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dtvmcdonald · 18th May 2017, 2:00 pm

I've tried the usual test image DVDs and they look OK, especially
the frequency response. There are modest white lines after black areas,
see the boy's right hairline. This would be expected from a modest
(30%) peak in the RF response at about 1 or 1.3 MHz away from 45 MHz,
unequal on the two sides.
The tonal response is OK.
I have no "test card C" source. I have the test DVDs from this and other British
forums but cannot play them on my players. I can however put that image you
just sent on a USB key and play that. Note that it will be played to NTSC and
converted to 405 by the Aurora. This is unoptimal. I could generate System A
directly using my HackRF, but only static images.

I tested the first three audio tubes and they appear OK. The X41 triode is clearly
OK as it oscillates nicely; I tested the multigrid section with the triode grid
connected to the cathode.The audio output is, as I said, soldered in. I can get
a scope probe to its socket to see if it is working. I should check the speaker.
The three tubes fit loosely in their sockets, but wiggling them does not
seem to make any difference so its possible they are contacting. The ones that
did not get hot in the set didn't get hot in the tube tester.

What I really need is some idea of the signal voltages through the audio chassis.
I really really really do not want to remove the CRT to get at it. That is really
bad design. I don't think that a max of 0.2 volt audio to the top of the volume
control can be right. I am going to try as hard as I can to at least diagnose the
problem with the audio chassis in place.

18th May 2017, 2:00 pm	#41
dtvmcdonald Pentode Join Date: Mar 2016 Location: Champaign, Illinois, USA. Posts: 227	Re: Marconi 702 advice I've tried the usual test image DVDs and they look OK, especially the frequency response. There are modest white lines after black areas, see the boy's right hairline. This would be expected from a modest (30%) peak in the RF response at about 1 or 1.3 MHz away from 45 MHz, unequal on the two sides. The tonal response is OK. I have no "test card C" source. I have the test DVDs from this and other British forums but cannot play them on my players. I can however put that image you just sent on a USB key and play that. Note that it will be played to NTSC and converted to 405 by the Aurora. This is unoptimal. I could generate System A directly using my HackRF, but only static images. I tested the first three audio tubes and they appear OK. The X41 triode is clearly OK as it oscillates nicely; I tested the multigrid section with the triode grid connected to the cathode.The audio output is, as I said, soldered in. I can get a scope probe to its socket to see if it is working. I should check the speaker. The three tubes fit loosely in their sockets, but wiggling them does not seem to make any difference so its possible they are contacting. The ones that did not get hot in the set didn't get hot in the tube tester. What I really need is some idea of the signal voltages through the audio chassis. I really really really do not want to remove the CRT to get at it. That is really bad design. I don't think that a max of 0.2 volt audio to the top of the volume control can be right. I am going to try as hard as I can to at least diagnose the problem with the audio chassis in place.