hi all, another project i got a 1949 motorola model 7vt5r and the chassis has TS18 on it does anyone have a schematic for this set i would feel better having some guidance befor recapping this. the 7jp4 im not sure how im going to check it because my bk440 only shows an 8 inch tube.

The Sams and factory manual are here:

http://www.earlytelevision.org/tv_schematic_diagrams_postwar.html

m5 is the ballast tube, does anyone know how many resistors are in this metal tube and what the values are because the schematic shows m5 at the line in as 37 ohms, or how to test to see if its good. the amount for an original ballast is just nuts at 85.00 i would rather use ceramic resistors to make this up if i had to.

m5 is the ballast tube, does anyone know how many resistors are in this metal tube and what the values are because the schematic shows m5 at the line in as 37 ohms, or how to test to see if its good. the amount for an original ballast is just nuts at 85.00 i would rather use ceramic resistors to make this up if i had to.
Capacitance voltage drop is the way to go! I know it isn't authentic, but neither is a cluster of high wattage resistors. Plus, there is a cushioning effect on the inrush current.
The original ballast tube had some kind of an iron alloy wire, that would rust through. That's the reason, the new ballasts are glass, that are filled with, what I understand is nitrogen gas. :yes:

ok so i got the resistances and there is a 200 ohm 2- 105 ohms and a 37 ohm so if i redo this resistor network could i use 2 100 ohm 10watt resistors for the 105 ohm resistors, and a 33 ohm 3 watt for the 37 ohm and 2- 100 ohm 10 watt resistors in series for the 200 ohm ? they are alittle low on the 33 to 37 and 100 to the 105 resistors but i dont know what the wattage would be for each one. does anyone know what the hv should be at the crt ?

I agree - capacitance droppers are the way to go.

Here's a schematic of mine: https://flic.kr/p/mbSWqg

further reading: http://www.videokarma.org/showthread.php?t=249434


If you stick with resistors, I'd go with 120 or 133 ohms rather than 100. They are used to drop the line voltage for the series string tube filaments. Add the filaments up and you'll find that 105 was a little low to begin with and now we have higher line voltages.

You have 0.3 amps running through each so the power is I2 x R or 0.3 * 0.3 * 100 = 9W if you go with 100 ohms. A good rule of thumb is to double the wattage so I would use 20W resistors.

10W is fine for the 200 ohm. The 37 ohm resistor is not critical so 33 will be fine. It's just there to limit the surge current to the selenium voltage doublers on power up.

ok so the 2-100 ohm 10 watt resistors are ok in series for the 200 ohm, and the 33 ohm is ok for the 37 ohm but is 3 watts ok for this one ? is there any way to somehow modify temporaraly my bk440 crt tester to test this 7jp4, there is no listing for the 7jp4 but there is a listing for an 8 inch crt. i have many ceramic resistors and to make up even the 133 ohm would it be possible to use a 100 and a 50 ohm resistors both 10 watts each in series would this stay 10 watts at 150 ohms or would the wattage now be 20 watts.

You could see if the filament lights up, but a 440 cannot supply the correct voltages to check for emissions.

The 8 inch CRTs listed in the 440 setup chart are conventional magnetic deflection CRTs like the 8DP4 not the electrostatic 8BP4.

150 is a little high and starve the tubes filaments a bit but probably OK at least for testing. The 100 ohm resistor would dissipate twice as much as the 50 ohm so the combination would be a 15W resistor.

ok so i should just try to get 120 or 133 ohms at 20 watts. so if 2 10 watt resistors are in series would this increase the wattage or would it stay the same ? could you tell me what the heater voltage is for the 7jp4 crt, i have never worked on this kind of set, sorry for so many questions,lol...

ok so i should just try to get 120 or 133 ohms at 20 watts. so if 2 10 watt resistors are in series would this increase the wattage or would it stay the same ? could you tell me what the heater voltage is for the 7jp4 crt, i have never worked on this kind of set, sorry for so many questions,lol...

Practically all the CRT's of the day have 6.3 volt, 600ma heaters. That's why there's a series-parallel arrangement of the tube heaters. Most of the receiving tubes in the sets are 300ma heaters.

ok so i should just try to get 120 or 133 ohms at 20 watts. so if 2 10 watt resistors are in series would this increase the wattage or would it stay the same ? could you tell me what the heater voltage is for the 7jp4 crt, i have never worked on this kind of set, sorry for so many questions,lol...

