ECC81 with broken glass envelope meets 2 x LND150 transistors

[dougietamson]

I have a broken Mullard ECC81 valve where the glass envelope had split neatly around where the bottom mica plate was supposed to be.
I un-clipped the the internals down to the copper wires, tinned them and soldered in a couple of LND150 high voltage N-Channel depletion mode transistors, £1.10 each.

It's now a solid state FrankenECC83

Currently only sellotaped together, any suggestions for glue?

Here it is in the phase inverter socket of my JCA22H amp.
https://www.youtube.com/watch?v=VohL5NQni2I

[Station X]

Heat shrink adhesive sleeve around the join.

[G6Tanuki]

Superglue dribbled into the crack, left to dry and any excess shaved-off using a scalpel?

In times-past there was a glass-glue type stuff available in kits for filling chips in windscreens; it hardened using UV light and then you shaved it down with a razor-blade before polishing it. Not sure if it's still available but it was specially designed so its refractive-index was closely matched to that of the glass so the repair would be invisible.

[dougietamson]

Originally Posted by G6Tanuki

Superglue dribbled into the crack, left to dry and any excess shaved-off using a scalpel?

In times-past there was a glass-glue type stuff available in kits for filling chips in windscreens; it hardened using UV light and then you shaved it down with a razor-blade before polishing it. Not sure if it's still available but it was specially designed so its refractive-index was closely matched to that of the glass so the repair would be invisible.

I have a tube of the windscreen stuff to repair a stone chip, no UV source so left it in the sun for ages, seems ok, the old Saab passed her MOT every time

[dougietamson]

Here's the pinout:

Anode pins 1&6 = Source
Grid pins 2&7 = Gate
Cathode pins 3&8 = Drain

[robinshack]

Don't forget an LED to mimic the heater!
Rob

[dougietamson]

Originally Posted by robinshack

Don't forget an led to mimic the heater!
Rob

Good idea!

Maybe I should use one of my many xmas tree lights or a proper pilot light for a warm glow.

This particular amp has 12v dc for the filaments so, I could add 2 like a real ECC83, one for each triode

[Lloyd 1985]

Nice!

There is a newer version of the old glass glue, Loctite super glue for glass, it’s rubbish!!! I stuck a GEC radio dial back together with it, the cracks were still clearly visible, and after a few years it fell apart! I had noticed when it dried it was sort of soft and rubbery, unlike the old glass glue which dried hard, and is still holding a wine glass together after 20 years!

Regards
Lloyd

[Radio Wrangler]

All it needs is a tiny, tiny sign inside reading "In case of emergency, Break Glass."

David

[Cruisin Marine]

Where is a glass blower when you need one?

[dougietamson]

Originally Posted by Cruisin Marine

Where is a glass blower when you need one?

I was thinking of getting the blow torch out, would have to shield the transistors though and would end up melting the solder. Crimping might work.

[boiss]

Waiting for my LND150s to arrive from China, 13th April they say. I will use them as temporary replacements for impossible to get 1920s valves.

[dougietamson]

Originally Posted by boiss

Waiting for my LND150s to arrive from China, 13th April they say. I will use them as temporary replacements for impossible to get 1920s valves.

I bought mine from a UK supplier, £1.09 each and £2.99 p&p

https://www.switchelectronics.co.uk/...00v-30ma-to-92

[dougietamson]

Here's the results from a simple test circuit with sine wave input

DC voltage measurements.

Anode resistor 100KΩ
Cathode resistor 2.2KΩ

HT supply - 200.3
Anode voltage - 161.2
Voltage drop across anode load - 39.1 = 0.39mA

Input 500Hz sine 0.62Vp-p 0.22Vrms (47KΩ grid stopper)
Output (at 0.022µF 400v coupling cap) 19.33Vp-p 6.64Vrms

[dougietamson]

Here's the voltages for a 12AX7, Brimar 12AU7 (1950's seems ok) and the SolidStateAX7

HT = 200v - 100KΩ load resistor - 2.2KΩ Cathode resistor - 0.022µF coupling cap - 47KΩ Grid stopper - 12Vdc heater pind 4/5

12AX7
Anode v drop = 56.9
cathode v drop = 1.22

Brimar 12AU7
Anode v drop = 108
cathode v drop = 2.38

12ax-fake-7
Anode v drop = 38
cathode v drop = 0.823

Doug

[Silicon]

It would be interesting to see how far up the frequency scale you could get with the LND150 before the gain starts to drop.

[sdsharma]

How to connect this 2 x LND150?

[Station X]

As shown in post #5.