Hi, I recently purchased a Paton VCT off Ebay and am currently restoring same. I have circuits of the VCT-2 and the VCT-V and they are very very similar in all respects except for the internal valve. The tester I have, is set up for a 6v vibrator supply which is missing, a 240vac supply and 4.5vdc for mA's, ohms and DC Volts ranges. The valve that came in the set is a 6j8g which is a triode heptode and is set up with an anode cap. This valve is in the socket as indicated by the two schematics mentioned above for a 6x5/1V??
I have the set working and measuring accurately on the 4.5vdc circuit and have replaced paper caps and out of spec resistors and the 25Kohm power resistor. I have also built a solid state 6v vibrator from 2 * 2N3055's which works fine on the bench, but not run in the set as yet. My problem is why is there a 6j8g valve in the set??? I read some previous forums by Marcc and Risk who had experience with these testers. Can anyone help?

It should be fairly obvious as to which valve goes in the beast.

Mine is a VCT-V. That takes a 1V which has the same pin socket (UX-4) as the vibrator (scary). It is a single diode heater tube.

The later model had a 6X5 which is a double diode with similar specs to the 1V only 6X5 is a duo diode and they only used half. 6X5 is an octal base the same as 6J8 ..BUT as you say 6J8 is a triode heptode, pentagrid converter.

6J8 has the same heater pinout as 6X5 (2&7) and same cathode pinout (8) Plates of 6X5 are 3 & 5.

If none of the other pins other than a plate (3) or (6) were wired. Then the 6J8 would work as a diode. For how long, or well is conjecture and damn barbaric.

Do check that the octal socket is wired as for either half a 6X5

Check the 6X5 for heater cathode short before use as some variants of them are notorious for doing it..

Watch the fingers on Meg Ohms & cap test ...It bites.

Marc

Hi Marc,
Thanks for the quick reply.
The fitted socket is an Octal base, pin 1(NC), pins 3,4,5 and 6 interconnected with an anode lead and cap joined at pin 5. Pins 2 and 7 go to a 5V labelled heater connection(yes 5V) tabs on top of the transformer. Pin 8, the cathode joins onto B9+B11+A(common rail)+B1+B2+B3+Ext Volts(+). So it appears wired for a 6X5 but the anode cap has me stumped. It looks as though it has not been a modification as the soldered connection and the anode lead seem original. And yes your point about 3 and 6 the two plates on a 6j8 being joined only would work as a diode, makes sense to me, but this has 3,4,5,6 wired together which means the grids are wired to the plates. I do not have a 6X5 yet, will get one off ebay. I am very tempted to reconfigure octal socket to take a half wave 6X5 and see what it does. Also thanks for the heads up on the megaohm test, the operators manual did say to use "special" aligator clips as the output voltage across the probes is around 225 volts. I think I will try it the way it is before doing any mods just for curiosity sake, can't hurt can it?? Cheers

Methinks he who did this act may be named Titus?

That was a wilful exercise in fitting that 6J8. The top cap of 6J8 is the signal grid.

If you have a look at a Lyric 70 Series in "Rider" (Nostalgia air - resources) You will note I think a 27 Triode being used as the rectifier for the grid of 50 (output) it needs around -80V on the grid as it has around 300V on the plate.

Tying the grid to plate is done there.

I would wire it back to a 6X5 with the AC on either pin 3 or 5. Cathode stays put feeding out B+ & clear the rest of wires.

You can build a minature into a dead octal valve socket but watch the heater current, PIV. & efficiency.

Silicon diodes will cause a significant increase in HT voltage which will need adjusting.

Marc

Yes the curious case of 6j8g. I checked the 70 series, so it can be done. I have used silicon diodes on a cinevox amplifier while waiting for a tube and that worked okay so there are options. But you are right I think the 6X5 is the best. I will let you know how it all pans out. Only thing is, is 5v on the heater of a 6X5 enough? Thanks for your help.
Cheers

6X5 pull double the heater current of 6J8.

Check which tapping the compensator is on. There is a position for adjusting the line voltage "Line Check"

Set that & (Line) adjust the meter to full scale deflection then re-check voltage.

Another issue that may be present: Mine had seen a lot of work and vibration, which had cut into wires. On the back of the meter movement, behind the mounting bracket of my VCT-V, is a screw (so what?... some say)

The significance of this is that the srew rattled loose. It secures parts within the movement. This enabled it to cause contact with the mounting bracket and flash over, destroying the "hair springs of the movement.

You would be well advised to check that the situation does not exist in yours & repair and insulate, if it does.