BTW, two ten watt resistors in series do equal twenty watts. Also two ten watt resistors in parallel equal twenty watts.

BTW, two ten watt resistors in series do equal twenty watts. Also two ten watt resistors in parallel equal twenty watts.

True, but if the resistors are not equal value, the power will not be shared equally. If one is twice the value of the other, it will get twice as hot.

well if i did do the 150 ohms then the value would probably rise even more when they get hot.

ok so i put the ballast together with the 150ohms in place temporaraly and the tubes are brightly lit but is there anything that is common with these sets why there is no hv and how do you check it without an anode button. there is ac going to the rec tube from the flyback but its low maybe 2kv. the flyback looks new its so clean. is there a common cap like the several 6kv caps that are in there, all the caps are original and i decided not to change any yet just the power supply caps i changed.

The 6KV wax caps will kill all HV and deflection. Don't expect any wax caps or lytics of this era to be good, 98% are bad from age by now.

ok so i recapped the power lytics would it now be a good idea to change the hv caps, the 6kv caps, and see what i get from there. the rest of the caps are aside from micas the same values as the color sets, 200v or 600v. the 6kv caps are stated to be oil caps does this make any difference oil or otherwise ?

JustRadios has the 6KV capacitors. They are bad if they are the black oily ones or the wax type. These were the major failure in these sets.

i went to just radios site and cannot find how to order these hv caps. is there a special way to navagate the site? the caps in there are oil so can just a film or metalized cap be used in place of oil ? i know mica caps in the hv area are sometimes used for oscillator timing, are these known to go bad even as old is 1949, some say they dont go bad but i dont know.

The justradios site has a capacitor shopping cart. Just click it and it will take you to all their capacitors. The original ones were wax, then oil from what I have seen. The ones from just radios are small tubulars. I have used them in all of my Motorola sets and in the high voltage of my Silvertone with total success. Without changing these the sets can act up in so many ways it'll drive you crazy. Also, the 12SN7 tubes can be somewhat critical in vertical and horizontal. Try several if stability or size issues crop up. Also, ohm out the horizontal centering pot. I had one that was 1/2 value and prevented the horizontal centering from working. I had to add resistors on both sides to bring the value to the one listed in the schematic. After that it worked fine.

i found it on just radios and is it ok to use .0047 6kv in place of .005 6 kv ? since i see this as an option but i really dont know.

I used those in both my Admiral and my Philco and they work just fine.

Gregb

Mica capacitors in the deflection stages can cause issues. As far as mica capacitors in any TV go always replace the ones in the deflection stage, but don't change the ones in the IF/tuner unless you have a darn good reason to believe they are bad.

Careful. The mica caps in the horizontal circuit (200pF, 680pF, 900pF) are rated for 2,000 volts. Hard to find mew mica caps rated for more than 1,000o volts and 900pF is an oddball valuee.

Some of the caps in the sweep circuits are tubular types. I've got four Motorola electrostatics running and they all have the tubulars still in them. The ones that look like brown dominos can give problems. In the sweep circuits I try to use 1600 volt replacements. They seem more stable than the 600 volt types (less fiddling with the horizontal and vertical hold).

Yes, there are some tubular ceramic caps. They are very reliable and I'd avoid messing with them.

does anyone know what the hv should be for the crt and is it a fixed voltage when done. also what is the B+ voltage and the B++ voltage , i have no info in the schematics as to what the voltages are.

Approximately

CRT = 5,500 at the highest potential right on the 1B3 rectifier. Not sure what you mean by fixed ?
B+ = 125
B++ = 250

fixed meaning how it was built originally, not having an adjustment. thanks for that info. one thing i noticed is voltages are jumping up and down as if its trying to get somewhere but then hits a block so its probably those .001 and .005 6 kv caps waiting for them from just radios.

to change the selenium rectifiers and put in 1n4007 diodes, if this is the ones to use do you know how the arrangement works with the resistor that goes along with and where it goes with the diode to lower voltage. and the value of the resistor used with silicon diodes for a set like this.

Yes, you can use 1N4007 which are rated for 1 amp. Even better use 1N5408 rated for 3 amps if you have some.

