cs4 voltage problem
- Thread starter John
- Start date
If OA measures 103V, what does OB measure? What about Breg on the populated side? (A side)
If Breg is 100V and OA is 103V, please let us know, as that would be most likely from a miswire
If Breg is 100V and OA is 103V, please let us know, as that would be most likely from a miswire
I would strongly suspect a miswire at the 6922 socket.
-PB
-PB
very carefully checked 6922 wiring and all seems good. Took some dc resistance readings on the 6922 and all seem good.
Cathode to ground with ""negative lead on cathode"" 25.5k ohms both triodes
Both grid to ground with either meter polarity 75K ohms
Both plate to ground 44K ohms.
Many thanks
John
Cathode to ground with ""negative lead on cathode"" 25.5k ohms both triodes
Both grid to ground with either meter polarity 75K ohms
Both plate to ground 44K ohms.
Many thanks
John
Hmm, could you post a photo of the C4S board on the offending side?
John said:
Ah, I didn't know that, that's helpful information. Hopefully the photos can reveal what's amiss.
fullheadofnothing
Moderator
Please do not post schematics for Bottlehead products. I will forward your measurements to PB.
I have been inspecting the pre amp all day. All wiring beeps out perfectly from all socket to C4S boards. However I may have run into a hint as to what is happening. Resistance measurements from T2 and T14 to ground read 85 K ohms and T4 and T12 read 75 K ohms to ground. The 10.5 K ohm resistor is installed correctly double checked. Any thought about this.
Many Thanks
John
Many Thanks
John
Paul Joppa
Moderator
My apologies for this late reply - I've been out of town and out of contact for the last week. Just got home last night.
It seems likely that there are shorts between the grid and plate of the 6922 - i.e. C1 to C2 and C6 to C7 - or perhaps both stoppers (220 and 100 ohms) accidentally are going to the same pins. Inspect those pins closely looking for possible connections or bridging. If the problem does not appear there, it would be relatively easy to measure the resistance between C1 and C2, and again between C6 and C7. This will test the short-circuit theory, even if the connection is not at the tube pins. If you can post a picture or pictures of the C socket showing the wiring to each pin, we can see if anything seems amiss.
It seems likely that there are shorts between the grid and plate of the 6922 - i.e. C1 to C2 and C6 to C7 - or perhaps both stoppers (220 and 100 ohms) accidentally are going to the same pins. Inspect those pins closely looking for possible connections or bridging. If the problem does not appear there, it would be relatively easy to measure the resistance between C1 and C2, and again between C6 and C7. This will test the short-circuit theory, even if the connection is not at the tube pins. If you can post a picture or pictures of the C socket showing the wiring to each pin, we can see if anything seems amiss.
Many Thanks Paul, No problem on the delay as you are helping me. I found no shorts between C1, C2 and C6, C7. I next removed the C4S boards and triple checked the Terminal strip wiring, and rewet all C4S solder joints. When unit was reassembled still had same problem of low OA voltage. I next removed tube A,B, and C and voltage raised to around 136 volts. I think my next step may be to remove and test transistors on C4S board although that will have to wait till Monday.
Tons of thanks for your help
Charette
Tons of thanks for your help
Charette
Paul Joppa
Moderator
Bingo!
If the voltage at the plate terminal (2, 7) rises to 136 volts with the 6922 removed, then the current through the 47K resistor to ground is 2.88mA - which should be the value on the OTHER SIDE of the PC board. Check the R1 which should be 113 ohms on the A side, and 301 ohms on the B side. I think you have 301 on the A side, but check both. You must have built both boards the same way.
If the voltage at the plate terminal (2, 7) rises to 136 volts with the 6922 removed, then the current through the 47K resistor to ground is 2.88mA - which should be the value on the OTHER SIDE of the PC board. Check the R1 which should be 113 ohms on the A side, and 301 ohms on the B side. I think you have 301 on the A side, but check both. You must have built both boards the same way.
Many Thanks go out to Paul. I did reverse the 113 and 301 ohm resistors....bad me. Unit fired up and passed signal, however one last problem. Gain mismatch with -30db input @ 1100 hertz signal on both channels I get output reading of 13.66 db on the left and 20.25 db on the right. This ratio stays consistent across the full frequency spectrum of frequencies. 6 db is a great number in balanced audio as pin 2 or 3 could be dropped but I am at a loss for this problem. I have change positions of the pentodes and tried a new dual triode to no avail. All DC voltage look equal except for the usual variations in Kreg which measure around 1.7 volts. Oh boy. Any ideas.
Many thanks
You guys have been the best
Charette
Many thanks
You guys have been the best
Charette
