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Old 30th Jul 2021, 5:39 pm   #1
radiograham
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Default Pye vt4.

Hi,decided to have a look at this pye vt4 i have had for a while,first of all there was a valve ef80 missing,this was replaced and valve heaters lit.I gave it 100volt ac via auto transformer first snipping the suppresor caps out.After an hour the voltage was increased to 200 and i could hear sign's of life through the speaker,the main smoothers were just warm,volts increased to 240,my daughter's 18 year old ears were borrowed at this point to listen for line whistle,she could'nt hear any so i switched off at this point and checked the lopt.The eht overwind was ok plus the anode winding,both valve's tested ok.after a few more check's i'm pretty sure the line linearity coil is open circuit,i have never come across this before was this a common fault? i was thinking is there a way to get it working without this just to get first light before going any further? also what is the correct way to change the ey51,this has those circular metal rings at the ends, do these come off? Graham.
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Old 31st Jul 2021, 5:52 pm   #2
radiograham
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Default Re: Pye vt4.

Yes i admit i got sidetracked by checking the lopt first,i then checked for line drive at the grid of the line output valve,the ecl80 line osc is not working,valve tests ok and i have tried a substitute,just found the line hold pot is intermittent and am fitting another,the line linearity coil is definitely o/c so this will have to addressed later. Graham.
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Old 31st Jul 2021, 6:49 pm   #3
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Default Re: Pye vt4.

One of the most complicated receivers of the period and it remained so for a few years.
An O/C line linearity coil is almost unheard of with the Pye V4. Did you clean the chassis before starting your work? If so you may have broken a fine wire from the coil. Worth having a very careful examination of the winding.

Start with the HT line. Make sure this is something near the published data. The VT4 are prone to line output transformer and scan coil failure. If you can scope the drive waveform to pin two of the PL81 it will confirm if the line oscillator is working. Replace the boost cap, line coupling cap and test. The scan coils can be checked by disconnection. It's the screened wire but I cannot remember the colour of the other one. Connections are under the scan coil mounting on a tag strip. Don't tackle anything else until you get the line timebase working. You will only mess yourself up! Good luck with it. The chassis has a very high component count. John.
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Old 31st Jul 2021, 7:22 pm   #4
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Default Re: Pye vt4.

This may help. J.
https://worldradiohistory.com/UK/Pra...on-1955-08.pdf
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Old 1st Aug 2021, 12:29 am   #5
radiograham
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Default Re: Pye vt4.

Hi,the vt4 is indeed not one for the beginner,i also have a v4 which i got going a few years ago this was a marathon as you say it has a very high component count.I haven't cleaned the chassis much apart from dusting so don't think i have broken any wire's.One thing i have noticed the main ht seems high well above normal,i am going to concentrate on the line tb and get this working first,not the easiest of chassis to work on,i will also change the 2 cap's you mention,the boost cap and the line coupler. Graham.
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Old 1st Aug 2021, 4:37 pm   #6
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Default Re: Pye vt4.

The H.T. might be reading a bit high due to lack of current being drawn from the line output stage due to a fault. Mains voltage these days appears to be higher than it was and worth a check for comparison. I'm 248v here and never less than 240. Make sure that the mains dropper has not been messed about with and take a visual look at that lin coil. J..
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