I don't bother using resistors, but if you want use around 47 ohm @ 5 watt in series which each diode. Either end - doesn't matter.

so if i decide to change the seleniums to 1n4007 diodes i wont use resistors and i will keep the ballast as, 130 ohms for the 105 ohms and the 33 ohms for the 37 ohms but should the 200 ohms be changed to a higher ohms because of the voltage difference on the b++ ??

If you want - doubt it will make much difference but 220 are probably easier to find than 200.

ok so there are a few mica caps rated for 2kv that are important in the vert and horiz section if these caps are bad or go bad are there any close substitutes that can be use to get by. i already did a search for these caps and no luck, as i figured. i think there was 3 micas not sure unless i check the schematic , 200, 680 ,900 , mmf . ceramic disc maybe the closest but not as stable but there must be something out there to use in place of an unobtainable part.

there is a 680pf 2kv ceramic disc in the rca or clones, would this even work in place of a 680pf 2kv mica capacitor. i know it wont be as good in some way but not sure, maybe this would create noise within the circuit depending on what circuit it is subbed in. if this were a timing circuit how may this possibly affect that circuit ? im just trying to find possible subs that may work if i find the micas are bad even though they are know to be reliable, but they do go bad.

i am also looking for the front fold down cover for the motorola table top tv model 7VT5 if anyone may have this and is willing to sell it please let me know. if i cant find it i may just make it. thanks.

Unless is it is a NP0 or C0G type, a ceramic caps value will vary with temperature causing the sync to be unstable. Don't worry about it. I've restored a bunch of these and those HV mica caps have all been fine.

the temperature that would cause sync to be unstable, would this heat be from the tubes or the cap in the cicuit. because the cap if were used could be moved to a cooler location, i dont know... :drool:

The ambient temperature under the chassis will rise while the set is playing from resistors, tubes, etc. Don't worry about it - odds are very good your caps are fine.

as for the selenium rectifiers i know if there is no output well then they are bad but what other things will they do when going bad . would they short in such a way where the voltage is there then drops then its back, this is what i have here testing the b+ and b++ and the voltage is jumping up and down and the seleniums are getting warm but not really hot. maybe this is consistant with a shorted cap, i dont know but trying to find out what these rectifiers do when going bad. could this happen where the voltage goes up and drops then goes up and down under a load ?

Just change all lytics and paper style caps, and the seleniums. Trouble shooting it with all those crap parts in it would be like trying to plug the holes in a boat with a chicken wire fence for a bottom. Lytcs usually don't just short, they can leak current at high voltage which you can NOT test for with a DMM, and this leakage may not be constant in magnitude.

60's sets may be worth troubleshooting, since their lytics, and mylar/paper caps are much less failure prone, but everything made before the late 50's (and select sets into the early 60's) with the older style caps just ain't worth trouble shooting with original caps installed. And even if you were to try with proper equipment (a tuning eye type capacitor checker such as a Heathkit C-3) you'd be hard pressed to find 2% of the caps good in most sets of that era.

all the lytics i changed already befor even plugging in i just thought that maybe the seleniums would break down under load.

i know mica caps in the hv area are sometimes used for oscillator timing, are these known to go bad even as old is 1949, some say they dont go bad but i dont know.

In the past I have read about confusion over the mica or micamold caps found in older equipment. What I read is that there were two kinds that were almost physically identical. One type was actually a true mica capacitor which is known to be very reliable and almost never need replacing. The second type was evidently a wax/paper cap wrapped up in the same type casing as the mica with the horrible color dot identifiers.

Of course the wax/paper would be the ones to replace. It all boils down to simply getting rid of all wax/paper caps as well as electrolytic on a VERY old set an starting from there with any further repair if any is even needed. Also, if I were to do this semi restoration on a very old set (as I have), I would let the set work for several hours over a period of days. I have found that the longer a set works, the more "kinks" just go away more or less.

Finally, the selenium rectifiers will let you know when they fail as a smell like no other will fill your air space. :nono:

The square caps wwith the color dots are either mica, or paper, but the paper ones are much larger, both in capacitance and physical size, the real small ones are mica. The larger ones are paper.

ok, so to get the proper b+ and b++ voltages the set has to be on and everything in place as if its operating normally as this will have the proper load on the power supply. weather seleniums or silicon recs would this be the proper way to check these voltages ?