Repair of the movement will not be cheap if you "bend it"

Marc

Hi,
Yes I remember reading your post back in June 09??? regarding the screw on the back of the meter. I have had the meter out and repaired it as the coil was out of the bearing, the pointer bent and the springs were bent top and bottom, looks like someone had a go at it before. I also hotglued the connector screws in so they do not slip through into the back of the meter. Meter works full deflection now although I had to replace two resistors on the mA's ohms and DC volts circuit to allow the ohms adjust to get to zero. Seems okay now. I note your point regarding current on heater so will adjust as recommended. I am still waiting on 25k 50w adjustable power resistor. I have also made a half wave rectifier from an old octal base I had with 2 x 1n4007s and a 820k 10w resistor in series from pin 3 to pin 8, so if all else fails, that should work???
Cheers

The accuracy of the meter movement can be checked easily. Off the top of my head I think it's 1mA FSD.

The voltage out put of the Meg ohm range is specified, so you should be able to refer to that to ensure thatt he B+ rail is at its correct voltage.

Marc

Hi,
Yeah the meter is 100ohm 1mA FSD. I have now installed the power resistor and when plugged into 240V mains I get 225V out at the megaohm setting which is right according to the manual. Also get 300 and 40 out of the secondary as per the VCT-V schematic. I have checked electrolytics, used the paper neon test and checked a 5Z3 on merit and element shorts, it all seems to work fine. I have also tried my homemade 6V solid state vibrator and the element of the 6j8g glows but I get no secondary voltage which has me a little stumped, perhaps the 6j8g does not work for the 6v vibrator supply. The other problem I have is that when on the 4.5v cell the low ohms, ohms and ohms x 10 and DC volts are a little out of calibration when compared to two digital voltmeters. Even when adjusted to FSD and zeroed the meter is out. I am not sure how to rectify this, I know that in low ohms there is a resistive shunt and on ohms and DC volts it is in series. It seems like this model VCT is a cross between the VCT-V and the VCT-2 with minor differences in the secondary outputs, and no diode test button like on the VCT-2.

There could be an out of whack resistor in there. There is a card inside mine noting that one resistor "was specially selected" despite it being marked for what it should have been.

Translated, (i.e. management / sales terms expained) that means that some lacky got landed with a bucket full of duds and had to pick out the ones needed for the VCT. This was apparently cheaper than making one the correct value.

I could lift the chassis & see which one it was.

The vibrator would have run at around 150 - 200 Hz. If you are missing the original advise & I will see whats' in mine. I have that info with the circuit.

Vibrators tend to gobble current. I have a 6V Tractor so a big 6V DC power supply is not an issue. If it works on mains it should work on Vibrator.

There may be an issue with the vibrator? I was toying with the idea of a 555 switching a Mosfet. Prefferably a TV type that has a flywheel diode in it. The back EMF from a transformer can be very destructive.

There was another Military version with diode test and made by Transmission Products (I think)

Marc

Hello,
Yeah any advice would be great as I want to get it right. I have replaced a number of out of spec resistors and have used pots to help calibrate by trial and error. I noticed inside my meter there is a coiled wire in series with the positve terminal and the coil which measured 103 ohm. Could this be the issue?

I have now replaced the 6j8g, which incidently worked as a rectifier with a 6x5GT wired as a half wave rectifier, l have also replaced other out of spec resistors to calibrate the meter to respective ranges. The unit is now working in all respects.

I have just acquired a good Paton Palec VTC if anyone needs any info. I also have the auxilliary small pin valve board that goes with it plus all the circuits.
After reading your posts above, I will be checking caps, resistors and cleaning switch contacts etc.
Peter

I also have just acquired a Paton Palec VTC in very good cosmetic condition. Apart from it's hinged lid being missing, it seems complete. I managed to find the user manual on line with the list of settings for the valves to be tested. I'm new to this hobby and I'm a bit confused by the various models in the VTC range. I believe my unit is the straight out VTC model.

Any information that can be provided regarding the the battery needed for my unit would be greatly appreciated. I'm also interested in trying to source an extension board or any relevant circuit diagrams.

The serial Number will be the guide to which mode it is. They are not all the same.

I serviced one recently, and as I have indicated, mine has a 1V and UX4 pin Vibrator. Mine is just VCT & I think the other one was VCT-V?

The chassis & Vibrator as well as the sockets and an extra push button, were on the -V and it's a different chassis, 6X5 rectifier (1 plate used 1/2 wave)

Marc