71A

[MrCurwen]

I recently bought a nice pair of Westinghouse 71A's. They look very cool, but I wonder what is the purpose of the little metal piece protruding from the base to the side?

[pieter t]

Part of lock mechanism; depends on type of socket.

[MrCurwen]

The 71A has an UX4 base, I've never used it before but I believe it doesn't have a 'collar' so to speak. Perhaps in the old days some had?

[kevinkr]

Originally Posted by MrCurwen

The 71A has an UX4 base, I've never used it before but I believe it doesn't have a 'collar' so to speak. Perhaps in the old days some had?

Yes.. I've got a few of the old style sockets here. The tubes twist in the base and lock.

71A is noted for having misaligned filaments. (I've got more than a few useless ones for this reason) Check yours to make sure that the filaments are relatively equidistant from both sides of the grid. You can do this by looking carefully down from the top making note that the curvature of the dome may be misleading.

[H.Michi]

I also have a few useless 71A.
Have you tried 71A pri amp?

[Cassiel]

71A is noted for having misaligned filaments. (I've got more than a few useless ones for this reason)

Not totally useless. They will amplify. An OK regen radio could be made.

[H.Michi]

Originally Posted by stalker

Not totally useless. They will amplify. An OK regen radio could be made.

A 71A / 6DJ8 switchable sound processer was built yesterday. Combination of 71A and line transformer NP-8 ex-Tango works nicely.The primary coil of NP-8 was connected in parallel, so its impedance ratio changed to 2.5Kohm from 10Kohm , and eventually the transformation ratio has become 1:0.49. This solution fits to a low amplification factor 3 of 71A.
Incidentally the thread of #26 in this forum was of informative and valuable for me.

Operating condition of 71A:
Plate voltage: 122V
Plate current: 10mA
Grid bias: -26V

Sound impression:
Good in transparency on 71A, while wider range on 6DJ8-SRPP.
There was no significant differnce between them.
However I would rather wait for a month or so for a overall evaluation.

[Cassiel]

However I would rather wait for a month or so for a overall evaluation.

Wise. It usually takes me a month to know if something stays or goes.


Looks well built. Schematic?

[kmtang]

I bought a pair of 71A few months ago and I don't know what to do with it.

Possibly it would be good to use them for the line amp.

Johnny

[H.Michi]

Originally Posted by stalker

Wise. It usually takes me a month to know if something stays or goes.


Looks well built. Schematic?

Thank you for your interest to my sound processor.
I shall upload the schmatics as soon as I finished drawing.

Attached is a bottom view of 71A sound processor.