As a rule, seleniums are trouble waiting to happen. I usually start with about a 22 ohm 5 watt in series with the silicon replacements and once things are running I can change the value slightly up or down to compensate. Not using a dropping resistor in series will raise B+ too high and it can cause instability issues (voice of experience).
Also, make sure the IF tubes are good and have no grid leakage. I have had many problems with the TS-4 and the TS-18 chassis with these tubes.
Those tubular ceramic caps are fine 99% of the time. It's the 6KV ones that will cause problems.
If I remember right you are going to use the capacitive ballast system. If you are going to use the black, iron wire ballst, a variac is a must. At their age they make all kinds of noise when turned on until they stabilize. The glass ballast is fine.
I use a ts-18 as a daily driver for the news and weather. I like the Motorola electrostatics. They are reliable once up and running!

ok so all caps are changed and also the lytics except the 5- 6kv caps as i clipped one by one to see if this was the problem and it still is not right. and now i changed the seleniums to silicon diodes and a dropping resistor in place but i still have the same thing where once the tubes light and things start to conduct the voltages are jumping up and down and i have no clue why. it seems as if something is preventing the voltage from advancing. unless i need to put the 5- 6kv caps in and this is the problem but still waiting for just radios .

just disregard the last post the 6kv caps came in today and i got a raster and 4kv of hv, and should be higher but its in a really fast verticle roll that if i adjust the vert hold and vert size i can get it to stop for a second then goes nuts again and the vert hold has to be turned to max at one end to get it to stop rolling for only the moment. so i guess ill be looking for resistors in that circuit . theres one resistor off the vert hold checks good and there is another of the vert size and thats good as well.

ok here comes the problems , i got a picture but from left to right i have 3 images and the verticle and vert size are not good cant get the full screen without it rolling so bad that it almost goes to a line across. and the brightness cannot be up all the way it gets dim and brightens up alittle if i turn it down.

ok the horizontal is fixed now got a single image. now im trying to find 8-9 volts of ac to isolate the heater in the crt to see if its any good it is very dim and the bright pot is fine the hv is 5kv any resistors at the brightness pot or around i checked and are good. i figure this is the only way i can see if the crt is good by adding a few more volts to see if it brightens because there is 6.6 volts at the crt now so 8-9 volts should show something or at least give me an idea. this series string filiment, by taking the crt out of the string i should be able to twist them together just for a test as the heater voltage will rise from the crt out of the string.

Did you test the crt with a crt tester?

Did you test the crt with a crt tester?

dont have a tester for the 7jp4

This brings up a good question, is there a tester that came with the connector to test a 7JP4? Or does one have to use a clip lead connector? I have four different crt testers and not one of them even lists this crt.

Gregb

I have one from Eico that will test them. But like most members, it's easier to test in a known working chassis.

no there is no adapter for this tube there are voltages said that the tube needs to test accurately and should be done with a tester that lists that tube. i applied 9 volts ac to the heater and was not really any difference in brightness so now im going back to the chassis to look for another culprit like in the video output section, matbe something there like a resistor went up in value. if the tube was that bad at 6.6 vac then 9 vac should have brightened it up noticeably but didnt.

does anyone know what kind of crt tester tests 7jp4 tubes. name and model number?

I have one from Eico that will test them. But like most members, it's easier to test in a known working chassis.

And that is what I have done in the past when the need came about.

Gregb

Precision CR-30, Sencore CR-70 & CR-7000 and a Beltron (not sure of the exact model #).

Those will only test emissions though. Electrostatic CRTs do not use an ion trap and the phosphor can get dim from ion bombardment even though emissions are good. Operating in a working set is really the best test.

well i got the chassis going and i have 2- 7jp4 crts 1 rca and a sylvania. the rca has a clear picture but is very dim and the sylvania is so silvery i cant get much of a picture maybe if i lower the bright almost all the way ill be able to see it, washed out. hv is 5 kv and voltages at the video out tube are perfect and i applied 9 volts to the rca crt and didnt get any brighter so maybe they are gassey, they are old. i clipped one wire from the crt heater and completed the string circuit while trying the 9 volts ac. so i guess if everything checks out within the operating circuit then i guess its safe to say these crts are done.

heres with the light on and light off, yup they look done... :sigh: sorry 1 is upside down.

