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Old 27th May 2018, 1:04 pm   #21
FERNSEH
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Default Re: Firestone 13G3 Television

Hi Roger,
Don't give up on this project.
Try exchanging the connections to the Y plates to the X plates and see what happens.
The attachment shows the deflection circuits of the Teletone TV149. The Y plate coupling capacitors have an unusually low value of 0.005mfd. The coupling capacitors have to be good for >5000volts.

DFWB.
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Old 27th May 2018, 1:11 pm   #22
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Default Re: Firestone 13G3 Television

Hello David and Buggies,
I don't know really what happen with this crt. I will try to exchange the plates and see. all the capacitors are new especially those 6kv link to the def H and V plates.
I have the complete schematic of this set at hand, that's why I could make the full restoration up to now.
Roger
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Old 27th May 2018, 1:54 pm   #23
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Default Re: Firestone 13G3 Television

Quote:
Originally Posted by rogerdup View Post
Not good news. When disconnecting the wires to the vertical deflection plates, the same raster appear instead having a nice horizontal line. Have checked with the ohmeter and found no short between the V plates. I am sure there is something wrong inside the crt. it seems not having survived well the trip from USA to France..Too bad,I'm sad.
The DC voltages can still be correct in the vertical output stage with no actual deflection if the vertical osc has stopped. Have you checked the outputs on the anodes of the vertical output stage on the scope ?.. that there is a high voltage vertical sawtooth there at least a few hundred volts anti-phase on each anode.

Or are you saying that connecting the vertical def plates loads down the sawtooth output from the vertical output amp?

I think its unlikely the CRT as if the gun structure was broken (can happen but fairly rare) you wouldn't have the well centered (out of focus) H trace.

When the def plate coupling caps go leaky it usually causes a significant beam offset and loss of EHT too.

These RF power supplies the EHT is significantly affected by the position of the spring clip (many have this) on the glass envelope of the 1B3 that provides the + feedback and also by the condition of the tuning capacitor, make sure it is a new silver mica type.

Last edited by Argus25; 27th May 2018 at 2:01 pm.
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Old 27th May 2018, 1:59 pm   #24
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Default Re: Firestone 13G3 Television

Does the vertical centering control move the horizontal line up and down?

DFWB.
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Old 27th May 2018, 2:04 pm   #25
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Default Re: Firestone 13G3 Television

Thanks folks for the answers.
Yes the centering control works. But why when I disconnect the V plates, I still have a raster as in the photo instead having a line?
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Old 27th May 2018, 2:08 pm   #26
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Default Re: Firestone 13G3 Television

Probably stray coupling unless the focus is miles out.

No proper ramp = no proper scan.

Lawrence.
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Old 27th May 2018, 2:16 pm   #27
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Default Re: Firestone 13G3 Television

If the V centering control works, your CRT is likely good. The V centering control alters the DC vertical deflection plate voltage, so the plates are working fine. So now you know there is no or little AC vertical deflection voltage coming out of the vertical deflection output amp. It could be that stage, but likely the vertical osc is not running.

Also, if the EHT is out of spec, the focus voltage will be too. It just looks like a very de-focused beam.
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Old 27th May 2018, 2:29 pm   #28
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Default Re: Firestone 13G3 Television

Quote:
Originally Posted by FERNSEH View Post
The Y plate coupling capacitors have an unusually low value of 0.005mfd.
Couldn't agree more, I guess its possible but in most electrostatic deflection sets these are usually in the region of 0.05uF with 2 to 4Meg def plate resistors to get an adequate low frequency response for linear vertical deflection, so I wonder if it is a mis-print on the schematic, might not be , but worth checking the actual value of the caps in the set. (Anywhere from 0.001 to 0.005uF is fine for coupling to the H def plates).

Ignore my remark about the spring clip in post 23, this set has a separate feedback winding on the EHT transformer. Also there is a tuning control in parallel with the 750pF tuning capacitor on the EHT transformer, this will affect the EHT too.

Last edited by Argus25; 27th May 2018 at 2:36 pm.
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Old 27th May 2018, 3:12 pm   #29
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Default Re: Firestone 13G3 Television

From Frank's tube data website: https://frank.pocnet.net/sheets/093/7/7JP4.pdf

It's safe to say that the sawtooth drive to the deflector plates must be at least 800 volts P - P for a full scan. Easy to achieve by employing differential amplifiers.
So the HT supply for the timebase amplifiers must be greater than 500 volts?

