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Poor regulation on G6 .

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colourmaster
(@colourmaster)
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Hi Everyone, I obtained a 26" single standard G6 for my collection. It had been working well but has developed a fault. When it's switched on the picture takes a while to appear very slowly coming on blurred and over scanned. If the brightness is turned up the picture balloons and disappears with the sound going low. If the brightness is returned to normal setting the picture re appears slightly better but not perfect. I'm wondering if the shunt stabliser is not working properly. Any advice would be appreciated. Regards Gary. 

g6 1
 
Posted : 15/12/2019 4:58 pm
Nuvistor
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First impression is low EHT voltage, I don’t know the G6 but I would be checking voltages around the line stage. Low emission EHT rectifier a good possibility , GY501? The CTV sets I worked on had a 1k resistor in the cathode circuit of the PD500 to set up the shunt regulator. If that voltage is above 1.2v with the brightness turned off then the PD500 is drawing too much current and requires checking, that voltage should reduce as the brightness increases. Though I  suspect it’s low EHT rather than the shunt regulator.

 

Frank

 
Posted : 15/12/2019 5:18 pm
PYE625
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Interesting that the sounds goes down as the brightness is increased..... would suggest too much current being drawn in the line stage dragging down the HT to me. Something not right with the shunt regulator, perhaps it is conducting and shunting the EHT hard on all the time ?

I'm sure you won't leave the set on for very long in the fault condition.....sorry to state the obvious Gary. ? 

To understand the black art of electronics is to understand witchcraft. Andrew.

 
Posted : 15/12/2019 5:43 pm
Till Eulenspiegel
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There's a fair number of high value resistors in the grid circuit of the PD500 stabiliser valve.   Chances are one or more have gone high.  I don't have the Philips G6 service manual to hand and my only reference will be the information in one of the Radio and Television servicing books. Will do that now.

Till Eulenspiegel.

 

 
Posted : 15/12/2019 6:16 pm
colourmaster
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@pye625

Hi, I haven't had the set on long in case anything gets damaged. I'll check that I have 1.2 volts across the resistor on top of the eht box with the guns switched off. Then see from there. I personally think it's a slow GY501. I ordered a nos boxed Gy501 from a seller but when I unpacked it there was a PL509 in the box instead so I'm stuck until I obtain another. 

 
Posted : 15/12/2019 6:22 pm
Jayceebee
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From the G6 stock fault section of the forum "Poor EHT regulation, check resistance of the heater chain of V5004 comprising L5518 and R5055 (2.75 Ohm). This is quickly done by measuring between pin 8 and 1/5/9 in the valvebase."

 

John.

 
Posted : 15/12/2019 7:18 pm
Till Eulenspiegel
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Hi Gary,  resistor R5035 might have gone high.   The shunt stabiliser valve grid senses variations of boost HT through this resistor. Also check the line output valve grid resistors R5036, R3037 and R5039.

 

G6 ltb
G6 eht

Till Eulenspiegel. 

 

 
Posted : 15/12/2019 7:23 pm
colourmaster
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Hi David & John, thanks for your advice. I'll check the things you have mentioned and report back. Regards. Gary. 

 

 
Posted : 16/12/2019 6:25 pm
colourmaster
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Today I'm hoping to tackle the eht issue on my G6, Til has very kindly supplied me with a NOS Gy501 and PD 500 with some high value resistors.

Regards. Gary 

 
Posted : 28/12/2019 10:29 am
colourmaster
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Hi Everyone I've sorted the G6 regulation fault out. It was nothing more than a tired GY501. The boost is set for 550volts and the PD 500 set for 1.2 volts. I have to say its got a lovely picture. Regards. Gary. 

g6 1
g6 2
g6 3
g6 4
 
Posted : 28/12/2019 3:10 pm
malcscott, Jayceebee, PYE625 and 6 people reacted
Nuvistor
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Excellent news ? 

Frank

 
Posted : 28/12/2019 3:20 pm
PYE625
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Yes, that is good news and a relief I bet.... nothing too sinister. A good picture indeed. ? 

To understand the black art of electronics is to understand witchcraft. Andrew.

 
Posted : 28/12/2019 4:31 pm
colourmaster
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Yes it is a relief as with these old colour sets you always worry about the lopt when low eht occurs. The valve looked original so it's done well. 

 

 
Posted : 28/12/2019 5:23 pm
Till Eulenspiegel
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Hi Gary,  glad the valves did the trick.   OK, those valves may generate X-rays but when the shunt stabiliser circuit is correctly set-up excellent EHT regulation is possible.  

Always worth remembering that when the CRT is cut-off the PD500 dissipates 25watts!  

Till Eulenspiegel. 

 

 

 
Posted : 28/12/2019 9:17 pm
PYE625
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Forgive my ignorance here, but is the set EHT voltage higher for the larger 26inch as compared to a 22inch CRT?

To understand the black art of electronics is to understand witchcraft. Andrew.

 
Posted : 28/12/2019 10:54 pm
Nuvistor
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Not that I remember, 25kv, some of the more modern (80-90’s) CRT’s may have been higher but the EHT for the first large CRT’S was 25kv. The smaller ones, 18-20 inch could have been less though.

Seem to remember that above 25kv X rays become more of a problem.

Frank

 
Posted : 29/12/2019 10:21 am
Cathovisor
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@nuvistor

The EHT for my 90s Panasonic is supposed to be a maximum of 27KV from memory - I rather hope it's less. 

Many years ago, I read - Television, maybe? - that the emissions follow the 21st power of the EHT voltage so very logarithmic indeed. 

 
Posted : 29/12/2019 10:27 am
Till Eulenspiegel
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25KV was the norm for 22 and 26" sets.   The old roundies like the RCA CTC7 and my Pye operated at 23KV

Wasn't the BRC 2000 CTV was adjusted for 24KV?

The very late production CRT sets had much more than 25KV. Some were getting nearer 30KV!  Shed no tears for the passing of those horrible sets.  

Till Eulenspiegel.

 

 
Posted : 29/12/2019 11:03 am
Cathovisor
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The only time I routinely encountered EHT well above 25KV was in large projectors and projection sets - we had a few Mitsubishi 3-tube projection TVs 'in-set'.

 
Posted : 29/12/2019 4:05 pm
colourmaster
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Hi Everyone 

Well it's lasted a week, I was watching some trade test colour films this morning thinking what a good picture this set produces. After an hour the screen went blank and smoke appeared. I'll have a look and report back. 

 

 
Posted : 04/01/2020 1:15 pm
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