Ampro 16mm Stylist projector woes.

[paddy ryan]

Hi again,
I am gradually losing the plot on my restoration of the projector valve amp. I have replaced all capacitors, and have the amp live and working, but no Gain. I can just about hear the film soundtrack through the speakers if I put my ear to it! I have changed and checked all valves, but notice that the 6BR7 valve seems dead. It is always cold and theres no glow. I have changed it a couple of times with spares, but no joy. The base connections all look okay. I am a beginner in this field and have no sophisticated gadgets to check further, any advice please.
Secondly,on my Ampro Premier 20, the amp is completely dead. The fuse blows when I turn it on. I have checked by sight the fuse line to the transformer and can can see nothing wrong there. I have ordered a new rectifier valve to see if that works, but any advice please on these two problems. many thanks

 

[rjenkinsgb]

What are the voltages on all the 6RB7 pins?
See here for the pinout:

6BR7, Tube 6BR7; Röhre 6BR7 ID18676, Vacuum Pentode | Radiomuseum.org

Tube 6BR7 or Röhre 6BR7 ID18676, Vacuum Pentode, Noval, 9 pin miniature (USA pico-9) B9A and RF/IF-Stage shown. Radio tubes are valves.

www.radiomuseum.org

Does it have 6.3V AC between pins 4 & 5? If you measure the resistance between 4 & 5 on a valve (out of circuit) what reading do you get??

For the other amp, does it blow the fuse with all valves unplugged?

 

[paddy ryan]

Thanks for that, I will go back in and investigate!

 

[Nigel Goodwin]

Valve amplifiers are dead easy to repair, as they are so simple - you rarely need anything other than a multimeter (an analogue one is fine), and a finger

As rjenkinsgb has said, check the heater and voltage - if the valve isn't lighting up, and doesn't feel warm, then the problem is with the heater or supply. A common issue (back in those long ago days) was loose connections in the valve base, easily cured either by replacing the base, or simply tightening the pins with a small screwdriver.

The one that's blowing fuses, it would be EXTREMELY rare for a faulty valve to blow fuses, with the possible exception of a valve rectifier - assuming it uses a valve one? - and as you've ordered one presumably it does?. Just turn the amp on with the rectifier valve removed, and see if it still blows the fuse - but it's very unlikely to be a valve - I've repaired countless valve products over many decades, and it's not something valves do, and the circuit configuration mostly precludes it anyway.

Do you have a schematic for the amp?.

 

[rjenkinsgb]

Good point on the loose pins, I never thought of that!

Another possible problem, one I had with the 1950s Recordon I've been refurbishing was that some simple plug and socket connectors were so badly tarnished there was no contact through them at all - even the four pin jones plug for mains in did not connect initially, it needed a serious scrub.

 

[paddy ryan]

Thanks for all your great advisories. I will get to work on them.

 

[paddy ryan]

Further to my projector amp problem, I have now checked all the valves, they are okay. But the fuse blows whether I have the amp on or not, yet the main motor runs fine. The fused line runs to the transformer, but why would the motor keep running with the fuse blown. I will post a schematic asp, but can"t figure this one out?

 

[paddy ryan]

schematic for premier 20

 

[rjenkinsgb]

The transformer power is shown as from P2 pins 11 & 12, separate from the motor and lamp.

If the fuse in that circuit is blowing with the switch (S4?) is off, it implies there is a ground fault on the transformer?

What does P2 connect to?

 

[paddy ryan]

There is no pin 2? There is a pin 12, which runs from the fuse to the amplifier transformer.
(Its all a 6 pin jones connector,);
pin 11 to switch 4 (volume control) to the Amp transformer
pin 10 to switch 3 (lamp)
pin 9 to the motor terminals
pin 8 to switch-projection lamp
pin 7 to chassis.
Hope this helps!
Many thanks for your help

 

[rjenkinsgb]

P2 (Plug 2, presumably) is the ID of the six pin connector on the schematic.

I meant what does it connect to outside of the diagram???

 

[paddy ryan]

it connects to the back panel of the projector, which takes the mains cable, and is also the location of the fuse holder,, jacks and speaker switch, as well as a screw adjust for (PEC volts, which I assume is a potentiometer). I hope that explains it!

 

[rjenkinsgb]

Can you check for resistance or continuity from P2 pin 7 to each other pin on the connector?

Which fuse is blowing - one on the back panel (off the schematic) or the one shown in the to transformer connection to P2 pin 12?

 

[paddy ryan]

Sorry, I was away yesterday. There is only one fuse to the whole projector, and that is the one on the schematic, which is the one in the transformer connection to P2 pin 12. There is no other. Its the one that is evident on the back panel array, No continuity from pin 7 to any other pin.
Continuity from pin 8 to 12, 10 to 11 ,9 to 10, 9 to 11. hope this helps.

 

[paddy ryan]

Sorry, I was away yesterday. There is only one fuse to the whole projector, and that is the one on the schematic, which is the one in the transformer connection to P2 pin 12. There is no other. Its the one that is evident on the back panel array, No continuity from pin 7 to any other pin.
Continuity from pin 8 to 12, 10 to 11 ,9 to 10, 9 to 11. hope this helps.

 

[rjenkinsgb]

If that fuse blows without you turning on SW4 to apply power to the transformer, there can only be a ground fault in the transformer.

 

[Les Jones]

When you say no continuity in post #14 what are the actual resistance reading and what is the highest resistance value that your meter is capable of reading ?
What state are switches 1,2 ,3 in when you made the readings ?
Was connector P2 plugged in or is it not connected to anything ?
Can you do an insulation test between P2 pin 12 and chassis ground using a high voltage insulation tester ? (500 volt range if it has different settings.)

Les.

 

[paddy ryan]

Sorry Les, but I am a strict amateur at this and some of your observations are too tech for me! I understand the question about P2, which was not connected when I tested continuity only. I have not tested anything live, being a beginner, playing safe. I don't have the means to use a high voltage insulation test, but I appreciate your help, and will for the time being, go through the ground fault tests. Thanks to you and to rjenkinsgb for all your kind help.

 

[Les Jones]

With the evidence that you can provide it looks like there is a short between the primary winding and the transformer core or between the winding and the inter winding screen. This is the same conclusion as rjenkinsgb made in post # 16. I would have expected your tests to show some continuity between P2 pin 7 and pin 12. (A good fuse would need to be in place for this test to be valid.) As you can't provide a resistance reading between these two points it looks like whatever method you are using to test continuity requires quite a low resistance value to show continuity.
Is the connector that mates with P2 connected to the auto transformer ?

Les

 

[paddy ryan]

Yes. I am going to plod on with your advice and see what I can find. Would a new transformer be the end result if the transformer found faulty? Anyway I am away for a week or so, so if you don't mind I will let you know how I fare with the tests in a week or so. Many thanks