Cute maggie console all tube B&W mid 60's - Page 3 - Videokarma.org TV - Video

DaveWM · #31 11-30-2009, 06:48 PM

oh and I made up a nice little cathode checker from a dead octal tube base and a socket from the parts bin, all direct connections but for pin 8 which has two color coded wires with clips on the end. The only problem was it added too much height to the tube and the plate lead would not reach so I jsut used a short jumper for that. bypassed with a 1uf and check with both a DMM and a simpson analog, same readings.

DaveWM · #32 12-01-2009, 10:24 AM

before I go off the deep end the play is to clean all tube sockets and the yoke socket as well, clean the brt/con/horz/vert pots. should have done that 1st.

if that does not help the interlace, then I will do some tube swapping with a working set.

if no improvement I will try some voltage checks although I don't think that will help since it is subtle and intermittent (the interlace comes and goes).

wa2ise · #33 12-01-2009, 06:49 PM

Quote:

Originally Posted by DaveWM

If someone can explain how the interlace is controlled pls jump in.

Vertical sync has twice horiz frequency serrations, and sync separators are essentially low pass filters. In one field of video, the vert sync starts at a regular timed horiz sync pulse, the other field it starts at a halfway point between regular timed horiz sync pulses. The object is to try to avoid the horizontal sync from contaminating the vertical sync pulses and vertical oscillator circuits. If that happens, the interlace gets "line paired" and you lose vertical resolution. Scan lines on top of each other instead of halfway in between. But keeping the horizontal sync pulse out of everything else in the TV set is easier said than done, it gets into most everything. Maybe if the vert circuits use horiz B+ boost, a filter cap is not filtering well enough?

DaveWM · #34 12-01-2009, 11:59 PM

I tried to attache the schematic, it was too big. I will try again later, hope you can point out a possible problem area.

DaveWM · #35 12-02-2009, 12:18 AM

there is a .047 cap coming off the screeen of the HOT to ground, perhaps some kind of decoupler? I do not recall checking that one. It looks like a decoupling network as after the cap there is a 8200 5w resistor then it goes to the 245v B+, the Screen of the vert output is connected directly to the 245v source.

I am guessing the .047 cap will work as a decoupler at the freq of the HOT.

If the cap was bad it would have to be open (if it was leaky I would have a drag on the B+) I will try just jumping another cap and see if it has any effect. It's one of those brown dipped one, and I already had a couple bad one of those (leaky, .22uf 200v). The 400v ones tested ok, but I did not test that one.

all the filter can caps and doublers were replaced. as well as the electrolytic cathode bypass caps .

DaveWM · #36 12-03-2009, 08:39 AM

no change after jumping a new cap on that HOT screen.

think it is time to break out the scope and snoop around. I will check the wave pattern on a good set (same chassis) vs this one, on the grid of the vert output tube. then I will adj the vert hold so I get the over lap, that way I hope I can see what the pattern looks like, and if I can see the diff.

one thing I was checking was the voltages of the vert out, 0 on grid, 22 on cathode, all 3 of these chassis have this result, yet the sams say should be
-2.7 and 15. I have checked both the coupling cap and grid leak resistor, both ok. I tried different tubes, including some NOS (thinking it may have been gassy), I get some different cathode voltages (20-23) but the grid is always 0. I check with a DMM and a VTVM with and with out video signal.

The DMM would show millivolts some neg but very small like -50mv and it would jump around.

ctc17 · #37 12-03-2009, 11:26 AM

Sounds like you may have a leaky coupling or bypass cap in the vertical somewhere. All they need to do is get a tad leaky or off and they cause havoc and all kinds of weird issues. If that cap to the grid is even slightly leaky it will cause that to go positive.
Let me see if i have the schematic for this, do we have a model number?

DaveWM · #38 12-03-2009, 12:35 PM

c36-23-11

the coupling cap checked ok on the heathkit cap tester, but I will replace anyway. (the cap that goes to the grid of the 6EM5)

DaveWM · #39 12-03-2009, 12:38 PM

it does give a cathode current of 36ma, not sure how to check it unless I make up a remote socket with leads to connect up a meter on a 9 pin mini.

DaveWM · #40 12-03-2009, 12:40 PM

or could calcutlate it, I know I have a votage drop of about 21 volts, I will need to check the resistance (its part of the lineairity pot circuit).