DFWB.
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Old 27th May 2018, 5:19 pm   #30
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Default Re: Firestone 13G3 Television

I try exchanging the H and V plates without too much change. But looking carefully at the bottom of the screen it seems to have a fine raster. I don't know if it is a reflection of the upper which is actually bright.
All this could be like an important vertical linearity fault which compress the image.
Responding to Argus, yes it seems to me that 0,005mf capacitors for link to the 6SL7 is very low for this stage. In sets prototypes I build in the past, I remember to put 0,05mf.
Anyway, I'll took some time for further investigation this week and back to you friend with the results.
Tomorrow, I will be busy with the mecanician for the study of the 60 lines scanning disc Globe machine project.
Take care everybody and thank you for the advices !
Roger
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Old 27th May 2018, 8:10 pm   #31
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Default Re: Firestone 13G3 Television

Last minute: a friend bring me an oscilloscope, so it surely help for further investigations on repairing this set. Actually I get a strong noise in the loudspeaker aparently coming from the RF/IF stages, changing with the contrast and/or channel selector position. Last photo show a raster which looks like a very poor vertical linearity frame. I think about a strong interference coming from the previous stages affecting the sync signal.
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Old 28th May 2018, 12:41 am   #32
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Default Re: Firestone 13G3 Television

This image suggests there is now some activity in the vertical oscillator ...have the capacitors there been replaced and all the resistors checked? Now you have a scope it should be easier to fix.

It looks like you have replaced the top chassis electrolytics with Tesla brand ones is that correct ? they look good.
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Old 28th May 2018, 4:18 am   #33
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Default Re: Firestone 13G3 Television

Hi Argus,
I replaced all the capacitors and high value resistors on the VHV circuitry.
The vertical oscillator show some sawteeth at the scope, but lot of problem remains. The Tesla capacitor I found are NOS so, I spent time to reform them before they will be able to do the job again.
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Old 28th May 2018, 4:33 am   #34
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Default Re: Firestone 13G3 Television

The AC vertical deflection voltages on the two anodes of the 12SN7, should be about equal in amplitude an opposite in phase (polarity) and will probably each be in the range of 300 to 400V peak to peak. Try another 12SN7 or swap it with the 12SN7 in the H output stage as a test.
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Old 28th May 2018, 6:36 pm   #35
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Default Re: Firestone 13G3 Television

Hi everybody ,
I finally found the fault on the tv. A wire making a short to an end of the focus pot. See photo. Now I have to investigate why I heard this rough noise of the image frequency entering the sound circuitry. The sound is taken from the Video anode, and so, a slight detune and that's it Too bad..
Thanks for the interest of my messages!
Roger
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Old 6th Jun 2018, 6:12 pm   #36
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Default Re: Firestone 13G3 Television

The restoration of the Firestone is almost finished. Still some points to review:
a vertical linearity to better and the problem of the sound which tend to be poisoned by the image signal due to the sound frequency very close to the image frequency. 4.5mcs. The sound signal come from the video anode and pass through a filter. We have to increase the sound frequency channel up to 5 mcs to accomodate the RF modulator output.
I will change all the 5n ceramic decoupling capacitors of the if stages and have to check every resistor of those stages. Anyway the Firestone is on the way back to life !
Sorry for the poor quality of my screen shots. The crt is quite OK.
roger
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Old 6th Jun 2018, 6:19 pm   #37
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Default Re: Firestone 13G3 Television

Hi Roger,
I presume that you are using a system M modulator for the source of signals? I recall that very early 525 line receivers did not use the intercarrier method for the FM sound and had parallel sound and vision IF amplifiers.

DFWB.
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Old 6th Jun 2018, 7:30 pm   #38
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Default Re: Firestone 13G3 Television

Hi David,
I don't know exactly what the RF signal of the RCA modulator looks like, but it is a modern device perhaps not quite adapted to the old standards in term of sound and carrier frequencies separation. The TV149 use the same sound circuit taken from the video tube anode.
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Old 14th Jun 2018, 8:01 am   #39
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Default Firestone 13G3 linearity to be improved

Hello Everybody,
I finished restoring my Firestone 13G3 TV and after changing almost all the tubes and caps, it gives very good pictures.
The only point that is bothering me is the poor vertical linearity. The 5 meg pot is at the maximum. I don't know what to do to correct that. The sawtooth bent on the top.

Last edited by rogerdup; 14th Jun 2018 at 8:03 am. Reason: grammatical
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Old 15th Jun 2018, 8:15 pm   #40
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Default Re: Firestone 13G3 Television

"The sawtooth bent on the top."
Hi Roger, Is that the sawtooth waveform displayed on an oscilloscope or the image on the CRT? The latter might be "hooking" which is caused by instability of the frame sync at the start of the scan.
Are you supplying the receiver from a 625/50 source or 525/60?

DFWB.
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