effect.
Let me open up mine and take a look at it.
For some odd reason or other I neglected to install 10 ohm resistos in mine. BUT the V5 White wire to the heaters is the same as yours. So leave that be.
So much for my vision late at night. (I really should use my cheaters with this 32" monitor I'm using with the computer too. If all your cathode resistors are wired as shown in post 70, they are OK. No problems there. With V5 showing a weird double the voltage reading, I'd be looking at the socket, especially AFTER a change in tubes. I suspect one of the pins has separated and is not getting voltage to the tube as it's supposed to. Pull the tube on V5 and meter each of the pins from top to bottom (a probe on each side and measure ohms. If all ok, then I don't know what the hell is going on other than to take voltages when running of all the pins on that tube and compare them to the others.
I measured resistance of each pin from top to bottom and got 0.2 or 0.3 ohms on each. Here are my measurements for all 8 pins on the 4 output tubes
1 - 394.2 396.4 395.3 395.1
2 - 43.20 42.80 43.04 43.12
3 - 447.6 446.5 448.3 447.2
4 - 398.1 394.8 395.7 394.4
5 - 42.96 42.10 43.71 43.63
6 - 27.98 28.09 28.38 28.39
7 - 42.64 42.98 43.23 43.25
8 - 396.0 395.1 394.9 394.6
One odd thing (not related to my V5 issues - although obviously it must be fixed given the voltages I've been getting around the amp) is that wall voltage is measured at anywhere between 121VAC and 123VAC. The voltage at the fuse right where the power cord enters the amp is over 140VAC. Why is that happening?
At the wall outlet:
At the fuse:
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