22v/591ohms=.037 amps=37ma so seems like it is right on the nose.

DaveWM · #41 12-04-2009, 08:10 PM

finally popped the amp out while I wait on the vert out. sounded crappy, shorted filter cap. I used the dremel tool (looks like a bone saw) and just cut it off in place. I little messy and you need to protect other parts around if you slip, but very very fast and best thing is you leave the underside completly intact. drilled some holes, put in caps, pulled out the guts, put the top back on. I really like the fact that you can leave it all attached down below. The amp is SE with 2 EL84 tubes. I did not care for the single shared cathode resistor so changed it out for separates, upped the values some too to run the tubes a bit cooler. stayed with the orig values on the bypass caps.
(was a 100 ohm with a 20uf bypass, went with 250 ohm and 10uf on each tube). Before the bias was about 7v but now I found 12 on one and 4 on the other , yikes, got some nos tubes and now I get just under 8v on each withing .2v of each other. Sound MUCH better, I was getting all kinds of distortion. Granted changing the tubes would prob have been all that was needed, but I really like to check the bias so a good tube is not ruined by a bad one. The set came with out a MPX subchassis so I will have to search out ebay and see if I can find one, I want the stereo to work on FM.

I also will prob direct wire an input for the TV converter stereo out. The wafer switch is a little funky on this one and I cant seem to make out how to separate out the TV side into two channels like I did on my astrosonic. this wafer switch looks like its made from ceramic and you cant see the contacts, so with out a schematic its hard to figure how they took the single tv audio feed and get it two both channels. The astro was easy you could see the jumper wire in the wafer, I just cut it and installed another RCA jack.

oh the can on the tuner was open as well, loud hum when attached to the now repaired amp. bone saw to the rescue.

DaveWM · #42 12-05-2009, 07:45 PM

replaced the vert out tranny, no more retrace lines. Still have a little bit of an interlace issue, there is a .0051 5% cap on the grid of the vert osc, I picked up a .0051 1% silver mica (I think) that I will replace. Hopefully that will hold it steady, if not I still need to drag out the scope and do the side by side comparison. The audio is a little buzzy (sync buzz) but not too bad, beside I am going to be driving it off the converter anyway, but wanted to hear it thru the tuner 1st.

DaveWM · #43 12-05-2009, 09:54 PM

.0051 no change. gonna just let it run for a few hours and see if it settles down (I know I should have done that in the 1st place, I have never had it on for more than a few minutes).

I did install a 175ma cathode fuse on the HOT. Its spec to run at 124ma which it does, so this is in case something goes wrong with the HOT, maybe it would blow and save my flyback.

DaveWM · #44 12-06-2009, 08:46 PM

Quote:

Originally Posted by wa2ise

Vertical sync has twice horiz frequency serrations, and sync separators are essentially low pass filters. In one field of video, the vert sync starts at a regular timed horiz sync pulse, the other field it starts at a halfway point between regular timed horiz sync pulses. The object is to try to avoid the horizontal sync from contaminating the vertical sync pulses and vertical oscillator circuits. If that happens, the interlace gets "line paired" and you lose vertical resolution. Scan lines on top of each other instead of halfway in between. But keeping the horizontal sync pulse out of everything else in the TV set is easier said than done, it gets into most everything. Maybe if the vert circuits use horiz B+ boost, a filter cap is not filtering well enough?

gonna try jumping in a cap on the various filter caps to see if that has any effect.

DaveWM · #45 12-08-2009, 10:12 AM

Quote:

Originally Posted by wa2ise

Vertical sync has twice horiz frequency serrations, and sync separators are essentially low pass filters. In one field of video, the vert sync starts at a regular timed horiz sync pulse, the other field it starts at a halfway point between regular timed horiz sync pulses. The object is to try to avoid the horizontal sync from contaminating the vertical sync pulses and vertical oscillator circuits. If that happens, the interlace gets "line paired" and you lose vertical resolution. Scan lines on top of each other instead of halfway in between. But keeping the horizontal sync pulse out of everything else in the TV set is easier said than done, it gets into most everything. Maybe if the vert circuits use horiz B+ boost, a filter cap is not filtering well enough?

after re-reading what you said, I am going to see if I can figure out the network that comprizes the low pass filter. I think I get it now (did some reading on trouble shooting with a o scope, esp vert sweep and sync circuits).