Marcoin TF1101 sig gen

[ed731pdh]

Done something similar from Marconi, found a couple of settings dead, traced to brittle sleive over lintz wire that had caused it to part company.

[Refugee]

I should not have a problem with fine wires on the coils on this Marconi. They all look sturdy and are solid copper.

***

I got the Megger out to play today.
C20 phase splitter control grid was awful at 400K. I found a Mustard that looks like the replacements that had already been fitted to the oscillator section and tested it before fitting. C21 on the anode side of the phase splitter was 5 Meg and C22 cathode side was 25 Meg. The other two blue capacitors read 500K and 1 Meg so they were bad too.

I use the bung drill method for the metal canned types and this worked well. I de-solder the old wires where they go through the rivets in the bung and pull them out to leave the clear hole on one end and do the same at the other end The drill does not suffer badly with snatching due to it landing on the internal roll of foil that then rotates. The foil then needs to be dug out.
I then feed the new capacitor in with the lead through the original rivet and solder it and at the drilled end fit a grommet to fill most of the space and top off with epoxy.

[Refugee]

First light today.
Yes the red light did come on after a quick run up on the Variac.
The regulated power supply came up spot on but sadly dropped by about 8 volts during soak test.
A paper capacitor looks highly suspect and will be sorted out next session.
Also in the power supply something very interesting indeed lit up
It is a 6CD6.
To me it looks like a double cathoded beam tetrode with a common anode. It is internally connected to look like a single beam tetrode at the base pins. Perhaps I will have to start a new thread for it with loads of photos. I questioned it being the correct valve but the number is correct. It was difficult to get photos due to the top cap connector being well jammed on and there is no way I am going to risk trying to take it off to get the valve out. I would have to unlace the wiring to get the anode wire free. It is staying firmly plugged into the chassis.
I have got one hell of a stable instrument here even with a bit of drift on the HT.
Nixie tube counter time for the dial calibration check so more nice things to light up with this one

[Refugee]

Replacing the capacitor in the regulator produced an excellent result with the 6CD6 regulating very strictly indeed.

Yesterday evening I started up one of my frequency counters as an alternative to the scope and calibrated oscillator arrangement described in the manual.
All the ranges are reading low by about 2%. The figure quoted in the manual is 1.5%.
The only way I can see for this happening is by the capacitor between the two halves of the bridge having less leakage than before.
What do others think?

[Radio Fixer]

I wouldn't bother myself as I always have a freq. counter on a T.

Gary

[Refugee]

I have had a look at my photo of the inside of the oscillator box and the resistors that need to be selected are ordinary composition types that can go high in value while the other arm of the tuning has carbon film type resistors.
I will whip the cover off the box and check them before I put the main covers back on again as they could drift further in future.

[Refugee]

I took the cover off the oscillator and checked the resistors and as I predicted some of them are actually high and out of spec the worst of these being on the lower ranges.
The worst were the two 820K ones on the lowest range. These were reading over 1 meg.
I have not yet fitted the new ones due to a dinner call although I did get time to select them from stock parts.
My big Fluke came into play in order to double check my every day DMM.
The access to replace the resistors is easy enough so it is not a lot of bother to sort out.

[AlanBeckett]

I bet they wished at the time that they could easily get the sort of Resistors we can.
Changing them should be OK with a slight danger of damaging the Switch.

Alan