Hi all,
after re-stuffing the remaining caps on the CRT base board, I thought now might be a good time to power the set up before I fit the CRT.
I lugged the heavy PSU on to the bench and connected it up with the fuse to the mains EHT transformer disconnected.
In the second picture you can see the orange glow of the 100V reference for the focus regulator.
At first there was no line whistle, although there was a very loud noise coming from the frame coils. I swapped the Mazda PEN46 that I had fitted in the frame generator position with the VT127 (PEN46 clone) which I had in the line stage and this time I got line whistle, but no frame noise.
I did wonder if the Rayethon VT127 (which was a NOS WW2 air ministry valve) was no good in a self oscillating output stage. I didn't have a spare Mazda PEN46, but fortunately I did have a spare NOS VT127. Lucklily this one worked ok.
The third photo shows the faulty valve - it looks ok and I was the first person to open the box since it was re-labled with a CV number.
I attached a scope to the feedback winding of the frame output circuit and it showed a nice waveform which had 50Hz nicely in the range of the hold control. Turning up the height seemed to cause a breakdown which turned out to be the spark gap in the x100 scope probe
Notice the size of the flyback pulse on the scope
. Removing the probe enabled me to turn the height control right up. The scope probe survived intact
. I wonder how high the anode voltage goes during the frame flyback?
I attached the scope probe across the line coils and got a lovely waveform. Again 10KHz was easily in range of the hold control. I then fed in the test card from an Aurora and was able to lock the timebases. The scope picture shows a nice 10.125KHz locked waveform
The HT was 365V.
The flyback EHT was rather low at 4.11KV. Maybe the EY51 is a little tired. However, when the set was first obtained it was noted that there had been a wax leak from the line output transformer. It turns out that the wax from the EHT rectifier's heater winding has gone gooey, so maybe there is an EHT leak there. I must look out an EHT stick and try it.
That's all for now.
Cheers
Andy