Received new Bias Filter Cap yesterday and installed it today. R4B is now working again. Thanks to help from the list again. The replacement used was a Sprauge Atom 10uf @500V which is a bit overkill but was the closest I could find from either Digi Key or AES on the day I ordered.
Bias and S-Meter alignment now work perfectly. It was very interesting to note the difference in the 'magic eye' readings for the leakage tests on the old vs. new cap when testing on the old Heath C-3 meter. The eye would close down about half way on the 150V leakage test on the old filter cap and did not move at all on the new 500v cap. It sort of a tight fit and I had to ream out the holes in the p/s board a bit with my knife in order to fit the larger diameter leads on the new filter. Muting now puts the meter up to 60 over and the 40 over at 15V sets up nicely. I also received a new or newer V1 and Audio output V7 which made little if any noticeable difference but now the Rx has only 1 tube that tests a bit weak on the B&K 707. Nice to have it running in the shack on a cold rainy day. Now to paint the top cover and it will be pretty decent. Nice to have it back on the air. On Thu, Feb 24, 2011 at 9:36 PM, Paul Gerhardt <[email protected]> wrote: > Garey > Thanks > > Will look some more at the electrolytics C11 or 91? (the cap between > D6 and gnd) I have about 23-24V on Q4. Will keep looking.... > > Paul > > On Thu, Feb 24, 2011 at 6:02 PM, Garey Barrell <[email protected]> wrote: >> Paul - >> >> OK. What you MAY be seeing is a very high ESR (dried out) C11 (I assume you >> mean C91 here?). Essentially this looks like a resistor to AC and lets the >> voltage rise to peak. -70 to -80 VDC isn't all that bad if it's really DC. >> You should measure about -36 VDC at the Emitter of Q4. Another possibility >> is a leaky C178. >> >> -45 is about right for the RF GAIN pot, R83, R123 junction. Don't forget >> about the MUTE shorting plug if the FUNCTION switch is anywhere past "ON". >> >> This is a very high impedance circuit, and it doesn't take much to load it >> down. >> >> 73, Garey - K4OAH >> Glen Allen, VA >> >> Drake 2-B, 2-C/2-NT, 4-A, 4-B, C-Line >> and TR-4/C Service Supplement CDs >> <www.k4oah.com> >> >> >> Paul Gerhardt wrote: >>> >>> More troubleshooting on this one today. >>> >>> Pulled out the D6 diode and C11 and both checked OK on DVM and Heath >>> Condenser checker so put parts back in and UNhooked the wire from C11 >>> Neg side and Bias Voltage went from -45 to -135 ripple looks fine. >>> >>> Next I Hooked the wire back on C11 and UNhooked the white-red from the >>> side of the RF gain pot. Now have -65 Volts at C11 (Where schematic >>> says -80V) and S Meter is on 60 over in Standby (and all other >>> positions). >>> >>> Hooked RF Gain (Red White that goes to Mode Switch) back on and C11 >>> Voltage back to -45 V. >>> >>> Measured V5 voltages and all are OK except Pin 1 is -2.3 instead of >>> -1.1. 70V and 110V and fil on the other pins are all OK. >>> >>> Something is pulling the bias down excessively it seems but I have run >>> out of time and ideas for today. >>> >>> >>> >>> >>> >>> On Tue, Feb 22, 2011 at 11:32 AM, Paul Gerhardt<[email protected]> >>> wrote: >>> >>>> >>>> Got some time to poke at this some more. Voltage at V2 does not set >>>> up according to Sec 6.4.9 Bias and S-Meter Adj section of manual. >>>> 1. hook up meter >>>> 2. set -1.35 had to turn control all the way to get this voltage >>>> 3. S1 Adj sets 'ok' >>>> 4. Set -15 - very low like -3 Volts >>>> >>>> Going back to the power supply I am only getting -45V at the -80V test >>>> point, (C11 and D6) after the bias diode in the power supply. So >>>> either something is bad in the few bias supply components or something >>>> in the reading is 'dragging it down' B+ is good and both sides of >>>> power transformer ohm out the same so I think the transformer is OK. >>>> >>>> Ohming out the three diodes I get a much higher 'forward' resistance >>>> on the bias diode D6. like 15k one way and 30k the other way. The >>>> two B+ diodes have a much lower forward resistance so this may be a >>>> problem. >>>> >>>> Plan now will be to unhook the 'circuit' and see if bias goes up and >>>> if not look at D6 and C11 as R141 and R96 are both within tolerance. >>>> >>>> Any other thoughts B4 I remove the little power supply board? >>>> >>>> Paul - >>>> >>>> Same result if you unplug the MUTE cable at the receiver? FAST and/or >>>> SLOW the same? >>>> >>>> Possibly bad V1, V4 or V5, unplug one at a time. Does S-Meter go up to >>>> full scale? Voltage at TP-2? >>>> >>>> 73, Garey - K4OAH >>>> Glen Allen, VA >>>> >>>> Drake 2-B, 2-C/2-NT, 4-A, 4-B, C-Line >>>> and TR-4/C Service Supplement CDs >>>> <www.k4oah.com> >>>> >>>> >>>> Paul Gerhardt wrote: >>>> >>>>> >>>>> My B-line has been working but today that after hooking it back up >>>>> (was working on a TR-4) I noticed that the R-4b was not muting or >>>>> going into Standby. >>>>> >>>>> In standby or ext mute (w/o short in RCA Mute)audio is distorted >>>>> RF Gain only raises S Meter to 20 over or so. >>>>> >>>>> Something seems to have changed since I used it last a few weeks ago. >>>>> >>>>> Could this be a tube failing or ?? >>>>> >>>>> >>>>> >>>> >>>> >>>> -- >>>> Paul Gerhardt >>>> K3PG >>>> http://pgerhardt.blogspot.com >>>> QRP ARCI 6674 >>>> FP 274 >>>> >>>> >>> >>> >>> >> > > > > -- > Paul Gerhardt > K3PG > http://pgerhardt.blogspot.com > QRP ARCI 6674 > FP 274 > -- Paul Gerhardt K3PG http://pgerhardt.blogspot.com QRP ARCI 6674 FP 274 _______________________________________________ Drakelist mailing list [email protected] http://mailman.zerobeat.net/mailman/listinfo/drakelist