I wonder if they made brighteners for those tubes:scratch2:

From what I've read brighteners don't really help electrostatic CRTs.

Did you check these voltages on the CRT ?

pin 2 (cathode) - 0 -220 volts (brightness control)
pin 5 (A1) - 1,600 - 2,400
pin 9 (A2) - 5,000 - 6,000

bandersen , the pin 9 would be hv and i checked that right off the 1b3 and its at 5kv and pin 5 is focus and dont know if it makes much difference but the focus works very good on this crt even though its dim. the brightness i did check but an exact voltage i would have to check again but at 0 volts IIRC is full bright and the pot goes to .8 volts. i really hope i missed something here and these crts are infact good. there is one thing i dont understand is at the 6sL7 pin 5 there is a cap to ground, looks like a small dog bone type and its about 1/4 inch long and its got colors on it and at random it will arc between the leads and i dont know if this has anything to do with anything although im sure its not supposed to arc this way. it seems there is hv there and is seeking ground. well if i did miss things here i certainly want to find out, i dont want to condem these crts if they are not bad. ok i just revised the bright voltage 0-220 v , A1 is right about 1600v vary with focus control, A2 just touching 5kv.

ok with all being said above im sure now the crts are bad because i said i applied 9 volts to the crt heater with a separate transformer but i had the wrong tap hooked up i had 7 volts. so now i applied 13 volts @ 300 milliamps which then the voltage came down to 9.5 volts ac and i tried this with the sylvania crt which when plugged in to the chassis the heater was bearly visable at 6.6 volts but after applying the 9.5 v the heater lit well like any other heater i have seen and the picture was bright and watchable in a lighted room. the other crt , the rca did get brighter but not much still watchable in a lighted room. so i know im done with the chassis except for the arcing from pin 5 of the 6sL7 cap to ground, maybe this is caused from bad crts, i dont know. i checked the ohms at 1-14 the heater pins on both crts and they are the same so why would one bearly light but the other seems to light normal. i could see if resistance went up on the crt heater that bearly lights but they are both the same. the sylvania , the gun at the heater looks new no marks or heater signs or discoloration from heat but the rca heater part is black and shows signs as if it has been used alot. so what may cause the heater to not light properly with the proper voltage, but rather more voltage.

Could be the phosphor is wearing out. I have about a dozen 7JP4s that all test the good emissions well into the green but the brightness varies considerably when used in a TV.

BTW the CRT filament current is 600mA and 6SL7 arcing is a common issue with these sets. The 6SL7 plate voltage is derived from the HV output through that string of megaohm resistors so make sure they are all good and not arcing.

well all i had to try was 300ma but to be so bright with the increase in voltage and the filiment still with that added voltage dont look bright at all like its getting to much voltage as it would get brighter with added voltage. those resistors, there is 2 of them ? increasing the heater voltage would have a positve affect on worn out phosphor ? is it at all possible that this sylvania crt has a defect in the heater like maybe a higher voltage filiment was put in because from several different 7jp4 tubes i looked at all had the heater housing turned black from heat and maybe lots of use yet this one has nothing on the heater housing at all that would suggest lots of use and by putting higher voltage to the heater it did not make the heater much brighter at all where as i thought it would have. the reason i ask this is because i get just bearly a shadow for a picture in a dark room as if there were no hv but adding this voltage was like having a new tube, it went from one extreme to the other.

There are around eight resistors in the HV divider string. It's all the ones around the centering controls. If any of them are faulty it could allow too much voltage on the 6SL7 plates and they'd arc over. I'd try replacing the 100K right off of the 1B3 HV rectifier too.

Don't recall hearing of much luck with increasing the filament voltage on a 7JP4. Could be why they didn't make brighteners for them.

well i dont know what to think by upping the heater voltage and having a difference of day and night it made, but this one the voltage made a difference but i would still like to get one that works the way it should. the extra voltage on top of 6.6 ac was only 3 volts is this about what a brightener would raise a tube to or more ?

You can put a brightener on a strong new tube (of nearly any type CRT or signal) and get a noticeable boost in performance. Cathode emission behavior is proportional to heater voltage, and life span is inversely proportional.

You could operate that 6SN7 at 3.3V or 12.6V if the benefit of either one was more important than the downside.

