Mic G7 Tube cold ??

:grin: Hi,

Thank to Gyraf for the DIY Projet it's great ...

I have a problem, I'm juste built a Mic G7 by Gyraf, and i have the good voltage on the PSU and on the Mic whithout the tube, and then i put the tube, the 6,3 voltage down near zero Volt, and the tube are cold Do you think my tube is bad !! and how i can sheck the tube.

Thank for your help :thumb:

Thom form paris

Are you sure it's an EF86 tube?

Have you allowed the tube time to heat up? At first they'll draw a lot of start current, which will lessen when it's heated up.

Other than that, make sure that your powersupply is able to drive the tube - it needs some 200mA current. Are you using the right type (to-220 housing) LM317 regulator?

Jakob E.

Sounds like a strange kind of short circuit.

Did the heater supply voltage return to 6.3V when you removed the tube?

Check your wiring in the cable and microphone very carefully.

what is the ac voltage that feeds the heater part of the supply It is >9Vac I hope.

What transformers did you use and did you build the circuit as per the schematic?

[quote author="Gus"]what is the ac voltage that feeds the heater part of the supply It is >9Vac I hope.

What transformers did you use and did you build the circuit as per the schematic?[/quote]

I use a 9V 3VA transformers and i buid the circuit exactly like the schematic :?

The first (9V) transformer probably needs to be 5VA or larger in order to be able to drive both the heater and the second transformer..

9V/3VA is only 330mA, which is not really enough to drive both the 200mA to the tube AND the second transformer

Jakob E.

[quote author="gyraf"]The first (9V) transformer probably needs to be 5VA or larger in order to be able to drive both the heater and the second transformer..

9V/3VA is only 330mA, which is not really enough to drive both the 200mA to the tube AND the second transformer

Jakob E.[/quote]

Thank you for your advices, I'm going to change the transformer 9V for a minimun 5VA; needs it to change also the transformer 15V 3VA :?:

Thom

No, the second transformer should be fine at 3VA.

The components list at the G7-page says:
http://www.gyraf.dk/gy_pd/g7/gic.htm
...
Psu:
(220V Model)
1 pcs. Transformer 220:9V, ~5VA
1 pcs. Transformer 220:15V, ~3VA
...

Jakob E.

[quote author="gyraf"]No, the second transformer should be fine at 3VA.

The components list at the G7-page says:
http://www.gyraf.dk/gy_pd/g7/gic.htm
...
Psu:
(220V Model)
1 pcs. Transformer 220:9V, ~5VA
1 pcs. Transformer 220:15V, ~3VA
...

Jakob E.[/quote]

:guinness: Thank i'm :? if it's my bad transformer. I inform you when i change it.

:thumb: Thom