Telequipment D83. technical description or schematics - UK Vintage Radio Repair and Restoration Discussion Forum

fredino · 30th Jul 2008, 8:06 am

Hello,
Since some time I am using the oscilloscope Telequipment D83. The Oscilloscope is in very good conditions, the oscilloscope tube looks like new
(brightness, sharpness). But unfortunately, after 30min or 1 hour the luminosity drops and drops to zero. Some time after switch off. the oscilloscope works fine again... My Question: I have looked on the internet for an technical description or schematics, but I did not found anything about the D83. Who can help me? Thanks,
fredino
excuse me for my English.

Mark the Mender · 30th Jul 2008, 9:07 am

Hi and welcome, i found a copy of the manual for this on Bama, iI have pm'd you the link.

cheers Mark

WME_bill · 16th Oct 2008, 12:13 pm

D83. Fading display. I have struggled in the past with this, and found it was usually due to the resistors in the EHT voltage chain changing high under stress. They are normal types rated at around 250V, but are being used with much greater voltages across them. The D83/D75 series originally used several in series. Look at the grid feed chain - R317,318,319,321,322, all originally 10M. Later models used only two resistors, 30M + 20M. If only the focus failing, look at the focus chain, R324,325 (10M), 326, 7.5M, later models 2 of 8.2M. Maplin used to keep the Mullard/Philips VR25 high voltage metal glaze resistors rated at 1.1kV, but I think no longer. The usual 1/4w carbon or metal film will only take 150v or so. Traditionally the 1w carbon film was used, rated at 350V. I suggest you experiment by changing the resistors in turn for new ones, of any type. If that cures the problem, then go in search of high voltage metal glaze types for a permanent repair. Your temporary ones will last for a time. I see that RadioSpares currently do the VR series, so that is a possible source. The individual values of the replacements are not critical, as long as the total is comparable. I take it you have the manual and circuit diagram. There were slight changes between the 1973 and 1978 circuits, but either edition should do. BillN

30th Jul 2008, 8:06 am	#1
fredino Retired Dormant Member Join Date: Jul 2008 Location: germany, dresden Posts: 1	Telequipment D83. technical description or schematics Hello, Since some time I am using the oscilloscope Telequipment D83. The Oscilloscope is in very good conditions, the oscilloscope tube looks like new (brightness, sharpness). But unfortunately, after 30min or 1 hour the luminosity drops and drops to zero. Some time after switch off. the oscilloscope works fine again... My Question: I have looked on the internet for an technical description or schematics, but I did not found anything about the D83. Who can help me? Thanks, fredino excuse me for my English. Last edited by Mike Phelan; 30th Jul 2008 at 8:47 am. Reason: Removed poll and edited www reference to avoid appearance of a link

30th Jul 2008, 9:07 am	#2
Mark the Mender Retired Dormant Member Join Date: Apr 2008 Location: Warrington, Cheshire, UK. Posts: 421	Re: Telequipment D83. technical description or schematics Hi and welcome, i found a copy of the manual for this on Bama, iI have pm'd you the link. cheers Mark

16th Oct 2008, 12:13 pm	#3
WME_bill Octode Join Date: Oct 2007 Location: Exeter, Devon, UK. Posts: 1,554	Re: Telequipment D83. technical description or schematics D83. Fading display. I have struggled in the past with this, and found it was usually due to the resistors in the EHT voltage chain changing high under stress. They are normal types rated at around 250V, but are being used with much greater voltages across them. The D83/D75 series originally used several in series. Look at the grid feed chain - R317,318,319,321,322, all originally 10M. Later models used only two resistors, 30M + 20M. If only the focus failing, look at the focus chain, R324,325 (10M), 326, 7.5M, later models 2 of 8.2M. Maplin used to keep the Mullard/Philips VR25 high voltage metal glaze resistors rated at 1.1kV, but I think no longer. The usual 1/4w carbon or metal film will only take 150v or so. Traditionally the 1w carbon film was used, rated at 350V. I suggest you experiment by changing the resistors in turn for new ones, of any type. If that cures the problem, then go in search of high voltage metal glaze types for a permanent repair. Your temporary ones will last for a time. I see that RadioSpares currently do the VR series, so that is a possible source. The individual values of the replacements are not critical, as long as the total is comparable. I take it you have the manual and circuit diagram. There were slight changes between the 1973 and 1978 circuits, but either edition should do. BillN