You need to find someone with a working restored set to hook your tubes up to in order to properly test them. It could still be a cathode-grid voltage issue plaguing you.

all the voltages are where they should be thats why i couldnt understand why the day and night difference with this crt with 3 volts more. the chassis i have here is done except for a few resistors to check and based on the picture quality with the added voltage of that crt its looking really good for a 60 year old tv.

well i got a super bright 7jp4 and it was regunned, dont know when it was done but the neck where it was cut is actually a little bit smaller in diameter then the rest of the neck on the tube itself. the difference in the 2 diameters is so obvious and the line is visable where it was cut. i didnt know this until i unraveled the aluminum and paper from the neck so i can clean it up. so i have a few resistors to change and ill post a picture of the result when i am done. i got 2 of these motorola sets one i recapped and the other was for parts so i went back to this friend of mine that i got these sets from and i did know he had a third set but i had to dig for it and found it with this crt in it, big surprise. i do have a cabinet not the one with the cover if anyone may need a cabinet for maybe the front plastic part or whole. the cabinet is a 7VT1. does anyone know if an admiral b@w set is worth anything, this is one of those 2 tone red and white sets its in very good shape all knobs, cord, antenna, complete im not sure when these sets came out maybe late 50s or early 60 -61 dont know..

Weird - never heard a 7JP4 being rebuilt. Wouldn't think it'd be worth the effort back then.

If it's an Admiral like this, it's from 1957: https://flic.kr/p/r4DsgR

Usually go for $50-$75 in good, unrestored condition.

here is the pics ,its done for now but kind of got the buzzing in the audio like its not tuned all the way and cant get rid of it but channel 2 is better then channel 3 but its ok. the filiment string on this set calls for 105 ohms x2 , i have 150 ohms x 2 and the crt filiment voltage is 6.06 vac so for it to be right it would show 6.30 on the dvom. wondering if this heater voltage is to low or would it hurt anything along with the other tube heaters are alittle low. i did have 130 ohms x 2 befor and i am debating if i should put it back so as the heaters will be alittle higher, what do you guys think ?

Slightly low heater voltage = slightly longer tube life, but slightly reduced tube performance during that life. If you are going to use it a lot keep it that way so it lasts, but if it is going to be a shelf queen that occasionally is powered on to give a Brilliant demonstration of the pinnacle of the performance of that design, then going for 6.3 is fine.

One good idea is to get what IIRC are called TVS diodes. They are essentially AC voltage Zener clamps. Install one across the CRT heater to prevent line voltage spikes from potentially damaging it. There is a good thread either here or on ARF about them in 3" Pilot sets.

here is the 7jp4 that was regunned, notice the difference in the diameter of the glass where the weld took place the top section is clearly smaller then the bottom. and i spoke to someone about this tube and he also said these tubes were not rebuilt because of the type of glass used back then on these tubes would not hold up to certain temperatures during the rebuild process and he was surprised to know that i had one that was redone. early television museum told me they most likely will not be rebuilding the 7jp4, i dont know the exact reason maybe be infact because of the glass i didnt question it further.

I'm very interested to see that someone successfully rebuilt a 7JP4. As far as I know, Scotty at Hawkeye wasn't able to do it. It might have been because guns weren't available.

well i have a verticle problem where it just wont stop rolling really bad after a few minutes on it starts, but now i lost alot of horizontal width dont know what happened so now i got 2 major problems, any hints out there... :scratch2: :D

well it appears that the horizontal size pot is getting hot and smelling bad so something went bad here. i had a spare and put it in but no difference so its staying off until i find whats happening here , it maybe a mica cap in that circuit maybe shorted, dont know. i have micas and compared readings in nf with the ones in the set and are good and seems to be no shorts so now it may be the horiz sweep transformer, again not sure.

ok found that problem but what would keep the horiz oscillator from running correctly. if i touch pin 1 of the afc- horiz oscillator with my dvom in voltage check mode the oscillator runs and the pic is ok. the pic is pulled in on both sides, horiz, when turned on then i touch that pin 1 a slight arc and its fine. something seems to keep the oscillator from running when turned on. and the voltages are high where they should be low like 70v is 200 v.

well nothing but trouble with this set now the hv shut down and the 100 ohm resistors at the hv oscillator tube are getting hot , dont know where to go from here. ok my mistake hv is ok but this horizontal issue where the oscillator for the horiz hold wont start unless i turn the horiz pot to one one to get it running and then its fine but i cant turn this knob every time i turn it on. at a loss, help

I've never had a problem quite like this before, but I'd start by checking all the parts around the size control. It's got B++ on one side and the T-6 hor sweep output transformer on the other. The other side of that winding goes to some capacitors and T5. Assuming all the caps are OK, the only path for DC to smoke the pot is through T5 and T6 so I'd suspect those parts.

i even checked the ohms on all 3 transformers and they check right on. t-4 and t-5 have resistors a 15k and a 27k the 27k measures 37k , thats all i really found. and when i got done recapping this set had a verticle problem but no horizontal problem.

ok i found the problem, there is a 20mmf cap off t-5 that was bad however the parts chassis i have has a different cap, colors are not the same but it works horizontal oscillator is right there now but i dont know what value this cap is because i am alittle short left to right on the horiz size so this cap must set the frequency and must be right to have the right size on the screen. next is the verticle, maybe another cap as i think there are 2 or 3 in that circuit, non stop rolling but i can put a resistor from ground to the .004 can and stop the rolling but temporary. that cap is at pin 2 of v12 and this cap sets the oscillator in motion and if it dont run i learned that it will take out the horizontal size pot very quickly. this capacitor that went bad is a dogbone type and im wondering if a ceramic disc 20 pf can be used in place of this 20 mmf .

The original ceramic tubular caps had an excellent temp coefficient and were very stable. Make sure you replace it with a C0G or NP0 type.

i know that resistor and the .05 cap and if i take them both off i still have 250 volts using the frame ground and b++.

Think about it - what would you expect to see? 0 volts ? That would mean the frame was at the same potential as B++

Also what about that 0.01 off V11 going to the frame (chassi) ? Which schematic are you looking at - Motorola or Sams ?

Think about it - what would you expect to see? 0 volts ? That would mean the frame was at the same potential as B++

Also what about that 0.01 off V11 going to the frame (chassi) ? Which schematic are you looking at - Motorola or Sams ?

well looking at sams and motorola schematics they both dont show a .01 at v11 but this set had one and it was original motorola cap never touched so i put a new one back i also checked it and its right on the money. so in taking one leg of that cap off gives me the verticle hold, and i think its excessive voltage on the frame from somewhere. befor i put the silicon diodes in i never checked if this problem was there befor and if the diodes were in wrong somehow the set im sure wouldnt work. i would have expected some voltage from static or leaking voltage from the rf section and beyond, like maybe 10 -50 volts maybe alittle more but not 250 volts dc. the .01 leg is off got verticle, the resistor from b- and the .05 disconnected i still have 250 volts , frame ground to b++.

well looking at sams and motorola schematics they both dont show a .01 at v11

So leave it out then. It might have been a revision.

So leave it out then. It might have been a revision.
problem is, it was in the circuit and there is a reason why it cannot be in there now, like the voltage on the frame ? im baffeled now....

ok so leaving the .01 disconnected didnt last its rolling again so i put it back. i looked at near everything here and it just wont stop rolling. i subbed tubes, mica caps, verticle hold pot, for the verticle and horizontal micas as well and all makes no difference. , there has to be a reason why it wont stop rolling all the caps that came out were put back with the same values. i went over everything i did and cant find a thing wrong. does anyone know where i can go from here because i am burned out at this point and maybe someone out here can mention something that i missed. i cant get an acurate voltage reading on tubes in the verticle circuit because the voltage is all over up and down as it rolls out of control. i dont know if the horizontal may have something to do with verticle or is upsetting it for some odd reason. right now the horizontal is ok just alittle short on the width. so maybe something is interfearing between both vert and horiz and the verticle is taking it the worst. HELP :sigh:

i dont know if its possible if there is a problem in the video amp or video output since i was thinking that everything has to go into the video amp and output, just guessing at this point since i didnt check anything in those areas.is this at all possible ???

I'm very interested to see that someone successfully rebuilt a 7JP4. As far as I know, Scotty at Hawkeye wasn't able to do it. It might have been because guns weren't available.

Here is another rebuilt 7JP4, so must have be doable.

http://www.ebay.com/itm/Late-Rebuild-7JP4-Tests-Strong-/201319933110?pt=LH_DefaultDomain_0&hash=item2edf9a64b6